(916) 482-5200

The Link Between Bacteria and Weight Gain

Published: July 11, 2011

Recent research is revealing what complex creatures you and I are. If you count the number of cells which we consist of, then “we” are 90% foreign bacteria. If you tally it by weight these tiny living things are, in the aggregate, are still a presence. Perhaps 3 pounds of our total weight are bacteria, mostly living in our guts.

Despite nearly different 1000 species of bacteria living in our gut, three distinct types bacterial communities have been identified by scientists. This discovery might partially explain why some of us are skinny and some are fat. After all, some people really do seem to gain weight no matter what they eat, and their gut bacteria might be playing a role in that.

We depend upon the bacteria in our guts to do useful things for our bodies. Our friendly tenants plug gaps in our own cellular machinery to produce things like vitamin K and B vitamins, which left to our own devices would be in scarce supply. Additionally, we humans cannot digest the cellulose which is found in all plant cell walls. Our gut microbes can.

(By the way, termites use their gut microbes to digest wood cellulose, why this useful trick has been managed by so few organisms is a fine mystery in biology)

Cellulose, once broken down into its component sugar (glucose) is digestible.
Since some people’s guts surely harbor bacteria that are better at this than others, this seems a perfectly sensible explanation for how some people gain weight regardless of what they eat.

Assume that Fats McGee, desperate to lose weight lays off the donuts (which contains starch – highly digestible by all humans) in favor of fruits in vegetables, which consist of large amounts of cellulose, pectin, and other minimally digestible complex carbs. Fats is doing what he can to cut calories, but hard at work in his gut are overzealous bugs, which have the ability to chomp up these normally undigested bits of fiber better than the run-of-the-mill bacteria.

You can see where this leads – frustration for McGee. His weight stays up despite eating apples, carrots and celery. He has been thwarted by his own gut. Studies in mice show this to be a very real phenomenon. Transplant bacteria from fat mice into ones that were raised germ free and they will get fatter than ones who got their bugs from donors who were skinny!

Does this research open the door to better control of weight related diseases through manipulation of the bugs that live inside us? It almost certainly does, but as always the devil will be in the details. We have yet to figure out how these different ecosystems behave, let alone how to get them to do what we want.

I am confident this area of research is going to mean breakthroughs for weight control, obesity related illnesses and diseases of the gut. They won’t come tomorrow, but they should come in the next decade. This is good news from the world of basic science.