The small intestine
The small intestine is where most nutrients from your food are absorbed – including fat. Scientists have discovered that the number of bacteria responsible for fat absorption increases within 24 to 48 hours of eating fatty foods. These bacteria release enzymes that digest that fat, then stimulate its absorption in the small intestine. If the bacteria are continuously present, this can lead to excessive intake of fat and subsequently to obesity.
Fat absorption
In the study, the researchers compared sterile mice (without microbes in their intestines) with normal mice. Both groups of mice were on a high-fat diet. The sterile mice were unable to absorb the fatty foods via the intestines, and secreted the fat in their droppings. Soon after these mice were administered microbes that contribute to fat absorption, their intestines began absorbing fat. In the normal mice the fatty food ensured a quick increase in the number of microbes from the Clostridiaceae and Peptostreptococcaceae families, which are known for their role in fat absorption. By contrast, there was a decrease in bacteria from the Bifidobacteriacaea and Bacteriodacaea families, which are associated with thinness.
Obesity
This is one of the first studies to show that specific microbes of the small intestine contribute directly to the absorption of fat. The study also shows that eating a high-fat diet can drastically change the composition of the intestinal flora. The results could be used in the future for treatment against obesity, by reducing the bacteria that contribute to fat absorption or by increasing the bacteria responsible for less fat absorption. This however does not mean that gut flora causes obesity. The answer ultimately lies in the amount and composition of food ingested.