Scientists aren’t clear on the exact relationship between the Firmicutes to Bacteroides/Prevotella (F:B) ratio, fecal short-chain fatty acid (SCFA) levels, and obesity. This observational human study analyzed 3-day dietary intakes, physical activity levels, body mass index, fecal microbiota, and SCFAs in both lean and overweight/obese research participants (n=94).


They found that diet and physical activity levels were similar between groups. Compared to lean participants, those who were overweight/obese had higher SCFAs overall: higher fecal acetate, propionate, butyrate, and valerate. Researchers observed no significant differences in F:B ratio between the groups, but among all participants, higher Bacteroides/Prevotella counts were associated with lower fecal SCFAs. F:B ratio correlated with higher fecal SCFAs.

The results suggest that SCFAs and F:B ratio vary together and may be interrelated. Colonic fermentation patterns may be altered — but not necessarily by diet — leading to different SCFA concentrations in fecal samples of lean and overweight/obese humans.

This study is limited by the lack of mechanistic insight into these associations and its reliance on self-reported data about diet and physical activity.


Fernandes J, et al. (2014) Adiposity, gut microbiota and faecal short chain fatty acids are linked in adult humans. Nutrition & Diabetes doi:10.1038/nutd.2014.23