Why Is It Harder to Maintain Weight Loss Than to Achieve It?

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There are many effective diets for losing weight, but the vast majority of dieters have a hard time keeping it off, and scientists are just beginning to find out why that is.

By Kate Wheeling


(Photo: Alan Cleaver/Flickr)

’Tis the season for holiday weight gain — the time of year when dieters learn the hard way that all it takes is a few family dinners to regain all that weight you just spent two months losing.

Research bears this out: Up to 80 percent of dieters wind up back at — or above — their initial weight. But exactly why it’s so hard to prevent this “yo-yo effect” has long been a mystery. In a new study, researchers from Israel used a mouse model of yo-yo dieting to find a likely culprit for such widespread post-diet weight increases: an altered microbiome.

Obesity in both mice and humans triggers a cluster of metabolic issues including insulin resistance, hypertension, and increased body fat. Once the weight comes off, these symptoms tend to fade quickly, but the microbiome — the ecosystem of microorganisms that both inhabit and influence the function of the human body — takes longer to recover, the new study found.

The researchers fed mice an alternating cycle of high-fat food followed by normal chow, so that the animals gained weight, then lost it, then re-gained it even faster again. The study showed that, in mice, as in humans, subjects that had lost weight and then went back on a high-fat diet gained weight even faster the second time around.

It took more than five months for the mice’s microbiomes to return to normal after they lost the excess weight — five times longer than it took them to put the weight on in the first place. When the researchers transferred the abnormal microbiome of newly svelte mice into normally fed mice that had never been obese, the normal mice also packed on pounds quickly when given the high fat diet, indicating that the altered microbiome indeed sped up weight gain, in combination with a fattening diet.

So how exactly did the mice’s microbiomes influence their weight? The team found that the altered microbiomes in previously obese mice produced less of two kinds of flavonoids — dietary compounds derived from plants: arpigenin and naringenin. Previous research has found these flavonoids are linked to how much food we consume, the generation of fat cells, and the breakdown of lipids. Adding those flavonoids back into the intestinal milieu of the mice on diets with oral supplements slowed the rate of relapsed weight gain when the mice were put back on a high-fat regimen.

The researchers created a machine learning algorithm — a computational tool that can find meaningful patterns buried within vast amounts of data — to predict not only which mice will gain weight, but how much they will gain, based on the make-up of their microbiomes. Such a tool could someday help predict on a personalized basis which diet will result in weight changes for humans, or who will be most susceptible to post-diet weight gain, according to the authors.

These findings, however, will need to be confirmed in human subjects before they can be applied to people, the researchers caution. But their study at least provides a glimmer of hope that manipulating microorganisms could someday help humans break free of the yo-yoing diet cycle.