A new study found that women who ate a serving a day were 34% less likely to become depressed than women who ate less than half a serving a week.
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Women who regularly eat full-fat yogurt may be less likely to develop depression than those who eat it less often, according to a new study of nearly 15,000 people. Although the research could not prove a cause-and-effect relationship, the authors suggest that probiotics—live bacterial cultures present in fermented foods—may play a role in influencing mood.

This association was not true for men, nor for people who ate low-fat yogurt or took prebiotic supplements, which are thought to promote the growth of beneficial gut bacteria. In fact, eating low-fat yogurt was linked to higher rates of depression. In that case, however, researchers say it’s likely that depression influenced people’s eating habits—not the other way around, because the results were no longer statistically meaningful when the early depression cases were excluded.

Clinical depression is expected to become the leading cause of disability in industrialized countries by 2030, the authors wrote in the September issue of the Journal of Nutrition. The disease’s causes are complex and not entirely understood, but scientists know that genetics, environmental, and lifestyle factors can all contribute.

Some research has suggested that the variety of microbes living in a person’s intestines may influence his or her mood and anxiety levels; studies have even shown that altering mice’s gut microbiomes can have an effect on their personalities.

So researchers wanted to see if regularly eating yogurt or taking a prebiotic fiber supplement, both of which can influence gut bacteria, might make a difference in whether people developed depression. To do that, they tracked diet and health information from 14,539 men and women—all of whom were depression-free at the start of the study—for about 10 years.

Over that time, 727 participants were diagnosed with depression. The researchers found no correlation between taking a prebiotic and depression, nor did they find an increased risk for men who ate yogurt.

When they looked specifically at women, however, they made an interesting discovery: Those who consumed the highest amount of full-fat yogurt (at least seven servings per week) were 34% less likely to become depressed than those who ate the least (less than half a serving a week).

Surprisingly, they found the opposite association for low-fat yogurt: Study participants who ate the most were 32% more likely to develop depression than those who ate the least. But the majority of these cases were reported in the first two years of follow-up, the authors say, suggesting “reverse causality.” In other words, it’s likely that people who were already depressed (but not diagnosed yet) chose to eat more low-fat yogurt.

When the researchers looked at additional data not included in their analysis, they confirmed that depressed women did, in fact, eat more low-fat yogurt. “Sadly, we have no data in our study to determine the reason why,” says lead author Aurora Pérez Cornago, PhD, a nutritional epidemiologist at the University of Oxford.

This is one of the first studies to investigate the potential association between pre- and probiotic consumption and the onset of depression in otherwise healthy adults, Pérez Cornago says. She does point out the known health benefits of yogurt, but says it’s too early to tout it specifically as a mood booster.

“Yogurt is a nutrient-dense food and its consumption may benefit individuals with lactose intolerance,” she says. “It has also been related to lower obesity and diabetes risk. But in our opinion, we need more studies to clarify why this yogurt-depression association may differ by fat content before recommendations on consuming low- or full-fat yogurt can be given to women concerned about their mental health.”