Calories Burned by Bacteria in the Gut
100 trillion microbes may be conspiring to make you fat. That’s the implication of a recent study on the relationship of gut bacteria to diet and obesity in mice. It might be a long stretch from mice to men - or maybe not.
Bacteria "R" Us
The human gut (also called the intestines) is chock full of bacteria that help digestion and fight disease. In fact, of all the cells that make up the human body, microbe cells outnumber "human" cells by 10 to 1.
A while ago Dr. Jeffrey Gordon and his research team from Washington University in St Louis noticed that overweight people and lean folks have different gut bacteria. Obesity is associated with more of the bacteria called Firmicutes, while leanness is associated with more bacteria from the Bacteroidetes family. The scientists wondered if the difference in gut bacteria had a role in obesity.
To test his assumption about gut bacteria and obesity, Dr. Gordon created an animal model. He raised mice in a germ-free environment; consequently, they had no gut bacteria. He then infused the mice with a typical mix of bacteria found in the human gut. The human bacteria flourished in the mice and so Dr. Gordon began his research.
The scientists fed different diets to two groups of mice with the identical gut bacteria. Half the mice ate a “Western Diet” full of sugar and fat, and the others ate a minimally processed diet low in sugar and fat. When the bacteria were re-measured, the mice eating the Western Diet had more Firmicutes while those eating the unprocessed diet had more Bacteroidetes. As expected, the mice on the Western Diet were fatter.
But, here is the interesting part: when the scientists transplanted gut bacteria from the "Westernized" mice to new mice that were still germ-free and then fed the new mice the unprocessed diet, the new mice gained more weight than was expected on the unprocessed diet.
It was as if the Firmicutes bacteria was much better at extracting calories from food. When those bacteria broke nutrients down to energy, the nutrients produced more calories than was expected.
Don't despair. In another study, Dr. Gordon measured the gut bacteria of obese humans as they tried to lose weight on a low calorie diet. He found that their Firmicutes bacteria fell while their Bacteroidetes bacteria rose as the study subjects lost weight. Perhaps gut bacteria can be altered after all.
Obviously much more research is needed to understand the role of gut bacteria in human obesity, but it could be that gut microbes do have some role and Western diets might make it worse. The research could explain why it’s often hard to lose weight, and it gives us yet another reason to put the kibosh on processed food.
Does this study make you think twice about processed food?