John Cummings | University of Dundee (original) (raw)

Papers by John Cummings

British Journal of Cancer, May 1, 1994

Intakes of starch, non-starch polysaccharides (NSPs), protein and fat have been compared with col... more Intakes of starch, non-starch polysaccharides (NSPs), protein and fat have been compared with colorectal cancer incidence in 12 populations worldwide. There were strong inverse associations between starch consumption and large bowel cancer incidence (large bowel r =-0.70, colon r =-0.76). There was no

Gut, Jul 1, 1991

Dietary sulphate may affect colonic pathophysiology because sulphate availability determines in p... more Dietary sulphate may affect colonic pathophysiology because sulphate availability determines in part the activity of sulphate reducing bacteria in the bowel. The main product MRC Dunn Clinical

British Journal of Nutrition, May 1, 1996

The digestibility of the starch in plant foods is highly variable, and is dependent on a number o... more The digestibility of the starch in plant foods is highly variable, and is dependent on a number of factors, including the physical structure of both the starch and the food matrix. An in vifro technique has been developed to categorize starch in plant foods according to its likely rate and extent of digestion in the human small intestine. The in vitro method provides values for rapidly digestible starch, slowly digestible starch and resistant starch (RS). In the present study values for the RS content of foods, as measured by the analytical technique, were compared with the recovery of starch from these foods when fed to healthy ileostomates. Nine ileostomy subjects were given a plysaccharide-free diet with a breakfast supplement, on each of 2 d (two subjects) or 3 d (seven subjects), of biscuits made from wheat, potato or banana flours or from moist-heat-processed wheat or maize flours. RS intakes measured in vifro ranged from 8.5 to 15.0 g/d for the test biscuits, and mean starch recoveries in ileostomy effluent were 1004 (n 5, range 91-106) % of those values, but there was substantial variation between individuals. It is proposed that RS is defined as 'the sum of starch and starch-degradation products that, on average, reach the human large intestine'. The analytical method for the measurement of RS in vitro based on this definition is shown to provide an accurate prediction of the average amount of starch that is likely to escape complete digestion and absorption in the human small intestine.

Gut, Mar 1, 1976

A new method is described for measuring the mean transit time (MTT) of digesta through the human ... more 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 800% transit time (80% TT). Mean values on three dietary regimes for the MTT-C (54 2 h + 2'5) and MTT-S (54-2 h + 2.6) were lower than that for 80 % TT (63 1 h + 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.

Carcinogenesis, 1996

High red meat diets have been linked with risk of sporadic colorectal cancer, but their effects o... more High red meat diets have been linked with risk of sporadic colorectal cancer, but their effects on mutations which occur in this cancer are unknown. G->A transitions in K-ras occur in colorectal cancer and are characteristic of the effects of alkylating agents such as A'-nitroso compounds (NOC). We studied the effect of red meat consumption on faecal NOC levels in eight male volunteers who consumed diets low or high in meat (60 or 600 g/day), as beef, lamb or pork, whilst living in a metabolic suite. Increased intake of red meat induced a significant (P < 0.024) 3-fold increase from 40 ± 7 to an average of 113 ± 25 ug/day NOC, a range of exposure in faeces similar to that from tobaccospecific NOC in cigarette smoke. The diets were isoenergetic and contained equal amounts of fat, but concentrations of heterocyclic amines were low. Faecal excretion of the promotor ammonia was significantly increased to 6.5 ± 1.08 mmol/day. When the high red meat diets were supplemented with 20 g phytate-free wheat bran in six volunteers there was no reduction in NOC levels (mean 138 ± 41 ug/day NOC), but faecal weight increased. Higher starch and non-starch polysaccharide intakes reduced intraluminal cross-linking in microcapsules (r =-0.77) and reduced faecal pH (r =-0.64). In two volunteers there was no effect of 600 g white meat and fish on faecal NOC (mean low white meat diet 68 ± 10 ug/day, high white meat diet 56 ± 6 ug/day) nor on faecal nitrate, nitrite and iron. Faecal nitrite levels increased on changing from a white to red meat diet (mean high white meat diet 46 ± 7 mg/day, high red meat diet mean 80 ± 7 mg/day). Increased endogenous production of NOC and precursors from increased red meat, but not white meat and fish, consumption may be relevant to the aetiology of colorectal cancer.

Evidence for the occurrence of microbial breakdown of carbohydrate in the human colon has been so... more Evidence for the occurrence of microbial breakdown of carbohydrate in the human colon has been sought by measuring short chain fatty acid (SCFA) concentrations in the contents of all regions of the large intestine and in portal, hepatic and peripheral venous blood obtained at autopsy of sudden death victims within four hours of death. Total SCFA concentration (mmol/kg) was low in the terminal ileum at 13±6 but high in all regions of the colon ranging from 131±9 in the caecum to 80± 11 in the descending colon. The presence of branched chain fatty acids was also noted. A significant trend from high to low concentrations was found on passing distally from caecum to descending colon. pH also changed with region from 5-6±0-2 in the caecum to 6-6±0 1 in the descending colon. pH and SCFA concentrations were inversely related. Total SCFA (~imol/l) in blood was, portal 375±70, hepatic 148±42 and peripheral 79±22. In all samples acetate was the principal anion but molar ratios of the three principal SCFA changed on going from colonic contents to portal blood to hepatic vein indicating greater uptake of butyrate by the colonic epithelium and propionate by the liver. These data indicate that substantial carbohydrate, and possibly protein, fermentation is occurring in the human large intestine, principally in the caecum and ascending colon and that the large bowel may have a greater role to play in digestion than has previously been ascribed to it. Address lor correspoidc;Kcc: D)r J 11 < uLImiHilgS. Dunn (linical Ntitrition (cntrc. MOTc Iennis CoUrt Road. (aimbridgc (132 101-Reccic (l tor publiltiotn 19 Mirclh 1987

Proceedings of the Nutrition Society, 1981

British Journal of Nutrition, May 1, 1982

British Journal of Nutrition, Nov 1, 1983

The capacity of wheat bran to impair mineral absorption independent of its phytate content was st... more The capacity of wheat bran to impair mineral absorption independent of its phytate content was studied by metabolic balance studies in man. 2. Three breads were prepared, equivalent to white, brown and wholemeal, by adding bran in different quantities to white flour. Calcium, iron, zinc and sodium phytate were added to the loaves to make the amounts equal in all breads. 3. Six healthy volunteers were studied for three consecutive 24-d-periods during which they ate a controlled diet, typical of that normally consumed in the UK but with 200 g bread/d. Only the type of bread changed between each dietary period. 4. The phytate contents (mmol) of 200 g of each of the breads after baking were: white 2.3, brown 2.1 and wholemeal 2.2; non-starch polysaccharide contents (9) were: white 3.3, brown 10.9 and wholemeal 18.7 5. The increased amount of bran in the breads increased stool output in the expected way but no change was seen in Ca, Zn and Fe balance. Blood levels of these minerals remained unchanged. 6. It is concluded that wheat bran and, in particular, the cell-wall polysaccharides of bran, are unlikely to exert a significant effect on mineral absorption in man, in amounts customarily eaten, independently of the effect of phytate present in the bran.

British Journal of Nutrition, Mar 1, 1989

1. The suggestion that there is a sustained enhancement in metabolic rate after exercise was inve... more 1. The suggestion that there is a sustained enhancement in metabolic rate after exercise was investigated during the course of a study in which six nonnal-weight volunteers (three men, three women) took part in a 9-week training programme. Baseline values were assessed in a 3-5 week control period of minimal activity before training. At the end of the study the subjects were capable of running for 1 h/d, 5 d/week. 2. Throughout the entire study the subjects were maintained on a constant diet. Measurement of energy expenditure by the doubly-labelled water (' H , l8O) method showed that the subjects had an energy imbalance of + 3 YO in the control and-20% at the end of the training period. The subjects were in positive (1.1 (SE 0.2) g) nitrogen balance in the second week of the control, and in negative (-06 (SE 0.3) g) N balance in the last week of the exercise period. 3. Over the course of the study maximum oxygen consumption (

British Journal of Nutrition, 1981

1. The dietary intakes of sixty-three adults, randomly-selected from the electoral role of a larg... more 1. The dietary intakes of sixty-three adults, randomly-selected from the electoral role of a large village near 2. Mean (~s D) daily intakes (g) for men and women respectively were: energy (MJ) 10.0*2.4, 8.252.1; fat

British Journal of Nutrition, May 1, 2002

The defining effect of prebiotics is to stimulate selectively the growth of bifidobacteria and la... more The defining effect of prebiotics is to stimulate selectively the growth of bifidobacteria and lactobacilli in the gut and, thereby, increase the body's natural resistance to invading pathogens. Prebiotic carbohydrates may also have additional, less specific, benefits because they are fermented in the large intestine. The prebiotic carbohydrates that have been evaluated in humans at the present time largely consist of fructans or galactans. There is consistent evidence from in vitro and in vivo studies that these are not digested by normal human enzymes, but are readily fermented by anaerobic bacteria in the large intestine. There are no reports of faecal recovery of measurable quantities of prebiotic carbohydrates. Through fermentation in the large intestine, prebiotic carbohydrates yield short-chain fatty acids, stimulate the growth of many bacterial species in addition to the selective effects on lactobacilli and bifidobacteria, they can also produce gas. Along with other fermented carbohydrates, prebiotics have mild laxative effects, although this has proved difficult to demonstrate in human studies because the magnitude of laxation is small. Potentially, the most important effect of prebiotic carbohydrates is to strengthen the body's resistance to invading pathogens and, thereby, prevent episodes of diarrhoea. At the present time, this effect has not been convincingly demonstrated in either adults or children, although there have been attempts to ameliorate the diarrhoea associated with antibiotics and travel, but without success. However, prebiotic carbohydrates clearly have significant and distinctive physiological effects in the human large intestine, and on the basis of this it is likely that they will ultimately be shown to be beneficial to health.

British Journal of Nutrition, Sep 1, 1986

The effect of age, sex and level of intake of dietary fibre from wheat on large-bowel function in... more The effect of age, sex and level of intake of dietary fibre from wheat on large-bowel function in thirty healthy subjects

Journal of Clinical Investigation, Apr 1, 1978

Gut, Jun 1, 1990

Hydrogen gas, which is produced during fermentation in the human colon, is either excreted in bre... more Hydrogen gas, which is produced during fermentation in the human colon, is either excreted in breath or metabolised by gut bacteria through a variety of pathways. These may include methanogenesis, dissimilatory sulphate reduction, and acetogenesis. To determine which of these routes predominates in the large intestine, stools were taken from 30 healthy subjects and incubated as 5% (w/v) slurries with Lintner's starch. In 23 of 30 subjects, methane production was the main method of hydrogen disposal. In the remaining seven, high rates of sulphate reduction were recorded together with raised production of H2S. All samples showed relatively low rates of hydrogen evolution and of acetate formation from CO2 and H2. Sulphate reduction and Rate ofhydrogen Rate ofsulphate accumulation* reductiont Viable count SRB Treatment (nmollg dry wt/d) (nmol/g dry wt/d) (loglo/gdrywtfaeces) Fresh faeces 72-5 (13-2) 321-8 (36 4) 9 0 (1-6) Ambient temperature for 24 h 54 6 (11-6) 281-2 (29 4) 9 0 (1-2) Freezing in 10% w/v glycerol 3 5 (0-9) 146-7 (28 4) 6-0 (1-7) *9 hour incubation; t48 hour incubation. SRB =sulphate reducing bacteria.

Applied and Environmental Microbiology, Nov 1, 1988

A mixed culture of human fecal bacteria was grown for 120 days in a three-stage continuous cultur... more A mixed culture of human fecal bacteria was grown for 120 days in a three-stage continuous culture system. To reproduce some of the nutritional and pH characteristics of the large gut, each vessel had a different operating volume (0.3, 0.5, and 0.8 liter) and pH (6.0, 6.5, and 7.0). A mixture of polysaccharides and proteins was used as carbon and nitrogen sources. Measurements of H2, CH4, S2-, sulfate reduction rates, sulfate-reducing bacteria (SRB), and volatile fatty acids were made throughout the experiment. After 48 days of running, porcine gastric mucin (5.8 g/day) was independently fed to vessel 1 of the multichamber system. The mucin was extensively degraded as evidenced by the stimulation of volatile fatty acid production. In the absence of mucin, sulfate-reducing activity was comparatively insignificant and methanogenesis was the major route for the disposal of electrons. The reverse occurred upon the addition of mucin; sulfate reduction predominated and methanogenesis was completely inhibited. This was attributed to release of sulfate from the mucin which enabled SRB to outcompete methanogenic bacteria for H2. SRB stimulated by mucin were acetate-utilizing Desulfobacter spp., lactate-and H2-utilizing Desulfovibrio spp., and propionate-utilizing Desulfobulbus spp. When the mucin pump was switched off, the multichamber system reverted to a state close to its original equilibrium. These data provide further evidence that sulfated polysaccharides such as mucin may be a source of sulfate for SRB in the human large gut.

Gut, Sep 1, 1978

Short chain fatty acid absorption from the human rectum has been studied in 46 subjects attending... more Short chain fatty acid absorption from the human rectum has been studied in 46 subjects attending an obesity clinic, using a dialysis bag technique. From a mixed electrolyte solution, acetate concentrations fell from 97 0 to 64-2 mmol/l, and sodium from 97-8 to 85 1 mmol/l with respective net absorption rates of 8-1 and 5-2 [Lmol/cm2/h. From a solution with mixed short chain fatty acids