It’s possible you don’t think about it often, but I expect you know that whenever you eat, you feed not only yourself but also trillions of microbes that live in your guts. Of course it’s natural to be somewhat disgusted by this strange arrangement, but these microbes are being seriously and extensively studied, and it looks like they’re considerably more interesting than you may realise.
Quite apart from the massive impact they have on your health, especially with regard to autoimmune disease and even metabolic syndrome, there’s increasing evidence that gut bugs are a major factor in your ability to gain or lose weight.
First, consider that American farmers have known for decades that animals fatten up faster on antibiotics – which disrupt the gut microbes. 80% of all antibiotics sold in the US go to livestock.
In research, specially bred microbe-free mice simply don’t gain weight, no matter what and how much they are fed. But when these mice had gut bugs introduced their body fat more than doubled, even though they ate the same. If the gut bugs introduced came from obese mice, the weight gain was considerably larger. (1)
As for us humans, many studies have found that the gut bugs in overweight individuals are clearly quite different from those in lean individuals. There’s a striking lack of diversity, with large increases in some strains and others in decline. The question is, does being overweight change that balance of gut bugs, or does a change in the amounts and types of bugs cause weight gain? It could be a bit of both, but from that mouse research and many other human studies, it looks like the latter is by far the most significant factor. (2)
So, look after your gut bugs and they will look after you.