Intestinal Bacteria May Cause Weight Gain

Why are some people skinny, even though they eat large amounts of food, while others become fat? Jeffery Gordon of Washington University in St. Louis thinks it's because some people have types of bacteria that cause them to absorb more calories from their food.

You have two absorption systems in your body. You absorb most of your food as it passes through your small intestines. Food that is not absorbed in the small intestine goes to your colon. The colon contains a huge colony of bacteria that work to ferment undigested carbohydrates such as soluble fiber into short chain fatty acids and simple sugars that can then be absorbed through the colon walls into the bloodstream. Most people get about ten percent of their total calories from food absorbed through their colons.

Animal studies lead us to the next step. The dominant bacteria in the gut of obese mice are Firmicutes, types of bacteria that have more genes for breaking down the complex starches and fiber. Mice who are thin have more Bacteroidetes in their guts, and these bacteria are not as efficient in breaking down fiber and complex carbohydrates. Transplanting Firmicutes bacteria into the guts of lean mice made them fat.

These researchers also found that fat humans had far more Firmicutes bacteria than thinner ones. They then asked their overweight subjects to go on a low-fat, low-refined- carbohydrate diet for one year. As they lost weight, their bacteria changed to predominantly Bacteroidetes.

Today you may be able to lose weight by changing the composition of your diet in a way that changes the bacteria in your gut so you absorb fewer calories. In the future, you may be able to get a pill that contain primarily Bacteroidetes bacteria, take it daily and watch the pounds melt off because of the change in intestinal bacteria. Fitness, Nutrition and Health newsletter