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Participants randomized to the high fiber diet featuring legumes (HLD) will add approximately 30 grams of dietary fiber per day from legume dishes, ensuring a total intake of approximately 50 grams of dietary fiber per day.

Participants randomized to the healthy American diet control arm will receive pre-portioned meal replacement entrées with legumes replaced by lean chicken or meat.

The high fiber diet featuring legumes (HLD) provides pre-portioned entrées for two meals per day in months 1-3, and one meal per day in months 4-6. Participants continue on the diet in months 7-12 but assume responsibility for food preparation. The HLD will contain approximately 250 grams (g) of legumes per day (\~1 ½ cups cooked legumes) in months 1-3 provided in two pre-portioned single serving entrées (i.e. \~125g in each serving). A study nutritionist provides in-person and written guidance for including side dishes that are nutritionally balanced with energy intake to lose 1-2 pounds of weight per week.

High Fiber Diet Featuring Legumes (HLD)

The healthy American diet provides pre-portioned meal replacement entrées with legumes replaced by lean chicken or meat. Participants continue on the diet in months 7-12 but assume responsibility for food preparation. A study nutritionist provides in-person and written guidance for including side dishes that are nutritionally balanced with energy intake to lose 1-2 pounds of weight per week.

Healthy American Diet

Terry Hartman, PhD, MPH, RD

Terry Hartman, PHD, MPH

This study tests whether a high-fiber diet based on legumes, such as dry beans, can lead to sustained reductions in obesity and colon cancer risk in persons at highest risk, namely overweight or obese, post-polypectomy patients.

An important knowledge gap concerns the role of fiber in sustaining reduced energy intake to simultaneously manage weight and influence human colorectal cancer risk. Epidemiologic studies have shown an association between a high fiber diet featuring legumes (HLD) and reduced obesity and lower risk for adenoma recurrence or colorectal cancer. There are many plausible mechanisms to explain why high-fiber diets, and especially a HLD, may reduce colorectal cancer risk. First, fiber is fermented by the colonic microbiota to produce short chain fatty acids (SCFA). The SCFA, butyrate, has a remarkable array of colonic mucosal health promoting, anti-inflammatory, and anti-neoplastic properties. Secondly, microbiota break down plant cell walls releasing phytochemicals, which also have powerful anti-inflammatory and anti-carcinogenic effects. Thirdly, colonic transit is accelerated, reducing contact time with luminal carcinogens, such as heterocyclic amines formed from cooked red meat, and secondary bile acids, induced by a high fat diet and synthesized by the colonic microbiota.

Dr. Stephen O'Keefe's lab performed a human randomized controlled crossover feeding study (participants receive both diets) comparing high and low- fiber diets. The study measured mucosal biomarkers of cancer risk (proliferation - % epithelial cells staining positive for Ki67, inflammation - cluster of differentiation 3 (CD3)+ intraepithelial lymphocytes, cluster of differentiation 68 (CD68)+ lamina propria macrophages) made by fecal sampling and colonoscopy. Results suggested that within weeks these markers responded favorably to the high-fiber diet with proliferative rates and inflammatory biomarkers decreasing and microbiota composition adapting to increase butyrogenesis.

The researchers of this study have previously found that fiber may also reduce cancer risk indirectly by promoting weight loss, improving insulin sensitivity and decreasing inflammation. On average, individuals consume a similar weight of food daily; thus, replacing energy dense foods (higher kcal/g, e.g., high fat) with lower energy density foods (lower kcal/g), like legumes, should potentiate weight control. Viscous fiber intake is associated with longer gastric emptying times which over time might contribute to postponing the next eating occasion. Diet may also induce changes in gut microbiome composition leading to negative energy balance. Emerging human evidence links the gut microbiome with insulin resistance, inflammation, and obesity and with adenomatous polyps and colon cancer. In this current study, characterizing gut motility, microbiome, and metabolome composition profiles that may influence weight loss and have a role in the prevention or recurrence of adenomas and colorectal cancer, will provide novel and potentially therapeutic information.

The goal of the research is to conduct a clinical trial featuring study-provided pre-portioned entrées and strategic nutritional instruction to guide participants to integrate legumes into a healthy high-fiber diet pattern. Participants will be provided two entrées per day during months 1 through 3, and one entrée per day during months 4 through 6. Participants will continue their diets during months 7 through 12 but will be responsible for food preparation. The research will target a population at high risk for colorectal cancer, overweight and obese participants with a history of a colon polyp in the past 3 years, to test whether a high-legume, high-fiber diet will simultaneously increase weight loss and suppress intestinal biomarkers of cancer risk compared to a control diet (healthy American). In addition, it will explore potential mechanisms through which the high-legume intervention diet facilitates weight loss and intestinal health.

Fiber-rich Foods to Treat Obesity and Prevent Colon Cancer

De-identified participant phenotypic data will be made available for sharing but limited to health/biomedical purposes including age, obesity status, presence of colon polyps and history of diabetes. The data will be coded and only the coded data set, and not the master list, will be shared.

Participants will have their body weight measured (in pounds) on a regularly calibrated digital scale while wearing light clothing without shoes.

Colonic mucosal proliferative biomarker Ki-67+ will be measured.

Colonic mucosal proliferative biomarker Ki-67+ will be measured

Gut transit time is assessed using an indigestible single-use SmartPill capsule, a receiver, and display software. The SmartPill capsules were discontinued and no longer available after 2023 so participants beginning after January 19, 2024 will not complete this assessment.

Fasting plasma insulin, a biomarker of insulin resistance is measured by blood test.

Fasting plasma glucose, a biomarker of insulin resistance, is measured by blood test.

Serum C-reactive protein, an indicator of systemic inflammation, is measured by blood test.

CD3+ intraepithelial lymphocytes, a colonic mucosal inflammatory biomarker of colon cancer risk, will be measured by mucosal biopsy.

CD68+ lamina propia macrophages, a colonic mucosal inflammatory biomarker of colon cancer risk, will be measured by mucosal biopsy.

Spots Global Cancer Trial Database for healthy american diet