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People who struggle to maintain a healthy weight after dieting may do so because their gut bacteria retains a memory of their past weight.

Stashed in: Nutrition, Microbiome, Obesity

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The study, in mice, suggests that yo-yo dieting is not simply a reflection of people returning to unhealthy eating habits, but could be driven by long-term changes in gut bacteria brought about by obesity.

The scientists observed that the changes to the gut microbiome brought about by obesity persisted for five times as long as the actual period spent dieting and predisposed the mice to rapidly regain weight.


In the study, published in Nature, obese mice were switched from a high fat diet to balanced nutrition until they were indistinguishable from a control group of mice in terms of weight and a range of metabolic factors, such as blood sugar levels.

However, the scientists found that the formerly obese mice retained differences in their gut bacteria after dieting that tended to increase the rate at which they put on weight once they were given access to high fat food. When the guts of the control mice were seeded with bacteria from the obese group they too put on weight more rapidly.

The scientists suggest that the mechanism may have evolved to act as a physiological “buffer” against weight loss in times of food scarcity.

However, in the case of obesity, the mechanism may work against the person by leaving them liable to put weight back on rapidly once they stop dieting.

When people who have long-term obesity lose weight through dieting, in up to 80% of cases they put weight back on again within 12 months.

Cork said that the composition of gut bacteria is notoriously difficult to shift, however, and that any treatment would involve a long course of antibiotics to eradicate the existing population of microbes, rather than being a case of eating “a few probiotic yoghurts”. “If you try to introduce something else in a small quantity the bacteria in your gut out-competes them,” he said.