Effect of Diets Varying in Iron and Saturated Fat on the Gut Microbiota and Intestinal Inflammation: A Crossover Feeding Study among Older Females with Obesity

Obesity is considered an independent risk factor for colorectal cancer (CRC). Altered nutrient metabolism, particularly changes to digestion and intestinal absorption, may play an important role in the development of CRC. Iron can promote the formation of tissue-damaging and immune-modulating reactive oxygen species. We conducted a crossover, controlled feeding study to examine the effect of three, 3-week diets varying in iron and saturated fat content on the colonic milieu and systemic markers among older females with obesity. Anthropometrics, fasting venous blood and stool were collected before and after each diet. There was a minimum 3-week washout period between diets. Eighteen participants consumed the three diets (72% Black; mean age 60.4 years; mean body mass index 35.7 kg/m²). Results showed no effect of the diets on intestinal inflammation (fecal calprotectin) or circulating iron, inflammation, and metabolic markers. Pairwise comparisons revealed less community diversity between samples (beta diversity, calculated from 16S rRNA amplicon sequences) among participants when consuming a diet low in iron and high in saturated fat vs. when consuming a diet high in iron and saturated fat. More studies are needed to investigate if dietary iron represents a salient target for CRC prevention among individuals with obesity.