Dietary fibre and large bowel cancer

Dietary resistant and butyrylated starches have different effects on the faecal bacterial flora of azoxymethane-treated rats

Epidemiological studies have suggested that dietary fibre lowers the risk of colorectal cancer, which may be due to increased butyrate production from colonic fermentation of a type of fibre, resistant starch (RS). The present study investigated the effects of dietary RS and butyrylated RS on the faecal microbiota of rats treated with azoxymethane. A total of four groups of nine rats were fed diets containing either standard maize starch (low-amylose maize starch (LAMS), low RS), LAMS with 3 % tributyrin (LAMST), cooked 10 % high-amylose maize starch (HAMS, high RS) or cooked 10 % butyrylated HAMS (HAMSB). Faecal samples were examined by denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S rRNA gene fragments. Multivariate analysis demonstrated no differences between faecal microbiota before treatment but revealed differences in DGGE patterns between diet groups, with the exception of the two low-RS groups (LAMS and LAMST). Subsequent analysis identified eleven DGGE bands contributing significantly to the differentiation between diets. These phylotypes belonged to Clostridiales (five), Lactobacillus (one) and Bacteroidetes (five) lineages. Rats fed HAMS had increased concentration of propionate in their distal colonic digesta and developed faecal populations containing Ruminococcus bromii-like bacteria. HAMSB increased propionate and butyrate concentrations in distal colonic digesta and was associated with the appearance of two non-butyrate-producing bacteria, Lactobacillus gasseri and Parabacteroides distasonis. In conclusion, supplementation with specific dietary RS leads to changes in faecal microbiota profiles that may be associated with improved bowel health.

Effects of Flax Fiber on Laxation and Glycemic Response in Healthy Volunteers

We investigated whether a flax supplement taken orally or baked in a bakery product would effect the physiological responses characteristic of soluble and insoluble fiber, i.e., laxation and glycemic response, respectively. In Study 1, 26 healthy young adults consumed up to 15 g of fiber from a proprietary flax fiber supplement or as a psyllium supplement for 2 weeks once usual fecal weights were established. Changes in dietary fiber intake and acceptability of both products were evaluated. An increase in fecal weight was found with both fiber treatments. Supplemental fiber at intakes of 9.0 g/day (flax) and 10.4 g/day (psyllium) gave fecal bulking capacity of about 2.9 and 4.8 g of fecal weight/g of fiber, respectively. In Study 2, the effect of flax bread versus control white bread on glycemic response was studied. Eleven fasting subjects completed four test periods (duplicate trials of each bread) under standardized glycemic testing conditions. Paired t tests were used to analyze test compared with control peak blood glucose values (6.6 +/- 0.9 mmol/L compared with 6.9 +/- 0.7 mmol/L, P < .05, respectively) and area under the curve (AUC) (669 +/- 53 compared with 693 +/- 57, P = .015, respectively). Peak blood glucose values and AUC were improved by ingestion of flax fiber in healthy subjects. In conclusion, a flax fiber supplement provides the benefits of soluble and insoluble fiber.

Colorectal cancer and the relationship between genes and the environment

Colorectal cancer (CRC) is a significant cause of morbidity and mortality in developed countries, with both genetic and environmental factors contributing to the etiology and progression of the disease. Several risk factors have been identified, including positive family history, red meat intake, smoking, and alcohol intake. Protective factors include vegetables, calcium, hormone replacement therapy, folate, nonsteroidal anti-inflammatory drugs, and physical activity. The interaction between these environmental factors, in particular diet and genes, is an area of growing interest. Currently, oncogenes, tumor suppressor genes, and mismatch repair genes are believed to play an essential role in colorectal carcinogenesis. When considering the genetics of CRC, only 10% of cases are inherited and only 2-6% can be ascribed to the highly penetrant genes, such as APC, hMLH and hMSH2. Lower penetrance genes combined with a Western-style diet contribute to the majority of sporadic CRCs. The purpose of this article is to give a brief overview of the epidemiologic studies that have been conducted and present the major findings. Here, we examine the molecular events in CRC, with particular focus on the interaction between genes and environment, and review the most current research in this area.

Fat and dietary fiber intake and colon cancer mortality: a chronological comparison between Japan and the United States

To estimate the role of dietary fiber (DF) and fat in the striking growth of colon cancer mortality in Japan after World War II, we analyzed relations between the above variables in comparison with those in the United States. In the United States, fat intake grew by only one-third over the past 70 years (from 124 g in 1909-1913 to 166 g in 1984), whereas colon cancer mortality increased fourfold (from 5 to 20 per 100,000). In Japan, although fat intake roughly doubled during the 40 years after World War II (from 20 to 38 g), colon cancer mortality grew 5.5-fold (from 2 to 11 per 100,000). It is difficult to give a consistent explanation for the growth patterns of colon cancer mortality in both countries on the basis of fat consumption as a cancer promoter. In the United States, DF intake continuously dwindled at a level always less than in Japan throughout this century. DF intake in Japan also declined rather steadily, except for war time, over the past 80 years. However, with regard to the growth pattern of colon cancer mortality, it began rising steeply around the period when the daily DF intake diminished below 20 g, suggesting the presence of a threshold level in this neighborhood in preventing the development of colon cancer.

Mechanisms and experimental and epidemiological evidence relating dietary fibre (non-starch polysaccharides) and starch to protection against large bowel cancer

The cause of human colo-rectal cancer is unknown, although international and racial comparisons suggest that diet may be important. Within populations, risk of cancer is also affected by genetic factors which remain to be elucidated. Dietary fibre and NSP consumption is not always high in populations at low risk of colo-rectal cancer, but rates are fast increasing with westernization (and meat and fat consumption) in Japan. The suggestion that dietary fibre is protective in colo-rectal cancer is based on the fact that cereal fibre from bran increases faecal weight, dilutes large intestinal contents, and speeds up transit time. In animal models, bran reduces the number of tumours induced by chemical carcinogens, and cellulose may have a similar effect. The faeces of some individuals contain mutagens, some of which have been identified as fecapentaenes and heterocyclic amines. Bran reduces faecal mutagenicity, although the mutagen concerned is unknown. Most dietary fibre is fermented in the large gut by anaerobic bacteria and little remains in faecal matter. Recent observations have shown that substantial amounts of starch survive digestion in the small bowel and are available also for fermentation in the large gut. The metabolic consequences of fermentation may be important in carcinogenesis via altered N metabolism, SCFA production, and pH reduction. Methane is also produced in some individuals, but, contrary to previous findings, is not a risk factor for large bowel cancer. Starch appears to be beneficial as a substrate for fermentation because yields of the SCFA butyrate are increased both in vitro and in vivo. Butyrate is an energy substrate for the colonic mucosa and an anti-proliferative and differentiating agent in cell culture lines. Possible mechanisms whereby starch and NSP may protect against colo-rectal cancer, therefore, exist. The majority of individual case-control epidemiological studies suggest that fibre-containing foods are protective in colo-rectal cancer, although this effect is largely due to vegetable, rather than cereal, consumption. Case-control studies of diet and large bowel cancer may, however, reflect the effect rather than the cause of the disease, so that confirmation of the possible protective effects of starch and NSP is needed from accurate prospective studies both of diet and associated risk factors.

Eating patterns in childhood and adult health

This paper first reviews the evidence that the pathogenesis of many diseases which present in adult life begin in childhood, and that intervention in childhood may delay their onset. The diseases discussed include ischaemic heart disease, malignancy, cerebrovascular accidents, hypertension and obesity. The factors determining food habits are described and the possibilities of influencing food preferences and eating patterns in childhood are explored.

Diet, nutrition, and cancer. The role of fiber

The mechanisms by which dietary fiber could inhibit development of colon cancer include effects on fecal weight and transit time, adsorption of bile acids, dilution of colonic contents, production of short chain fatty acids (products of fiber fermentation), inhibition of dehydroxylation of bile acids, and regulation of energy intake. Review of the literature suggests that effects on fecal weight and transit time and adsorption of bile acids are not likely mechanisms. Since concentration of bile acids is lower in feces of less susceptible populations, dilution of colonic contents may contribute to fiber effects. High colonic pH is associated with promotion of cancer and production of short chain fatty acids would counteract this effect. Animals maintained on calorie-restricted diets exhibit fewer spontaneous or experimentally induced tumors. Regulation of energy intake by fiber may contribute towards reduction of colon cancer incidence in man especially when caloric content is low from infancy.

Dietary fibre consumption and its association with large bowel cancer in man

The hypothesis that lack of fibre in the diet is responsible for a variety of large bowel problems, including cancer, has stimulated much discussion and research over the past 15 years. However, the epidemiological examination of this hypothesis has been hampered by the absence of data on the fibre content of most of the world's foods. In studies in Britain and Scandinavia where consumption of the chemical fraction of dietary fibre, the non-starch polysaccharides, has been determined using accurate methods, significant negative association between colon cancer occurrence and NSP consumption have been shown. Fibre may therefore be protective to populations otherwise assumed to be at risk from a westernised type of diet. At present, methodological problems preclude the use of case-control studies in confirming or refuting these associations.

Epidemiology of dietary fibre and colorectal cancer: current status of the hypothesis

The hypothesis that lack of dietary fibre in the diet is responsible for a variety of large bowel problems, including cancer, has stimulated much discussion and research over the past 15 years. However, the epidemiological examination of this hypothesis has been hampered by the absence of data on the fibre content of most of the world's foods. In Scandinavia and Britain where the consumption of the major chemical fraction of dietary fibre, the non-starch polysaccharides, has been measured using accurate methods, significant negative associations have been shown with colon cancer occurrence. These studies suggest that non-starch polysaccharides may be protective in populations at otherwise high risk of colon cancer from an excess of meat and fat. However, methodological problems in the assessment of non-starch polysaccharide consumption in individuals preclude the use of case control studies in verifying these associations within a single homogeneous population.

Absorption of short-chain fatty acids from the human colon measured by the 14CO2 breath test

The absorption and metabolism of short-chain fatty acids (SCFAs) have been studied in 31 patients. Physiological amounts (7.5 mmol) of (1-14C)-labeled acetic, propionic, and butyric acid and (2-14C)-labeled propionic acid were instilled into the cecum and ascending part of the colon during colonoscopy, and the metabolism of acids to CO2 was measured for 24 h by the 14CO2 breath test. During the first 6 h the cumulative output of 14CO2 from the (1-14C)-labeled acetic, propionic, and butyric acids were (median and range) 50% (46%-56%), 50% (43%-56%), and 63% (58%-73%) and during 24 h 55% (50%-63%), 58% (46%-60%), and 70% (63%-83%), respectively, of the instilled dose. The elimination patterns of the (1-14C)-labeled acids were rather similar, although butyric acid was eliminated to a somewhat greater extent than acetic and propionic acid (p less than or equal to 0.01). (2-14C)-labeled propionic acid was eliminated more slowly than (1-14C)-labeled propionic acid, with a cumulative output of 37% (30%-39%) after 6 h (p less than 0.01), but reached the same value after 24 h, 54% (47%-60%). In agreement with findings in other species, humans have a great capacity for uptake and metabolism of SCFAs formed in the colon.