Chapter 22 - Dietary Fiber, Soluble and Insoluble, Carbohydrates, Fructose, and Lipids

Abstract

Diets that have been shown to reduce chronic disease risk focus on increasing intake of foods naturally high in fiber with minimal processing including fruits, vegetables, legumes, and whole grains. Despite evidence for reduced disease burden from both epidemiological and clinical trials, current intake levels of such foods are well below dietary recommendations. Consequently, low intakes of dietary fiber significantly reduce the amount of fermentable substrate available to the gut microbiota as a source of metabolic fuel and likely lead to a less than favorable gut microbial profile. Major end products of gut microbial fermentation of nondigestible and undigested carbohydrates are short chain fatty acids (SCFAs), which have been associated with decreasing the risk of gastrointestinal disorders, cardiovascular disease, and cancer. The ratio of the major SCFAs (acetate, propionate, and butyrate) produced is highly dependent on the chemical composition of the substrate source. A mismatch exists between our archaic genome and gut microbiota, which has evolved primarily on plant-based diets that are high in dietary fiber and fermentable substrate, and our modern diets that contain low intakes of plant-based foods. This deficiency may provide some explanation for the rise in chronic diseases in Western nations. Emerging evidence suggests that interindividual differences in the gut microbiota are influenced by diet (probiotics, prebiotics) or antibiotics and may be linked to variations in physiology, including lipid metabolism that may predispose an individual to risk of certain chronic diseases. Diet is one of the key modulators of gut microbial communities and may provide a tailored approach for optimizing human health.