Depression and anxiety are national health issues that affect a large percentage of the population. Recent research has shown that those who suffer from obesity may be more likely to experience depression and anxiety. The new study was performed by researchers at Joslin Diabetes Center and found that bacteria in the gut microbiome can cause depression and anxiety in people with obesity.
The researchers observed depressive and anxious behaviors in mice who were put on a high-fat diet and became obese. They said that the mice on the high-fat diet were more depressed and anxious than the mice who were on a regular diet. They also found that when the mice were given antibiotics that would change the gut microbiome, the behaviors resolved themselves.
“What this study says is that many things in your diet might affect the way your brain functions, but one of those things is the way diet changes the gut bacteria or microbes. Your diet isn’t always necessarily just making your blood sugar higher or lower; it’s also changing a lot of signals coming from gut microbes and these signals make it all the way to the brain,” says Ronald Kahn, a researcher on this study.
The mice were given four animal behavior tests, which are generally used when performing drug assessments for treatment of depression and anxiety. In each of the four tests, the mice who were on the high-fat diet showed significantly higher rates of depression and anxiety than the mice who were on the normal diet.
Bacteria in the Gut Causes Depression and Anxiety
The researchers were able to pinpoint bacteria in the microbiome as the cause of this increase in depression and anxiety by transferring bacteria from the mice who were on the high-fat diet into mice who did not have any bacteria in their gut.
The mice who were injected with the gut bacteria from the high-fat diet mice then began to show anxious and obsessive behaviors. If the bacteria were taken from a mouse who was on a high-fat diet but had then been treated with antibiotics, the injected mouse did not show signs of depression or anxiety, even though it had not been treated with antibiotics itself.
The researchers then examined the hypothalamus and nucleus accumbens in the brains of the mice, to test the theory that these areas become insulin-resistant when a high-fat diet is consumed. These are two areas of the brain responsible body metabolism and mood and behavior, respectively.
“We demonstrated that, just like other tissues of the body, these areas of the brain become insulin resistant in mice on high-fat diets,” Kahn says. “And this response to the high fat is partly, and in some cases almost completely, reversed by putting the animals on antibiotics. Antibiotics are blunt tools that change many bacteria in very dramatic ways. Going forward, we want to get a more sophisticated understanding about which bacteria contribute to insulin resistance in the brain and in other tissues.”