Short chain fatty acids such as acetate, propionate, and butyrate, are produced by microbial breakdown of fiber in the colon. These molecules are believed to contribute to the link between high-fiber diets, the gut microbiome, and health. However, evidence is still lacking on how high-fiber diets that differ in protein, carbohydrate and fat affect circulating short chain fatty acids, and also on how changes in these molecules in turn relate to cardiovascular and metabolic health.

A newly published study in The American Journal of Clinical Nutrition is the first to compare the effects of 3 high-fiber diets differing in protein, carbohydrate, or unsaturated fat on different types of short chain fatty acids circulating in the blood. Based on previous literature, the authors hypothesized that acetate, the main short chain fatty acid in the blood, increases with all high-fiber diets, but differently based on the macronutrient composition of the diet.

A total of 163 adult men and women that participated in the OmniHeart study were included in this analysis. Participants in this randomized crossover feeding trial were provided with 3 high-fiber isocaloric diets, each for 6 weeks, in random order: a predominantly plant protein-rich diet, a carbohydrate-rich diet, and an unsaturated fat-rich diet. Short chain fatty acid concentrations in the blood were determined at baseline and at the end of each diet period. The researchers also evaluated how changes in circulating short chain fatty acids were associated with measures of cardiometabolic health and appetite.

This study reports, for the first time, how macronutrient composition of high-fiber diets affects microbiota-derived circulating short chain fatty acids. Study results indicate that all 3 high-fiber diets increased circulating short chain fatty acids, but the effects differed by the macronutrient composition of the diets. According to lead author Noel Mueller (Assistant Professor at the Johns Hopkins Bloomberg School of Public Health) and colleagues, “The widescale adoption of low-fiber dietary patterns in the US and abroad has been accompanied by rises in metabolic and cardiovascular diseases, but the mechanistic link remains unclear. Our results suggest that short chain fatty acids produced by gut bacteria may be involved. In our trial, all high-fiber diets increased short chain fatty acids in the blood. The plant protein-rich version had the strongest effect on acetate, the short chain fatty acid most beneficially associated with glucose metabolism and cardiovascular health.” These results support recent US dietary guidelines that emphasize the importance of high-fiber dietary patterns as well as plant sources of protein, that promote both gut microbiota diversity and cardiometabolic health.

Reference Mueller NT, Zhang M, Juraschek SP, Miller ER, Appel LJ. Effects of high-fiber diets enriched with carbohydrate, protein, or unsaturated fat on circulating short chain fatty acids: results from the OmniHeart randomized trial. Am J Clin Nutr 2020 Jan 11 (Epub ahead of print; DOI: https://doi.org/10.1093/ajcn/nqz322).  

Images credit: canva.com

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