The following Mark's Daily Apple article was written by Mark Sisson,

and is narrated by Tina Lehman.

Could gut bacteria be to blame for your stubborn belly fat? We know how important gut health is for overall health.

We understand that it improves digestion, that our pursuit of extreme sterility has compromised our immune systems,

and that the gut biome is ideologically involved in the pathogenesis of various health and disease states.

We're even familiar with the more esoteric functions of gut bacteria, like converting antinutrients

into bioavailable nutrients, synthesizing sex hormones and neurotransmitters, and mitigating

the allergenicity of gluten. But what about gaining

and losing body fat? The real reason most people get interested in diet in the first place.

Are the bacteria in your gut responsible for the fat on it? Maybe. The animal literature shows

that direct manipulation of the gut biome can affect body weight and resistance to obesity.

In one paper, transplanting the gut bacteria from obese mice into lean mice led to a 60% increase in body fat

and a rapid 14-day descent into insulin resistance following the gut flora alteration. Another found that mice

seeded with bacteria from lean mice even appear resistant to developing obesity when consuming

fecal matter, a basic, if disgusting form of fecal transplant from obese mice. At least in mice, obese gut bacteria and

lean gut bacteria are well established and appear to be causally related to body weight. In humans,

the evidence is more mixed. Some studies find a higher proportion of firmacute bacteria and fewer bacteria from

bacteriotees in the obese and overweight, while others find the opposite.

The only concrete conclusion from a 2012 meta-analysis was that obesity in humans tends

to track with an increase in members of the fermicutes phylum. As for direct

interventions, changes to the gut bacteria certainly accompany weight gain, but it's unclear

whether the relationship is coincidental or causal, and if causal, in which direction causality

...