Fiber can make your gut grow

Perceptions of flatulence from bean consumption among adults in 3 feeding studies

Background

Many consumers avoid eating beans because they believe legume consumption will cause excessive intestinal gas or flatulence. An increasing body of research and the 2010 Dietary Guidelines for Americans supports the benefits of a plant-based diet, and legumes specifically, in the reduction of chronic disease risks. The purpose of the current research was to investigate the perception of increased flatulence and gastrointestinal discomfort among participants who consumed a ½ cup of beans daily for 8 or 12 weeks.

Methods

Participants in three studies to test the effects of beans on heart disease biomarkers completed the same weekly questionnaire to assess gastrointestinal discomfort issues such as increased flatulence, stool changes, and bloating. Studies 1 and 2 were randomized crossover trials. Participants consumed ½ cup of pinto beans, black-eyed peas, and canned carrots as control (n = 17) in Study 1 for three randomized 8-week phases. For Study 2, participants ate ½ cup baked beans or canned carrots as control (n = 29) for two randomized 8-week phases. Study 3 was a parallel arm trial with 40 subjects receiving ½ cup pinto beans and 40 consuming a control soup for 12 weeks. Changes in the frequency of perceived flatulence, stool characteristics, and bloating were the primary outcome measures. Chi-square distributions were examined for the presence or absence of symptoms and demographic characteristics to determine differences by gender, age, body mass index (BMI), and bean type.

Results

Less than 50% reported increased flatulence from eating pinto or baked beans during the first week of each trial, but only 19% had a flatulence increase with black-eyed peas. A small percentage (3-11%) reported increased flatulence across the three studies even on control diets without flatulence-producing components.

Conclusions

People's concerns about excessive flatulence from eating beans may be exaggerated. Public health nutritionists should address the potential for gastrointestinal discomfort when increasing fiber intake from beans with clients. It is important to recognize there is individual variation in response to different bean types.

Resistant carbohydrates stimulate cell proliferation and crypt fission in wild-type mice and in the Apc(Min/+) mouse model of intestinal cancer, association with enhanced polyp development

Fermentation of carbohydrates in the colon can stimulate cell proliferation and could thus be a cancer risk. The effects of resistant carbohydrates, i.e. those not digested and absorbed in the small intestine, on cell proliferation, crypt fission and polyp development were investigated in wild-type and adenomatous polyposis coli multiple intestinal neoplasia (Apc(Min/+)) mice. Fifteen 4-week-old female wild-type and fifteen Apc(Min/+) mice were used for each group and fed a chow diet, a semi-synthetic diet or the semi-synthetic supplemented with wheat bran or an apple pomace preparation, both high in resistant carbohydrates, for 8 weeks. Tissue from all mice was used to measure cell proliferation and crypt fission and tissue from the Apc(Min/+) mice was scored for polyp number and tumour burden. There were slight reductions in intestinal mass in the mice fed the semi-synthetic diets and this was increased by the inclusion of resistant carbohydrates. The Apc(Min/+) mice had elevated cell proliferation and crypt fission in the distal small intestine and colon and these were increased by the resistant carbohydrates. Bran or apple pomace significantly increased polyp number in the proximal third of the small intestine. Apple pulp more than doubled polyp number throughout the small bowel (99.2 (SEM 11.1) v. 40.0 (SEM 8.2), P<0.004). Bran and apple pomace increased polyp diameter and hence burden in the colon by 243 and 150 %, respectively (P<0.05). In conclusion, both types of resistant carbohydrates increased polyp number and tumour burden and this was associated with elevated epithelial cell proliferation and crypt fission.

Nutritional characterization and measurement of dietary carbohydrates

Dietary carbohydrate characterization should reflect relevant nutritional and functional attributes, and be measured as chemically identified components. A nutritional classification based on these principles is presented, with a main grouping into 'available carbohydrates', which are digested and absorbed in the small intestine providing carbohydrates for metabolism, and 'resistant carbohydrates', which resist digestion in the small intestine or are poorly absorbed/metabolized. For the available carbohydrates, the chemical division into the starch and total sugars categories does not adequately reflect the physiological or nutritional attributes of foods. Characterizing carbohydrate release from starchy foods provides insight into some of the inherent mechanisms responsible for the varied metabolic effects. Also, a pragmatic approach to product signposting consistent with guidelines to limit free (or added) sugars is proposed. The most prominent of the resistant carbohydrates are the non-starch polysaccharides (NSP) from plant cell walls, which are characteristic of the largely unrefined plant foods that provide the evidence base for the definition and measurement of dietary fibre as 'intrinsic plant cell-wall polysaccharides' as proposed in conjunction with this paper and endorsed by the scientific update. Indigestibility in the small intestine was not considered to be an adequate basis for the definition of dietary fibre, as there is insufficient evidence to establish public health policy by this approach and concerns have been raised about potential detrimental effects of high intakes of rapidly fermentable resistant carbohydrates. Functional ingredients such as resistant starch and resistant oligosaccharides should therefore be researched and managed separately from dietary fibre, using specific health or function claims where appropriate. This structured approach to the characterization of nutritionally relevant features of dietary carbohydrates provides the basis for establishing population reference intakes, nutrition claims and food labelling that will assist the consumer with properly informed dietary choices.