EFFECT OF CARBOHYDRATE SOURCE ON POSTPRANDIAL

BLOOD GLUCOSE IN SUBJECTS WlTH TYPE 1 DIABETES USlNG

INSULIN LISPRO

Nadia H.J. Mohammed

A thesis submitteâ in confomity with the mquimments for the ûegme of Master of Science,

Griduate Department of NutrStionaI Sciences Univemity of Toronto

@ Copyright by Nadie ~ o h a ~ h e d 2001

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To my parents

TABLEi OF CONTENTS page

ACKNOWLEDGEMENT ..........i....................................... iu

.......................................................... LIST OF TABLES

LIST OF FIGURES .........................................................

LIST OF APPENDICES ...................................................

ABSTRACT .................................................................. vïii

CHAPTER 1 INTRODUCTION AND LITERATURE REVIEW 1.1 Introduction .....................................................

................................................. 1.2 Literature Review 1.2.1 De~tionofDiabetesMe~tus .................... ... 1.2.2 Prevalence ................................................ 1.2.3 Classification ......................................*...... 1.2.4 Diagnosis ................................................. 1.2.5 Type 1 Diabetes Mellitus ................................

............................... 1.2.6 Type2DiabetesMelliais 1.2.7 Complications ............................................

.................. 1 -2.8 Monitoring Blood Glucose Control ..................... 1 -2.9 Intensive Blood Glucose Control

1.2.10 Treatment ................................................. ........ . 1.2.1 O 1 Non-f harmacological Therapy

.................... 1.2.10.1.1 Exercise 1 .2.10. 1.2 Nutritional Management ..

.......................... 1.2.10.2 Insulin'ïherapy 1.2.10.3 Lispro Insulin ......W.........-...........

.......... 1 -2.10.4 Lispro and Meal composition ................................ 1.2.11 TheGlycemicIndex ............................. 1 -3 Study Objectives and Hypothesis

.................................... 1.3.1 Study objectives .................................... 1.3.2 Study Hpthesis

CHAPTER 2

MATERIALS AND METHODS Subjects ............................................................

............................................. 2.1..1 Screening ..................................... Study Design and Protoc01

............................................. 2.2.1 Rationale ............................................... 2.2.2 Protocol

............................ 2.2.2.1 Hypogiycemia Test Meal Preparation ...........................................

............................... 2.3.1 Instant Mashed Potato .......................................... 2.3.2 White Bread

2.3.3 Spaghetti .............................................. ....................................... 2.3.4 Pearled Barley

............. ................... 2.3.5 . Pineapple Juice ... ........................................ Blood Glucose Analysis

............................................... S t a î i s t i c a l ~ s i s

CHAPTER 3 RESULTS 3.1 Subjects ........................................................... 36 3 -2 Glycemic Response Data ...............................-.....Le 38 3.3 Hypogiycemic Outcomes ....................................... 46

....................................... 3.3.1 Hypoglycemia 50 ................................. 3.3.2 Low B l d Glucose 50

3.3.3 GI and Pg in Relation to Hypoglycemic ............................................. Outcomes

CHAPTER 4. DISCUSSION AND CONCLUSIONS 4.1 Discussion ......................................................... 58 4.2 Potentid Practical Implications ................................ 64 4.3 Future Research ........-........................................... 66 4.4 Conchsions ...................................................... 66

REFERENCES ClTED 68

~Pl?ENDKEs 76

In the name of Allah, the most mercz~l, the most graciour

Fkst and forernost, I would like to thmk my hwband and e v q

member in my family. Without their unconditio~u~l love, patience and

support, I would not have been able tu accornplsh this work

I'm gratefùl d thanml tu my supervisor Dr. Wolèver, for his

continuous encouragement and i m a l ~ ~ ~ b l e guihnce throughout the

program- 1 would also like to thank Dr. Jenkns and Dr. Rao for their valued

input. Bank you fo Dr. Singer for appraising the thesis and Dr. El-Sohemy

for chairing my defense.

1 am irrdebted to al2 my subjects who volunteered to participate in my

stuc&- ïlbanks to everybody in my Zab group, d special t h k to Janet Vogt

for her heIpfu2 advice. Inmks to CZaudio in the Glycemic Index Testing

Offce for hm technical support. Also greati'y appreciated is thefiiendsh* of

everyone ut the Clinical Nuhition and Risk Factor Modzifiation Centre at

St. Miehael's Hospital. A special thmrAyou tu Zènith Xu for her kind heb.

1 would like to extend my thanh to the Faculty of Medicine in Kuwait

University, for ofering thk scholmship.

mis thesis was made possible by a grantfiom Eli Lil& company.

Table 2.1

Table 3.1

Table 3.2

Table 3.3

Table 3.4

Table 3.5

Table 3.6

Table 3.7

LIST OF TABLES

GI, Weigbt and Composition of Test Foods

M- Demographic and Biochemical Profile of the Sample at srreening

Two-Way AnalysiP of Variana ofLncremental Bkxxi Glucose Responses Mer Difllerent Types ofFood

Mean Bbod Ghicose Increments for Food Types vs. Time

Two-Way A d y s k of Variance of Area Under Giy- Curve (AUC) Mer Werent Types of Food

Mean Area Under the Curve (AU0 of the Glycedc Response Curve for Food Types

Number of Hypogiycemk and Low Blood Glucose Episodes per subject

Figure 2-1

Figure 3-1

Figure 3.2

Figure 3.3

Figure 3-4

Figure 3.5

Figure 3 -6

Figure 3.7

LIST OF FIGURES

Tes te Day Protocol

Correlation between Ghicometer a d YS1 Blood Glucose co~~centrations

Mean B W Ghicose Increments (by YSI) For Food Types vs. Time

Mean Blood Ghicose Concentrations (by YSI) For Dïfkent Test Foods

Correhtion Between Mean AUC of Test Foods and Their Glycemic Iodices

No. of Hypoglycemic and Low Bbod Ghrose Episodes per Food Types

Correlation of No. of Hypoglycemic Episodes (by Glucometer a d Y SI) with GI a d Pg

Correlation of No. of Low Bbod Glucose Episodes @y Glucometer and YSI) with GI and Pg

LIST OF APPENDICES

AppendixA Consent Fomi

Appendix C Weight and Nuîrient Content of Standard DBmr Meal

Appendix D Data Fonn

Appendk E Demograpbic and Biocbemical Pro& of the Subjects at s-

Appendk F TllSUlBl Types and Mean Doses Used By Subjects

.................. AD A ANOVA ..........-.. M T .................. AUC ................. BMI .................. CS11 ................. DCCT ....O..........- DM ................... FBG .................

IFG ................... .................... IGT

L ....................... LDL

SBGM ............O.-.. SEM ....................

...................... U YS1 ...................

The Americaa Diabetes Association Analysis of Variance AhnmeTransarninase Area Undet Giycemic Response Curve BodyMassIndex Coiitinuous Subcutaneous IrisulEnmn Diabetes Control and Complication Trial Diabetes Mellitus Fasting Blood G b s e Granis GestatiodDiabetes Giycemic Index Hours Hemogiobh Alc ImpairedFastmgGhicose Ingiiired Ghicose Tokrance -gram Litre hw-Densii Lipopmtem Mü1snole per Litre Propoen of carbohydnie absorbed as ghmse Correlationcoefficient SelfBbod Glucose Monitoring Standard Error of the Mean units Yellow Spring Instruments Adyzer

Effect of Carbohydrate Source on Postprandial Glycemia in Type 1 Diabetic Subjects Treated with

Lispro Insulin.

Master of Science, 2001 Nadia HJ. Mohammed

Graduate Department of Nutritional Sciences University of Toronto

ABSTRACT

Treatment o f type 1 diabetes (TID) with iispro h s u h reduces postprsndial

hyperglycemia, but because of its rapid onset of action, postprandial hypoglycemia may

occur. To see ifgiycemic index (GI) and proportion of carbohyârate absorbed as *se

(Pg) affecteci g iym-c responses and occurrence of hypogiycemia, 8 T1D subjects on

lispro were studied for 4 h on 5 &ys af€er o v ~ g h t fàsts. Subjects took their usual

insulin dose and ate 50g carbohydrate tiom a starchy food (Pg=I; instant potato G1=83,

white bread GI=71, spaghetti G P U , barley GI=ZS) or pineapple juice (Pg=0.5; 01-46).

Glycemic responses differed significantiy for the diffèrent foods and were close&

rehted to GI ( d . 9 8 , p

1. INTRODUCTION AND LITERATURE REViEW

1.1 INTRODUCTION

The therapeutic importance of tight blood glucose control is well

established in both type 1 (1) and type 2 (2) diabetes. G d blood glucose

control for people with type 1 diabetes depends on coordination of insulin

doses, quantity and timing of food intake, and physical activity.

The Arnerican Diabetes ASSOC-iation (ADA) recommends considering

total carbohydrate consumed rather than type of carbohydrae, thus \

traditionally ins& dose has been adjusted based on the amount of

carbohydrate in the mealS. However, meals may differ not only in the

amount of carbohydrate they contain, but also in the source. The Glycemic

Index (GI) is a classification of foods based on their relative blood glucose

raising potential(3), which in tum depends on the rate at which carbohydrate

is digested and absorbed (4). Oiir lab.has demonstrated that the GI of foods

is the same for people regardes oftheir glucose tderance (5). We have also

shown that lowering the GI of the diet improves b l d glucose control in

both type l(6) and type 2 (7) diabetes. More recently we have demonstrated

that day-to-day variation in both the amount of carbohydrate and the GI of

the diet of subjects with type 1 diabetes influences the glycemic control(8).

1

This suggests that to achieve optimal diabetic controi, adjwtment of insulin

dose should be based on both the amount and source of carbohydrate in the

meal to be consumed.

Recently, an analog of human insulin, lispro, is increashgly used

because of its more rapid and physiologie response. This results in reduced

postprandial blood glucose compared to reguiar bulin (9) and the potentid

for improved blood glucose control(10). However there is the potentiai for

postprandial hypoglycemia especially when a low carbohydrate meal is

consumed (11). This Mcates that the dose of lispro needed depends on the

amount of carbohydrate present in the meal. However, the= are no studies

yet on how to adjust lispro for dzerent types of carbohydrate foods.

The general purpose of the present study is to determine the pattein of

blood glucose response produced by an equivalent amount of different

carbohydrate f d s in type 1 diabetic subjects ushg insulin lispro, and to

determine the influence of carbohydrate source on lispro-induced

postprandial hypoglycemia The overall aim is to be able to advise diabetic

people whether to adjust lispro dose for different types of carbohydrate for

optimal glycernic control

1.2 LITRATURE REVIEW

1.2.1 Definition of Diabetes Mefitus

Diabetes Mellitus is defhed as a heterogeneous group of metabolic

diseases characterized by the presence of hyperglycemia due to defective

iasulin secretion, insulin action, or both.

1.2.2 Prevalence

Currently, diabetes has been diagnosed in 5% of Canadians or 1.5

million people (12). This number was expected to reach 2.2 million by the

year 2000 and 3 million by 2010 (13). Moreover, because U.S statistics

demonstrated that for every person with diabetes there is someone with

undiagnosed diabetes, these numbers most likely underestimate the

prevalence of the disease. Assumùig that the same situation is tme in

Canada, up to 10% of Canadian adults may currently have diabetes.

1 -2.3 classincation

Diabetes is recently reclassified into five distinct types based on the

pathogenesis rather than treatment (14). The vast majority of cases f d into

two broad categories, which are type 1 a d type 2 DM (discussed later).

Gestational diabetes (GDM) is any degree of glucose intolerance that is

recognized during pregnancy.

A variety of relatively uncornmon conditions are listed under "other

specifïc îypes". These consist mainly of specifïc genetically defïned fonns of

diabetes (e.g. abnormalities of insulin or its teceptor) or diabetes associated

with other diseases or drug use.

Impaired glucose tolerance (IGT) and mipaired fasting glucose (IFG)

are metabolic stages interniediate between

established diabetes. They are mt clinical

are risk factors for Miire development

disease.

nomal glucose homeostasis and

entities in their own rather they

of diabetes and cardiovascular

1.2.4 Diagnosis

The Diagnosis (14) of diabetes is established by a fasting plasma

glucose (FPG) value equal to or greater than 7.0 mmol L, a random plasma

glucose greater than 11.0 m V L with symptom, or plasma glucose value

in the 2-h sample of the oral glucose test (75g - glucose load) greater than 11 .O mmoVL.

Diagnosis of IGT depends on a plasma glucose value in the 2-h sample

of the oral glucose test (75g - glucose load) between 7.8-1 1.0.

Impaired fasting glucose (WG) has been established to iden* another

intermediate stage of abnomal glucose homeostasis analogous to IGT. IFG

is diagnosed by a fasthg plasma glucose value between 6.169.

1.2.5 Type 1 Diabetes MeIlitus

Type 1 DM commonly occurs in childhood and adolescence, thus is

also known as Iwenile-onset diabetes. It represents about 5-10% of all cases

of diabetes. It results fiom absolute deficiency of insulin secretion due to

destruction of the B-cells of the pancreas, the etiology of which is either an

autoimmune cell mediated or idiopathic.

1.2.6 Type 2 Diabetes Mefitus

Type 2 DM is the cornmonest type of diabetes. Approximately 3% to

5% of the general adult population has unrecognized type 2 diabetes. It may

range ftom predominant insulin resistance with relative insulin deficiency to

a predominant secretory defect with insuliÙ resistaiace. Studies have

identified increased risk associated with older age, central obesity, certain

ethnic back grounâ, physical inactivity, hïstory of GDM, overt

cardiovascular disease, high fasting insulin levets, and IGT (1 5,16,17).

1.2.7 Complications

Diabetes is a serious M.th problem associated with acute and chronic

complications. It often disables people in their middle years and as a group,

people with diabetes die younger than those not affited by it (18).

Major acute complications are hpglycemia and hyperglycemic crises

including ketoacidosis and hyperglycemic-hypemsmolar states.

The chronic hyperglycemia of diabetes is associated with long term

macro and microvascualr disease causiag damage, dysfunction, and

ultimately failure of various vital or- especially the kidney, eye, nerves,

heart and biood vessels,

Diabetes (both type 1 & type 2) is a major cause of coro- artery

disease, which is the leading cause of death in Canada. Morbidity and

mortaliîy rates are 2-to4fold higher than in age-and sex-matched groups in

the non-diabetic population (19,20,21,22,23) it is &O a leading cause ofnew

cases of blindness and kidney disease in adults.

1.2.8 Monitoring Blood Glucose Control

Daily Self Blood Glucose Monitoring (SBGM) has markedly improved

the ability to acutely control blood glucose levels. It permits recognition of

low levels of blood glucose before hypoglycernia occurs (24,25) and allows

people to assess the effècts of diet, exercise and changes in treatment

regimens.

People with type 1 diabetes often use pre-meal and bed time tests, as

well as intermittent ps t meal testing to adjust insulin doses. Testing for

glycated hemoglobin, as it refleck average blood glucose levels of

approximately the previous three months, should be pe150-d penodically

to assess long-term glucose control (26). A specific type of glycated

hemoglobin, HbAlc, is a tool for assessrnent of the preceding 6 8 weeks

(27)-

1.2.9 Intensive Blood Glucose Control

Epidemiological studies and studies done in animal models of diabetes

implicate hyperglycemia in the pathogenesis of long-terni complications of

diabetes. Consequently the aim of diabetes management is to maintain the

glycernic status as close to the no& range as safey possible.

Intensive insulin therapy was applied in the Diabetes Control and

Complication Triai @CCT) by multiple daily insulin injections administered

as basal insulin with short-acting bolus insulin (basal-bolus) adjusted

according to SBGM, meal composition and level of physical activity.

Continuous subcutaneous insuiin infusion (CSII) using a pump is an

alternative to multiple daily injections. DCCT achieved inipmved b l d

glucose control, which in turn effectvely delayed the omet and slowed the

progression of diabetic complications (1).

1 -2. 1 O Treatment

The primaty goal of therapy is to avoid acute & long-terrn

complications. In addition, the person's quality of life & overd sense of

weU-being should be considered. Depending on the type of diabetes and the

therapy required, this objective may be more or less dSicult to achieve

without acute adverse effkcts. Thus treatment must be tailored individilally

based on medical & social factors. If medication is required to achieve

diabetic controI, it should be optimized with regular physical activity and

healthy eating.

Since my thesis is about people with type 1 diabetes, I'Il d y focus

on them in my discussion.

1.2.1 O. 1 ~ o n - ~ h ~ c 0 1 0 g i c a l Therapy

While insulin therapy is essentid for M e in people with type 1

diabetes, it should be optimized with regular physical activity and

nutritionally adequate food intake.

An active He style pmmotes cardiovascular fitness and well being

(28). However the net effect of exercise on glycemic control is unpredictable *

and varies among individu& with type 1 diabetes because many variables

innuence glucose supply and utilkation. These include the state of nutrition

and metabolic control before and at the onset of the exercise, duration and

intensity of exercise, fitness of the patient, type, dose and site of insulin

inj ec tion (29).

In general, low to moderate intensity exercise lowers glucose levels

both during and d e r the activity, inc~iea~ing the risk of hypoglycemic

episode. Conversely, intense exercise raises glucose levels and can lead to

progressive hypergIycemia and even ketosis. Accordingly, physical activity

may require the adjustment of insulin and carbohydrate intake both before

and after the activity to prevent exercise-induced hypoglycemia In addition,

fiequent blood glucose monitoring should aid any adjetment. Obviously,

intensive diabetes management plus SBGM provide flexibility in

appropriately modi@ing insulin for exercise (343 1).

The advantages of increased activity levels must be balanced against

the risks due to diabetic complications or other medical conditions; thus,

plans for physical activity should be individuaiized.

1 -2.1 0. 1 -2 Nutritional Management

As fàr as nutrition is concerned, it should contribute through dietary

recommendations to irnprove glycemic control and avoid short-term

symptoms fkom hypoglycemia and hypergiycemia.

In Canada, dietary recommendations for people with diabetes are the

same as those for the gewral population, k d follow the principles of

Canada's guideliws for healthy eating (32). ControUed fat intake for the

prevention of cardiovascuiar diseases is the underlyhg principle of the

recommendations. For adults with normal lipid levels and reasonable weight,

the guidelines reconimend daily fat intake not to exceed 30% of total da@

energy requirements, where sahirated and poly-msaturated fats each not

exceeding IO%, with the remainder coming h m mono-unsahirated fat (33).

Protein intake, preferably fiom vegetable sources, should range fiom 10-

20% of total energy with daily intake of about 0.86glKg, which is similar to

that of the general population. The remainder 50-60% of the individual's

energy requirements should corne fiom dietary carbohydrates, especiaiiy

those . unrefined, slowly absorbed, and rich in soluble fibers (33).

On the other band, the ADA nutrition recommendations stress

individualkation of diet based on the patient Westyle, and the results of

clhical monitoring. It is recontmended that proteins, saturated ht, a d poly-

unsaturated fat contribute a total of 30=4û% of daiiy ewrgy intake, and the

remainllig 60-70% to come h m a combination of carbohydrates and mono-

unsahuated fats (34). Daily fiber intake of at least 25-35gld is reconmiended.

Soluble fiber intake has been associated with reduced blood glucose

responses, and improved blood glucose control(35)

Several health agencies recornmend an h a s e of low-GI foods in the

diets of individuals with diabetes (36,37,38). However, the ADA has

questioned the clinical utility of the GI and recommends tbat priority should

be given to the amount rather than the source of carbohydrate (39). ,

On the contrary, Jenkins focused on the concept of 'spreading the

nutrient load'. He suggested 4 factors that prolong the time of nutrient

absorption fiom the gut, understanding of which is helpful in the dietary

management of both diabetes and hyperlipidemïa. These are increased food

fiequency (nibbling), viscous soluble fibers, low GI foods, and enzyme

~ ï i t o r s of absorption (34). He added that m y higbfiber f d s that lower

LDL cholesterol also have low glycemic indices, such as bkley, beans, etc.

Therefore, exp1oration of low-GI f d s might be used to expand, rather than

limit, the carbohydrate food choices of people with diabetes.

1.2.10.2 Insulùi Therapy

Classically insuJin pfeparations can be classified according to theii

time of omet and duration. In ascending order, these include short acting

(Regular), intermediate acting W H , Lente) and long acting (Ultralente).

Intermediate and long acting insuiin injecti011~ provide appropriate basal

circulating insulin concentrations overnight and between meals. Pre-meal

bolus injections of short acting are given to prevent an excessive rise in

postprandial blood glucose immediately after meals (40).

Combinations of these insulins can be given in a variety of protocols.

In the split-mixed protocol, mixture of short and longer acting msulni is

administered twice a day, before breakEast and dirmer. Altematively, in the

basal-bolus protocol, also known as multiple daily injections, short-acting

insulin is given before each m e 4 while N'PH or Ultralente injections

provide basai requirements (4 1).

The available short acting insulin preparations have vatious

shortcomhgs. The most evident is a delayed omet of action and

uiappropriately long duration of action. Studies indicate that the peak effect

of Regular insulin occurs h m 2 to 6 heurs d e r injection, and its effect may

last as long as 16 hours (42). In addition, it was f o d diat Reguiar insulin

should be given fiom 30 to 60 minides before d s to achieve optimal

control of postpraadial glucose (43).

This is fàr tlom normal physiology where endogenous, pancreatic

insului secretion is stimulated irnmediately after blood glucose concentration

begins to rise following food ingestion, so that insulin concentration peaks

fat around 60 minutes postprandial, then declines over 3 hours to reach a

basefine level.

This departine in the pharmacokinetics of Regular insulin ftom normai

pancreatic insului springs fiom the fact that injecteci human insulin must be

in a mommeric fom before it c m be absorbed through the capillary

membrane into circulation. However, the himian insulin molecule has a high

tendency for seKassociation (44). When Regular insuiin solution is stored in

vials or cartridges, insulin molecules are in a polymeric, mostly hexameric

form to maintain stability. The dissociation rate into monomeric molecules is

low at the injection site, hence the delay in peak insulin concentration and

activity after subcutaneous injection (45). The end of the insulin B chain

(specifically Proline at position B28) is the site responsible for the self-

association of insului molecules.

Recently, bul in analogues have been developed which overcome

many of these problems. They are very rapiidly absorbed so that their onset

and peak action are closer to the injection time, which matches more closely

the postprandial glucose excursion (46).

1.2.10.3 Lispro Insulin

[LYS (B28), Pro (B29)I-h~man msulin (Lyspro or Lispro (Humalog)) is

an insulin analog in which the natucal amino acid sequence of the Bchain at

position 28 and 29 is inverted. These changes result in reduced capacity for

self-association (47), and account for the monomeric behaviour of Lispro in

solution (48), and for the faster phannacodynarnic action than Regular

insulin when injected subcutaneously (49).

Lispro insulin beguis to work within 15 minutes after subcutaneous

injection, peaks in about one hour, and has duration of 2 to 4 hours.

Compared to Reguiar insulin, Lispro insulin has a %ter absorption and a

more rapid elimination, effectively produchg a shorter duration of action,

which may offer an advantage over Reguiar insulin in the control of blood

glucose after meals (49).

Studies addressing mealtime glycemic control using Lispro iniifody

indicate that the postprandial rise in blood glucose is signiscantly lower,

approximately 1 to 4 ~ l l t l ~ V L , than with human Regular insulin (50,5 1) .The

best postprandial contml was obtained with an injection immediately before

the meal. Even if Lispro is injected shortly after the meal, the postprandial

glycemia is still well controlied (52,53).

The long-tem dycemic control as reflected by an improvement in the

HbAlc level is better with insulin Lispro than with human Regular insulin

(54), provided tbat an appropriate basal insuiin regimen is used to take into

account its shorter diwtion of action (55).

In type 1 diabetic patients, the hypoglycemia rate was found to be 12%

iower (particularly at night tirne) during treatment with Lispro compared to

Regular insulin (56). In addition, rate of severe hypoglycemia (defïned as

coma or requiruig glucagons or IV glucose), can be reduced by 30% with

insulin Lispro (57).

1.2.10.4 Lispro and Meal Composition

M. BU& (58) demonstrated the importance of meal composition in

relation to lispro-induced Post-prandial hypoglycemia. He used isocaloric

meals with different carbohydrate content. His expriment revealed that pre-

prandial lispro has tendency for Post-prandial hypogiycemia in the setting of

reduced carbohydrate iotake. This is consistent with other studies showing

that amount of carbhydraate in individual f d s inauences postprandial

blood glucose response (59). The author concluded that lispro dose need to

be adjusted depending on meal composition to avoid hypoglycemia

On the other han& M. Strachan (11) examined the effect of meal

composition on postprandial glycemia to establish optimal time for lispro

administration. He assumed that because meal composition affects rate of

gastric emptying (60,61) which in tum affects timing of post-prandial blood

glucose rise (62), meal composition has to be considered when timing of

lispro administration is adjusted. So he concluded that for meals with high

carbohydrate content, the optimal time for lispro administration is pre-

prandial. However, for meals with hi& fàt content, pst-prandial

administration is preferred to minsnize risk of pst-prandial hypogiycemia.

A group of patients with type 1 diabetes on Lispro insulin mêet

regularly at the Clinical Nutrition Center at St. Mchael's Hospital, Toronto,

Ontario. They have reported that a h consuming some foods but not others

(e.g. spaghetti, beans) thei. blood glucose &op initially, followed by 'a late

rise (Wolever TMS, personai communication). Both beans and spaghetti are

low-glycemic index f d s that are digested and absorbed slowly resulting in

delayed pst-prandial blood glucose rise. So probably in case of low-GI

carbohydrates, the blood glucose lowering action of iispro precedes the

absorption of carbohydrate resulthg in ~vch desirable pattern of blood

glucose response. Numerous studies have shown that pst-prandial blood

glucose and insulin responses are intluenced by both the amount of

carbohydrate consumed and its source (Brand et al. 1985, Jenkins et al.

1985, Wolever et al. 1996 and others). SO, ifcarbohydrate f d s differing in

terms of GI, nature, proportion of carbohydrate absorbed as glucose (Pg),

etc. produce significantly different blood glucose responses, then alteration

in either the dose andor timing of lispro administration may allow people

with type 1 diabetes to achieve more acceptable pattern of blood glucose and

reduce the risk of pst prandial hpglycemia.

1.2.1 1 The Glycemic Index

Systematic classification of f d s according to their glycemic

responses was first undertaken by Otto and Nüdas (3) in an attempt to

incorporate foods into diabetic diets in amounts inversely proportional to

their glycemic responses. The glycemic Index (GI) was developed

independently as ranking of foods based on theu postprandial blood glucose

responses compared with a reference food. More precisely, it is deîined as

the incremental area under the glucose ciirve of a 50g carbohydrate portion

of a test food divided by the incremental area under the glucose c w e of a

50g carbohydrate portion of a standard reference food (white bread) and

17

multiplied by 100 (3). Several methods have been used to calculate the area

under the glycemic-response cunre (63) and resuit in markedly different

areas and GI values (3). Woiever and Jenkllis use the incremental area for

calculations, where the area below the b a s e k glucose value is not inchded

in the calculation (64). Area d e r the cuve (AUC) is calculated by using

what has corne to be known as the 'the trapezoidal de ' . This calculation for

AUC is well described in the literature (3). In 1981 Jenkms et al (65)

published the fht lid of GI vahies for 62 f d s .

Studies have shown that both the amount and source of carbohydrate

innuence the acute blood glucose response to meah in normal (59), type

2(66) and type 1(67,68) diabetic subjects. Furthemore, Wolever et al have

shown that in type I diabetes, coasistency in both the amount and GI of

dietary carbohydrate is associated with ùnproved blood glucose control

indicated by H b ~ l c (8). This supports adherence to a consistent diabetic diet

plan. However, people with diabetes regard following a strict diet a burden.

Liberalization of the diet is an alternatik that is suggested to relieve tbis

bwden without adverse effects on glycemic control. To achieve optimal

glycemic control with a Ii'beralized diet, education about adjusting insulin for

both the amount and the GI of dietary carbohydrate is needed. This is

consistent with a study showing that unlike in type 2 diabetes, blood glucose

control in subjects with type 1 diabetes was not related to the composition of

the diet in te- of diet GI and amount of Carbohydrate and fiber intake (69).

This suggest that as long as insulin dose is adjusted to reflect food intake, the

composition of the diet may not be important for optimizing glycemic

control. This fact mostly applies to diabetics on intensive insulin treatment.

Although it is generally agreed that different carbohydrate f d s have

different glycemic effects, controversy exist about the therapeutic

implications of this information for diabetes. High carbohydrate diets are

recommended for individuais with diabetes and hyperlipidemia but the type

of carbohydrate is likely to be important in determinùlg the metabolic

response to such diets. Increasing carbohydrate intake with high GI f d s

may increase blood glucose, insulin, and triglycerides concentrati0~1~ (70).

However, increasing carbohydrate intake with low GI starchy f d s may

allow carbohydrate intake to be increased witbut these unwanted effects. In

long-term trials, low GI diets with no change in dietary fiber content result

in modest but signincatlt improvements in overall blood glucose control in

patients with type 1 diabetes as measured by glycated hemoglobin (6).

Perhaps of greater therapeutic importance is the abiüty of low GI diets to

reduce insului secretion and lower blood lipid concentration in patients with

hypertriglyceridemia (3). h o , low GI starchy foods improved glycemic

control and lowered sennn cholestero1 m type 1 diabetic children (71).

1.3 STUDY OBJECTIVES AND HYPOTHESIS

1.3.1 Study Objectives

1.3.1.1 To detemine the pattern of b l d glucose response for equivalent

a m t of carbohydrate foods with different Glycemic Index values d e r a

standard dose of lispro in type 1 diabetic subjects.

1.3.1.2 To determine how equivalent amount of carbohydrate f d s with

different Glycemic Index values idluence the pst-prandial hypoglycemia

induced by Lispro.

1 -3 -2 Study Hypothesis

1.3.2.1 Significantly different blood glucose responses will be elicited by

equivalent amounts of carbohydrate fiom different sources with different

Glycemic Index values in subjects taking a standard dose of lispro.

1.3.2.2 Postprandiai hypoglycemia will be elicited by lispro in subjects

taking equivalent mmunts of carbohydrate h m different sources more

fiequently with foods baving lower Glycemic Index a d lower Proportion of

carbohybte absorbed as glucose.

2. MATERIALS AND METBODS

2.1 SrnJECTS

Volunteers were recniited by study invitation posters distributecl in

Endocrinology clinics in 6 major hospitals in Greater Toronto area and in

Clinical Nutrition Centre at St. Michael's hospital, and by 3-day newspaper

advertisement on three occasions.

Recruiûnent period lasted 10 months between Feb 2000-Nov 2000,

during which subjects were tespondhg sporadically and not in groups.

A lecture was given to nurses and dietitians working in Clinical

Nutrition Centre explainhg the purpose and procedures of the study and

subject criteria to heQ in recruitment process.

A totd of 17 people were screened, 14 were eligible according to our

study criteria, and 11 of these were recniited. They were 8 femaie and 3

male subjects. Three female subjects withdrew d e r 1-2 test sessions for

personal reasons. So a total of 8 subjects each successfully completed the

whole 5 tests. Each subject needed a period of 5-8 weeks to complete the

study.

2.1.1 Screening

Subjects were interviewed pria to study commencement in the

screening session to assess suitability for participation. EligibIe subjects

were male or non-pregnant females, 14-75 years of age, with type 1 diabetes

who intensively seKmanaged their diabetes using lispro insulin for at least 3

months, the dose of which was adjusted based on the amount of

carbohydrate in the meal. Usual fasthg blood glucose had to be between 4

and 16.7 mmoVL, and HbAlc lower than or equal9.1%. Other inclusion and

exclusion criteria are listed below:

Inclusion criteria:

14-75yrswithtype 1DM

On insulin lispro for at l e s t 3 months

Male or non-pregnant females

Moderate to good glycemic control WAlc 1 9.1%; normal 4.5- 5.8%).

Usual fasting blood glucose between 4 and 16.7 mmoYL

Willllig and able to coiriply with shdy protoc01 and give U i f o d consent.

Exclusion criteria:

a History of severe hypogiycaemia (needs assisame of amther person)

more than once withh the last 3 monthS.

a Use of dnigs other than insulin that affect carbohydnte metabohm

(e.g. oral hypoglycemic agents, steroids). Use of stable doses of beta-

blockers or thiazide diuretics for the treatment of hypertension is

dowed.

Symptomatic gastroparesis or other gastrointeshl condition

affecthg digestion or absorption of nutrients.

a Use of drugs afEecting gastrointestinal motility or nutrient digestion or

absorption.

a Surgery, infection or signincant cardiovascular event within the last 3

months.

a Liver disease; severe rend failure or r d dialysis.

History of HIV infection or hepatitis.

Substance abuse.

Females already ptegnant or intendhg to become pregtiant driring the

study, or sexuaily active with childbearbg potential not ushg birth

control methods.

+ Lactating females less than 6 months after delïvery.

4 Participation in another medical, surjgical or pharmaceutical

investigation.

Any other physical, mental or behavioral condition that may make

participation of the subject dangerous to the subject's health or that of

others, or affect the results obtained.

In the screening session subjects came fasting to Clinical Nutrition

Centre at St. Mchael's Hospital. The study protocol was described and

queries of the subjects were answered. Also they were given instructions

about the standard dimer and snack for the night of the test. Then subjects

who were willing to participate signed on a consent fonn (Appendix A) and

were asked to give a fasthg bblood sample for biochemical analysis of blood

glucose, iipids, HbAlc, AST, creatinine and ma. A snack was given after

blood collection.

Mernards they answered a questionnaire about their medical history

and home blood test results (Appendix B), their height and weight were

measured and before they leave they were provided with the standard d i r

for the f h t test.

2.2 STUDY DESIGN AND PROTOCOL

SLMichael's Hospital Research Ethics Board approved the shidy

protocol. The study had a randombed, cross-over design.

Eligible subjects came to Glycemic Index Testing Office (55 Queen

St. East, 2d floor) on five occasions at weekly intends in the moming

between 8:O and 8 3 0 am after 10 to 12 buis ovemight h t for a 4%hom

test (testing day protocol, Figure. 2.1). In each test day they were studied

with one of the following 5 test foods: instant mashed potato, white bread,

spaghetti, pearled barely and pineapple juice, each containing 50g glycemic

carbohydrate.

2.2.1 Rationale

The rationale for choosing the above test f d s was to study 4 starchy

carbohydrates with a 3-fold Merence in terms of their GIS to elicit blood

glucose responses over a-wïde range. Pineapple juice was included because

the carbohydrate it contaùis consist of sugars (sucrose, glucose, and

hctose) that overall elicit a dwerent glycemic profile. These foods also

m e r in the proportion of carbohydrate absorbed as glucose (Pg). Starchy

foods have a Pg = 1 because they are totally absorbed as giucose, while

& =-s-ri. FBG = Fasting Blood Glucose

Figure 2.1 Testing Day Protocol

pineapple juice bas a Pg = 0.5 because sucrose is absorbed as half glucose

and half hctose (72).

2.2.2 Protocol

For dinner and snack (if n o d y coasumed) on the evening before

each test day, they consumed a standard meal that was provided, and nothing

else except for water. This meai consisted of a number of Choice Bars

(Mead Johnson) and a- c m of Ensure F o d a (Ross, Abbott Laboratones),

which is similar in ewrgy and carbohydrate content to their normal dinner

(Appendix C: Weight and nutrient content of standard dinner). If the subject

had to break his overnight fbt due to hypoglycemia, the test was cancelled

and rescheduled for amther day.

Upon arriva1 on the moming of the test, the subject was weighed and a

fasthg hger-prick capiiIary blood sample was obtained with Autolet

lancets. If blood glucose was less than 4 or more than 16.7, then the test was

cancelled for that day, and was rescheduled for another day. If blood glucose

was in the above range, the test was carried out and the subject took the dose

of insulin lispro that he or she would normally take before eating 50g of

carbohydrates.-For each subject, the same dose of lispro was repeated at the

same tirne (before the start of the test meal) on each of the test days.

Within few (2-7) minutes d e r lispro administration, the subject started

to eat a test meal containhg 50g available carbohydtate h m a standard

portion of instant potato, white bread, spaghetti, pineapple juice or pearled

bdey (GI, weight, and composition of test meals shown on Table 2.1). Test

meals were fed to subjects in random order.

Test meals were served with 250 ml water or tea (up to 50ml2% d k

and 2 bags of non-nutrient sweetener are allowed if desired). The drink

chosen remained the same for each subject for all subsequent tests. Test

me& had to be consumed withh 10 min. Additional finger-prick samples

were obtained haKhourly for 4 ho= after the start of the test meal

(Appendix D: Data Form). Each capillary blood sample was split into 2

aliquots; 3 drops of blood was saved in fluorocitrate tubes for subsequent

glucose analysis using a YS1 glucose analyzer. Results of which used for

study analysis. An additional drop was used for immediate analysis by

glucorneter (Precision TM, Abbott Laboratories, Columbus, -OH). The

glucorneter resdts were used to cietennine eligi'bility of f&hg blood

glucose, for subject safety, and for analysis of hypogiycemic outcornes.

During the test, subjects were expected to remain seated and they were

not pennitted to smoke. M e r the test was over, a snack or lunch meal was

provided if desired.

Table 2.1

GI, Weight and Composition of Test Foods

Weight

Moisture

Total Fat

Total carbohydrate

Available carbohYdrateB

Instant White Pineapple spaghettir P emled potato' 13readt ~uice # ~ a r l e y ~

83 71 46 41 25

67.3 67** 373 72.3 79.6

6.1 9.1 1.5 11.1 8.4

4.5 NIA N/A 7.2 7.6

0.6 0.4 0.4 1.6 1.5

1.9 NIA NIA 0.5 1 .O

4.2 2.1 O 2.0 11.2

Weight and composition in grams.

Portion size and nutrient composition baçed on a d y s k (TMS Wolever). * Portion size and nutrient composition based on food tables. * GI values nom literature (Foster-Powell K et al 1995) ** Weight of fiou.. * Available carbohydrate = total carbohydrate (by difference) -total dietsry nkr.

To minnnize withh- subject variation, data were only included for

tests when the subject's fastmg plasma glucose on the study days varied by

no more than 6 mmoVL. Tests outside this range were repeated.

2.2 -2.1 Hypoglycemia

According to our protocol, hpglycemia was recorded if blood

glucose dropped below 3.0 mmoi/L at the time of blood s a m p b based on

the glucometer or the YS1 analyzer retrospectively, or if at any time the

subject experienced imtohbIe symptoms of hypoglycexnia. At this point the

test was terminated and depending on the severity of hmycaemia, subject

was treated with oral dextrose, *ose Tablets or simp1y H cup of juice and

something to eat if required. Then blood glucose was monitored until it was

recovered-

Time to hypoglycemia was recorded exactly as minutes at which

hypoglycemia (based on glucorneter-or symptoms) occurred nom the start of

the test food or retrogradely as discovered by YS1 blood d y z e r .

The occurrence of 'low'blood glucose was defined as a reaâing less

than 4.0 mmoVL by glucometer or YS1 anaiyzer.

2.3 TEST MEAL PREPARATION

Portion sizes of white bread, potato, spaghetti, and barley were

determined based on d y s i s of moisture, ash, protein, fat and total dietary

fiber with available carbohydrate calculated by diffe~ence (Wolever TMS).

Portion size of pineapple juice was determined based on food Tables.

2.3.1 Instant Mashed Potato:

2 5 W boilùig water and '/z tbs salt was added to 67.3g of potato,

stirred mtil unifody hydrated. It was pqared just before servïng.

2.3 -2 White Bread

White bread was baked in 525g loaves containhg 250g carbohydrates.

250g of warm water was mixed with 334g of d-purpose flour (Robin hood),

7g sucrose, 6.5g Quick Rise Instant Yeast, and 4g of salt. The ingredients

were placed into an automatic bread d e r (BlackBcDecker) according to

instructions and mixed, kneaded and baked over a 2-hour p e n d Loaves

were cooled at room temperature for 1 hr and weighed. C ~ s t ends were

sliced off and discarded. The remainder of the loaf was cut into 105g

portions contalliing 50g carbohydrate, packed into plastic freezer bags and

fiozen. Prior to consumption, bread was thawed in microwave oven.

2.3.3 Spaghetti

72.30 of plain spaghetti (No Name Spaghetti) was boiled in a covered

pot in about 175ml-salted water for 15 min mtil all water was absorbed. It

was prepared the nigM before the test, kept in ikidge and micro waved before

consumption.

2 -3 -4 Pearled Barley

79.6 g of pearled barley m. Goudas) wai boiled in a covered pot in about 250ml-sdted water for about 2(hnin until aU water was absorbed. It

was prepared the night before the test, kept io fiidge and micro waved before

c onsumption.

2.3.5 Pineapple Juice

373 g of unsweetened pineapple juice (Dole), (approximately 1%

cups), was served after reiiigeration.

2.4 BLOOD GLUCOSE ANALYSIS

Blood giucose measurements were obtained ushg an automatic

glucose analyzer (Yellow Springs Instruments YS1 Myzer) , which &es

the glucose oxidase technique (73). A standard glucose solution (10mmoVL)

was used to calibrate the equipment. Ali the saniples were andyzed ody

after the reading of the standard solution gave values in the range of 9.8-10.2

mmoVL. This standard was run before each set of samples belonging to a

single test meal of each subject.

When D-glucose in blood sample makes contact wÏth the immobilized

enzyme glucose oxidase, it is rapidly oxidized pduciog hydrogen peroxide

(H202). The H G is, in turn, oxidized at the platinum d e , producing

electrons. Thus, a dynamic equilibrium is achieved when the rate of H202

production and the rate at which it leaves the immobiîized emyme layer are

equivalent and is indicated by a steady state tesponse. The electron flow is

linearIy proportional to the to the steady state of H202 concentration and

therefore, also to the concentration of glucose (74).

As with direct oxygen measurement, whole blood or hemolysed blood

interferes with methods rneasuritlg H202 directly. This problem is

circumvented with the YS1 analyzer by enclosing the enzyme in a semi

permeable polycarbonate envelope. This allows measurement in whole

blood, senmi or plasma

2.5 STATXSTICAL ANALYSIS

Lotus 123 97-dtion database software was used. Results were

expressed as means +/- SEM. Mean incremental areas mder the glucose

curves, ignoring any areas below the fast& level were calculated (3).

The GI for each test food was calculated for each subject using the

incrementd area under glycemic response cinve for 50 g of carbohydrate

fiom that test food and expressed as a percentage of the response to 50 g of

carbohydrate f?om white bread. Calculated GI values were divided by 1.4 to

be expressed by glucose scale (GI of glucose = 100). AUC of white bread

for one of the subjects was zero, and therefore food GIS pertaining to his

tests could not be calculated. As a result, these were omitted fkom the

calculation of mean GIS of foods, and n was considered to be 7 rather than 8.

Mean blood glucose increments and mean areas mder the glucose

response curve for food types were compared ushg two-way analysis of

variance. The Newman-Keuls method was used to adjust for multiple

~~mparisons.

Hypoglycemia and low blood glucose happened kquently based on

both glucorneter and YS1 ivralyzer. Least squares linear regression analysis

was perfonned to evaluate how hypoglycemia, low blood glucose, and time

to hypoglycemia correlate with several independent fktors such as

fkequency at which subject went hypogLycemic/low, kting blood glucose

concentration, food GI, and food Pg. Multiple regression d y s i s was a h

perfiormed to evaluate the correlation between hyjmglycemic outcomes; time

to hpgiycemia; and low blood giucose, aed the abve fàctom when

combined. Differences were considered statistically significant when p

3. RESULTS

3.1 SUBJECTS

8 subjects, 3 males and 5 females, each completed 5 test sessions.

Their age ranged between 14 and 74, with a mean of 36.75 years. Mean

duration of diabetes was 13 years, with a range of 2-32 yem. They were on

insulin Lispro for at least 3 months, with HbAlc raaging between 0.05 and

0.087. Main subject description is summarized in Table 3.1 (fully detarled in

appendix E).

All 8 subjects were using lispro and human insulin in a multiple

injection (basal-bolus) regimen. Seven subjects were treated with

intermediate acting insulin to provide basal needs. Two of these were on

Lente Uisuiin and five were on NPH insulin (3 taking it twice daily, 2 ody in

the evening). The remahhg 1 subject was on continuous subcutaneous

insulin infusion (CSII by pump releasing lispro at a basal rate of 1.2 Uh).

The mean of their total evening insulin dose was 15.9 f 4.5 U (range 6 to 44

U). The mean of their total monhg dose was 8.6 f 2.7 U (range 6 to 44 U).

The mean of their total lispro bolus intake was 8.3 f 2.5 U (range 2.6 to 24)

for the evening and 6.6 f 2.7 U (range 2 to 25) for the moniing. Appendix F

describes the insulin treatment of the subjects.

Table 3.1

Main Demographic and Biochemical Profile of the Sample at Screening

BMI

FPG (mrnoUL)

- Values (where applicable) are means f SEM * Indicates gJycated hemoglobin (Normal range 0.035 - 0.065)

The subjects completed a total of 40 tests. An additional 5 tests were

perfonned, as repetitions to those where the subject's fhsting blood glucose

varied by more than 6 mmoYL on the study days according to our study

protocol. One test couldn't be repeated because the subject could not attend.

3.2 GLYCEMIC RESPONSE DATA

Blood glucose concentrations were measured by glucometer as well as

by YS1 anaIyzer. Linear correlation showed that readings obtained fiom

these two methods are siificantly correlateci, where the slope eqiials 1.05 f

0.01 and the correlation coefficient (r) = 0.97 at p

- S m

25- --- Line of Identity

0 /

0

I I

8 a 2 2 0 - 0 8 % g 8 g w E 15-

8 , 1 s > 10- m u &

5-

O " I I I I 1 O 5 10 15 20 25

Bbod Gkrocse Concentration by Glucometer (mroYL)

Figure 3.1

Correlation between Glucometer and YS1 Blood Glucose Concentrations

+PdatQ +Wb Bread +- Pineapple Juice *Spaghe(G -0- Bariey

Figure 3.2 Mean Blood Glucose Increments @y YSI) for Food

Types vs. Time

Figure 3.3

Mean Blood Glucose Concentrations (by YSI) For Different Test Foods

Pineapple juice shows a high early blood glucose increment peak followed

by rapid decline.

Two-way ANOVA of blood glucose increments vs. tirne for food types

(Table 3.2) shows a significant effect of food type (P4).05) h m 30 to 180

minutes, and a highly si@cant effect of subject (P

Table 3.2

Two-Way Analysis of Variance of Incremental Blood Glucose Responses After Different Types of Food

30min

Source SS MS F P- Val Foods 234.9 4 58.7 11.2

C0nt' d: Two-Way A d p i s of Va- of focrementa1 B h d Ghmse Respo- After Different Types of Food

Source SS Q F P-Val Foods 147-6 4 36.9 6.6

Table 3.3

Mean Blood Glucose Increments for Food Types vs. Time

Pearled Barky Spgkttr* Pineapple White Bread Illstant Potuto J i e

- VaIues are means f SEM expressed as nmiol/L. - Cornparison of al1 means: means sharing same letter superscript are not sign%cantiy Fiifferent. Means with differenî superscripts are s igdbdy Merent at f l .05.

The mean mas under glucose response curve (Am) for food types

were examined. Two-way ANOVA of AUC (Table 3.4) shows that the

variation in AUC for food types can be explained by the signincant effects

of both food type @ < 0 .05) and subject (P

Table 3.4

Two-Way Analysis of Variance of Area Under Glycemic Curve (AUC) Mer DifEerent Types of Food

Source

Foods

Subject

Error

Total

p p p p p

1214845.8 4 30371 1.45 5.5976174

Table 3.5

Mean Area Under the Glycemic Response Curve (AUC) for Food Types

Food Tpes AUC

-

Pearled Barley

Spaghetti

Pineapple Juice

White Bread

Instant Potato

- Vahies are means * SEM expssed as mmolmia/l 0 - - Cornparison of d means: means shering same letter superscript are not q @ b n t f y

different. M~eans with différent mpema@ts are signiscantiy different at @.OS.

Glycemc Index

Figure 3.4

Correlation Between Mean AUC of Test Foods and Their Glycemic Indices

blood glucose G . 0 m V L ) , time to hypoglycemia, and low blood glucose

(Le. < 4.0 mmoYL).

Based on YSI, all 8 subjects experienced hypoglyrcemia compared to

ody 5 subjects based on the glucometer. Out of the 40 tests, hypoglycemia

occurred more fkequently based on the YS1 (17/40, Le. 42.5%) than the

glucometer (12/40, Le. 3W). This is consistent with our observation that

YS1 readings were on average lower than glucometer readings for the same

blood samples. The fhquency at which each subject had hypoglycemia

ranged fiom 0.2 to 0.8 (i.e. 1 of 5 to 4 of 5 tests) with both methods of

measurement. Hypoglycemia occurred with aU food types at times ranghg

fkom as early as 87 minutes, up to the end of the 4-hour test period (240

minutes).

3-3-2 LOW BLOOD GLUCOSE

AU subjects at some point had low blood glucose based on glucometer

and YSI. Similar to hypoglycemia, episodes of low *ose occurred more

fkequently based on YS1 (22140) than glucometer (20/40). The fhquency at

which each subject had low blood glucose ranged nom 0.2 to 1 (le. once to

aIl5 tests) on both YS1 and glucorneter.

Table 3.6 summarizes number of hypoglycemic and low glucose

episodes per subject based on glucometer a d YSI. The number of

hypoglycemic and low glucose episodes based on food type is illustrated in

Figure. 3.5 as detected by YS1 and glucometer. Episodes of hypoglycemia

and low glucose occmed most hquently with pkapple juice.

3.3.3 GI AND Pg IN RELATION TO HYPOGLYCEMIC OUTCOMES

The number of hypogiycemic and low glucose episodes was plotted

agakt food GI and Pg in Figure 3.6 and Figure 3.7, respectively. Resuits

fiom linear regression showed that food GL was not significantly related to

number of hypogiycemic or low blood glucose crpisodes. However, Pg was

inversely related to number of hypoglycemic (YS0 and low blood glucose

(glucometer) episodes @ < 0.05). Nevertheless, the number of points (types

of test meals) is small to draw conclusions.

Simple correlation was perfo~ned to obtain the relationship between

the occurrence of hypoglycemia, low blood glucose and GI and Pg of the

foods. There was no signincant correlation between food GI and

hypoglycemia or between food GI and low blood glucose by YS1 or

Table 3.6

Number of Hypoglycemic and Low Blood Glucose Episodes per subject

Numbers represent No. of episodes occurring in 5 tests.

Hypoglycemia

LowBlood Glucose

Subjects

Glucorneter YS1 Glucorneter YS1 -

2

3

1 2 O

1

4

4

3 O

2

4 O

3 1 2 1 4 1 4 1 3

3 1 3 4 4 1 5 1

5 6 1

1

7 4

5

1

1

% T o t a l 12 17 20 22

O Barley Pineapple Juice Potato Z Spaghetti White Bread

Test Foods

ü P - Low Blood Glucose

O Barley Pineapple Juiœ Potato Ir' Spaghetti White Bread

Test Foads

Figure 3.5 No. of Hypoglycemic and Low Blood Glucose

Episodes per Food Types

Figure 3.6

Correlation of No. of Hpglycemic Episodes (by Glucorneter and YSI) with GI and Pg.

"Law" (meter) vs. GI

"Low" (meter) vs. Pg a 1

Figure 3.7

"Law" (Ys9 vs. GI 8 1

Correlation of No. of Low Blood Glucose Episodes (by Glucorneter and YSI) with GI and Pg.

glucometer. However, Pg was significantly related to YSL-based

hypoglycemia (r = 0.46, slope = - 1-13, P

Table 3.7

Multiple Regression Analysis

Dependent 1 Variables Fas ting r Subject BIood GI pg G k o s e

- -

Occurrence of Hypogiycemia §*

Glucometer

Occurrence of Low Glucose $*

Glucometer

YS1

Time to Hypoglycemia *

YSI*"

* ~efined as blood glucose < 3 nmoYL or symptoms of hypogiYCenga ~enned as blood ghrose < 4 inmVL.

* Number of observations = 40 ** Numbet of observations = 12 *** Number of observations =16

3

Values are X coefkients

r

-

(slope) fobwed ôy p vahies. NS = not signiscant.

4. DISCUSSION AND CONCLUSIONS

4.1 DISCUSSION

The purpose of this study was primarily to compare the pattern of

blood glucose response for carbohydrate f d s with Merent GI values in

type 1 diabetics on Lispro insulin. This was examined in two ways. The h t

method was plotting the measuced blood glucose increme~~ts vs. time for

each food to obtain the correspondhg curves. Another method was

cornparhg mean AUCs for Metent f d s .

The results obtained h m both methods indicate that the source of

carbohydrate significantly Muences blood glucose responses in type 1

diabetic subjects using insulin lispro. We believe that our study design was

strong enough to detect real differences, which were not due to error or

chance. These foods dEered in their glucose response because their GI

values dfler over a wide range, i .e. their carbohydrates are digested and

absorbed at different rates depending on thek nature (starch vs. sugar) and

chernical structure (amylose: amylopectin ratio). Among starchy test foods,

barley and spaghetti, which have relatively low GI values (25 and 41

respectively) produced significantly lower glucose increments compared to

bread and potato which have relatively high GI values (71 and 83

respectively) between 60 and 120 minutes, as shown in Table 3.3.

Furthemore, the mean AUC for potato was significautly greater than that

for spaghetti and barley (Table 3.5). The mean AUCs for test f d s were

signifïcantly related to the respective GI values (Figure 3.4) obtained h m

the lïterature (these GI values were determined in normal and type 2 diabetic

subjects). This incücates that the GI is valid in this group of subjects with

type 1 diabetes using lispro.

In the case of pineapple juice, GI done caowt explain its blood

glucose response pattern. Pineapple juice contains sugars that dser fiom

starchy f d s in 2 ways. Sugars are absorbed more rapiâly compared to

unprocessed starchy carbohydrate. Therefore, although it has a GI lower (GI

= 46) than 2 of the starchy f d s , the initial (30 minutes) mean blood

glucose increment for pineapple juice was greater than al1 the starchy foods

(Table 3.3). However, shortly after that, its incremental blood glucose fêUs

rapidly and, by 90 minutes, it becomes no longer different fiom that of

barley (Gr = 25). This is probably because sucrose, the main coristituent of

pineapple juice is half glucose and half hctose. Fmctose, in him, has a very

small effect in raising blood glucose, which lends pineapple juice its Pg

value of 0.5, and exp1abs the rapid deche in blood glucose incremental

curve.

Despite having different Pg, mean AUC for pineapple juice retained its

median location among other test foods (Table 3.5) because AUC is rehted

to GI rather than Pg.

Our finding regardhg the signifïcance of source of carbohydrate on

glycemic response contradicts with current ADA Recommendations (1994)

on dietary cahhydrates, which state: "From a cfinical perspective, fbt

priority should be given to the total amount rather than the source of

carbohydrate consumed". One reason for the disagreement maybe that, for

this study, we selected carbohydrate sources with a wide range of GI, which

we expected to produce a wide range of glucose responses. However, in

practice, cornmon foods nom difEerent sources may not have large

Herences in GI and, thus, would not be expected to affect giucose

responses (Wolever et al. 1994). Thus, source of carbohydrate will affect

postpmdial glucose responses only if the GI values of the different f d s

differ by a sutnciently large amount. In addition, other factors such as

number of subjects king tested and variation between and within-subjects

may all affect the ability to detect difEerences in blood glucose responses to

different f d s .

Another aspect, which may infiuence the validity of our conclusions, is

the use of individual foods rather tban mixed meah in our experiment. Some

studies showed that diBeremes in source of carbohyclrates make no

merences to glycemic responses in the context of mixed me& because of

the potential effects of fat and protein on glucose response. However, faulty

methods were used in a numbet of the studies cited to support this position

(Wolever and lenkùis. 1986). In addition, there are other studies showkg

that GI retains its predictive ability in the mixed d setting (Collier et

d.1986). Furthemore, alterhg diet GI was fomd to improve overall blood

glucose control in diabetes (Wolever et al. 1992a).

Apart fiom GI and Pg, methodological factors may also înfiuence

profoundly the interpretation of glycemic response data (3). Factors that

might innuence blood glucose value obtained include: method of blood

sampiing subject characteristics (e.g. body fatness, glucose tolerance status,

insulin resistance); dose and timing of lispro and long-acting insulin; degree

of diabetic control and particularly the fasting blood glucose value on the

day of the test.

Om results indicate that subject factors had a significant effect on

blood glucose increments throughout the test (Table 3.2) and on the area

under the glycemic response curve (Table 3.4). This is because subjects

m e r fiom each other. In addition, variability could arise fkom within-

subject variation. That is, when a group of subjects test a food once, the

glycemic response obtained in each subject may Vary considerably (3) which

doesn't necessarily mean real dif fe~e~:es between the subjects.

Our measurement of glucose response was based on capillary whole

blood, because it is simple, non-invasive a d f d a r to our patients. In

addition, it was suggested that the use of capillary compared to venous blood

is more precise, as the glycemic responses are gceater in capillary biood.

That is, greater absolute differences between f d s and greater heterogeneity

between means d o w detedion of small differences in glycemic responses to

diflierent foods, and thus more experimental power is obtained (61).

Both glucorneter and YS1 d y z e r were used to masure capillq

glucose concentration. The former measures it in plasma; the latter in whole

blood. Glucose concentration is lower in red blood cells compared to

plasma; therefore, our hding that glucose concentration measurements

using glucorneter were greater was not unexpected.

The second objective of the study was to determine if the source of

carbohydrate expressecl as GI and Pg c m predïct the occurrence and timing

of hypoglycemia induced by iispro.

Results h m simple and multiple tegression d y s i s showed that the

tendency of haviag hypoglycemia postprandially was inversely mlated to Pg

(O* in YSI-based hypoglycemia). Similarly, the occurrence of low glucose

was sigdicantly related to Pg (YS1 and giucorneter). GI did not contribute

signincantly to the aforementioned correlations.

Om explanation for the finding that Pg predicts occurrence of

postprandial hypoglyceniia and low glucose is that Pg detemiines the

amount of carbohydrate absorbed as glucose, which in tum directly

influences its avdability in blood. The results of blood response studies

(Lee and Wolever) indicate that the less glucose consumed, the quicker the

blood glucose drops to baselb. Accordingiy, the occurrence of

hypoglycemia and low glucose is more likely expected with carbohydrate

foods having lower Pg (Le. more sucrose) regardless of their GI values.

GI did not predict occurrence of hypoglycemia and low glucose. Low

GI carbohydrates produce relatively lower glucose increments and smaller

AUCs, yet because they are absorbed slowly their glucose increments are

sustained for a longer tïme than the high GI carbohydrates. This may be why

we found no significant tendency for low GI to be related to hypoglycemia.

On the other hand, other fkctors could be responsible for missing a

signincant correlation between GI and hpglycemia such as the high

variability of giucose responses in type 1 diabetes. More power may be

needed to obtain a signifiant result.

When time to hpgiycemia was assessed, it was not found to be

signiscantly related to Pg. However, it was directly related to GI and FBG

(YS1 only; in multiple regression only, F0.05). Therefore, should

hypoglycemia happen, it wiU occm eariier with foods hahg lower GI

values and in subjects baving lower basehe glucose.

4.2 POTENTUU, PRACTICAL IMPLICATIONS

The current fïnding regardiig the signincant effect of the source of

carbohydrate (GI and Pg) on postprandai glycemia is relevant to every day

life of type 1 diabetics, especially those who are intensively treated with

lispro. One possible practical miplication of this shdy is that education

about insulin adjustment for the GI and Pg of dietary carbohydrate may be

needed to achieve optimal glycemic control. This is especially important

with diabetics following libersrlized diet. We have shown that high GI

starchy carbohydrates producecl on average greater glycemic responses up to

3 hours *postpratldidy compared to those with low GI. So, it may be

beneficial to advise diabetics to arlminrstei 0 a relatively larger dose of lispro

for higher GI carbohydrates Furthemore, spaghetti, which is low GI, slowly

digested carbohydrate showed unfavorable siycemic response after lispro in

the sense that blood glucose dmpped early for a while before it became

sustained for the rest of the c w e . So there is a potential for early

postprandial hypoBlyda, although we could not demonstrate it. So,

alteration in either the dose or timing of lispro by admiiiistering a smaller

dose or admmiste~g the dose a& eatiog may aliow patients to achieve a

more acceptable pattern of blood glucose.

One of the fkdhgs was thet f i t juices are more readily absorbeci

caused an initial greater and fater rise in postprandial glucose than starchy

carbohydrate. Furthemore, they are more Iürely to predispose to

hypoglycemia than starchy carbohydrates. Thmefore, if juices are to be

taken, then tighter contro1 of blood glucose may be achieved if a larger dose

of lispro taken preprandially. If this is the case it may be necessary to take a

snack to prevent late postprandial hpglycemia

4.3 FUTURE RESEARCH

One area for fiÙtrae research is to examine the effect of carbohydtate

source on postprandial glycemia in the context of mixed rneals rather than

individual carbohydrates (as m our study) to look at the possible

confounding variable effects of fat and protein. This way, the validity of our

conclusions in normal meal conditions can be d e t e e ,

A M e r step would be to examine the glycemic response to dif5erent

GI meals with different doses of lispro. Variation in timing of lispro

injection can also be tried. These procedures would be helpful in

detemiinùig how best to adjust the dose of lispro for diffierent carbohydrate

sources.

4.4 CONCLUSIONS

There were 2 objectives outlined in this thesis. The primary objective

was to compare postprandial glycemic response profile for equivalent

arnounts of carbohydrate foods k m different sources with different

glycemic index (GI) values aAet a standard dose of lispro in type 1 diabetic

subjects. The data supported my first hypothesis that signiscantly different

blood glucose responses will be elicited by quivalent amounts of

carbohydrate fkom dierent sources having different GI vaiues.

M y second objective was to determine how equivalent amounts of

carbohydrate foods with Merent GI values influence the postprandial

hypoglycemia induced by lispro. W e hpthesized that postprandial

hypoglycemia will be elicited by lispro in type 1 diabetic subjects taking

equivalent arnounts of carbohydrate firom different sources more fkequently

with foods having lower GI d lower proportion of carbohydrate aôsorbed

as glucose (Pg). The resuhs supported the hypothesis for tbe Pg but not for

the GI. However, GI innuencecl the timing of postprandial hypoglycemia

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