Microbes and Weight: Do Gut Bacteria Influence How We Eat?

Did you know that you’re an ecosystem? Our bodies are host to trillions of microbes, with bacterial cells outnumbering our own 10 to 1. The highest concentration of bacteria is in the colon and small intestine, where food is broken down into energy and nutrients we can use. The bacteria passed on from our parents, plus external factors like diet, hygiene and antibiotic use, give us each a unique gut flora composition that changes daily. Science is still unfolding the mystery of how these dynamic micro-populations affect our overall physiology, including how changes in gut flora affect digestion and appetite.

There are two main divisions, or phyla, that influence digestion: bacteriodetes and firmicutes. Many in the intestine are beneficial, carrying out a symbiotic relationship with the host by extracting calories from food and turning indigestible carbohydrates into short chain fatty acids for use by the host cells.

While both phyla are mostly “friendly bacteria,” their changing proportions in the gut have been shown to affect how efficiently the intestines absorb calories. A 2005 Washington University study suggested that the proportions of these two bacteria in the gut are related to weight gain; fat mice tended to have more firmicutes, and fewer bacteroidetes, in their guts than lean mice. Since humans also host these two types, the results may apply to us, too.

Firmicutes tend to draw the maximum calories from food, making it easier to gain weight. While this function was a positive for our hunter-gatherer ancestors, efficient calorie extraction is not a problem for people eating today’s Standard American Diet. The gut population could change in response to a number of environmental factors: antibiotic use, improved hygiene and cleanliness in the food supply.

The host response changes along with the bacteria population, which “may predispose you to a variety of diseases of which obesity and metabolic syndrome are perhaps the most mild,” says Andrew Gewirtz, co-author of a study linking gut bacteria to inflammation. Research is under way to map the “other genome” of intestinal bacteria and illuminate the relationship between microbial genes and disease. With advances in metagenomics, we may soon be able to know our gut type as easily as we know our blood type.

Follow Erin on Twitter: @ErinPie

Image: dearmax