Weight gain happens when we consume more food than we can burn, and weight loss happens when we burn more energy than we consume. But why do some people seem to eat whatever they want and not gain weight, and others appear to gain weight even if they eat reasonable amounts of food? The answer, at least in part, may be found in the bacteria that live in our guts.
Our latest research, published in the International Journal of Obesity, shows that people who have a stable weight over nine years or lose weight, have a larger number of different types of microbes in their guts, eat more fibre and have a higher abundance of certain types of gut microbes.
In the past decade, researchers have found that the microbes in our gut have a strong effect on various aspects of our health. Studies in mice have demonstrated that how the body converts food into energy depends in large part on the different types of microbes a person has in their gut and also on the kind of microbes they carry.
In a recent study, scientists in Israel found that mice who were put on a yo-yo diet slowly gained weight compared with mice on a steady diet – despite the fact that both groups received the same amount of calories overall.
One of the effects seen in the mice that were put on the yo-yo diet was a decrease in their gut microbiome diversity. Also, when they transplanted the microbes from the yo-yo dieters into the guts of non-yo-yo dieters, the mice on steady diets gained weight – showing that the altered microbes were the cause of the weight gain. But is this relevant to humans?
In humans, comparing microbes in the gut in obese and thin individuals, scientists have already shown that lean people have many more species of intestinal bacteria than obese people.