It’s a well-known story: Make a resolution to lose weight in the new year. Go on a diet and lose some kilos. Gradually slip back into the old eating patterns and gain all the weight back.

Dieting—a temporary change in eating patterns, with restriction of certain ‘bad’ foods—isn’t all it’s cracked up to be. Most of us already know it’s not a way to keep off the weight in the long term. And now, a mouse study from researchers from the Weizmann Institute of Science in Rehovot (Israel), led by Eran Segal and Eran Elinav shows why short-term dieting might be even more harmful for weight and metabolic health compared to not dieting at all.

In their study, Elinav and Segal found slim mice that started to eat a high-fat diet gained weight, but when they returned to eating a normal diet they soon returned to a normal weight. Then, when these same mice were exposed again to a high-fat diet, they gained weight. All perfectly as expected.

According to the researchers, obesity followed by short-term dieting could leave a lasting mark on the gut microbiota

But there was an interesting twist the second time the mice switched to the high-fat diet: the mice gained weight even faster than they did the first time. The researchers wondered: what could have accounted for this turbo-charged weight gain?

The researchers found a clue inside the intestines of the mice. When the mice went from slim to obese the first time, their gut microbiota composition changed. But when they lost the weight after dieting, the gut microbiota did not return to its original composition; it was as if obesity followed by short-term dieting had left a lasting mark on the gut microbiota.

The change was not a positive one: when researchers took a separate group of mice on a high-fat diet, they found the ones receiving the microbiota from the short-term dieting mice gained weight faster than those receiving the microbiota from mice of identical weight who had never cycled through a diet. So the high-fat diet plus gut microbiota dysbiosis (as a result of dieting) appeared to create the perfect conditions for rapidly becoming obese.

There was some good news in the study: the researchers found two ways to remedy the faster weight gain after dieting. For the mice that had the microbiota dysbiosis after dieting, fecal microbiota transplants from healthy mice on a normal diet slowed the secondary weight gain; and in addition, giving the post-dieting mice a daily combination two flavonoids (biologically active plant compounds found in foods)– apigenin and naringenin—did the same thing without affecting microbiome composition.

The work serves as a warning that short-term dieting may ‘scar’ the gut microbiota in a way that makes faster weight regain likely in the context of a poor diet. Yet, how well the findings apply to humans is not certain.

Especially relevant for humans is the question of whether the baseline nutrition matters in dieting—namely, does switching temporarily from a high-fat diet to a normal (nutritionally balanced) diet have the same effect on the gut microbiota as switching, say, from a normal diet to a calorie-restricted diet?

The medical problem remains, though, that not enough people maintain weight loss over the long term, to the detriment of their health. Rather than dieting, say health professionals, lifestyle shifts including diet and exercise are more likely to result in lasting weight loss. And with time, more knowledge of how the human gut microbiota affects obesity and metabolic health could bring the potential for addressing long-term weight loss in new ways.



Thaiss CA, Itav S, Rothschild D, et al. Persistent microbiome alterations modulate the rate of post-dieting weight regain. Nature. 2016; 540:544-551.