Pinto bean consumption changes SCFA profiles in fecal fermentations, bacterial populations of the lower bowel, and lipid profiles in blood of humans

Abstract

Beans improve serum lipids and may reduce the risk of colon cancer by increasing colonic SCFA formation. We assessed whether pinto bean consumption affects in vitro fecal bacterial fermentation and production of SCFA, colonic bacterial populations, and serum lipids. Adults grouped as premetabolic syndrome (pre-MetSyn) (n = 40) or controls (n = 40) were randomly assigned to consume either a bean entrée [1/2 cup (130 g) of dried, cooked pinto beans] or an isocaloric chicken soup entrée daily for 12 wk. Measurements included in vitro fecal fermentation of various resistant starch substrates, fecal bacterial speciation, and blood lipids. When expressed as a difference between baseline and treatment, propionate production from fecal material fermented in vitro with bean flour was higher (P < 0.02) in volunteers consuming beans than in those consuming soup. During the treatment period alone, bean consumption did not affect propionic acid production with any substrate but lowered (P < 0.02) butyric acid production when cornstarch was the substrate. In all volunteers, bean consumption decreased fecal production of isovaleric (P < 0.05) and isobutyric (P < 0.002) acids from cornstarch by as much as 50%. Of the bacterial populations tested, only Eubacterium limosum was affected by bean consumption and was ∼50% lower than in those consuming soup. Beans lowered serum total cholesterol (P < 0.014) by ∼8% in the controls and 4% in the pre-MetSyn group. Bean consumption lowered serum HDL-cholesterol (P < 0.05) and LDL-cholesterol (P < 0.05) in both groups without affecting serum triglycerides, VLDL cholesterol, or glucose. This study provides evidence that bean consumption can improve lipid profiles associated with cardiovascular disease, but does not clearly confer health benefits related to colon cancer risk. © 2007 American Society for Nutrition.