Could Bacteria Be Making You Fat?

By Denise Foley for Completely You

It may be the best excuse for being fat since the invention of “I have a glandular problem.” Seems like we might now be able blame bacteria for our excess pounds.

Current research is exploring the guts of obese people and lab animals for evidence that bugs make us overweight. Specifically, gut bacteria: intestinal microbes that store the energy from the food we eat as a spare tire or muffin top.

If you’re thinking “Ew, bacteria in my intestines?” and have images of the dinner table scene from Alien quivering in your head, relax. We all have bacteria colonies living below our equator -- 100,000 billion of them, in fact. The truth is that bacterial cells in the human body outnumber our own cells 10 to 1. That begs the question: Which is the parasite and which the host?

The More of This Bacteria You Have, the More Calories You Absorb
Fortunately, most of our gut bacteria are beneficial to our digestive and immune system. Still, a number of studies have found that obese people are more likely to have a lopsided ratio of bacteriodes to other gut microbes.

Bacteriodes are known for their efficiency in breaking down carbohydrates and slipping the calories to us, potentially promoting weight gain. Other microbes also help our cells absorb sugar, which may also pile on the pounds. By one estimate, gut bacteria may produce 100-200 more calories a day. Conservatively, that could mean a weight gain of 10 pounds a year.

And Bacteria Can Boost Your Appetite Too!
Evidence that gut bacteria are involved in obesity is so strong that the leader of one research team in Germany told the journal Nature that he could diagnose obesity with roughly 85 percent accuracy just from knowing the amount of certain intestinal bacterial species a person harbors.

Emory University scientists proved the bacteria-obesity link: They found that certain kinds of bacteria might encourage overeating in mice that have a genetic disorder affecting the immune system and that also have metabolic syndrome -- a dangerous constellation of symptoms including high cholesterol, high blood pressure and insulin resistance (prediabetes). When normal mice got a transplant of gut bacteria from the genetically damaged mice, they also overate, got fat and developed metabolic syndrome. (Read more about the study here.) The Emory researchers are now looking at humans with metabolic syndrome to determine if they have the same gut environments as the obese mice.

Can You Give Your Fat-boosting Bacteria the Boot?
Scientists are still trying to figure that out. And, unfortunately, they probably won’t for a while. As Coyle told me, it’s unclear whether losing weight depends on changing your bacterial balance -- or if your bacterial balance changes if you change your diet. And there’s no evidence, he says, that giving people probiotics (healthy bacteria) helps either.

But diet does seem to make a difference. When Washington University School of Medicine researchers transplanted gut bacteria from fat mice on high-fat diets to lean mice, the lean mice became fat too. So the best advice is to avoid a high-fat diet. We should all be doing that anyway.

Perhaps one day doctors will be able to replace an overweight person’s gut bacteria with that of a thin one and solve the obesity problem. But for now, says Coyle, “all this is in its infancy, with more to come.”

Want more healthy diet tips and research? Check out my recent article, “Fish Oil: The One Benefit You Haven’t Considered”


Denise Foley   is Completely You’s “News You Can Use” blogger. She is a veteran health writer, the former deputy editor and editor at large of Prevention, and co-author of four books on women’s health and parenting.