Fat, fibre and cancer risk in African Americans and rural Africans

TLDR

Colon cancer incidence is markedly higher in African Americans than in rural South Africans, a disparity linked to higher animal fat and lower fiber intake that elevates bile acids, reduces short‑chain fatty acids, and increases mucosal proliferation markers. The study investigates how variations in fat and fiber consumption affect these cancer‑risk biomarkers. A two‑week dietary intervention swapped high‑fat, low‑fiber western diets for low‑fat, high‑fiber African diets (and vice versa) in matched subjects under close supervision. The diet swaps produced reciprocal changes in mucosal biomarkers, microbiota, and metabolites, with African Americans showing increased saccharolytic fermentation, butyrate production, and reduced secondary bile acid synthesis.

Abstract

Rates of colon cancer are much higher in African Americans (65:100,000) than in rural South Africans (<5:100,000). The higher rates are associated with higher animal protein and fat, and lower fibre consumption, higher colonic secondary bile acids, lower colonic short-chain fatty acid quantities and higher mucosal proliferative biomarkers of cancer risk in otherwise healthy middle-aged volunteers. Here we investigate further the role of fat and fibre in this association. We performed 2-week food exchanges in subjects from the same populations, where African Americans were fed a high-fibre, low-fat African-style diet and rural Africans a high-fat, low-fibre western-style diet, under close supervision. In comparison with their usual diets, the food changes resulted in remarkable reciprocal changes in mucosal biomarkers of cancer risk and in aspects of the microbiota and metabolome known to affect cancer risk, best illustrated by increased saccharolytic fermentation and butyrogenesis, and suppressed secondary bile acid synthesis in the African Americans. African Americans have much higher colon cancer rates than rural South Africans, which is associated with dietary and metabolic differences. Here, O'Keefe et al.show that switching quantities of fat and fibre leads to reciprocal changes in gut microbiota, metabolites and cancer biomarkers.