Now that our view of gut bacteria has changed, we’re also finding that these microbes can influence whether a person will be fat or thin.
Gut bacteria act as a minibrain by producing a wide range of hormones. Because they contain neurotransmitters, they also communicate directly with the brain.
As a result, it is now believed that the bacteria in your gut can influence many bodily functions, including regulating the amount of food you eat.
For instance, when you eat a meal, your gut secretes hormones that activate signaling pathways to the brain. Eventually, these signals relay the message that you are full, so you can stop eating.
Many gut bacteria can manufacture special proteins, called peptides, that are similar to hormones that regulate hunger, raising the possibility that microbes are involved in appetite as well.
In twin studies, scientists looked at gut bacteria in obese and lean people.
They found that slender people had more diverse intestinal flora, especially of a type called bacteroidetes, which efficiently break down bulky plant starches and fibers into energy.
Researchers have also tested this hypothesis in studies involving mice that were bred to be genetically identical.
The mice were raised in a germ-free environment to rid their bodies of any bacteria, then had their guts populated with intestinal microbes collected from obese women or their lean twin sisters.
The mice ate identical diets, but those that received bacteria from the fat twin ended up with a higher ratio of body fat.
Another way gut microbes may shape our bodies is through their influence over food cravings.
We used to think that cravings were the body’s way of letting us know we were deficient of a particular nutrient. But emerging science suggests that these cravings may be shaped by gut bacteria.
For instance, researchers have discovered that the urine of people who crave chocolate contains very different microbiological components than those who do not.
This holds true even if they eat identical diets.