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Where keto works
Keto does seem to work for people with diabetes who are overweight, as a way of getting them off medications and kick-starting a better health pattern. As a sustainable diet it doesn't make sense, and not many people are still on a true one a year later.
The risk
The risk is restriction. A diet that cuts the number of foods thins the variety of plants the gut microbes get, and that can harm the microbes long term and cause problems for immune health and long-term health.
Why people feel better
Part of the benefit people report may come from a different change. Someone who moves from refined carbs and ultra-processed foods to real home-cooked meals could feel better just by raising fat and lowering refined carbs, without going to the extreme version.
How does ketosis work?
When carbohydrate intake drops low enough, insulin falls and the liver converts fatty acids into ketone bodies such as beta-hydroxybutyrate and acetoacetate. The brain cannot burn fat directly, but it uses ketones for a share of its energy. Russell Wilder at the Mayo Clinic introduced the ketogenic diet in 1921 as a treatment for epilepsy, building on observations that fasting reduced seizures.
How do low-carb diets compare over time?
A systematic review of randomized trials in type 2 diabetes, published in the BMJ in 2021 by Joshua Goldenberg and colleagues, found that low-carbohydrate diets were associated with remission at six months. At twelve months there was little to no difference from other diets, and the benefit on blood sugar measures had faded.
How does a ketogenic diet affect gut bacteria?
In a 2020 paper in Cell, Qi Yan Ang, Peter Turnbaugh, and colleagues at the University of California San Francisco studied a ketogenic diet in 17 adults with obesity for four weeks and in mice. The diet lowered levels of Bifidobacteria, a group of bacteria often considered beneficial. In mice, it also reduced the number of Th17 immune cells in the intestine.
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