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7/31/2019 One-Year Weight Maintenance After Significant Weight Loss in Healthy
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One-year weight maintenance after significant weight loss in healthy
overweight and obese subjects: does diet composition matter?13
Elizabeth A Delbridge, Luke A Prendergast, Janet E Pritchard, and Joseph Proietto
ABSTRACT
Background: For many people, maintenance of weight loss is elu-
sive. Whereas high-protein (HP) diets have been found to be supe-
rior to high-carbohydrate (HC) diets for weight loss in the short
term, their benefits long term are unclear, particularly for weight
maintenance. Furthermore, the literature lacks consensus on the
long-term effects of an HP diet on cardiovascular disease risk
factors.
Objective: The objective was to investigate whether macronutrientdietary composition plays a role in weight maintenance and in
improvement of cardiovascular disease risk factors.
Design: The study comprised 2 phases. Phase 1 featured a very-
low-energy diet for 3 mo. In phase 2, the subjects were randomly
assigned to an HP or an HC diet for 12 mo. The diets were iso-
caloric, tightly controlled, and individually prescribed for weight
maintenance. The subjects were overweight or obese but otherwise
healthy men and women.
Results: The subjects lost an average of 16.5 kg during phase 1 and
maintained a mean (6SEM) weight loss of 14.5 6 1.2 kg (P ,
0.001) during phase 2; no significant differences between groups
were observed. By the end of the study, reductions in systolic blood
pressure were 14.3 6 2.4 mm Hg for the HP group and 7.7 6
2.2 mm Hg for the HC group (P , 0.045). Forty-seven percent of
the 180 subjects who began the study completed both phases.
Conclusions: The results indicate that the protein or carbohydrate
content of the diet has no effect on successful weight-loss mainte-
nance. A general linear model analysis indicated that dietary
treatment (HP or HC) was a significant factor in systolic blood pres-
sure change and in favor of the HP diet. This trial was registered at
www.clinicaltrials.gov as NCT 00625236. Am J Clin Nutr
2009;90:120314.
INTRODUCTION
In recent years there has been renewed interest in high-protein
diets for weight loss. An increase in the protein content of the diet
is usually accompanied by a reduction in carbohydrate content;
thus, the terms high protein and low carbohydrate are used
interchangeably in the literature; despite the protein content of
dietary treatment ranging from 25% (1) to 45% (2). Many studies
with a duration of up to 6 mo have found that diets high in protein
achieve greater weight loss than do high-carbohydrate diets
(24).
Very-low-energy diets (VLEDs) have been used effectively for
at least the past 20 y to achieve large and rapid weight losses.
Whereas one analysis of the literature found that long-term
weight regain experienced by individuals who followed a VLED
is no worse than weight regain experienced by individuals who
followed low-energy diets (5), another review found that indi-
viduals who followed VLEDs maintained a significantly greater
weight losses than did subjects who followed a low-energy
balanced diet (6). The type of diet and intensity and duration of
follow-up are likely to have an effect on the long-term success of
weight maintenance.
Little research has been done on the role of a high-protein (HP)diet on the maintenance of weight loss. Lejeune et al (7) showed
that, in overweight and obese subjects who followed a VLED for
4 wk (mean weight loss: 6.36 2.0 kg), a higher-protein, weight-
maintenance diet resulted in significantly less weight regain over
the subsequent 6 mo (0.8 compared with 3.0 kg; P, 0.05)). The
higher-protein diet consisted of 18% protein and was compared
with a 15% protein control diet. The higher-protein group
consumed the additional protein in the form of protein supple-
ments, whereas the control group consumed their usual diet
without additional supplements. Weight maintenance after
weight loss was also investigated by Claessens et al (8). In their
study, overweight and obese subjects underwent weight loss by
following a VLED for 5 to 6 wk. The subjects were then ran-domly assigned to an HP or high-carbohydrate (HC) weight-
maintenance diet for 12 wk. Subjects in the HP diet group
consumed 25% of their energy intake as protein and protein
supplements twice daily. The HC group consumed 55% of their
energy as carbohydrate, along with twice daily maltodextrin
supplements. The HP group maintained greater weight loss than
did the HC group.
The purpose of our study was to achieve a large and rapid
weight loss using a VLED and to then investigate the effects of 12
mo of weight maintenance with a low-fat, HP diet or a low-fat,
HC diet on body weight in overweight and obese men and
women. The subjects were free-living and were not provided with
any food or supplements during the weight-maintenance period.
1From the Department of Medicine, Heidelberg Repatriation Hospital,
Heidelberg, Australia (EAD and JP); the Department of Mathematics and
Statistics, La Trobe University, Bundoora, Australia (LAP); and the Depart-
ment of Physiology, University of Melbourne, Parkville, Australia (JEP).2 Supported in part by Meat and Livestock Australia.3 Address correspondence to EA Delbridge, Department of Medicine, Build-
ing 24, HeidelbergRepatriation Hospital, 300 Waterdale Road,Heidelberg3081,
Victoria, Australia. E-mail: [email protected].
Received November 9, 2008. Accepted for publication August 28, 2009.
First published online September 30, 2009; doi: 10.3945/ajcn.2008.27209.
Am J Clin Nutr 2009;90:120314. Printed in USA. 2009 American Society for Nutrition 1203
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SUBJECTS AND METHODS
The study was approved by the Human Research Ethics
Committees of the Royal Melbourne and Austin Hospitals. The
subjects were recruited by newspaper advertisement and word of
mouth. They were men and women aged 18 to 75 y whosebody mass indexes (BMI; in kg/m2) were 30 or 27 and hadcomorbidities. In providing their informed consent to partici-
pate, the subjects indicated their willingness to be randomly
assigned to study groups and to adhere to the study protocol.
Individuals with a history or presence of significant disease,
endocrine disorder, psychiatric illness, and alcohol or drug abuse
were excluded. In addition, women were excluded if they were
lactating, pregnant, or planned to become pregnant during the
study.
Study design
The study had a parallel, randomized design that consisted of
2 time phases. Phase 1 was a 3-mo intensive weight-loss phase
that all subjects began at the start of the study. Phase 2 refers to
the 12-mo weight-maintenance phase during which eligible
subjects were placed on either an HC or an HP diet after the
completion of phase 1. Phase 1+2 refers to the entire study
duration, ie, both phase 1 and phase 2.
Dietary instructions
During phase 1, the subjects were provided with the com-
mercially available VLED, (Optifast; Nestle Nutrition, Frankfurt,
Germany). As per the manufacturers recommendations, the
VLED was consumed 3 times/d as a meal replacement for a 12-
wk period and was taken as a milkshake, soup, or dessert. The
subjects were also permitted to consume up to 2 cups of low
starch vegetables daily with a small amount of oil (5 mL) and
a minimum of 2 L water or low-energy drinks. This providedsubjects with 500550 kcal/d. The subjects attended the clinic
individually each fortnight to be weighed, counseled on the use
of the VLED, and be provided with a 2-wk supply of the VLED.
The subjects were required to lose 10% of their body weightduring phase 1 to progress to the weight-maintenance phase
(phase 2). In phase 2, the subjects were randomly assigned to the
HC or HP dietary group (see Statistics). Harris-Benedict equa-
tions were used to estimate individual basal metabolic rate
(BMR) (9). Each individual subjects total energy expenditure
was calculated as BMR multiplied by an activity factor of 1.3,
which was considered appropriate for weight maintenance in
mildly active adults. The subjects were counseled to consume an
energy intake consistent with weight maintenance, and this in-formation was reinforced at each of the monthly visits attended
by subjects during phase 2, particularly if subjects began to
regain weight. The subjects received meal plans and recipes
appropriate to the dietary group to which they had been allo-
cated. They bought and prepared their own food and were in-
vited to attend group cooking classes that were specific to the
HP or HC dietary treatments.
Subjects in the HP group were instructed to consume 30% of
their intake as protein, whereas subjects in the HC group were
instructed to consume 15% of their intake as protein. Both
dietary groups were recommended to consume lean red meat
34 times/wk to meet the recommended intakes of iron and zinc
in line with Australian Dietary Guidelines. Both groups were
advised to reduce their fat intake to ,30% of their intake, with
a particular emphasis on reducing saturated fat. Carbohydrates
with a low glycemic index (GI) were recommended to both
groups. Issues such as comfort eating, snacking, reading food
labels, and healthy carryout and eating-out options were ad-
dressed during monthly counseling sessions. The subjects were
also encouraged to practice healthy behaviors such as aerobic
exercise 3 times/wk.
Data collection
The screening visit included a medical history, physical ex-
amination, and blood test. Body weight was measured at each
visit at approximately the same time of day by using the same
digital calibrated scales. The subjects wore street clothing, re-
moved their shoes, and voided their bladder before being
weighed. At each visit, bioelectrical impedance analysis was used
to measure body composition (Tanita TBF-300; WW Wedder-
burn Pty, Ltd, Sydney, Australia) by using the standard adult
mode of measurement. At each visit, waist and hip circum-
ferences were measured to the nearest 0.5 cm, and the mean of 2readings taken with a spring-loaded tape measure was recorded.
Waist circumference was measured at the level of the umbilicus
and hip circumference at the level of the greater trochanters.
Dietary compliance was estimated by using 3-d food diaries. The
subjects were instructed by a dietitian to provide as much in-
formation on food and drinks consumed (eg, brand name, vol-
ume, weight, and ingredients) over 3 consecutive days (2
weekdays and 1 weekend day). The food diaries and instructions
for their use were provided at months 8 and 14 of the study. The
subjects were asked to complete the diaries immediately before
their scheduled visits at months 9 and 15. The diaries provided
data on energy intake midway through and at the end of phase 2
the weight-maintenance phase. Food diaries were analyzed byusing Foodworks Professional Edition version 3.02.581 (Xyris
Software, Highgate Hill, Australia). Twenty-four-hour urine
samples were collected to coincide with food diary collection
midway through (month 9) and at the end of phase 2 (month 15).
The subjects were thoroughly educated on the procedure for
collecting an accurate 24-h urine sample and were also provided
with written instructions. The subjects were instructed to collect
all urine excreted after the first volume voided in the morning
until and including the first morning urine voided the following
day. Blood samples were collected via venipuncture after an
overnight fast. The analyses were performed by the Pathology
Department at the Royal Melbourne Hospital.
Statistics
The subjects were randomly assigned to the HP or HC group
by using randomly chosen block sizes of 2, 4, and 6 within 8 strata
that accounted for sex, BMI (,35 or 35), and age (,40 or40 y). After successfully completing phase 1, eligible subjectswere allocated to the next available treatment in the computer-
generated randomized list of treatments for their corresponding
strata.
All P values were 2-sided, and a P value 0.05 was con-sidered to indicate statistical significance. Values are provided as
mean 6 SEM unless otherwise indicated. The analysis was
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performed by using Minitab statistical software (version 14.0;
Minitab, Inc, State College, PA).
The statistical analysis of study completion measurements
consisted of 2 distinct analyses. The first was a primary intention to
treat (ITT) analysis that consisted of 2 different approaches to
missing data. The first approach used was the last observation
carried forward (LOCF). The second approach was return to
baseline (RTB) for study dropouts. The second analysis considered
study completers only (CO). For each measurement analysis, 2general linear models (GLMs) were fit: the first dealing with
measurement changes over phase 1+2 from baseline and the
second dealing with measurement changes during phase 2. Each
GLM had treatment group (HC or HP), sex (male or female), and
the interaction between treatment and sex as fixed effects.
The response variable for the first GLM (phase 1+2) was the
change in the measurement of interest at study completion
compared with baseline and included the measurement at baseline,
baseline weight, and age as covariates. The response variable for
the second GLM (phase 2) was the change in the measurement of
interest at study completion compared with the measurement at
completion of phase 1. Change of measurement at completion of
phase 1 compared with baseline and age were included as covari-ates. To assess the strength of linear relations between paired data,
we used Pearson correlation coefficients. The associated P value is
reported to test for nonzero correlation.
RESULTS
Baseline characteristics
The subjects were well matched according to baseline char-
acteristics (Table 1). There were no significant differences in
baseline demographic, anthropometric, or metabolic variables
between the subjects who went on to be randomly assigned to
either of the 2 dietary groups in phase 2.
Attrition
As can be seen in Figure 1, 180 persons were screened to take
part in the study. One man was excluded at the screening stage
because of a diagnosis of hemochromatosis. Of the 179 subjects
that began phase 1 of the study, 20 voluntarily withdrew because
of intolerance to the meal replacement. Fourteen subjects did not
succeed in losing the required 10% of their body weight. Four of
these 14 subjects were not included in the analysis because they
had not adequately complied with the study protocol because
they attended less than one-half of the required visits during
phase 1. Four subjects who successfully completed phase 1
decided not to continue in the study. One hundred and forty-one
(70 men and 71 women) subjects (78% of the initial number
recruited) completed phase 1 and progressed to phase 2, in
which they were randomly assigned to either an HP or HC diet.
There were 35 men in both the HC and HP diet groups and 35women in the HC group and 36 in the HP group.
After randomization, approximately equal numbers of subjects
withdrew from each dietary treatment group. Three subjects who
withdrew from the HP group were not included in the analysis
because they did not attend a sufficient number of scheduled
appointments to be considered compliant with the protocol. One
subject withdrew from the study after randomization and before
commencing any of the phase 2 procedures. No subject withdrew
because of symptomatic adverse effects of the diet. Forty-two
subjects completed the HP diet, and 42 subjects completed the HC
diet, which indicated that 59.6% of the 141 subjects who com-
menced phase 2 completed this phase. Except for age and blood
pressure measurements, there were no significant differences inbaseline characteristics between the subjects who completed the
study and those who dropped out. On average, the subjects who
completed the study were older (46.4 6 1.1 y) than those who
dropped out (40.0 6 1.0 y) (P , 0.001). Compared with the
subjects who dropped out, the subjects who completed the study
also had, on average, a higher baseline systolic blood pressure
(136.3 6 1.8 mm Hg compared with 129.1 6 1.6 mm Hg; P =
0.004) and a higher baseline diastolic blood pressure (85.3 6 1.2
mm Hg compared with 82.0 6 1.0 mm Hg; P = 0.032).
Anthropometric data
At the completion of phase 1, the mean weight loss experi-
enced by all subjects was 16.5 6 0.5 kg (P , 0.001), as seen in
Table 2. This equated to a mean weight loss of 14.7% (99% CI:
215.47,213.92; P, 0.001). All anthropometric measurements
decreased significantly during phase 1 for all subjects. The
subjects who completed both phases of the trial experienced
a small but significant increase in weight and BMI during phase
2 (weight: 3.6 6 0.9kg, P , 0.001; BMI: 1.260.3, P , 0.001),
as evident in Table 3. However, weight at completion of the
TABLE 1
Baseline (before phase 1) characteristics of the subjects who began phase 21
Characteristic HC (n = 35 M, 35 F) HP (n = 35M, 36 F)
Age (y) 44 6 1.1 43.7 6 1.4
Weight (kg) 109.4 6 2.6 114.0 6 3.0
BMI (kg/m2
) 38.6 6 0.8 39.3 6 0.8
Waist circumference (cm) 113.5 6 1.8 116.5 6 2.0
Fat (%) 42.4 6 1.0 (63) 41.7 6 1.0 (68)
Systolic blood pressure (mm Hg) 131 6 2.1 135 6 1.8
Diastolic blood pressure (mm Hg) 83 6 1.3 85 6 1.3
Total cholesterol (mmol/L) 5.4 6 0.1 (66) 5.5 6 0.2 (60)
HDL (mmol/L) 1.2 6 0.04 (65) 1.2 6 0.03 (59)
Triglycerides (mmol/L) 1.9 6 0.2 (65) 2.1 6 0.4 (61)
1All values are means 6 SEMs; n in parentheses. HC, high carbohydrate; HP, high protein. There were no significant
differences between groups.
HIGH-PROTEIN DIET AND WEIGHT MAINTENANCE 1205
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study was on average 14.5 6 1.2 kg (P , 0.001) less than the
baseline weight for all completing subjects, which equates to
a decrease of 12.98% (99% CI:214.96,211.00) in body weight
(Table 4). There was no difference between the HP and HC
groups in weight or BMI changes during phase 1 or phase 2:
15% of the HC group compared with 26% of the HP group lostadditional weight during phase 2 (P = 0.205). During phase 2,
42.5% of the HC group and 47.6% of the HP group regained
,20% of the initial weight lost during phase 1.
Whereas all subjects experienced a significant decrease in both
fat mass and fat-free mass during phase 1, all subjects experi-
enced a significant increase in fat mass and no significant change
in fat-free mass in phase 2. When the results for phase 1 and 2 are
taken together, from the beginning to the end of the study, all
subjects experienced significant decreases in weight, fat mass,
and fat-free mass, with no difference observed between the
groups. Significant reductions in waist and hip circumferences
were achieved during phase 1, with no further changes in these
measurements during phase 2. The reductions, however, were
maintained until the end of the study by those completing the
study (Table 4).
The ITT analysis of those who withdrew from the study (Table
4), in which baseline weights (RTB) or the last recorded (LOCF)
weight were carried forward and analyzed, still showed that there
was no difference in weight loss between the HP and HC dietary
groups after 12 mo of dietary counseling.
Lipids
As is evident in Table 1, mean lipid concentrations were in the
normal range at baseline for all subjects. For all subjects who
completed phase 1, total cholesterol and triglycerides decreased
significantly after the VLED (Table 2). At the end of the study,
total and LDL-cholesterol and triglyceride concentrations in
those subjects who had gone on to complete phase 2 (CO)
remained significantly reduced compared with baseline con-
centrations (Table 4). Although the changes in LDL during both
phases I and II were not significant, LDL cholesterol decreased
significantly from baseline by the end of phase 2 (Table 4). There
was no change in HDL during phase 1 (Table 2); however, duringthe 12 mo of the dietary treatment in phase 2, a significant in-
crease in mean HDL (P , 0.001) was observed (Table 3) and
was sustained until the end of the study by the completing
subjects (Table 4). There was no difference in lipid concen-
trations between the 2 dietary groups at baseline or at the end of
phase 1 or phase 2. The significant changes in total, LDL, and
HDL cholesterol and in triglycerides experienced by the subjects
who completed phases I and II were not observed in the ITT
analyses (Table 4).
Blood pressure
Blood pressure measured in the 2 dietary groups was within thenormal range at the commencement of the study (Table 1) and
remained so for the duration of the study. Pairwise comparisons
across all subjects showed a significant mean decrease in SBP of
13.2 6 1.4 mm Hg (P , 0.001) from baseline to the end of
phase 1 (Table 2). After the subjects were randomly assigned to
the treatment groups at month 3, no significant difference in
mean SBP decrease from baseline was detected between the 2
groups (CO) at this time (P = 0.375). The mean decrease in SBP
during phase 1 was 12.3 6 2.1 mm Hg for the HC group and
14.9 6 2.1 mm Hg for the HP group (Table 2).
Although subjects in both treatment groups experienced a sig-
nificant increase in SBP during phase 2 (4.7 6 1.9 mm Hg, P ,
0.014; Table 3), all subjects who completed the study experiencedan overall decrease in SBP from baseline of 11.1 6 1.7 mm Hg
(P , 0.001) (Table 4). For those subjects who completed the
study (CO), the mean decrease in SBP from baseline to the end of
the study was 14.3 6 2.4 mm Hg for the HP group and 7.7 6 2.2
mm Hg for the HC group (Table 4), and the difference between
the 2 groups was statistically significant (P , 0.045). When this
finding was investigated further by using a GLM, the dietary
treatment (HP) was found to be a significant fixed effect in
influencing SBP in subjects who completed the study and in the
ITT analyses (Table 5). The estimated model coefficient for
treatment indicated that a larger decreases in SBP can be expected
with an HP diet after weight loss. The subjects baseline SBP and
FIGURE 1. Status of subjects throughout the trial. 1Subjects with
a diagnosis of hemochromatosis that precluded participation.2
Poorcompliance with protocol; did not attend a sufficient number of studyvisits.
3Decided not to continue in study after randomization.
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baseline weight, along with age, were found to be significant
covariates.
Further statistical analyses were then conducted to investigate
the effect of the dietary treatments on SBP during phase 2. A
GLM was used that considered sex, treatment, sex treatment
interaction, age, and a reduction in SBP during phase 1 ( Table
6). It was found that the dietary treatment was a significant fixedeffect in the CO and LOCF analyses and was nearly significant
in the RTB analysis; the estimated model coefficient indicated
larger expected increases in SBP for the HC diet. The SBP re-
duction at month 3 was a significant covariate in the CO and ITT
analyses.
A significant mean decrease in DBP of 8.56 1.1 mm Hg (P,
0.001) was detected across all subjects at the end of month 3
(Table 2), with no significant difference between treatment
group reductions in DBP after randomization (P = 0.283). As
was observed for SBP, all CO subjects experienced a further
small but significant increase in DBP during phase 2 (3.7 6 1.4
mm Hg, P , 0.012; Table 3), but there was no difference in the
increase between the 2 dietary groups. Again a GLM was usedthat considered sex, treatment, sex treatment interaction, age,
and a reduction in DBP during phase 1. Only the reduction in
DBP reduction at month 3 was a significant covariate for pre-
dicting reduction in DBP during phase 2 for the CO and in the
ITT analysis (Table 6).
At the studys completion, the mean decrease in DBP from
baseline for the CO was 7.8 6 1.8 mm Hg for the HP group and
2.4 6 1.7 mm Hg for the HC group (P , 0.034) (Table 4).
However, pairwise comparisons to account for individual sub-
jects showed that both groups experienced comparable mean
increases in DBP of 3.7 mm Hg from month 3 to study
completion (Table 3). A GLM using dietary treatment as a fixed
effect did not show it to be significant. The covariate baseline
DBP was significant for the CO and in the ITT, whereas weight
was a significant covariate for the CO (Table 5).
Dietary complianceCompliance with the dietary recommendations was assessed
with food diaries and by the objective measures of urea ex-
cretion and weight maintenance. Food diaries in conjunction
with 24-h urine collections were satisfactorily completed by 6
menand 5 women in the HP group at month9 and by 10 men and
6 women in the HP group at month 15. In the HC group,
complete food diaries and 24-h urine collections were ade-
quately completed by 5 men and 5 women at month 9 and by 9
men and 4 women at month 15. There was no difference in
weight regain between those subjects who did and did not
supply food diaries in conjunction with urine collections; the
subjects who did comply regained 2.9 6 0.7 kg and those who
did not comply regained 3.1 6 0.5 kg by the end of the study(P = 0.375)
Estimated energy requirements for weight maintenance were
calculated for the mean body weight of the men and women.
When these estimates were compared with the energy intakes
calculated from the subjects food records, it was apparent that,
on average, women in both study groups had underestimated
their food intake and thus their energy intakes (mean calculated
intake = 2044 kcal; mean reported intake = 1370 kcal; P ,
0.001). The men, however, did not show such disparity in their
reported and calculated energy intakes (mean calculated in-
take = 1771 kcal; mean reported intake = 1765 kcal; P =
0.961).
TABLE 2
Measurement changes from baseline to the end of phase 1 for all individuals who completed phase 1 or who were
randomly assigned to the high-carbohydrate (HC) or high-protein (HP) group at the end of phase 11
Measurement change Al l (n = 159) P HC (n = 70) HP (n = 71) P
Weight (kg) 216.5 6 0.5 ,0.001 217.6 6 0.8 217.4 6 0.7 0.837
BMI (kg/m2
) 25.7 6 0.2 ,0.001 26.2 6 0.3 25.9 6 0.2 0.379
Waist (cm)2
214.2 6 0.5 ,0.001 214.3 6 0.8 215.2 6 0.7 0.394
Hips (cm)3
211.0 6 0.3 ,0.001 210.8 6 0.5 211.7 6 0.4 0.172
Fat mass (kg) 212.8 6 0.6 ,0.001 213.8 6 0.84 213.5 6 0.9 0.725
Fat-free mass (kg) 23.4 6 0.4 ,0.001 23.7 6 0.4 23.6 6 0.7 0.908
Cholesterol change4
20.65 6 0.08 ,0.001 20.65 6 0.11 20.59 6 0.09 0.641
HDL change5
20.003 6 0.02 0.878 20.015 6 0.02 0.003 6 0.03 0.605
LDL change6
0.14 6 0.5 0.763 0.59 6 0.92 20.33 6 0.09 0.323
Triglyceride change7 20.90 6 0.19 ,0.001 20.87 6 0.16 20.62 6 0.13 0.210
SBP change8
213.2 6 1.4 ,0.001 212.3 6 2.1 214.9 6 2.1 0.375
DBP change8
28.5 6 1.1 ,0.001 27.4 6 1.4 29.8 6 1.8 0.283
Pulse change9
24.7 6 0.9 ,0.001 24.5 6 1.2 25.3 6 1.6 0.668
1All values are means 6 SEMs; n = 159 subjects who completed phase 1, regardless of whether or not they continued
on to phase 2. DBP, diastolic blood pressure; SBP, systolic blood pressure.2 n = 149 (all), n = 66 (HC), n = 68 (HP).3 n = 148 (all), n = 65 (HC), n = 68 (HP).4 n = 125 (all), n = 63 (HC), n = 54 (HP).5 n = 124 (all), n = 62 (HC), n = 54 (HP).6
n = 117 (all), n = 58 (HC), n = 52 (HP).7 n = 125 (all), n = 62 (HC), n = 55 (HP).8 n = 130 (all), n = 62 (HC), n = 59 (HP).9
n = 98 (all), n = 45 (HC), n = 46 (HP).
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TABLE
3
Measurementchangesfromtheendofphas
e1totheendofphase2forallindividualswhocompletedphase1orwhowererandomlyassignedtothehigh-carbohydrate(HC)or
high-protein(HP)group
1
CO
CO
LOC
F
RTB
Measurementchange
All(n=82)
P
HC(n=40)
HP(n=4
2)
P
HC(n=70)
HP(n
=68)
P
HC(n=70)
HP(n=68)
P
Weight(kg)
3.6
6
0.9
,0.0
01
4.3
6
1.4
3.0
61
.1
0.4
76
3.8
6
0.9
3.1
6
0.8
0.5
44
9.5
6
1.2
8.3
6
1.2
0.4
82
BMI(kg/m2)
1.2
6
0.3
,0.0
01
1.4
6
0.5
1.0
60
.4
0.5
88
1.3
6
0.3
1.1
6
0.3
0.6
24
3.3
6
0.4
2.8
6
0.4
0.3
67
Waist(cm)2
0.0
16
0.8
8
0.9
94
0.9
26
1.5
20.8
161
.0
0.3
38
0.0
56
0.9
4
0.68
6
0.7
2
0.5
99
6.1
6
1.2
5.5
6
1.2
0.7
35
Hips(cm)2
0.4
36
0.7
7
0.5
73
0.8
96
1.2
0
0.0
260
.94
0.5
82
0.4
36
0.7
2
1.02
6
0.6
3
0.5
34
5.2
6
0.9
4.4
6
0.9
0.5
59
Waist-hipratio
2
20.0
06
0.0
0
0.2
44
0.0
06
0.0
1
20.0
160
.00
0.1
83
0.0
06
0.0
0
0.00
6
0.0
0
0.4
82
0.0
26
0.0
05
0.0
16
0.0
1
0.4
43
Fatmass(kg)
3.7
6
1.2
0.0
04
3.2
6
1.4
4.2
62
.2
0.6
85
1.8
6
1.0
3.0
6
1.2
0.4
30
6.6
6
1.3
7.0
6
1.3
0.8
27
Fat-freemass(kg)
0.6
16
0.3
6
0.0
94
0.8
96
0.4
3
0.3
460
.58
0.4
48
0.8
56
0.5
6
20.17
6
0.3
8
0.1
49
2.1
6
0.6
0.7
86
0.5
5
0.1
26
Totalcholesterol3
0.4
56
0.1
1
,0.0
01
0.3
66
0.1
7
0.5
460
.13
0.3
94
0.4
16
0.1
1
0.40
6
0.0
9
0.9
45
0.4
86
0.1
0
0.4
16
0.0
9
0.6
44
HDLcholesterol
0.1
76
0.0
2
,0.0
01
0.1
66
0.0
3
0.1
860
.04
0.7
60
0.1
36
0.0
2
0.15
6
0.0
3
0.6
11
0.1
26
0.0
2
0.1
26
0.0
3
0.9
49
LDLcholesterol3
20.5
16
0.7
1
0.4
79
21.4
16
1.5
0
0.3
360
.09
0.2
49
20.6
06
0.7
6
0.24
6
0.0
6
0.2
73
20.5
76
0.7
6
0.2
16
0.0
7
0.3
15
Triglycerides
3
0.2
16
0.0
9
0.0
24
0.3
06
0.1
1
0.1
360
.15
0.3
35
0.2
16
0.0
6
0.09
6
0.0
9
0.2
41
0.3
86
0.0
8
0.2
76
0.1
2
0.4
22
SBP4
4.7
6
1.9
0.0
14
7.5
6
2.3
1.9
62
.8
0.1
29
5.8
6
1.5
1.2
6
1.7
0.0
42
6.9
6
1.5
4.7
6
1.9
0.3
64
DBP4
3.7
6
1.4
0.0
12
3.7
6
1.9
3.7
62
.2
0.9
86
3.4
6
1.5
2.3
6
1.4
0.5
80
5.3
6
1.3
4.1
6
1.5
0.5
43
Pulse5
21.4
6
1.3
0.2
93
20.6
6
2.1
22.3
61
.5
0.5
28
21.1
6
0.9
23.4
6
1.2
0.1
36
20.2
46
1.1
21.1
6
1.5
0.6
69
1
Allvaluesaremeans6
SEMs.CO,
completersonly;LOCF,
lastobservationcarriedforward;RTB,returntobaseline;SBP,s
ystolicbloodpressure;DBP,diastolicbloodpressure.
2
n
=76(all),n
=36(HC/CO),n
=40(HP/CO).
3
n
=75(all),n
=36(HC/CO),n
=39(HP/CO).
4
n
=67(all),n
=33(HC/CO),n
=34(HP/CO).
5
n
=51(all),n
=27(HC/CO),n
=24(HP/CO).
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TABLE
4
Measurementchangesfrombaselinetothee
ndofphase2forallindividualswhocomplete
dphases1and2orwhowererandomlyassignedtothehigh-carbohydrate(HC)orhigh-pro
tein(HP)groupattheend
ofphase11
Measurementchange
CO
CO
LOCF
RTB
All(n=82)
P
HC(n=40)
HP(n=
42)
P
HC(n=70)
HP(n=68)
P
HC(n=70)
HP(n=68)
P
Weight(kg)
214.5
6
1.2
,0.0
01
214.3
6
2.0
214.8
6
1.5
0.8
41
213.8
6
1.3
21
4.3
6
1.1
0.7
70
28.1
6
1.4
29.1
6
1.3
0.6
10
BMI(kg/m2)
25.1
6
0.5
,0.0
01
25.1
6
0.8
25.1
6
0.5
0.9
79
24.9
6
0.5
2
4.8
6
0.4
0.8
82
22.9
6
0.5
23.2
6
0.4
0.7
47
Waist(cm)2
216.0
6
1.1
,0.0
01
215.4
6
1.7
216.5
6
1.4
0.5
91
214.1
6
1.1
21
4.5
6
1.1
0.7
93
28.1
6
1.3
29.7
6
1.3
0.3
76
Hips(cm)2
211.5
6
1.0
,0.0
01
210.5
6
1.7
212.4
6
1.2
0.3
65
210.3
6
1.0
21
0.7
6
0.9
0.7
64
25.5
6
1.1
27.3
6
1.0
0.2
47
Waist-hipratio
2
20.0
56
0.0
0
,0.0
01
20.0
56
0.0
1
20.0
56
0.0
1
0.6
02
20.0
46
0.0
0
20
.046
0.0
0
0.8
06
20.0
36
0.0
0
20.0
36
0.0
0
0.9
99
Fatmass(kg)
29.9
6
1.4
,0.0
01
210.5
6
1.7
29.3
6
2.1
0.6
59
210.9
6
1.2
2
9.9
6
1.5
0.5
85
25.5
6
1.1
25.7
6
1.4
0.9
28
Fat-freemass(kg)
23.6
6
0.4
,0.0
01
22.9
6
0.5
24.2
6
0.6
0.1
14
22.9
6
0.5
2
3.6
6
0.6
0.3
97
21.5
6
0.3
22.6
6
0.5
0.0
66
Totalcholesterol3
20.3
96
0.0
9
,0.0
01
20.3
06
0.1
4
20.4
86
0.1
1
0.3
44
20.2
26
0.1
0
20
.286
0.0
9
0.6
18
20.1
56
0.0
7
20.2
76
0.0
7
0.2
29
HDLcholesterol3
0.2
06
0.0
2
,0.0
01
0.2
16
0.0
3
0.1
96
0.0
4
0.7
39
0.1
16
0.0
3
0
.146
0.0
3
0.4
75
0.1
06
0.0
2
0.1
16
0.0
3
0.7
47
LDLcholesterol4
20.3
06
0.0
9
0.0
01
20.2
56
0.1
3
20.3
56
0.1
2
0.5
69
20.1
66
0.0
9
20
.176
0.0
9
0.9
40
20.1
26
0.0
6
20.2
16
0.0
7
0.3
31
Triglycerides
3
20.7
46
0.1
3
,0.0
01
20.9
06
0.2
3
20.6
06
0.1
5
0.2
70
20.6
26
0.1
3
20
.566
0.1
2
0.7
38
20.4
46
0.1
2
20.2
56
0.1
0
0.5
55
SBP5
211.1
6
1.7
,0.0
01
27.7
6
2.2
214.3
6
2.4
0.0
45
25.0
6
1.6
21
1.7
6
1.8
0.0
06
23.9
6
1.2
28.2
6
1.6
0.0
37
DBP5
25.2
6
1.3
,0.0
01
22.4
6
1.7
27.8
6
1.8
0.0
34
23.1
6
1.4
2
6.3
6
1.5
0.1
34
21.2
6
0.9
24.5
6
1.1
0.0
27
Pulse5
27.4
6
1.4
,0.0
01
26.2
6
1.7
28.6
6
2.1
0.3
98
23.9
46
1.1
2
7.1
6
1.4
0.0
84
23.1
6
0.9
24.7
6
1.3
0.3
11
1
Allvaluesaremeans6
SEMs.CO,
completersonly;LOCF,
lastobservationcarriedforward;RTB,returntobaseline;SBP,s
ystolicbloodpressure;DBP,diastolicblood
pressure.
2
n
=77(all),n
=37(HC/CO),n
=40(HP/CO).
3
n
=66(all),n
=33(HC/CO),n
=33(HP/CO).
4
n
=60(all),n
=28(HC/CO),n
=32(HP/CO).
5
n
=75(all),n
=36(HC/CO),n
=39(HP/CO).
HIGH-PROTEIN DIET AND WEIGHT MAINTENANCE 1209
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Actual protein intake was calculated from urinary urea mea-
sured in 24-h urine volume by using the following formulas (10):
Urinary urea in mg=dL urinary urea
3242h urine volume=100 1
Urinary urea nitrogen Equation 130:47 2
Nonurea nitrogen mg=d weight of the subject kg331
3
Protein intake g=d Equation 2 Equation 3=100036:25
4
The subjects were assumed to be in nitrogen balance and from
this we could calculate nitrogen and thus protein intake. From
measured urinary urea, the average protein intake at month 9 (half
way through phase 2) was calculated to be 95.9 g/d for the HC
group and 120.8 g/d for the HP group (Table 7). At month 15(end of phase 2), the mean protein intakes for the HC and HP
groups had increased significantly from month 9 to 110.2 and
136.1 g/d respectively (P , 0.006).
The mean (6SD) total urine collected was 2370 6 808 mL
for the whole study population, with volumes ranging from 1092
to 3959 mL for the 3 time points at which it was measured. This
is in line with expected urine output over 24 h. There were no
significant differences in urine volume between the HP and
HC groups at any time point. The correlation between protein
intake estimated from food diaries and calculated from urine
urea output was investigated by using Pearsons correlation
coefficients. A significant positive correlation of 0.329 (P =
0.036) was seen at month 9 and 0.353 (P = 0.010) at month 15.A paired-sample t test showed no difference in protein intake
estimated by food diaries or calculated by urinary urea for the
HC group at month 9 (Table 7). However, the protein intake
calculated from urine urea was significantly higher than the
estimated intake from food diaries for HC group at month 15
and for the HP group at months 9 and 15. Two-sample t tests
showed no significant difference in protein intake between the
TABLE 5
P values for fixed effects and covariates analysis in which the response is the measurement change from baseline to study completion for the general linear
models (phases 1 + 2)1
Measurement
SBP DBP
LOCF RTB CO LOCF RTB CO
Fixed effects
Treatment 0.006 0.050 0.032 0.179 0.028 0.064
Sex 0.753 0.776 0.927 0.059 0.591 0.287
Treatment sex 0.841 0.325 0.602 0.988 0.821 0.656
Covariates
Baseline ,0.001 (20.57) ,0.001 (20.36) ,0.001 (20.48) ,0.001 (20.78) ,0.001 (20.37) ,0.001 (20.63)
Weight ,0.001 (0.20) 0.002 (0.14) 0.008 (0.25) 0.058 (0.07) 0.074 (0.05) 0.043 (0.12)
Age 0.004 (0.30) 0.217 (0.12) 0.015 (0.40) 0.298 (0.08) 0.520 (20.04) 0.781 (0.03)
1Coefficients for covariates are in parentheses. SBP, systolic blood pressure; DBP, diastolic blood pressure; CO, completers only; LOCF, last observation
carried forward; RTB, return to baseline.
TABLE 6
P values for fixed effects and covariates analysis in which the response is the measurement change from month 3 to study completion for the general linear
model (phase 2)1
Measurement
SBP DBP
CO LOCF RTB CO LOCF RTB
Fixed effects
Treatment 0.003 0.004 0.051 0.195 0.254 0.045
Sex 0.317 0.299 0.829 0.290 0.104 0.477
Treatment sex 0.970 0.131 0.837 0.807 0.654 0.933
Covariates
Month 3 change ,0.001 (20.57) ,0.001 (20.42) ,0.001 (20.61) ,0.001 (20.54) ,0.001 (20.47) ,0.001 (20.73)
Age 0.305 (0.14) 0.163 (0.13) 0.901 (0.01) 0.550 (20.07) 0.815 (0.02) 0.255 (20.07)
1Coefficients for covariates are in parentheses. SBP, systolic blood pressure; DBP, diastolic blood pressure; CO, completers only; LOCF, last observation
carried forward; RTB, return to baseline.
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HC and HP groups estimated from food diaries at month 9, but
there were significant differences between the protein intakes
estimated from food diaries at month 15 and calculated from
urinary urea between the 2 groups at months 9 and 15 (Table 7).
The food diaries of the HC group indicated that the groupconsumed, on average, significantly greater than the recom-
mended 15% of their energy from protein at both months 9 and 15
and significantly less than the recommended 55% of their energy
from carbohydrate (Figure 2). The mean macronutrient con-
sumption of the HP group reported in food diaries was not sig-
nificantly different from the recommended intakes. Because of
the small sample sizes, the P values reported for this analysis
were obtained by using Wilcoxons signed rank test. Both the HP
and HC groups consumed minimal amounts of alcohol (,
3% ofenergy intake), and there were no significant differences between
the 2 groups in their consumption at either time point.
The mean fiber intake reported in the food diaries was 21.7 g/d,
with no significant difference between the 2 groups or over the 2
TABLE 7
Protein intake reported in food diaries and calculated from urinary urea in the high-carbohydrate (HC) and high-protein (HP) groups
Month 0 Month 9 Month 15
n
Calculated from
urine urea n Food diary
Calculated from
urine urea P1 n2 Food diary
Calculated from
urine urea P1
g/d g/d g/d g/d g/d
HC group 65 97.2 6 4.83
10 90.8 6 6.2 95.9 6 3.6 0.553 13 87.4 6 8.1 110.2 6 4.8 0.004
HP group 66 100.36 3.6 11 103.9 6 10.1 120.8 6 5.2 0.011 16 112.6 6 7.6 136.1 6 5.7 0.035
P4
0.145 0.139 0.007 0.001 0.040
1Paired-sample t test (intragroup comparison).
2Approximately one-third of the participants who provided food diaries and 24-h urine samples at month 9 also provided them at
month 15.3
Mean 6 SEM (all such values).4
Independent sample t test (intergroup comparison).
FIGURE 2. Recommended compared with reported macronutrient intakes in the high-protein (HP) and high-carbohydrate (HC) diet groups at months 9 and
15. Month 9 represents the half-way point of phase 2, and month 15 represents the end of phase 2. HP group: n = 11 at month 9, and n = 16 at month 15; HCgroup: n = 10 at month 9, and n = 13 at month 15. The dashed lines represent recommended intakes (HC diet: 15% protein, 55% carbohydrate, and 30% fat;HP: 30% protein, 40% carbohydrate, and 30% fat). The bold lines represent the median data for the group, and P values represent the differences betweenreported and recommended intakes.
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time periods. There were no significant differences in any other
reported nutrient intakes between the 2 groups.
DISCUSSION
Weight maintenance
Dietary studies investigating HP diets are usually conducted in
the context of weight loss. Although randomized trials have
indicated that carbohydrate-restricted diets are advantageous
compared with higher-carbohydrate diets in achieving weight
loss over 6 mo, longer trials have shown that the advantage is not
sustained for 1 y (4, 11, 12). In this study, significant weight loss
after 3 mo of intensive dietary treatment was maintained for
a year by following either an HC or an HP weight-maintenance
diet. Others have found that diet composition does not influence
weight regain when protein intake is kept constant and energy
intake is ad libitum (13).
Body composition
Some studies have found the loss of fat mass to be significantly
greater in subjects following an HP diet as opposed to a higher-
carbohydrate diet (3, 14), even with equivalent energy intakes and
weight loss between the groups (15). However, the findings are
inconsistent. One study observed that subjects following a low-
carbohydrate diet lost significantly more lean tissue than did
subjects following a low-fat, energy-restricted diet (16). Clifton
et al pooled data from 3 studies of 12-wk intakes of isocaloric HP
(2740% energy) and standard protein (1520% of energy)
intakes (17). No difference was found between the diets for
weight, fat mass, and lean mass loss.
Cardiovascular disease risk factors
Numerous studies have provided convincing evidence for the
benefits of HP diets on cardiovascular disease risk factors (18).
Energy-restricted, HP diets have frequently been found to de-
crease triglycerides (4, 19, 20) and increase HDL cholesterol (4,
20) compared with energy-restricted, higher-carbohydrate diets.
These improvements occurred even when there was no difference
in weight loss between the HP and HC or low-carbohydrate
treatment groups (15, 21). When protein intake was constant but
carbohydrate intake was reduced from 60% to 40%, the same
reduced triglyceride and increased HDL pattern followed (22).
It is plausible that the decreased carbohydrate-load charac-
teristic of an HP diet can induce a reduction in blood pressurethrough a reduced insulin response. Insulin has been found to
increase blood pressure (23, 24); subsequently, a reduction in
insulin secretion may decrease blood pressure. Although there is
evidence to suggest that HP diets induce a reduction in systolic
and diastolic blood pressure in the short term (25, 26), a sys-
tematic review of low-carbohydrate diets found no change is
systolic blood pressure in participants following such diets (27).
In this study, all subjects experienced a reduction in blood
pressure during phase 1 while following the VLED. However,
during phase 2, only subjects in the HP diet group were able to
sustain the reduction. The blood pressure of subjects in the HC
group significantly increased during this time.
Diet
It has been suggested that, compared with high-GI carbohy-
drates, low-GI carbohydrates may delay the return of hunger and
reduce subsequent food intake (28). In the present study, both
groups were prescribed low-GI carbohydrates, which possibly
contributed to the overall satiety of both diets.
The increased satiety arising from an HP diet has been well
established. In an ad libitum setting, this results in a spontaneousdecrease in food intake (3, 14, 29). However, in this study, the
subjects in the HC and HP groups were prescribed isocaloric meal
plans, and the data suggest that the subjects were compliant with
macronutrient recommendations. Had the dietary prescriptions
been more along the lines of ad libitum HP or HC diets,
a spontaneous reduction in food intake may have been observed.
Any potential satiating effect of protein on appetite may have
been obscured in this study by the macronutrient and energy
restrictions imposed on subjects through the meal plans provided.
Dietary compliance
A strength of this study was its free-living setting, in which nofood was provided to subjects. However, this strength was also
a weakness because it is difficult to measure dietary compliance.
Reported energy intakes in both the HP and HC groups remained
isocaloric, which supported the lack of difference in body weight.
The difference in reported and calculated energy intakes for
women suggested that the women had underestimated their food
and thus energy intakes. Such a discrepancy was not found for the
men. These findings are not unprecedented. A comparison of
energy intakes determined by food diaries and energy expen-
diture measured by doubly labeled water found that middle-aged
women taking part in a long-term diet-intervention trial under-
estimated their energy intake (30). In the current study, neither
group reported a significant increase in energy intake betweenmonths 9 and 15, despite a significant increase in weight ex-
perienced by the HP group (month 9, 1520 kcal; month 15, 1589
kcal; P = 0.620) and the HC group (month 9, 1639 kcal; month
15, 1678 calories; P = 0.864).
In this study, urinary nitrogen was not measured, but rather was
calculated from urinary urea. Although this technique is not
commonly used, its use in dietary studies such as this is not
unprecedented (31, 32), and it has been found to be a valuable
approach to assessing nutritional therapy (33).
According to the analysis of food diaries, the HP group
reported excellent compliance with their macronutrient recom-
mendations at months 9 and 15 (Figure 2). The protein intake of
this group, calculated from urinary urea, supported the food diaryreports. The HC group, however, struggled to consume the
recommended amount of carbohydrate (55%) and to limit their
protein intake to 15%. The most recent data on Australian food
intake reports that the average intake of protein for Australian
males and females is 17% of energy intake (34). Our results
suggest that subjects in the HC group were unable to sustain the
prescribed lowered intake of protein. Although the HC groups
mean protein intake during the study (21.7% of energy intake;
87.4 g/d indicated by the food diary or 110.2 g/d calculated) was
significantly higher than the 15% prescribed, it was still sig-
nificantly lower than the HP groups intake of 30.2% at both time
points. (Table 7 and Figure 2). Although satiety was not formally
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measured in this study, it is possible that the HC group was not
sufficiently satiated with the 15% protein recommendation. It is
also tenable that the HP group may have been more truthful in
recording their food intake. The authors are cognizant that the
numbers of subjects completing food diaries and urine collections
was disappointingly low, and, as such, are conservative in their
declarations of dietary compliance.
Attrition
Dropout rates in year-long studies of persons following HP
diets have ranged from 31% to 48% and from 37% to 50% for
persons following low-fat diets (35). The percentage of subjects
who dropped out of the weight-maintenance dietary phase (phase
2) of our study was in keeping with these findings (41%). The
percentage of subjects who began and completed both phases 1
and II of the dietary treatment was 47%. Although the number of
subjects who withdrew from the study was high, the rate of
attrition in both dietary treatment groups was equal, which
suggests that the reason for withdrawal was not diet related.
To preserve the validity of comparisons between treatment
groups, the ideal outcome would have been to follow all subjectswho underwent randomization to completion of the study (36).
However, although this was not possible, we do not view this as
a limitation of the study because the available data were handled
by using the most appropriate statistical methods (CO, LOCF,
and RTB). Furthermore, the sample size was large and the
analyses using the RTB and LOCF methods supported the
findings of those that completed the study, which thus
strengthened the integrity of our results and provided reassurance
that the results were not unduly biased by attrition.
Conclusions
The present study investigated whether dietary compositionplays a role in improving weight maintenance after weight loss.
Both the HP and HC groups sustained weight losses that were
statistically and clinically significant. This indicated that free-
living overweight and obese people were able to comply with
dietary recommendations and keep weight off over 12 mo. No
statistically significant difference in maintained weight loss was
observed between an HP and an HC diet. The effect of the in-
creased protein intake on appetite may have been masked by the
energy prescription imposed on subjects.
The authors responsibilities were as followsEAD: had full access to all
of thedata in the study andtakes responsibility forthe integrity of the data and
the accuracy of the data analysis; LAP: performed the statistical analyses;
JEP: contributed to the writing and editing of the text; and JP: oversaw
the study design, was involved in the data collection, and contributed
to the writing and editing of the text. JP sits on the Advisory Board for Opti-
fast, the VLED product used in phase 1 of the trial. None of the other authors
had a conflict of interest to disclose.
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