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    Why diets don’t work: ‘obesity-causing’ bacteria linger in the gut

    30 November 2016

    New research published in the journal Nature suggests that intestinal microbes play an unexpectedly important role in recurrent obesity — a phenomenon closely linked with ‘yo-yo dieting’.

    The study, by the Weizmann Institute of Science, concludes that the problem could be treated in the future by altering the composition of gut flora.

    Recurrent obesity occurs when, following a successful diet, obese people revert to old habits and gain more weight than they lost in the first place. During each round of dieting and weight gain, body fat increases proportionally, as does the risk of developing metabolic syndrome, diabetes, fatty liver disease and other obesity-related diseases.

    The researchers found that (in mice) after the cycle of weight gain and loss, all the body systems fully reverted to normal, except the microbiome. For about six months after losing weight, post-obese mice retained an abnormal ‘obese’ microbiome.

    In a series of experiments they demonstrated that the makeup of the ‘obese’ microbiome was a major driver of accelerated post-dieting weight gain. When the microbiome was treated with antibiotics, post-diet weight gain was eliminated.

    Dr Eran Elinav, the study’s lead author, said: ‘We’ve shown in obese mice that following successful dieting and weight loss, the microbiome retains a “memory” of previous obesity. This persistent microbiome accelerated the regaining of weight when the mice were put back on a high-calorie diet or ate regular food in excessive amounts.’

    Professor Eran Segal, who worked on a machine-learning algorithm which accurately predicted the rate of weight regain in each mouse based on the characteristics of its microbiome, said: ‘By conducting a detailed functional analysis of the microbiome, we’ve developed potential therapeutic approaches to alleviating its impact on weight regain.’

    Instant analysis
    One of the problems facing serial dieters is that they often find any weight they have lost following a diet then goes back on, sometimes leading them to be heavier than before they started dieting. This leads to so-called ‘yo-yo’ obesity with a pattern of weight loss and then increasing weight gain.

    The reason for this is unclear but this study may suggest a possible answer. Analysis of intestinal microbes (the gut microbiome) in mice show that the abnormal patterns of microbiomes in obese mice persist even after significant weight loss. This then caused accelerated weight gain when the mice were put back on a high-calorie diet or ate normal food in large quantities.

    The authors believe this has a potential therapeutic application for the future but much more work still needs to be done in humans and a magic microbiome bullet to reduce obesity remains way into the future. Expect to hear more on this, though, in the coming years.
    RH
    Research score: 3/5