When microbes play spoil-sport in diet-related weight gain

Credit: Pixabay
Credit: Pixabay

Ever had this bad experience of gaining back more pounds after you successfully lose some? Seems like you are not alone and your metabolism is not the only thing to blame.

‘Weight cycling’, or the repeated loss and gain of weight is far too often the complaint of people who put on weight despite exercising regularly. Until now, the reason behind this “yo-yo effect” has been poorly understood and there has been much speculation on different factors that might be causing this.

Now, by studying this effect in mice, Eran Elinav and his colleague Eran Segal from the   have shown that the yo-yo effect might be at least partly driven by the gut microbiome. Microbiome refers to the huge community of bacteria and other microbes that share our bodies, in this case, present in the gut.

Most of us live in a symbiotic relationship with microbes in our body, that help us carry out various metabolic activities. Our gut bacteria helps us to digest our food and extract energy from it and what we eat changes the microbiome too. They undergo diet-induced changes in terms of which species are abundant. Elinav and Segal discovered that some of the changes occur quickly, while others do not, and this discovery was important to better understand weight cycling.

The study was conducted by duplicating the “yo-yo” effect in mice based on dietary changes. The mice were fed with high-fat chow for a month, and they became obese. They were then switched to normal chow, and they lost weight. Again, they were fed with high-chow and they put on more weight than before .

When the mice were then put on normal diet and they returned to their baseline weight everything such as cholesterol, blood sugar, insulin, body fat, appetites, physical activity, and metabolic rates normalized, except their microbiomes.

When they first gained weight, several species of microbes in their guts became more common, others became rarer, and the overall community became less diverse. But as the mice lost weight, those microbial changes were slow to revert.

Through two detailed experiments, the study showed that the microbes that became more common during initial weight accelerated the weight gain in subsequent experiments. First, sterile mice (had no microbes of their own), lacking a gut microbiome were injected with the more common microbes and they were observed to put on more weight than usual.

Second, treating the dieting mice with high antibiotic doses to get rid of their existing gut microbes (an to reset their microbiome) and then feeding them with a high-fat diet caused a far-less exaggerated weight gain.

“This is by no means a recommendation to take antibiotics while dieting,” says Elinav. “That would have many side effects, and I don’t think it would be helpful. It was just a scientific way of showing that the microbes are doing something.”

“The study is likely to be a milestone towards understanding the complex mechanisms that lead to weight cycling,” says Abdul Dulloo from the University of Fribourg. Still, the model does not fully explain sudden weight gain in lean people having normal diets, but it is definitely a start. Also, humans are more complex than rodents.

Which is why the Israeli team are now studying human volunteers to see if they are affected by the same microbial lag—and to what extent.

“Until you measure it in humans, we just don’t know how long the window of susceptibility is,” says Elinav.

Elinav also believes that manipulation of the microbiome might also be useful in preventing the yo-yo effect. His team managed to slightly reduce it by giving their dieting mice a faecal transplant—filling them with stool from healthy individuals to reset their microbiomes. However, in humans this approach would be non-scientific and he is after something more precise.

Another important clue from the study is the effect of fatty food on microbe metabolism. When the mice ate fatty food, their gut microbes started enthusiastically breaking down flavonoids—nutrients that normally increase the burning of fat. Fewer flavonoids meant more weight. And when the team fed their dieting mice with flavonoid supplements, they prevented the rebound.

Again, this study provides some important clues on the relationship between microbes and weight gain, but a more thorough investigation is needed to understand the various mechanisms that might be involved.