Breath Hydrogen (H2) and Methane (CH4) Excretion Patterns in ...

Quarterly Journal of Experimental Physiology (1980) 65, 85-97

Breath Hydrogen (H2) and Methane (CH4) ExcretionPatterns in Normal Man and in Clinical Practice

K. TADESSE,* DOROTHY SMITH and M. A. EASTWODFrom the Department of Physiology, Edinburgh University, Teviot Place,Edinburgh EH8 9AG and Wolfson Gastrointestinal Laboratories, Department ofMedicine, Western General Hospital, Crewe Road, Edinburgh EH4 2XU

(RECEIVED FOR PUBLICATION 18 OCTOBER 1979)

Breath H2 and CH4 daily excretion patterns were studied in 20 healthy individualswhilst on their regular diets and fasting. The average H2 excretion level was found to be85 ml day-' on habitual meals and less than 35 ml day-1 whilst fasting. The meanexcretion in breath at any one time was less than 0-5 jimol I1 and individual breathsample excretion rarely exceeded 090 jumol .1-1. H2 excretion followed a regular pattern,being high in the morning, falling until about mid-day and rising during the earlyafternoon. The pattern of excretion remained essentially similar from day to day. Fastingdecreased the overall excretion level and abolished the afternoon rise. CH4 excretion didnot follow any regular pattern over the day and was individual with a third of theparticipants excreting above 0 1 ,Imol . I- 1 and the rest nothing or below 0 10 pmol . lIIn 15 of the subjects mouth-to-caecum transit time was measured employing the breathH2 test and using three different oligosaccharides of different molecular weight andvarying osmolalities. The mouth-to-caecum transit time (MCTT) for lactulose was foundto be 90+7 min, for raffnose 168 + 35 min, and for stachyose 290+ 0 min. Fasting anddifferent osmolalities of the same oligosaccharides did not alter the MCTT.Administering the three oligosaccharides to a patient with colostomy did not show adifference in the H2 evolution time. Using the breath H2 test as a method of detection oflactose intolerance showed that the test is relatively more reliable, non-invasive andsimple when compared to blood glucose measurement of mucosal lactase activity.

Anaerobic bacteria in the gastrointestinal tract of man produce partiallydegraded carbon compounds and a number of gases during metabolism ofcarbohydrates. Of these the major ones are volatile fatty acids (VFA) and thegases carbon dioxide (CO2), hydrogen (H2) and methane (CH4). The formationof H2 and CH4 is unique to anaerobic bacteria and no higher animal cell isknown to produce these gases [Mangold, 1934].

In healthy adult man, the whole gastrointestinal tract harbours somecommensal bacteria; but significant numbers occur only in caecum and colon.More than 95% of colonic bacteria are anaerobic [Hill and Drasar, 1975].Thus, in the normal situation, H2 and CH4 would be expected to be formed insignificant amount only in the caecum and colon. Once formed the two gases

*WHO fellow.85

86 TADESSE, SMITH AND EASTWOOD

are either passed as flatus per rectum or are absorbed into the portal bloodstream and excreted unchanged by the lungs [Kirk, 1949; Calloway, 1968]. Theconcentration of the two gases in the expired breath is very small (inmicromoles per litre), but methods of detection using gas chromatography arenow available [Calloway and Murphy, 1968; Levitt and Inglefinger, 1968;Tadesse, Smith, Brydon and Eastwood, 1979]. Using these methods it has beenshown that most of the H2 and CH4 formed in the gastrointestinal tract isexcreted through the lungs and the amount excreted is proportional to theamount produced in the lumen [Calloway, 1968; Levitt and Bond, 1970].

Recently, breath H2 and CH4 measurements have been suggested as valuablediagnostic tools and research aids. These may include the study of smallintestinal transit time [Bond and Levitt, 1975; Metz, Jenkins and Blendis,1976], the metabolism of dietary fibre in the colon [Hickey, Calloway andMurphy, 1972; Tadesse and Eastwood, 1978), the diagnosis of disaccharidasedeficiencies [Calloway and Murphy, 1968; Metz, Gassull, Leeds, Blendis andJenkins, 1976; Newcomer, Thomas, McGill and Hofmann, 1977], smallintestinal bacterial colonisation [Metz, Gassull, Drasar, Jenkins and Blendis,1976] and pneumatosis cystoides intestinalis [Gillon, Tadesse, Logan, Holt andSircus, 1978; Van der Linden and Marsell, 1979], and the study of bacterialactivity in the gut [Gilat, Ben Hur, Gelman-Malachi, Terdiman and Peled,1978]. The central principle in most tests is that any carbohydrate which is notdigested and absorbed in the upper small intestinal tract (i.e. unavailablecarbohydrate) reaches the bacteria in the colon and is fermented producing H2,CO2 and possibly CH4. Alternatively, in situations where anaerobic bacteriacolonise the upper small intestine, the bacteria compete for available nutrients,which are fermented anaerobically thereby producing gases. It follows, therefore,that measurements of H2 and CH4 levels in the expired breath and the timerelationship of the rise in breath concentration of the two gases following aspecified test meal is a relatively simple, non-invasive and therefore readilyacceptable technique for the study of some gastrointestinal functions.

Before wider application of the method is possible, a more detailed study ofthe normal excretion pattern of the two gases and factors which influence thispattern would help in the better understanding of the underlying process and inthe systematic utilisation of the method. In this paper we report the result ofinvestigations into the normal breath excretion pattern of H2 and CH4 duringthe day, the influence of overnight fasting on this pattern and factors whichmay influence results during application of the method.

Methods

Normal breath H2 and CH4 excretionTwenty subjects (10 male and 10 female) aged between 20 and 45 years were

studied. All were either hospital employees or physiology honours students andwere in good health at the time of investigation. Smokers did not smoke duringthe period of the experiment [Tadesse and Eastwood, 1977].

BREATH HYDROGEN AND METHANE EXCRETION PATTERN 87

At the start, the respiratory function and small intestinal absorptive capacitiesof the participants were assessed by using a spirometer for measurement of tidalvolume (VT), minute volume (VE) and vital capacity (FE V1) and a 5 g D-xyloseabsorption test followed by measurement of the 5 h excretion in the urine. Aone week recall dietary history was also taken by a dietitian, principally for theestimation of dietary fibre intake [Paul and Southgate, 1978].

The breath H2 and CH4 excretion patterns of the subjects were followed, onone day whilst taking their regular meals and on another day whilst fastingfrom 22:00h the day before to 15:00h the following day. Half of the subjects,unfasted, were further studied on three consecutive days and the other half onthree separate days in different weeks.

End-expiratory breath samples were taken at hourly intervals from 09:00 to17:00 h by a modified Haldane-Priestley alveolar air sampling technique [Metz,Gassull, Leeds, Blendis and Jenkins, 1976]. For the fasting situation sampleswere taken from 09:00 to 15:00 h. The H2 and CH4 concentrations in thebreath samples were analysed using a gas chromatograph with a katharometerdetector [Tadesse, Smith, Brydon and Eastwood, 1979].

Mouth-to-caecum transit time (MCTT)Fifteen of the volunteers participated in the MCTT study. The test involved

the administration by mouth of 10g of several oligosaccharides of differentmolecular weight, dissolved in 150 ml or 300 ml water, at 09:00 hr. End-expiratory breath samples were taken before the administration of the test mealand every 10 min thereafter for 5 h. The oligosaccharides used were thedisaccharide lactulose (Duphar Laboratories, Southampton), the trisaccharideraffinose (BDH Cliemicals, Poole, Dorset) and the tetrasaccharide stachyose(Wessex Biochemical Ltd., Bournemouth). The participants were randomlydivided into two groups of 8 and 7, and lactulose or raffinose 10g in 150 mlwater was administered without fasting. To test the effect of fasting andosmolality of the test solution, 4 of the participants took both theoligosaccharides at different osmolalities sequentially on separate days whilstfasting. For financial reasons stachyose was studied at one concentration onlyin two fasting individuals.The osmolalities of the test solutions were estimated by using an osmometer.

The viscosity of the solutions was also estimated by a modified Ostwaldviscometer, to see if there was a gross difference in viscosity between thedifferent oligosaccharide solutions.The time for H2 evolution from different sugars was investigated in a patient

who had had a descending colon colostomy following resection for rectalcancer. 10ml of a 20% solution (in water) of glucose, lactulose and raffinosewas instilled at about 25 cm distance from the stoma, separately and ondifferent days after an overnight fast. Several base line and post instillation gassamples were collected from breath and colostomy bag at 10min intervals forH2 and CH4 analysis.


Lactose tolerance (LT) testFor the LT test, 5 of the volunteers were used as controls and 10 patients who

were suspected of lactase deficiency on clinical grounds were studied. Fiftygrams of lactose in 250 ml water were drunk in the morning after an overnightfast. End-expiratory breath and venous blood samples were taken before thetest meal and every 30 min afterwards for 3 h. Blood samples were taken formeasurement of glucose concentrations [Varley, 1968]. On a separate day ajejunal biopsy was taken from the patients by means of a Crosby capsule andthe brush border lactase activity was determined on the mucosal samples[Dahlqvist, 1968].

Presentation of dataIn the normal breath H2 and CH4 excretion study, the values for the

concentration of the two gases in each breath sample were compiled for eachsubject and later plotted against the time of day. The H2 values for each hourof the day from all of the subjects were then pooled and the mean excretionpattern during the day was drawn for the group by plotting the mean valuesagainst the time of the day. Daily breath H2 excretion was estimated bymultiplying the mean H2 concentration per breath sample by the respective 24 hrespiratory volume of the subjects and the factor 0 80, the correlation coefficientbetween alveolar and mixed expiratory H2 concentration found by Metz et al.[1976] when validating the sampling method employed in this study [i.e. [H2]x 080 x VE X60 x 24].For the MCTT test, both the times from ingestion of the test meal to the first

significant size of breath H2 from base line level and when the breath H2 wasabove 0-90 ,umol . 1-1 were noted and compared.For the LT test, the maximum blood glucose rise from the fasting

concentration, the peak concentration of breath H2 excretion within 3 hfollowing the test meal, and the mucosal lactase activity were noted.Comparisons were made between the three measurements. For those who werelactase deficient, associated symptoms when taking the lactose and MCTT wererecorded.

Correlations between breath H2 and CH4 excretion and the estimated dietaryfibre intake, and between dietary fibre intake and MCTT, were calculated usingthe least-square linear regression. Student's t-test was used for the test ofsignificance.

Results

GeneralThe mean VT was 590 ml (range 500-760), VE-6-6 1 min (range 5 -0-9-01 . min),

FEV1 900% (range 80-96%) and dietary fibre intake 16 8 g-1 24 h (range 9-8-23-9). The 5 hours D-xylose urine excretion was normal in all the volunteersand ranged between 10-0-12 7 mmol which is 30-38 % excretion (lower limit ofnormal excretion is 29%). The osmolalities of the different test meals used are


Table I. Mouth-to-caesum transit time (min) of different oligosaccharide solutions measured bybreath H2 (when H2 > 0 0 pmol. 1- 1).

Lactulose Lactulose Lactulose Lactulose* Raffinose Raffinose StachyoseSubjects ** (470) (205) (550) (215) (125) (60) (215)

A 80 90 100 - 150 160 290B 110 70 100 200 200 290C 90 90 240 260D 80 70 70 90 80 70 -

Mean 90 80 85 95 168 173 290S.E.M. 7 6 15 5 35 40 0

*Pure crystalline lactulose.**Numbers in bracket indicate osmolalities in mosm/kg.

shown in Table I. Within the accuracy limit of the method, the viscosities of thesolutions used were not different from water.

Normal breath H2 excretionHydrogen excretion was found to have a regular pattern, being comparatively

high in the morning, falling until about mid-day and rising during the earlyafternoon (Fig. 1). The mean H2 excretion at any time during the day wasbelow 0 50 yimol .1-1 and individual breath samples rarely contained more than0 90 ,umol . l-'. The average daily breath excretion by an individual wascalculated to be 85 ml (range 50-188 ml). Measuring the breath H2 excretion ofan individual on separate days or on three consecutive days showed that thepattern of excretion remained essentially similar from day-to-day even thoughthere was slight variation in the actual amount excreted (Fig. 2). Figure 3demonstrates the excretion pattern of an individual over a 30 h period interruptedby 7 h sleep. Here again the regularity is maintained. There was no correlationbetween the amount of estimated dietary fibre intake and H2 excretion (r=0 18).

Normal breath CH4 excretionMethane excretion did not follow any regular pattern over the period studied

and was found to be individual (Figs. 3 and 4). A third of the participantsexcreted above 010 umol .1' (range 0-10-270 /umol.l-') and the rest below010 jymol .1'. The breath CH4 excretion status of each individual remainedunaltered during the different days tested. There was no correlation between theestimated dietary fibre intake and the level of CH4 excretion (r= -0 23).

FastingFasting decreased the overall H2 excretion level and markedly affected the

afternoon rise (Figs. 1 and 4). The average daily breath H2 excretion duringfasting was estimated to be less than 35 ml (range 0-133 ml). Methane excretionwas unaffected by fasting.


NORMAL BREATH H2 EXCRETION PATTERN DURING

pmol/l THE DAY OF 20 VOLUNTEERS (Mean ± S.E.M.) PPM1.0

- Regular Meal 20Fasting

0.75

C4 - ~~~~~~~~~~~~~~~~~~~15

I ,I

0.2

<05 T

09 00 10 00 1100 12 00 13 00 11 00 15 00 16 00 17 00TIME OF DAY (h)

FIG. 1. Normal breath H2 excretion pattern during the day of 20 volunteers, non-fasting andfasting (Mean±S.E.M.). Abscissa time of day (h) and Ordinate-breath H2 concentration(limol. l-') and PPM).

NORMAL DAILY BREATH H2 EXCRETION PATTERNOF TWO SUBJECTS

MO(/ PLOTS OF DIFFERENT DAYS) PPM80

SUBJECT 1 SUBJECT 23.0

-60x A

z2.0-\40

1.0 'A 72

0~~~~~~~I XI 0

1000 1100 1200 1300 1.00 1500 1600 1000 1100 1200 1300 11.00 1500TIME OF DAY (h1

FIG. 2. Normal breath H2 excretion pattern of two subjects (non-fasting), plots of different days.Subject (1)-plots of 5 consecutive days, subject (2)-plots of 4 different days in differentweeks. Abscissa time of day and Ordinate-breath H2 (umol -1 and PPM).

BREATH HYDROGEN AND EXCRETION PATTERN 91

pmol/1 BREATH H2 AND CH4 VARIATIONS DURING PPM

3.0 30 HOURS IN AN INDIVIDUAL-40

.4 x-----* Breath HydrogenI - @ Breath Methane

O 2.0-Z 30

4~~~~~~~~~~~~~~~~~~~~

coX.~~~~~~~~~~~~~~~~~C

0.5- IC /

* -'t¶ D B

1000 1300 1700 1930 2200 0100 0800 1000 1200 1500TIME OF DAY (h)

FIG. 3. Breath H2 and CH4 variation during 30 hours in an individual (non-fasting). Abscissatime of day and Ordinate-breath H2 and CH4 (pmol.l-1 and PPM). Gap between 1.00a.m. and 8.00 a.m. is sleeping period. Breakfast (B), Lunch (L) and Dinner (D).

BREATH H2 AND CH4 VARIATION DURING THE DAY

pmol/l IN AN INDIVIDUAL PPM3.0-

x-x H2 Regular Meal 60I-- H2 Fasting

0 *A--A CH4 Regular Mealz o-.-o CH4 Fasting 40

II

1.0 L- .; 200

0900 1000 1100 1200 1300 1400 1500TIME OF DAY (h)

FIG. 4. Breath H2 and CH4 variation during the day in an individual whilst fasting and non-fasting. Abscissa time of day; Ordinate-breath H2 and CH4 (jmol . -1 and PPM).


Transit time measurementThe mean non-fasting MCTT as measured when breath H2 rose above

0 90 ,umol/l was 105+15 min (S.E.M.) for lactulose and for raffinose 170+23min (S.E.M.) (P<0-02). In the fasting situation the mean MCTT for thethree oligosaccharides studied were-lactulose 90+7min (S.E.M.); raffinose 168+35min (S.E.M.); stachyose-290+Omin (S.E.M.). As measured by the presentmethod there was no significant effect of fasting on the MCTT (Table II).Changing the osmolality of the test solution did not alter the transit time of thespecific oligosaccharide significantly (Tables I and II). It is also interesting tonote that lactulose at the different osmolalities tested had a transit time notsignificantly different from lactose, administered in the usual way for LTtest (i.e. at about 600 mmol kg-1), in lactase deficient individuals. However,changing the oligosaccharide molecular weight altered the transit time, with thelarger molecular weight oligosaccharide having the longer transit time (P <0 05)(Table II). The representative plot of breath H2 changes against time for thethree oligosaccharides in the same fasting individual illustrates this point (Fig.5). Breath CH4 was unaffected by any of the three oligosaccharides and therewas no correlation between the dietary fibre intake and MCTT.

Table II. Mouth-to-caecum transit time (mean + S.E.M.).

Non-fasting FastingInitial > 09 Initial > 09rise imol. I1 rise iimol. -1'

Substance (min) (min) (min) (min)LACTULOSE (10) (4)

470mmol. I 78+7 104+13' 66+2 90+73205 mmol. kg-' 63 + 5 80+ 6

RAFFINOSE (9) (4)125 mmol. kg-' 128 +18 170+ 202 115 + 33 168 + 35460 mmol. kg-' - 90+19 173 +70

STACHYOSE (2)215mmol.kg-1 185+35 290+05

192p <0.02.34p <005.4p <005.

In the patient with colostomy, the base line concentrations of H2 in breathwere quite high on all the three test days (averaging 1 5 ,umol . 1), whilst in thebag there was almost none. After instillation of the test sugars there was nosignificant change in breath H2 excretion but there was a dramatic rise in thebag 10-20min later for all the three sugars. The subject was a non-excreter ofCH4 and remained so after the instillation of the sugars, despite a large H2increase.

Lactose tolerance testAll the subjects in this test had a normal fasting breath H2 excretion and blood

glucose concentration. In none of the 5 normal controls did the breath H2 rise


MOUTH TO CAECUM TRANSIT TIME OF THREEOLIGOSACCHARIDES IN A FASTING INDIVIDUAL

pmol/1 PPMpmol/i ~~~~~~~~~~~~~~803.5-

3.0-

-60

2.5-

~2.0 N

w ~~~~~~~LCD- 1.5 1

A1 /%

0.9 ( 20

0.51

60 120 180 240 300TIME (min)

FIG. 5. Mouth-to-caecum transit time (MCTT) of oligosaccharides (L-lactulose; R-raffinose; S-stachyose) given 10 g in 150 ml water to the same fasting individual on different days.Abscissa-time after ingestion of test meals (min); Ordinate-breath H2 concentration(pmol.-1 '). Line is upper limit of normal breath H2 excretion.

above 0 S5pmol.1-' at any time following lactose administration. Five of the(suspected) patients had no significant increase of breath H2 after lactoseingestion. This finding was supported by the blood glucose rise and the mucosallactase activity (Table III). In the other 5 patients, the breath H2 began to risefrom about 1 0 to 15 h and by about 3 h reached a peak of approximately3 0 umol .1'. This positive response coincided with the lack of a blood glucoserise and intestinal lactase activity (Table III). Accompanied symptoms aftertaking the lactose were abdominal discomfort, gaseousness, borborygmi anddiarrhoea in some.

Discussion

The results for the breath H2 and CH4 concentrations found here were similarto those previously reported [Levitt and Inglefinger, 1968; Calloway, 1968]. Thestudy on the pattern of excretion showed that breath H2 fluctuated in a regularmanner with a relatively high level of excretion early in the morning, a decreasein the level around mid-day and some rise early in the afternoon. Thisfluctuation appears to be related to the diet during the previous hours. Theearly morning increased values are probably due to the previous evening mealand the afternoon rise is related to breakfast. This is supported by thediminished morning increase after a long period of fasting or a light eveningmeal and the abolishing of the afternoon rise by avoiding breakfast. The patternof excretion remained constant, when tested on different days, probablyindicating the regularity of eating habits of the individuals.


Table 3. Results of 50 g lactose tolerance test and lactase activity.

Maximum Maximumblood glucose Lactase breath H2

rise activity rise MCTTPatients (mmol . 1-1) (pmol min -1 g- ) (,mol . 1-) (min) Remarks

Normal>1-0 >1-0 <1 0 50-100 values

1 0-1 --2 0-6 Normal3 0 3 Control4 0 5 Group5 06 2-4 07 057 1-4 0 0 Suspected8 - 17 0-1 Lactase9 3-8 9 4 0 Deficiency10 1-5 6-1 0-511 0-1 0 2-0 9012 0-2 5-0 60 Confirmed13 0-4 0 6 4-0 60 Lactase14 0 4 6-0 60 Deficiency15 - 0 40 60

Breath CH4, on the other hand, was found to be individual, with a group ofexcretors and non-excretors. There was no obvious daily pattern of excretion inthose who excreted CH4. The fluctuation in the level excreted during the daywas minimal and unaffected by fasting (Figs. 3 and 4). About a third of thegroup were found to be CH4 excretors and the rest non-excretors. This is inagreement with earlier reports ([Calloway, 1968; Levitt and Bond, 1970]. Thereason for the categorisation of people into the two groups is not clear.Suggested possibilities have been dietary difference, difference in gut flora andgenetic make-up [Levitt and Bond, 1970]. None of the available reports in thefield supports any one of these factors alone. Calloway, Colasito and Mathews(1966) studying the evolution of gases by intestinal bacteria in in vitro culturesof colonic digesta, found that when the digesta was cultured with differentsubstrates more CH4 was formed with amino acid substrates than withcarbohydrates. Results in this study show no association between CH4excretion and dietary protein, fat, carbohydrate or dietary fibre. Although thenumber of people involved was small, it is clear that carbohydrates whichaffected H2 excretion did not alter breath CH4 excretion. It has been reportedthat CH4 formation is dependent on H2 production. There has beenexperimental support for this from in vitro and ruminant studies [Wolfe, 1971;Hungate, 1976]. However, this does not appear to apply in man [Calloway,1968; Levitt and Bond, 1970]. Our results also show no relationship between H2and CH4 excretion. It is likely, therefore, that factors which influence CH4formation in man are different from those of ruminants and in vitro situations.

Various factors could influence the transit time of food through the gut. Thetype of food, its consistency, osmolality, viscosity and electro-motor activity ofthe muscles of the intestinal wall are amongst those implicated. Each of these

BREATH HYDROGEN AND EXCRETION PATTERN 95

factors may have different roles and degree of influence at different parts of thegut (i.e. stomach, small intestine, caecum, colon). Gastric emptying may bemore influenced by texture and colon transit by bulk. In this study mostvariables were kept as near constant as possible and the effects of change ofosmolality and molecular weight of the oligosaccharides assessed separately.The test meals were of similar consistency (liquid), containing in many wayssimilar carbohydrates and the viscosities of the substances were comparable.Thus, the expected influence on gastric emptying rate should be minimal. Also,liquids leave the stomach very rapidly and emptying is exponential, making thetransit time measured effectively small intestinal transit time (SITT). Bond andLevitt (1975) have demonstrated that the time delay between arrival of lactulosein the caecum and H2 evolution is about 5min. To our knowledge similarmeasurements in man for raffinose and stachyose are not available. But, in vitrostudies on culture from colonic digesta of dogs show that the twooligosaccharides ferment at a slower rate compared to monosaccharides[Rackis, Sessa, Steggerda, Shimizu, Anderson and Pearl, 1970]. We have shownhere that the three oligosaccharides as indicated by breath H2 rise, havesignificantly different MCTT (alias SITT). Therefore, the apparent difference inMCTT is either a true reflection of transit time difference or difference infermentation rate at the caecum. The result from the subject with a colostomysupport the former, since all the sugars increased H2 production at the samespan of time. Yet, the results do not rule out the possibility that breath H2increase may be dependent on the quantity produced per unit time, which mayvary for the different sugars and hence affect the time between ingestion andsufficient H2 production to increase breath H2. From the practical point ofview, irrespective of the reason for the difference, there appears to be variationin the MCTT in the same individual when using different oligosaccharides,stressing the need for standardisation of the test chemical.

The lack of effect of osmolality on the MCTT may be due to thecomparatively small range of osmolalities studied. Fasting appears to benecessary only to obtain an initial low level of breath H2.The results for the lactose tolerance tests show that breath H2 change

correlated quite well with the blood glucose and mucosal lactase activity. Infact it seems to clarify border line and false positive results. From the patient'spoint of view it is relatively simple and it is particularly suited for screeningpurposes, where only two breath samples, one base line and another 3 h postcibum, may be enough. Fasting before the test is not important since the breathH2 change in positive cases is very high and this would make the test mostconvenient for field studies and mass screening. The test may also be useful fordetermining the degree of lactase deficiency by doing graded tests and thiswould help in dietary advice to be given.

In conclusion, breath H2 excretion in the normal situation is very low andfollows a regular pattern of fluctuation during the day. The excretion level isaffected by diet and fasting. In contrast, CH4 excretion is individual andunaffected by fasting and administration of oligosaccharides. Thesecharacteristics of breath excretion of the two gases make H2 the most suitable


for tests of gastro-intestinal functions. In some of the tests, e.g. disaccharidetolerance test, fasting of the individual is not important. The MCTT isdependent on the molecular size of the carbohydrate used and it is important toindicate the oligosaccharide used when reporting results. The most suitable timefor performing breath H2 test appears to be around mid-day, since it is the timewhen breath concentration is at its minimum.

Acknowledgments

We acknowledge the help of Dr. R. Passmore for useful criticism and encouragement,WHO for their assistance with the fellowship to K.T., and Vitamins Incorporated,Chicago for financial help.

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