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Breath methane excretion was measured in 274 healthy subjects from 2 rural communities in northern Nigeria. Studies in 24 adults showed a normal faecal flora with no enteric pathogens. Breath methane was detected in 122 (77%) of 159 adults, 19 (40%) of 47 older children (2-6 years), and 4 (8%) of 68 young children (< 2 years). Women were slightly more commonly breath methane-positive than men (82% versus 75%, respectively). Hyperventilation did not influence the specificity of the breath methane assay, although levels were circa 30% lower after deliberate hyperventilation. Methanogens were estimated by enrichment culture of faeces from 49 subjects. Of the subjects 76% had faecal methanogens estimated at > or = 10(2)/g, 45% at > or = 10(4)/g, and 16% at > or = 10(6)/g. There was no significant difference in distribution of methanogenic cultures between different age or tribal groups, and there were no obvious correlations between breath methane excretion and either the faecal carriage of methanogens per se or numbers present.

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1. The effect of acetate absorbed from the gut on glucose turnover has been determined in four healthy subjects during both fasting and an intravenous glucose infusion by using [U-13C]glucose. 2. In the first part of the study, after an overnight fast, a tracer dose of [U-13C]glucose was infused at a constant rate along with an infusion of saline for 7 h. In the second part the saline infusion was replaced by glucose at 4.25 mg min-1 kg-1. In both studies 15 mmol of sodium acetate was given by mouth at 15 min intervals from the fourth to the sixth hour. Glucose turnover, respiratory quotient, metabolic rate and blood levels of acetate, 3-hydroxybutyrate, lactate, insulin, glucagon and gastric inhibitory polypeptide were measured. 3. Glucose turnover rates (means +/- SEM) were 1.88 +/- 0.1 mg min-1 kg-1 during fasting and 4.0 +/- 0.08 mg min-1 kg-1 during glucose infusion. Acetate had no effect on glucose turnover, insulin, glucagon and gastric inhibitory polypeptide levels, but temporarily halted the rise in free fatty acids seen during the fasting study. No changes in oxygen consumption or carbon dioxide output occurred, in keeping with previous observations that acetate substitutes for lipid oxidation during metabolism and has no direct effect on glucose turnover.

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An investigation was made of the effect of changing mean transit time (MTT) by administration of drugs which affect colonic motility on faecal microbial mass in man. Senokot was used to accelerate and codeine and/or loperamide to prolong transit in subjects maintained on a constant high fibre diet. Doses of Senokot or codeine/loperamide were adjusted to halve or double transit time measured during a three week control period on diet alone. Stools were collected throughout and analysed for bacterial mass by a gravimetric procedure. Transit was measured by a continuous marker method. Senokot decreased mean transit time from 63.9 to 25.0 hours (n = 6), with increased stool weight from 148 to 285 g/day. Bacterial mass increased in all subjects from a mean of 16.5 to 20.3 g/day (dry weight) (p less than 0.025). Codeine/loperamide increased mean transit time from 47.1 to 87.6 hours (n = 5), with decreased stool weight from 182 to 119 g/day. Bacterial mass decreased in all but one subject from a mean of 18.9 to 16.1 g/day (NS). There was a significant correlation between transit time and bacterial mass in all three periods (r = 0.77, p less than 0.001). Changes in transit time are shown to alter microbial growth in the human colon and result in altered stool output, on a constant diet. Factors which affect transit may be as important as diet in determining large bowel function and hence susceptibility to disease.

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1. To evaluate the effect of age, sex and level of intake on the colonic response to wheat fibre, thirty healthy volunteers aged 17-62 years (nineteen men, eleven women) recruited from a local industry, were divided into four groups and given a controlled diet for two 3-week periods. The diet contained white bread during one period or one of four different amounts of bran-enriched wholemeal bread during the other (30, 60, 110, 170 g/d). 2. Wide variation was observed between subjects in stool weight on the basal diet and in response to wheat fibre. Stepwise regression analysis showed that the variation in stool weight was significantly related to sex (t 4.0, P less than 0.001) but not to age, height, weight or energy:fibre intakes on the basal diet. Stool weight in men (162 (SE 11) g/d) was approximately double that in women (83 (SE 11) g/d). Transit time and stool weight were closely related and the effect of sex on stool weight could be explained entirely by differences in transit. 3. The increase in stool weight with fibre was significantly related to dose (t 4.18, P less than 0.001) with approximately 1 g non-starch polysaccharides (the main component of dietary fibre) increasing stool weight by 5 g/d. Smaller increases in stool weight were seen in females, persons with initially low stool weights and small people. 4. Faecal carbohydrate excretion increased with the addition of bran mainly due to increased amounts of cellulose and pentose (arabinose + xylose), whilst digestibility of dietary non-starch polysaccharide fell from 77.6 (SE 2.3)% on the white bread diet to 65.6 (SE 2.4)% with the added bran (t 7.4, P less than 0.01, n26). 5. Faecal pH was more acid in men than in women and was related to methane production. Methane producers had higher faecal pH than non-producers (7.06 (SE 0.11) v. 6.65 (SE 0.1], lower stool weight (g/d; 93 (SE 12) v. 156 (SE 13] and slower transit times (h; 84.6 (SE 11.7) v. 48.6 (SE 6.6]. 6. These studies show that, when on similar diets, women have much lower stool weights and slower transit times than men. Furthermore, within the range of amounts of wheat fibre used in this and other published work, stool weight increases in linear proportion to the dose of fibre added to the diet. Methane excretion in breath is associated in this group of subjects with slow transit time and high faecal pH.

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In a study of breath methane concentration 43 percent of males and 49 percent of females produced detectable amounts. The proportion of methane producers increased significantly with age in males but not in females. Obesity as measured by the sum of triceps, forearm, suprailiac and subscapular skinfolds was significantly less in producers than non-producers. Amongst methane producers there was also an inverse relationship between skinfold thickness and the breath methane concentration. Breath methane concentrations were lower in males than females. In addition, a higher proportion of methane producers was found amongst secretors of blood group substances (ABH antigen) than non-secretors.

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The nutritional consequences of the ingestion of NAS depend on the quantity ingested. At lower levels there is little effect on the absorption of other nutrients and the colonic microbiological-salvage mechanism operates and a substantial proportion of the energy is made available to the body through fermentation. The exact amounts that can be tolerated in this way vary for individuals and are different for different compounds. At higher levels of intake the capacity of the colonic digester is exceeded and the decreased transit time affects N, energy, electrolyte and water metabolism. The responses to NAS are an example of how the animal body is dependent on the bacterial content of the colon to enable that organ to perform its function of water and electrolyte conservation.

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To test the hypothesis that fecal magnesium excretion is related to fecal volume, fecal specimens were collected from healthy persons who drank 32 single doses of poorly absorbed carbohydrate (mannitol, lactulose or raffinose): the concentration of Mg(++) (Y) in fecal water (X) was linearly and inversely related to fecal volume-that is, Y = 42-0.03 X. In contrast, after drinking magnesium sulfate, the concentration of Mg(++) in fecal water rose and, except after the lowest ingested dose of 10 mmol, the points relating Mg(++) concentration and fecal volume were outside the upper 95% confidence limit of the linear regression line. These findings could be useful when physicians are analyzing stool specimens for supportive evidence of magnesium misuse in baffling cases of diarrhea.

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Average intakes of nonstarch polysaccharides (dietary fiber), foods, and nutrients were measured in representative samples of 30 men aged 50-59 in 4 Scandinavian populations with a 3-4 fold difference in risk for large bowel cancer. The assessment technique, a 4-day weighed record of food consumed and duplicate collections of all food eaten, was validated by chemical analysis of the duplicates, by measuring 24-hour urine and fecal nitrogen excretion, and by comparing the constituents of the urine samples collected during the survey with similar collections 1-2 weeks later. There were good agreements between estimates of fat and protein intake obtained by food-table calculations of the 4-day weighed record and the chemically analyzed duplicates. Urinary plus fecal nitrogen excretion was equal to estimated nitrogen intake during the survey, and no discernable changes in urinary output occurred after the survey, thereby implying that dietary habits had not changed as a result of the investigative technique. It is concluded that the dietary data are indicative of current patterns of food consumption and are sufficiently valid for comparison with data on cancer risk in the 4 areas.

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Nonstarch polysaccharide (NSP) intake was measured in representative samples of 30 men aged 50-59 in 2 urban and 2 rural Scandinavian populations that exhibited a 3-4 fold difference in incidence of large bowel cancer. Intake was measured by chemical analysis of complete duplicate portions of all food eaten over one day by each individual. NSP intakes showed a rural-urban gradient, with 18.4 +/- 7.8 g/day in rural Finland and 18.0 +/- 6.4 g/day in rural Denmark versus 14.5 +/- 5.4 g/day in urban Finland and 13.2 +/- 4.8 g/day in urban Denmark. NSP intakes were also calculated (using food tables) from weighed food records kept over 4 days, one of which was the day on which the duplicate collection was made. Intakes were 2-2.5 g/day higher with this method than with direct chemical analysis, mainly because published tables of values have become outdated and inaccurate as a result of improved methods for measuring NSP in food. Individual variation from day to day in NSP intake was considerable. Average NSP intake and intake of some of its component sugars were inversely related to colon cancer incidence in this geographical comparison. To show a relationship at the individual level between diet and cancer risk in a prospective study would require detailed and accurate methods for the assessment of NSP consumption.

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We measured fecal composition after giving oral doses of mannitol, lactulose, or raffinose to ileostomy patients and to normal subjects in order to determine the colon's capacity for metabolizing these carbohydrates and to decide whether volatile fatty acids (VFA) or unabsorbed carbohydrate initiated diarrhea. Seventy-four percent of mannitol, 100% of lactulose, and 88% of raffinose passed unabsorbed through the small intestine of six patients with ileostomies. Dose-response experiments revealed that normal subjects could tolerate 120-220 mmol of mannitol, 73-146 mmol of lactulose, or 80 mmol of raffinose before fecal output of water exceeded 400 ml in 48 h or before test carbohydrate appeared in the stool. Mannitol could be metabolized to glucose; lactulose to fructose, galactose, and glucose; and raffinose to sucrose, melibiose, fructose, galactose, and glucose. The output of VFA in fecal water did not correlate with the moles of carbohydrate metabolized, and it did not greatly exceed the output of VFA in stools of equal volume that were induced by nonfermentable MgSO4. We conclude that the human colon is capable of removing appreciable amounts of single doses of these carbohydrates from fecal water. When this capacity is exceeded, unabsorbed carbohydrate rather than VFA prompts an increased output of fecal water.

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1. The effect of dietary fibre digestion in the human gut on its ability to alter bowel habit and impair mineral absorption has been investigated using the technique of metablic balance. 2. Five healthy male students were studied for 9 weeks under controlled dietary conditions and during the last 6 weeks they took 36 g pectin/d. Bowel habit, transit through the gut, faecal fibre excretion, calcium balance and faecal composition were measured. 3. During the control period only 15% of the dietary fibre ingested was excreted in the stools and when pectin was added to the diet there was no increase in fibre excretion. Stool frequency and mean transit time were unchanged by pectin but stool wet weight increased by 33% and faecal excretion increased (%) for fatty acids 80, nitrogen 47, total dry matter 28 and bile acids 35. Ca balance remained unchanged. 4. It may be concluded from these results that dietary fibre is largely metabolized in the human gut and dietary pectin completely so. This could explain its lack of effect on bowel habit and Ca balance. Other changes in the faeces may be related to an increase in bacterial mass.

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Epidemiological observations and animal experiments suggest that large bowel cancer is related to serveral factors. Among them, high dietary intakes of animal fat, the presence in the colon of relatively high levels of bile acids, specific patterns of intestinal microflora, slow transit through the gut, and low stool weights. Under metabolic conditions we have observed the effect on these variables of dietes containing 62 or 152 g/day of fat mainly of animal origin in six healthy young men over 4-wk periods. No change attributable to the diet was observed in the subjects' bowel habit, fecal weight, mean transit time through the gut, or in the excretion of dry matter. Total fecal bile acid excretion was significantly higher on the high fat diet (320 +/- 120 mg/day) than on the low fat diet (139.7) +/- 63 mg/day) t test = 7.78 P less than 0.001 as also was the total fecal fatty acid excretion, 3.1+/-0.71 and 1.14+/-0.35 g/day, respectively t test = 11.4 P less than 0.001). The fecal microflora including the nuclear dehydrogenating clostridia were unaltered by the dietary changes as was fecal beta-glucuronidase activity. Dietary changes which increase animal fat intake clearly influence fecal bile acid excretion in a way that would favor the development of large bowel cancer if current theories prove to be true. Dietary fat however has no effect on overall colonic function so other components of the diet must be responsible for the observed associations of bowel cancer with slow transit and reduced fecal bulk.

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Mixing the residue in the gut has been studied in 24 normal subjects using five different types of radio-opaque pellets. By giving single doses of different pellets to the subjects on three successive days and measuring their appearances in the stool by radiographs evidence of mixing was found in 83% of studies. Mean transit time (MTT) of markers through the gut was measured from the single dose studies (MTT-S) and also by giving the pellets to subjects continuously with each meal (MTT-C). By comparing MTT-C with MTT-S evidence was found for a mixing pool with exponential decay. The turnover time of this pool was estimated as about 30% of the total MTT.

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The effect on colonic function of adding wheat fiber for 3 weeks to the metabolically-controlled diets of six healthy volunteers has been studied. Increasing dietary fiber intake from 17 to 45 g/day increased fecal weight from 79 +/- 6.6 g/day to 228 +/- 29.9 g/day and shortened mean transit time, measured by a continuous marker method, from 57.8 +/- 8.3 hr to 40.3 +/- 8.9 hr. The increase in fecal weight was largely due to water. Fiber caused a dilution of fecal marker and an increase in fecal fat, nitrogen, and calcium output. Fecal sodium, potassium, and chloride showed only small changes but volatile fatty acid output increased significantly without concentrations changing. Fecal bile acid output increased from 199 +/- 46 mg/day to 279 +/- 46 mg/day. These changes are discussed in light of current views of the role of dietary fiber in protecting against colon cancer.

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A new method is described for measuring the mean transit time (MTT) of digesta through the human gut in which a constant amount of marker (radio-opaque pellets) is fed to subjects with each meal over a period of weeks, and its excretion measured in the stools. The MTT measured by this method (MTT-C) has been compared with MTT measured by giving single doses of similar markers to the same subjects (MTT-S) and with the 80% transit time (80% TT). Mean values on three dietary regimes for the MTT-C (54.2 h +/- 2.5) and MTT-S (54.2 +/- 2.6) were lower than that for 80% TT (63.1 +/- 3.0). The average MTT-C in a group of six healthy young men on an ad libitum diet was 2-3 days (range 0-7-4-0). When additional dietary fibre was added to a standard diet the average MTT-C fell (in all of five subjects) from 2-4 to 1-6 days. A continuous record of MTT-C is obtained by this new method which shows wide variations from week to week even on controlled dietary intakes. Using the single dose technique, evidence is produced which suggests that the MTT-S is a more accurate and reproducible method than the 80% TT.

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A method is described for measuring transit time through the gut which requires the collection of only one stool. A dose of 20 radio-opaque markers is given to the subject on each of three consecutive days with breakfast, each dose of marker being of a different type. The first stool passed after rising on the fourth day is collected and its marker content analysed. The method has been validated in 15 subjects by comparing it on 36 occasions with mean transit time measured by a continuous marker technique (MTT-C). In 35 of these studies transit measured from a single stool (SST) and MTT-C were significantly correlated R = 0.78 P less than 0.001. In one study the designated stool contained none of the SST markers. An alternative way of validating the SST method is described by comparing it with the average of the three mean transit times from three separate doses of marker (MTT-S). The average MTT-S agreed very closely with MTT-C in 36 studies R = 0.94 P less than 0.001 and proved a satisfactory alternative method for validating transit techniques. In a total of 66 studies in 22 subjects average MTT-S correlated significantly with SST, R = 0.85 P less than 0.001.

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Three-day faecal collections were obtained from 87 patients with a variety of gastroenterological diagnoses and 12 control subjects while consuming normal diets. Faecal weight, total fatty acids, and the proportion of hydroxystearic (OHSA) acid were measured. All patients had some easily detectable hydroxystearic acid. It was found that in general the percentage of OHSA in the faecal fatty acids increased with increasing fat output. Thus most patients excreting less than 20 g of fat per day had less than 5% OHSA while those with greater steatorrhoea had levels of 6 to 23%. Exceptions were patients with mild steatorrhoea with ileal disease, ileal resections, or small intestinal bacterial colonization, who had more than 5% OHSA whilst patients with colonic resection had much lower levels of OHSA than otherwise found. It is impossible to determine whether OHSA had a specific cathartic action from this study since the data implicated total fatty acids to the same extent.

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