Weight gain and depression can stem from social, environmental, and biological causes, says Roger McIntyre, MD, a professor of psychiatry and pharmacology at the University of Toronto. For example, people with financial insecurity or who’ve had troubled childhoods are at a higher risk of both obesity and depression.

Things in the environment also can play a role for those who live in “food deserts or food swamps,” McIntyre says. Living amid fast-food joints and convenience stores and far from grocery stores with fresh produce makes it harder to eat healthy.

The depression-weight link cuts both ways. People who are depressed are more likely to be obese. And people with obesity are at higher risk of depression.