Meat, starch and non-starch polysaccharides, are epidemiological and experimental findings consistent with acquired genetic alterations in sporadic colorectal cancer?

Gut microbial activity, implications for health and disease: the potential role of metabolite analysis

Microbial metabolism of proteins and amino acids by human gut bacteria generates a variety of compounds including phenol, indole, and sulfur compounds and branched chain fatty acids, many of which have been shown to elicit a toxic effect on the lumen. Bacterial fermentation of amino acids and proteins occurs mainly in the distal colon, a site that is often fraught with symptoms from disorders including ulcerative colitis (UC) and colorectal cancer (CRC). In contrast to carbohydrate metabolism by the gut microbiota, proteolysis is less extensively researched. Many metabolites are low molecular weight, volatile compounds. This review will summarize the use of analytical methods to detect and identify compounds in order to elucidate the relationship between specific dietary proteinaceous substrates, their corresponding metabolites, and implications for gastrointestinal health.

Dietary risk factors for ovarian cancer: the Adventist Health Study (United States)

Few prospective studies have reported dietary risk factors for ovarian cancer. A total of 71 histologically confirmed epithelial ovarian cancers occurred among 13,281 non-Hispanic white California Seventh-day Adventist women during follow-up. Participants were part of the Adventist Health Study (AHS) and had no history of cancer or hysterectomy at baseline in 1976 when they completed a detailed lifestyle questionnaire including a dietary assessment. The association of dietary variables with either all ovarian cancer cases or postmenopausal cases was tested using proportional hazards regression with adjustment for age and other covariates. The strongest hazardous risk factor associations among the food variables were found for meat intake with a risk ratio (RR) of 2.42 for intake > or = 1 time/week versus no meat (p for trend = 0.006), and cheese intake with a RR of 2.02 for intake of > 2 time/week versus < 1 per week (p for trend = 0.10), both of these being in postmenopausal cases. We found significantly reduced risk of all ovarian cancer with higher tomato consumption (RR = 0.32) comparing intakes > or = five times/week versus never to < 1 time/week (p for trend = 0.002), and also with higher fruit consumption (p < 0.01). A weak protective association was found with low fat, but not whole milk. Little confounding was observed between these foods.

Nutritional genomics: the next frontier in the postgenomic era

The interface between the nutritional environment and cellular/genetic processes is being referred to as “nutrigenomics.” Nutrigenomics seeks to provide a molecular genetic understanding for how common dietary chemicals (i.e., nutrition) affect health by altering the expression and/or structure of an individual’s genetic makeup. The fundamental concepts of the field are that the progression from a healthy phenotype to a chronic disease phenotype must occur by changes in gene expression or by differences in activities of proteins and enzymes and that dietary chemicals directly or indirectly regulate the expression of genomic information. We present a conceptual basis and specific examples for this new branch of genomic research that focuses on the tenets of nutritional genomics: 1) common dietary chemicals act on the human genome, either directly or indirectly, to alter gene expression or structure; 2) under certain circumstances and in some individuals, diet can be a serious risk factor for a number of diseases; 3) some diet-regulated genes (and their normal, common variants) are likely to play a role in the onset, incidence, progression, and/or severity of chronic diseases; 4) the degree to which diet influences the balance between healthy and disease states may depend on an individual’s genetic makeup; and 5) dietary intervention based on knowledge of nutritional requirement, nutritional status, and genotype (i.e., “individualized nutrition”) can be used to prevent, mitigate, or cure chronic disease.

Dietary fiber and colorectal neoplasia

PURPOSE

Dietary fiber has been implicated in colorectal neoplasia, despite conflicting evidence. This is a review of the currently available data on the role of dietary fiber in colorectal carcinogenesis.

METHODS

A literature search was conducted using the MEDLINE database. All case-control, longitudinal, and randomized, controlled studies published in English between 1988 and 2000 were identified, as were animal model studies in the period 1986 to 2000. Data from the various studies were tabulated and systematically analyzed, with particular emphasis on the effect of dietary fiber on tumor incidence and luminal parameters such as short chain fatty acids.

RESULTS

Epidemiologic correlation studies show a high intake of dietary fiber to be associated with a lower risk of colorectal neoplasia. Thirteen of the 24 case-control studies reviewed demonstrated a protective effect of dietary fiber against colorectal neoplasia, and 16 showed a protective effect of vegetables or vegetable fiber. On the other hand, of 13 longitudinal studies in various cohorts, only 3 demonstrated a protective effect of fiber and 4 a protective effect of vegetables or vegetable fiber. The five published randomized, controlled trials all investigated the effect of increased fiber intake on short-term adenoma recurrence; however, none showed any significant protective effect. Among 19 experimental studies in animal models, 15 showed a protective effect of fiber against tumor induction compared with controls. Animal studies also showed that poorly fermentable fibers (e.g., wheat bran and cellulose) were more protective than soluble fibers (e.g., guar gum and oat bran), which sometimes enhanced carcinogenesis. No clear correlation was found between luminal pH or short chain fatty acids and tumor induction.

CONCLUSIONS

On the basis of current data, there is little evidence to support the use of dietary fiber supplements to reduce the risk of colorectal neoplasia. Lifelong and early exposure may be important but are difficult to study. Other risk factors interact with the effects of dietary fiber.

Colon heat and colon cancer

Epidemiological findings on the relation between foods and colon cancer are inconsistent. Many, but far from all, found positive associations for meat and fat and negative ones for vegetables and fruits. Explanations so far have focused on direct biochemical conversions in the colon or transit time, but they remain unable to explain the contradictory observations. One aspect grossly ignored has been bacterially produced heat which is beyond somatic control. A present day affluent lifestyle includes a more sedentary life, the strongest of all risk factors for colon cancer, with more sitting and less diffusion of bacterial heat, more fat and sugar, rich in energy and less of energy poor foods like cereals. A temperature higher by less than 1 degrees C in the colon over decades may promote tumour growth to a distinguishable extent.

In vitro utilization of amylopectin and high-amylose maize (Amylomaize) starch granules by human colonic bacteria

It has been well established that a certain amount of ingested starch can escape digestion in the human small intestine and consequently enters the large intestine, where it may serve as a carbon source for bacterial fermentation. Thirty-eight types of human colonic bacteria were screened for their capacity to utilize soluble starch, gelatinized amylopectin maize starch, and high-amylose maize starch granules by measuring the clear zones on starch agar plates. The six cultures which produced clear zones on amylopectin maize starch- containing plates were selected for further studies for utilization of amylopectin maize starch and high-amylose maize starch granules A (amylose; Sigma) and B (Culture Pro 958N). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was used to detect bacterial starch-degrading enzymes. It was demonstrated that Bifidobacterium spp., Bacteroides spp., Fusobacterium spp., and strains of Eubacterium, Clostridium, Streptococcus, and Propionibacterium could hydrolyze the gelatinized amylopectin maize starch, while only Bifidobacterium spp. and Clostridium butyricum could efficiently utilize high-amylose maize starch granules. In fact, C. butyricum and Bifidobacterium spp. had higher specific growth rates in the autoclaved medium containing high-amylose maize starch granules and hydrolyzed 80 and 40% of the amylose, respectively. Starch-degrading enzymes were cell bound on Bifidobacterium and Bacteroides cells and were extracellular for C. butyricum. Active staining for starch-degrading enzymes on SDS-PAGE gels showed that the Bifidobacterium cells produced several starch-degrading enzymes with high relative molecular (M(r)) weights (>160,000), medium-sized relative molecular weights (>66,000), and low relative molecular weights (<66,000). It was concluded that Bifidobacterium spp. and C. butyricum degraded and utilized granules of amylomaize starch.

Role of red meat and arachidonic acid in protein kinase C activation in rat colonic mucosa

Two studies were conducted to investigate the role of meat and arachidonic acid in colonic signal transduction, particularly protein kinase C (PKC) activation. In Study 1, 26 male Wistar rats were fed a casein- or a beef-based diet for four weeks. PKC activity was measured from the proximal and distal colonic mucosa and diacylglycerol concentration from fecal samples. The beef diet significantly increased membrane PKC activity in the proximal and distal colon and cytosolic PKC in the distal colon. No differences were found in fecal diacylglycerol concentration for the rats maintained on the two diets. In Study 2, 57 male Wistar rats were divided into three dietary treatment groups: a control group, a group supplemented with arachidonic acid at 8 mg/day (an amount equivalent to that available from the beef diet in Study 1), and a group supplemented with fish oil at 166 mg/day. After a four-week supplementation period, 6 rats per group were used for colonic phospholipid fatty acid analysis and 13 rats per group were used for analysis of colonic prostaglandin E2 concentration, sphingomyelinase, and PKC activities. Supplementation of dietary arachidonic acid resulted in incorporation of arachidonic acid into colonic phosphatidylcholine, which was associated with an increase in mucosal prostaglandin E2 concentration compared with the fish oil group. However, arachidonate supplementation had no effect on sphingomyelinase or PKC activities. These data indicate that meat significantly increases colonic PKC activity, but this effect is probably not due to the arachidonic acid content of meat.