Dietary fat, bile acid metabolism and colorectal cancer.

Colorectal cancer (CRC) risk is predominantly driven by environmental factors, in particular diet. A high intake of dietary fat has been implicated as a risk factor inducing the formation of pre-neoplastic lesions (e.g., adenomatous polyps) and/or exacerbating colonic tumorigenesis. Recent data attributed the tumor-promoting activity of high-fat diets to their effects on gut microbiota composition and metabolism, in particular with regard to bile acids. Bile acids are synthesized in the liver in response to dietary fat and facilitate lipid absorption in the small intestine. The majority of bile acids is re-absorbed during small intestinal transit and subjected to enterohepatic circulation. Bile acids entering the colon undergo complex biotransformation performed by gut bacteria, resulting in secondary bile acids that show tumor-promoting activity. Excessive dietary fat leads to high levels of secondary bile acids in feces and primes the gut microbiota to bile acid metabolism. This promotes an altered overall bile acid pool, which activates or restricts intestinal and hepatic cross-signaling of the bile acid receptor, farnesoid X receptor (FXR). Recent studies provided evidence that FXR is a main regulator of bile acid-mediated effects on intestinal tumorigenesis integrating dietary, microbial and genetic risk factors for CRC. Selective FXR agonist or antagonist activity by specific bile acids depends on additional factors (e.g., bile acid concentration, composition of bile acid pool, genetic instability of cells) and, thus, may differ in healthy and tumorigenic conditions in the intestine. In conclusion, fat-mediated alterations of the gut microbiota link bile acid metabolism to CRC risk and colonic tumorigenesis, exemplifying how gut microbial co-metabolism affects colon health.

Interactions between the environmental and human microbiota in the preservation of health and genesis of disease: symposium report.

PURPOSE OF REVIEW: The purpose of this symposium was to bring thought leaders in the microbiome from the west to Africa to share their unique experiences with African investigators in order to build the foundations for scientifically rigorous explorations into the African human and environmental microbiome that may explain why disease patterns are different in Africa where the chief killers are infectious diseases, whereas noncommunicable diseases (NCDs) are the major threat to healthcare resources in the developed world. RECENT FINDINGS: The application of new high throughput technologies to the investigation of the microbiome and its metabolome has revealed mechanisms whereby a traditional African high fiber diet can suppress NCDs which include colon cancer, inflammatory bowel diseases, obesity, type 2 diabetes and atherosclosis. There is concern that with migration and westernization, NCDs are becoming more common in Africa and that food security is becoming impaired by unbalanced obesogenic foods rather than inadequate food intake. SUMMARY: There is an urgent need for the formation of combined African-Western research programs to identify what is good and bad in the African diet-microbiome axis to develop strategies to prevent the incidence of NCDs rising to western levels in Africa, at the same time offering novel prevention strategies against the #1 healthcare threat in the developed world.

A simplified method for the quantitation of short-chain fatty acids in human stool.

A one-vial extraction method for the quantitation of short-chain fatty acids (SCFAs) in human stool was developed. Samples were extracted with an acidified aqueous internal standard solution, sodium sulfate, and diethyl ether, followed by analysis with GC-FID. Accuracy, in terms of relative recovery, was typically between 90 and 110% for most analytes; without internal standard, the accuracy was about 5-34%; the linear dynamic range (LDR) was 0.05-50 µmol per gram; the limit of detection (LOD) was less than or equal to 0.05 µmol per gram; and the (lower) limit of quantitation (LOQ) was 1 µmol per gram. The method is suitable for quantitating acetic acid, propanoic acid, isobutyric acid, butyric acid, isovaleric acid, valeric acid, isohexanoic acid, hexanoic acid, and heptanoic acid. It is not suitable for the quantitation of formic acid. Application to human biological research was tested by the measurement of SCFA in heathy humans. This confirmed that the method performed adequately, and even better than expected, with values up to 150 µmol per gram.

Diet and the Human Gut Microbiome: An International Review.

This review summarizes the key results of recently published studies on the effects of dietary change and nutritional intervention on the human microbiome from around the world, focusing on the USA, Canada, Europe, Asia, and Africa. It first explores mechanisms that might explain the ability of fiber-rich foods to suppress the incidence and mortality from westernized diseases, notably cancers of the colon, breast, liver, cardiovascular, infectious, and respiratory diseases, diabetes, and obesity (O'Keefe in Lancet Gastroenterol Hepatol 4(12):984-996, 2019; Am J Clin Nutr 110:265-266, 2019). It summarizes studies from Africa which suggest that disturbance of the colonic microbiome may exacerbate chronic malnutrition and growth failure in impoverished communities and highlights the importance of breast feeding. The American section discusses the role of the microbiome in the swelling population of patients with obesity and type 2 diabetes and examines the effects of race, ethnicity, geography, and climate on microbial diversity and metabolism. The studies from Europe and Asia extoll the benefits of whole foods and plant-based diets. The Asian studies examine the worrying changes from low-fat, high-carbohydrate diets to high-fat, low-carbohydrate ones and the increasing appearance of westernized diseases as in Africa and documents the ability of high-fiber traditional Chinese diets to reverse type 2 diabetes and control weight loss. In conclusion, most of the studies reviewed demonstrate clear changes in microbe abundances and in the production of fermentation products, such as short-chain fatty acids and phytochemicals following dietary change, but the significance of the microbiota changes to human health, with the possible exception of the stimulation of butyrogenic taxa by fiber-rich foods, is generally implied and not measured. Further studies are needed to determine how these changes in microbiota composition and metabolism can improve our health and be used to prevent and treat disease.

Fiber, Fat, and Colorectal Cancer: New Insight into Modifiable Dietary Risk Factors.

PURPOSE OF REVIEW: To review recent data on the role and interactions of fiber and fat as dietary risk factors associated with colorectal cancer (CRC) risk in humans. RECENT FINDINGS: Fiber intake shows convincing and linear dose-response negative correlation with CRC risk. Dietary fiber stimulates butyrogenic activity of the gut microbiota, providing high amounts of butyrate that shows extensive anti-neoplastic effects. A high-fat diet promotes CRC risk through stimulated bile acid metabolism, facilitating bile acid conversion by the gut microbiota to tumor-promoting deoxycholic acid. Comprehensive interactions of these microbial metabolites are likely to underlie mechanisms driving diet-dependent CRC risk in different populations, but require further experimental investigation. Dietary fiber and fat shape the composition and metabolic function of the gut microbiota, resulting in altered amounts of butyrate and deoxycholic acid in the colon. Fiber supplementation and restriction of fat intake represent promising strategies to reduce CRC risk in healthy individuals.

High prevalence of osteoporosis in patients with chronic pancreatitis: a systematic review and meta-analysis.

BACKGROUND & AIMS: Patients with chronic pancreatitis may be at high risk for osteoporosis and osteopenia. We performed a systematic review and meta-analysis to determine the prevalence of osteoporosis and osteopenia in patients with chronic pancreatitis. METHODS: Articles were identified from MEDLINE, EMBASE, and SCOPUS databases (through October 2012) and a manual search of the literature. The primary outcome measure was bone density, measured by dual-energy X-ray absorptiometry (T-score or Z-score). When available, data on the prevalence of osteopenia, bone mineral density, and bone mineral content also were recorded. RESULTS: Ten studies including 513 patients were eligible for inclusion. Based on a random-effects model, the pooled prevalence rate for osteoporosis among patients with chronic pancreatitis was 23.4% (95% confidence interval, 16.6-32.0). The pooled prevalence for osteopenia was 39.8% (95% confidence interval, 29.1-51.6). The pooled prevalence rate for either osteoporosis or osteopenia was 65% (95% confidence interval, 54.7-74.0). CONCLUSIONS: Based on meta-analysis, almost 1 of 4 patients with chronic pancreatitis have osteoporosis, and almost two-thirds of patients have either osteoporosis or osteopenia. Osteoporosis and osteopenia are underappreciated sources of morbidity in patients with chronic pancreatitis. Bone health management guidelines are urgently required in patients with chronic pancreatitis.

Fibre-rich Foods to Treat Obesity and Prevent Colon Cancer trial study protocol: a randomised clinical trial of fibre-rich legumes targeting the gut microbiome, metabolome and gut transit time of overweight and obese patients with a history of noncancerous adenomatous polyps.

INTRODUCTION: Recently published studies support the beneficial effects of consuming fibre-rich legumes, such as cooked dry beans, to improve metabolic health and reduce cancer risk. In participants with overweight/obesity and a history of colorectal polyps, the Fibre-rich Foods to Treat Obesity and Prevent Colon Cancer randomised clinical trial will test whether a high-fibre diet featuring legumes will simultaneously facilitate weight reduction and suppress colonic mucosal biomarkers of colorectal cancer (CRC). METHODS/DESIGN: This study is designed to characterise changes in (1) body weight; (2) biomarkers of insulin resistance and systemic inflammation; (3) compositional and functional profiles of the faecal microbiome and metabolome; (4) mucosal biomarkers of CRC risk and (5) gut transit. Approximately 60 overweight or obese adults with a history of noncancerous adenomatous polyps within the previous 3 years will be recruited and randomised to one of two weight-loss diets. Following a 1-week run-in, participants in the intervention arm will receive preportioned high-fibre legume-rich entrées for two meals/day in months 1-3 and one meal/day in months 4-6. In the control arm, entrées will replace legumes with lean protein sources (eg, chicken). Both groups will receive in-person and written guidance to include nutritionally balanced sides with energy intake to lose 1-2 pounds per week. ETHICS AND DISSEMINATION: The National Institutes of Health fund this ongoing 5-year study through a National Cancer Institute grant (5R01CA245063) awarded to Emory University with a subaward to the University of Pittsburgh. The study protocol was approved by the Emory Institutional Review Board (IRB approval number: 00000563). TRIAL REGISTRATION NUMBER: NCT04780477.

Safety and efficacy of teduglutide after 52 weeks of treatment in patients with short bowel intestinal failure.

BACKGROUND & AIMS: Although home parenteral nutrition (PN) can save the lives of patients with massive bowel loss that results in short-bowel syndrome and intestinal failure, quality of life is impaired by PN and its complications. We examined the 12-month tolerability and efficacy of teduglutide to reduce PN dependency. METHODS: Patients who received teduglutide (0.05 or 0.10 mg/kg/d) for 24 weeks in a randomized controlled trial were eligible for a 28-week double-blind extension study; 52 patients were given 52 weeks of the same doses of teduglutide. We investigated the safety, tolerability, and clinical efficacy (defined as a clinically meaningful ≥20% reduction in weekly PN volume from baseline) at week 52. RESULTS: The most common adverse events reported included headache (35%), nausea (31%), and abdominal pain (25%); 7 patients withdrew because of adverse events (gastrointestinal disorders in 4). Both groups had progressive reduction in PN. At week 52, 68% of the 0.05-mg/kg/d and 52% of the 0.10-mg/kg/d dose group had a ≥20% reduction in PN, with a reduction of 1 or more days of PN dependency in 68% and 37%, respectively. Four patients achieved complete independence from PN. CONCLUSIONS: For patients with short-bowel syndrome intestinal failure, the efficacy of teduglutide was maintained over 52 weeks and the safety profile was sufficient for it to be considered for long-term use. Further studies are needed to determine whether these effects will translate into improved quality of life and reduced PN complications. ClinicalTrials.gov number, NCT00172185.

Teduglutide reduces need for parenteral support among patients with short bowel syndrome with intestinal failure.

BACKGROUND & AIMS: Teduglutide, a glucagon-like peptide 2 analogue, might restore intestinal structural and functional integrity by promoting growth of the mucosa and reducing gastric emptying and secretion. These factors could increase fluid and nutrient absorption in patients with short bowel syndrome with intestinal failure (SBS-IF). We performed a prospective study to determine whether teduglutide reduces parenteral support in patients with SBS-IF. METHODS: We performed a 24-week study of patients with SBS-IF who were given subcutaneous teduglutide (0.05 mg/kg/d; n = 43) or placebo (n = 43) once daily. Parenteral support was reduced if 48-hour urine volumes exceeded baseline values by ≥ 10%. The primary efficacy end point was number of responders (patients with >20% reduction in parenteral support volume from baseline at weeks 20 and 24). RESULTS: There were significantly more responders in the teduglutide group (27/43 [63%]) than the placebo group (13/43 [30%]; P = .002). At week 24, the mean reduction in parenteral support volume in the teduglutide group was 4.4 ± 3.8 L/wk (baseline 12.9 ± 7.8 L/wk) compared with 2.3 ± 2.7 L/wk (baseline 13.2 ± 7.4 L/wk) in the placebo group (P < .001). The percentage of patients with a 1-day or more reduction in the weekly need for parenteral support was greater in the teduglutide group (21/39 [54%]) than in the placebo group (9/39 [23%]; P = .005). Teduglutide increased plasma concentrations of citrulline, a biomarker of mucosal mass. The distribution of treatment-emergent adverse events that led to study discontinuation was similar between patients given teduglutide (n = 2) and placebo (n = 3). CONCLUSIONS: Twenty-four weeks of teduglutide treatment was generally well tolerated in patients with SBS-IF. Treatment with teduglutide reduced volumes and numbers of days of parenteral support for patients with SBS-IF; ClinicalTrials.gov Number, NCT00798967.

Is Salt at Fault? Dietary Salt Consumption and Inflammatory Bowel Disease.

Epidemiological trends have led to a growing consensus that diet plays a central role in the etiopathogenesis of inflammatory bowel diseases (IBD). A Western diet high in ultra-processed foods has been associated with an increased prevalence of IBD worldwide. Much attention has focused on components of the Western diet, including the high fat content, lack of fiber, added sugars, and use of additives, such as carrageenan and other emulsifiers. Less attention has been paid to the impact of high salt intake, an integral component of ultra-processed foods, which has increased dramatically in the US diet over the past 50 years. We review a growing body of literature linking the rise in dietary salt intake with the epidemiology of IBD, increased consumption of salt as a component of ultra-processed foods, high salt intake and imbalances in immune homeostasis, the effects of a high-salt diet on other inflammatory disorders, salt's impact on animal colitis models, salt as an underrecognized component in diet modification-induced remission of IBD, and directions for future investigation.

Recent studies have shown that high dietary salt intake is proinflammatory and contributes to chronic inflammatory conditions. Combined with investigations demonstrating low-salt exclusive enteral nutrition induced Crohn's remission, salt intake is likely a contributory factor to inflammatory bowel diseases' pathogenesis and severity.

Association between low colonic short-chain fatty acids and high bile acids in high colon cancer risk populations.

We propose that the influence of diet on colon cancer risk is mediated by the microbiota. To investigate how dietary fat influences risk, we compared the colonic contents of 12 adult high-risk African Americans (AAs) and 10 Caucasian Americans (CAs) who consumed a high-fat diet (123 ± 11 g/d and 129 ± 17 g/d, respectively) to 13 native Africans (NAs) who subsisted on a low-fat (38 ± 3.0 g/d) diet, all aged 50-60 yr. The colonic bile acids were measured by LC-MS and the short-chain fatty acids (SCFAs) by GC. The chief secondary colonic bile acids, deoxycholic acid and lithocholic acid, were correlated with fat intake and similar between AAs and CAs, but 3-4 times higher than in AAs (p < 0.05). The major SCFAs were lower in AAs (p < 0.001) and CAs (p < 0.001) compared to AAs, but conversely, the branched chain fatty acids (BFCA) were higher. Our results suggest that the higher risk of colon cancer in Americans may be partly explained by their high-fat and high-protein, low complex carbohydrate diet, which produces colonic residues that promote microbes to produce potentially carcinogenic secondary bile acids and less antineoplastic SCFAs. The role of BCFA in colonic carcinogenesis deserves further study.

Dietary fibre to reduce colon cancer risk in Alaska Native people: the Alaska FIRST randomised clinical trial protocol.

INTRODUCTION: Diet, shown to impact colorectal cancer (CRC) risk, is a modifiable environmental factor. Fibre foods fermented by gut microbiota produce metabolites that not only provide food for the colonic epithelium but also exert regulatory effects on colonic mucosal inflammation and proliferation. We describe methods used in a double-blinded, randomised, controlled trial with Alaska Native (AN) people to determine if dietary fibre supplementation can substantially reduce CRC risk among people with the highest reported CRC incidence worldwide. METHODS AND ANALYSES: Eligible patients undergoing routine screening colonoscopy consent to baseline assessments and specimen/data collection (blood, urine, stool, saliva, breath and colon mucosal biopsies) at the time of colonoscopy. Following an 8-week stabilisation period to re-establish normal gut microbiota post colonoscopy, study personnel randomise participants to either a high fibre supplement (resistant starch, n=30) or placebo (digestible starch, n=30) condition, repeating stool sample collection. During the 28-day supplement trial, each participant consumes their usual diet plus their supplement under direct observation. On day 29, participants undergo a flexible sigmoidoscopy to obtain mucosal biopsy samples to measure the effect of the supplement on inflammatory and proliferative biomarkers of cancer risk, with follow-up assessments and data/specimen collection similar to baseline. Secondary outcome measures include the impact of a high fibre supplement on the oral and colonic microbiome and biofluid metabolome. ETHICS AND DISSEMINATION: Approvals were obtained from the Alaska Area and University of Pittsburgh Institutional Review Boards and Alaska Native Tribal Health Consortium and Southcentral Foundation research review bodies. A data safety monitoring board, material transfer agreements and weekly study team meetings provide regular oversight throughout the study. Study findings will first be shared with AN tribal leaders, health administrators, providers and community members. Peer-reviewed journal articles and conference presentations will be forthcoming once approved by tribal review bodies. TRIAL REGISTRATION NUMBER: NCT03028831.

A prospective cohort analysis of gut microbial co-metabolism in Alaska Native and rural African people at high and low risk of colorectal cancer.

BACKGROUND: Alaska Native (AN) people have the world's highest recorded incidence of sporadic colorectal cancer (CRC) (∼91:100,000), whereas rural African (RA) people have the lowest risk (<5:100,000). Previous data supported the hypothesis that diet affected CRC risk through its effects on the colonic microbiota that produce tumor-suppressive or -promoting metabolites. OBJECTIVES: We investigated whether differences in these metabolites may contribute to the high risk of CRC in AN people. METHODS: A cross-sectional observational study assessed dietary intake from 32 AN and 21 RA healthy middle-aged volunteers before screening colonoscopy. Analysis of fecal microbiota composition by 16S ribosomal RNA gene sequencing and fecal/urinary metabolites by 1H-NMR spectroscopy was complemented with targeted quantification of fecal SCFAs, bile acids, and functional microbial genes. RESULTS: Adenomatous polyps were detected in 16 of 32 AN participants, but not found in RA participants. The AN diet contained higher proportions of fat and animal protein and less fiber. AN fecal microbiota showed a compositional predominance of Blautia and Lachnoclostridium, higher microbial capacity for bile acid conversion, and low abundance of some species involved in saccharolytic fermentation (e.g., Prevotellaceae, Ruminococcaceae), but no significant lack of butyrogenic bacteria. Significantly lower concentrations of tumor-suppressive butyrate (22.5 ± 3.1 compared with 47.2 ± 7.3 SEM µmol/g) coincided with significantly higher concentrations of tumor-promoting deoxycholic acid (26.7 ± 4.2 compared with 11 ± 1.9 µmol/g) in AN fecal samples. AN participants had lower quantities of fecal/urinary metabolites than RA participants and metabolite profiles correlated with the abundance of distinct microbial genera in feces. The main microbial and metabolic CRC-associated markers were not significantly altered in AN participants with adenomatous polyps. CONCLUSIONS: The low-fiber, high-fat diet of AN people and exposure to carcinogens derived from diet or environment are associated with a tumor-promoting colonic milieu as reflected by the high rates of adenomatous polyps in AN participants.

Products of the colonic microbiota mediate the effects of diet on colon cancer risk.

It is estimated that most colon cancers can be attributed to dietary causes. We have hypothesized that diet influences the health of the colonic mucosa through interaction with the microbiota and that it is the milieu interior that regulates mucosal proliferation and therefore cancer risk. To validate this further, we compared colonic contents from healthy 50- to 65-y-old people from populations with high and low risk, specifically low risk Native Africans (cancer incidence <1:100,000; n = 17), high risk African Americans (risk 65:100,000; n = 17), and Caucasian Americans (risk 50:100,000; n = 18). Americans typically consume a high-animal protein and -fat diet, whereas Africans consume a staple diet of maize meal, rich in resistant starch and low in animal products. Following overnight fasting, rapid colonic evacuation was performed with 2 L polyethylene glycol. Total colonic evacuants were analyzed for SCFA, vitamins, nitrogen, and minerals. Total SCFA and butyrate were significantly higher in Native Africans than in both American groups. Colonic folate and biotin content, measured by Lactobacillus rhamnoses and Lactobacillus plantarum ATCC 8014 bioassay, respectively, exceeded normal daily dietary intakes. Compared with Africans, calcium and iron contents were significantly higher in Caucasian Americans and zinc content was significantly higher in African Americans, but nitrogen content did not differ among the 3 groups. In conclusion, the results support our hypothesis that the microbiota mediates the effect diet has on colon cancer risk by their generation of butyrate, folate, and biotin, molecules known to play a key role in the regulation of epithelial proliferation.

Nutrition and colonic health: the critical role of the microbiota.

PURPOSE OF REVIEW: To highlight mechanisms whereby diet affects colonic function and disease patterns. RECENT FINDINGS: Topical nutrients are preferentially used by the gut mucosa to maintain structure and function. With the colon, topical nutrients are generated by the colonic microbiota to maintain mucosal health. Most importantly, short chain fatty acids control proliferation and differentiation, thereby reducing colon cancer risk. In patients with massive loss of small intestine, short chain fatty acid production supports survival by releasing up to 1000 kcal energy/day. Human studies show that the microbiota synthesizes a large pool of utilizable folate which may support survival in impoverished populations. Unfortunately, the microbiota may also elaborate toxic products from food residues such as genotoxic hydrogen sulfide by sulfur-reducing bacteria in response to a high-meat diet. The employment of culture-free techniques based on 16S regions of DNA has revealed that our colons harbor over 800 bacterial species and 7000 different strains. Evidence suggests that the diet directly influences the diversity of the microbiota, providing the link between diet, colonic disease, and colon cancer. The microbiota, however, can determine the efficiency of food absorption and risk of obesity. SUMMARY: Our investigations have focused on a small number of bacterial species: characterization of microbiota and its metabolism can be expected to provide the key to colonic health and disease.

The Need to Reassess Dietary Fiber Requirements in Healthy and Critically Ill Patients.

This article provides evidence that current dietary fiber intake levels may be insufficient to maintain colonic mucosal health and defense, and reduce inflammation and cancer risk in otherwise healthy people. Current commercial tube feeds generally overlook the metabolic needs of the colon and may predispose patients to dysbiosis, bacterial overgrowth with pathogens such as Clostridium difficile, and acute colitis. These results raise concern about the wide-scale use of prophylactic antibiotics in the intensive care unit and the use of elemental, fiber-depleted tube feeds. Nutrition support is not complete without the addition of sufficient fiber to meet colonic nutritional needs.

Association of Dietary Habits with Severity of Acute Pancreatitis.

BACKGROUND: The effect of diet on risk of acute pancreatitis (AP) has been suggested by prior studies, but the association of dietary habits with severity of AP has not been previously evaluated. OBJECTIVE: The objective of the study was to assess differences in reported dietary habits in patients with severe AP compared with those with mild or moderate AP. METHODS: A prospectively maintained cohort of patients with AP was utilized. A brief questionnaire on dietary habits was implemented. Dietary habits were categorized based on the overall type of diet, fruit/vegetable servings, fat content, dairy consumption, dessert/sweets consumption, and fluid intake. Patients were grouped into mild/moderate and severe AP. Multivariate analysis was used to determine whether dietary habits have an independent association with AP severity. RESULTS: 407 patients with AP were studied. Mean patient age was 51 y, and 202 (50%) were men. 29% of patients were smokers and 46% actively consumed alcohol. 225 patients had mild AP, 103 moderate AP, and 79 developed severe AP. The 3 groups were comparable in race, body mass index, etiology of AP, and comorbidities. Dietary factors were overall comparable between the groups except for diet type: subjects with severe AP had a higher percentage of consuming a meat-rich diet (84%) than patients with mild AP (72%) and moderate AP (67%) (P = 0.04). Based on multivariable logistic regression, the OR of developing severe AP was 2.5 (95% CI: 1.24-5.32, P = 0.01) between patients who eat a meat-rich diet and those who consume a vegetable-based diet. CONCLUSIONS: A meat-rich diet is independently associated with the development of persistent organ failure (severe disease) in patients with AP. These findings require further evaluation and could be useful for patient counseling, risk stratification, and disease prevention. This study is registered at clinicaltrials.gov as NCT03075605.

Environmental influences on the high mortality from colorectal cancer in African Americans.

Colon cancer is the second leading cause of cancer related death in American adults. The incidence and mortality are highest in African Americans (AAs) (incidence: 52 per 100,000) and lowest in American Hispanics (37 per 100,000). Comparative studies with Native Africans (<5 per 100,000) suggest that genetic susceptibility is an unlikely explanation and that environmental influences are to blame. Studies have suggested that risk is high because of excessive intakes of animal meat and fat products and differences in colonic bacterial metabolism, and that preventative and therapeutic management of colon cancer is compromised by the development of greater tumour virulence possibly resulting from disparities in educational and insurance status, screening behaviour, treatment patterns, social support, and access to and use of health care facilities. It should be possible to reduce the unacceptably higher rates of morbidity and mortality from colon cancer in AAs by dietary and lifestyle changes aimed at suppressing excessive intakes of animal meat and fat products, increasing the consumption of fresh fruit and vegetables, controlling energy balance, and by developing strategies to improve the availability, use and accessibility to health care resources.