A mother's diet during pregnancy affects a child’s long-term physical health, behavior and brain development. It may also make a difference to their child's mental health.

Researchers at the Oregon National Primate Research Center found that monkey mothers who were overweight or obese and ate a high-fat diet not only put their offspring at metabolic risk for becoming overweight, they also left them vulnerable to mental health issues like anxiety and depression.

The researchers tried to undo the damage by introducing a healthy diet to the young monkeys at an early age, but the attempt was not effective.

There were 65 female monkeys in the study. One group was fed a high-fat diet while the other group was fed a control diet. Researchers found both male and female offspring whose mothers ate the high-fat diet showed more anxiety compared to those whose mothers ate the lower fat control diet. The high-fat diet also interfered with the development of nerve cells containing serotonin, a chemical that is critical in brain development.

Impaired development of the central serotonin system in the brain may increase the risk of mental health problems like anxiety and depression in children. Even though the researchers tried to undo the damage by introducing a healthy diet to the young monkeys at an early age, the attempt was not effective.

“A lot of people are going to be astonished to see that the maternal diet has this big of an effect on the behavior of the offspring. We've always looked at the link between obesity and physical diseases like heart disease, but this is really the clearest demonstration that it's also affecting the brain,” said Joel Nigg, professor of professor of psychiatry, pediatrics and behavioral neuroscience at the Oregon Health and Science University School of Medicine, in a statement.

Observational studies using humans have found a link between maternal obesity and some mental health and neurodevelopmental disorders in children, but this study is the first to show that a high-fat diet may cause long-term mental health problems in children.

High-fat diets are increasingly common in developed countries, and in the United States over 60 percent of women of reproductive age are overweight while 35 percent are obese. Pregnancy is a particularly vulnerable time since pregnant women often find themselves ravenously hungry and believe that since they are eating for two, it is harder to overeat. This study suggests that the obesity epidemic in the U.S. may have significant repercussions for the mental health of future generations.

Making sure families have healthy food as part of pre-natal and post-natal care and educating pregnant women about the possible risks of eating a high-fat diet could reduce the number of mental health problems in tomorrow’s children.

The study is published in Frontiers In Endocrinology.