Gut microbes are all the rage and scholars everywhere are latching onto the fad. If you are over the age of 30, you have seen this too many times to count. Sugar causes diabetes, salt causes heart disease, trans fats cause everything, saturated fats were bad until they were good.
Now a paper in Nature claims an altered gut microbiota causes obesity.
In an earlier study, Gerald I. Shulman, M.D., the George R. Cowgill Professor of Medicine, observed that acetate, a short-chain fatty acid, stimulated the secretion of insulin in rodents. To learn more about acetate's role, they conducted a series of experiments in rodent models of obesity.
As the American Council on Science and Health has noted since fraudulent consumer groups like Center for Science in the Public Interest began suing and settling every time a rat died in a study, rodents are not little people. But rats beware, a comparison of acetate to other short-chain fatty acids found higher levels of acetate in critters that consumed a high-fat diet. They also observed that infusions of acetate stimulated insulin secretion by beta cells in the pancreas.
How? They don't know. You don't need a plausible biological mechanism to get mainstream science media churnalism coverage for probiotics, you just show an association.
When acetate was injected directly into the brain, it triggered increased insulin - by activating the parasympathetic nervous system, they say, noting that acetate stimulates beta cells to secrete more insulin in response to glucose through a centrally mediated mechanism, and also stimulates secretion of the hormones gastrin and ghrelin, which lead to increased food intake.
Still, how can they claim a causal relationship between the gut microbiota and increased insulin? After transferring fecal matter from one group of rodents to another, they observed similar changes in the gut microbiota, acetate levels, and insulin. So gut microbiota changed in response to changes in the diet and increased acetate production and then increased acetate led to increased food intake, setting off a positive feedback loop that drives obesity and insulin resistance.
As if that didn't convince you with science-y sounding rationale, they say this positive feedback loop is due to evolution.