Stomach flora cause weight gain after diets.

Weizmann institute researchers investigated the phenomenon of post-diet weight gain, also known as the "yo-yo effect". Dieters find that as they regain lost weight, they tend to add more weight than they lost. Moreover with each additional weight gain the level of fat in the body rises causing a rise in the risk of fat-related illnesses such as Type 2 diabetes, fatty liver and other features of metabolic syndromes.

The researchers discovered that the yo-yo effect is significantly influenced by stomach flora as was recently published in Nature magazine, and it can be mitigated by intervention in the function and makeup of these flora. The research was conducted by Dr. Eran Elinav of the Immunology dept. and Prof. Eran Segal of the Computers and Applied Math dept. at the Weizman Institute.

Dr. Elinav explained that "the research conducted on mice demonstrated that their stomach flora 'remembered' the previous weight and this precipitated weight gain as they ate high caloric foods or larger quantities of regular foods. By analyzing the various functions of the stomach flora, we were able to understand the contribution of these flora to weight gain and to develop diagnostic methods to treat the phenomenon."

Investigation of the structure and functions of the stomach flora revealed that when the mice gained weight and then reverted to their previous weight, all their body functions returned to their previous levels except for the stomach flora, which for a half a year after the successful weight loss retained the characteristics of the unhealthy stomach flora of fat mice.

Doctoral student Christhoff Theiss, a researcher in Dr. Elinav's laboratory collaborated with research student Shlomik Yitav and doctoral researcher Dafna Rothchild from Prof. Segal's laboratory, as well as with other scientists from various institutions around the country.In a series of experiments the scientists demonstrated that the 'fatty stomach flora' in the mice which gained and lost weight cause the yo-yo effect in these mice. When researchers removed the stomach flora of mice which had suffered from the yo-yo effect by using antibiotics, the effect was prevented. When these same flora were injected into regular mice they began to gain exaggerated levels of weight in comparison to other mice which were injected with regular stomach flora.

Using software which they had developed, scientists were then able to predict precisely, based on hundreds of characteristics of the stomach flora, the exact amount of weight gain that each mouse would gain under conditions of high-calorie diets. Using genomian and metabolic approaches they were able to identify a mechanism which causes the stomach flora to influence the level of post-diet weight gain. This mechanism is based on two molecules found in plant-based foods from flavinoids. The mice with a history of post-diet weight gain disposed of these molecules faster than others. Scientists discovered that these molecules are responsible for breaking down fatty tissue and the low levels of molecules in these mice precluded the production of energy from these fats which were then stored in the bodies of the mice.

By changing the makeup of the stomach flora and their functions scientists were able to prevent the yo-yo effect in these mice when they were given a high calorie diet. In one instance scientists added the two missing molecules to the mice's diet and the additional molecules instigated the production of energy from fat and thus prevented the yo-yo effect from repeating itself. This method might be more suitable for humans than intervening in their stomach flora. "

Professor Elinav says that the yo-yo effect is a huge problem affecting large portions of the world's population. "Obesity characterizes half of the world's population and its complications cause death and diseases like diabetes, fatty liver and heart disease. If the results of our research on mice apply to humans we can possibly use them to treat the problems of human obesity.