Weight gain happens when we consume more meat than we can burn, and weight loss happens when we burn more energy than we eat. 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 meat? 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 forms of bowel microbes.
In the past decade, researchers have found that the microbes in our bowel have a strong influence on various aspects of our health. Surveys in mouse have demonstrated that how the body converts meat into energy depends in large-scale part on the different types of microbes a person has in their bowel and including information on the kind of microbes they carry.
In a recent survey, scientists in Israel found that mice who were put on a yo-yo diet gradually gained weight compared against mouse on a steady diet despite the fact that both groups received the same sum of calories overall.
One of the impact seen in the mouse that were put on the yo-yo diet was a decrease in their gut microbiome diversity. Likewise, when they transplanted the microbes from the yo-yo dieters into the guts of non-yo-yo dieters, the mouse 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 men, scientists have already shown that lean people have many more species of intestinal bacteria than obese people.
Ive been on a yo-yo diet. Janson George/ Shutterstock.com
What twins taught us
Until now, however, there were no experimentations tying the bowel microbes to changes in weight over several years. For this reason, we decided to do an investigation into 1,632 females from the UK, all of them twins( about half of them identical ). The participates had their own bodies weight measured several years ago and, back then, they answered questions about the amounts and types of foods that they eat. We called them again then nine years later and, in addition to measuring their weight, we asked them to give us a poo sample so we could analyse the bacteria in their gut.
We found that most of the women gained weight over the nine years, but this was not fully explained by the number of calories in their diet when the study began. Why i am twins, it was also possible to calculate( employing the differences between identical and non-identical twins) how much of the weight gain can be explained by genes. Only 41% of the change in weight was explained by genes. That meant that there were other factors, in addition to genes and calories.
We discovered that women who eat high amounts of dietary fiber( found in fruit, veggies and whole grains) were less likely to gain weight than those who ate little fiber, even if they ate roughly the same sum of calories. Women who lost weight or had stable weight likewise had more diverse microbes in their guts. We were able to pinpoint some of the microbes that are different between women who had gained weight and those who had lost weight. Most of these microbes had already been discovered in mouse to be involved in better energy metabolism.
These outcomes show that the exciting examines in mouse about how microbes affect weight gain are likewise relevant in humans. They are also important because they will allow the working group, and other scientists, to investigate how to influence person or persons gut microbes employing probiotics and fibre so they are at a lower peril of developing obesity.
Ana Valdes, Associate Professor and Reader, King’s College London
This article was originally published on The Conversation. Read the original article.
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