Reduced dietary intake of carbohydrate, by obese subjects, results in decreased concentrations of butyrate and butyrate-producing bacteria in feces

Microbial Ecology Group, Biomathematics and Statistics Scotland, Metabolic Health Group, Rowett Research Institute, Greenburn Road, Bucksburn, Aberdeen AB21 9SB, UK

^* To whom correspondence should be addressed. Email: hjf{at}rri.ac.uk.

	Abstract

Weight loss diets for humans that are based on a high intake of protein but low intake of fermentable carbohydrate may alter microbial activity and bacterial populations in the large intestine and thus impact on gut health. In this study, 19 healthy, obese (BMI range 30-42) volunteers were given in succession three different diets:- maintenance (M) for three days (399 g carbohydrate/d); then high protein/medium (164g/d) carbohydrate (HPMC) and high protein/low (24g/d) carbohydrate (HPLC) each for four weeks. Stool samples were collected at the end of each dietary regime. Total fecal total short-chain fatty acid (SCFA) were 114 mM, 74 mM and 56 mM (P<0.001) respectively for M, HPMC and HPLC diets, and there was a disproportionate decrease in fecal butyrate (18 mM, 9 mM and 4 mM (P<0.001), with decreasing carbohydrate. Major groups of fecal bacteria were monitored using nine 16S rRNA-targeted fluorescent in situ hybridization probes, relative to counts obtained with the broad probe Eub338. No significant change was seen in the proportions of the bacteroides (Bac303) (mean 29.6%), or the clostridial cluster XIVa (Erec482, 23.3%), cluster IX (Prop853, 9.3%), or cluster IV (Fprau645, 11.6%; Rbro730 + Rfla729, 9.3%) groups. In contrast, the Roseburia spp. and Eubacterium rectale sub-group of cluster XIVa (11%, 8% and 3% respectively for M, HPMC and HPLC; P<0.001) and bifidobacteria (4%, 2.1% and 1.9%; p =0.026) decreased significantly as carbohydrate intake decreased. The abundance of butyrate-producing bacteria related to Roseburia spp. and E. rectale correlated well with the decline in fecal butyrate.