Stress may harm gut health as much as junk food

Be it financial worries, work pressures, or relationship problems, we all get stressed from time to time. To what extent does stress harm us, though? According to a new study, stress may be just as detrimental to our health as junk food — for women, at least.

Researchers found that stressed female mice experienced changes to their gut microbiota — that is, the community of microorganisms that reside in the intestine — comparable with what is seen in response to a high-fat diet. In male mice, however, stress appeared to have no effect on gut microbiota.

Study co-author Laura Bridgewater, of the Department of Microbiology and Molecular Biology at Brigham Young University in Provo, UT, and colleagues say that their findings indicate that the gut microbiota may play a role in gender-specific health outcomes in response to stress.

The researchers recently reported the results of their study in the journal Scientific Reports.

According to the American Psychological Association, around 80 percent of people in the United States report experiencing at least one symptom of stress in the past month.

It is common knowledge that stress can have negative implications for both emotional and physical health, including an increased risk of anxiety, depression, and obesity. The new study suggests that some of these implications may be down to how our gut microorganisms respond to stress.

Diet, stress, and gut microbiota

Bridgewater and her colleagues came to their findings by testing a large group of male and female mice. Half of the female mice and half of the male mice were fed a high-fat diet for 16 weeks, while the remaining mice were fed a standard chow diet.

After 16 weeks, the entire group of mice was subjected to mild stress once or twice per day for a total of 18 days. Stressors included a forced swim in cold water, damp bedding, and predator sounds and smells.

The researchers analyzed fecal samples taken from the mice before and after stress exposure, in order to determine how their gut microbiota had been affected by diet and stress.

Additionally, the team measured the rodents' anxiety levels, as determined by how far they were willing to roam in an open maze.

Stress 'causes distinct physical changes'

Both male and female mice demonstrated significant changes to gut microbiota in response to a high-fat diet.

Compared with female mice fed a high-fat diet, the team found that male mice fed a high-fat diet showed greater anxiety. In response to stress, the male mice fed a high-fat diet also showed reduced physical activity, compared with female mice fed a high-fat diet.

However, among mice fed the standard chow diet, the researchers found that female mice displayed gut microbiota changes in response to stress that were similar to those seen in response to the high-fat diet. No such response was seen in male mice fed standard chow.

According to the researchers, their findings indicate that stress may have different effects in men and women due to its impact on gut microbiota.

"Stress can be harmful in a lot of ways," says Bridgewater, "but this research is novel in that it ties stress to female-specific changes in the gut microbiota. We sometimes think of stress as a purely psychological phenomenon, but it causes distinct physical changes."

The team cautions that their study was conducted in mice, but they do believe that the results may apply to humans.

"In society, women tend to have higher rates of depression and anxiety, which are linked to stress. This study suggests that a possible source of the gender discrepancy may be the different ways gut microbiota responds to stress in males vs. females."