When we think about the link between food and feelings, it usually goes something like this: We feel sad, and then we eat something -- usually a comforting gut bomb of sugar, salt and fat -- to feel better. But what if this relationship were actually reversed? What if the things we ate were actually causing us to become more depressed over time, creating a destructive loop of sadness, bingeing, and sadness again?
That's the premise of a recent study, published in the American Journal of Clinical Nutrition, that suggests sugary and starchy foods could contributing to depression. Previous long-term studies have shown that people who eat pastries, sugary drinks and other refined carbohydrates have a higher risk of depression, but didn't determine what is it, exactly, about those foods that ties them to depression risk.
Columbia University psychiatry professor James Gangwisch wanted to find out, and to parse out the different effects that varying amounts of carbohydrates and added sugar have on mood. To do so, he looked back at data from nearly 70,000 postmenopausal women who participated in a research project in 1994 and then again in 1998.
Gangswisch and his team looked at both the quality and quantity of the carbs in the women's diets, applying glycemic index scores -- a scale from zero to 100 that measures how a food raises a person’s blood sugar level -- to what each woman was eating. (A food like steel-cut oatmeal, with a GI score of 55 or less, raises blood sugar levels less than instant oatmeal, which has a GI score of 70 or more.) They also calculated each woman's glycemic load, or the amount of carbs she was eating, to understand whether or not that had any link to her level of depression.
Gangwisch found that women who ate more high GI foods had a higher risk of depression. He also found that women who ate more dairy, fiber, non-juiced fruit and vegetables had lower odds of depression than the group. In essence, it’s not the amount of carbohydrate-rich foods a person eats -- it’s the quality of the carbohydrate that matters.
Crucially, Gangwisch also took a look at women who had no depression at the start of the study, but had depression by the time they had checked in again in 1998. He found that those who ate a high GI diet full of added sugars and refined grains were more likely to become depressed later on.
Foods with high GI scores -- like white bread, soda, boxed cereal, white rice and potatoes -- could be causing or worsening depression symptoms, according to Gangwisch’s analysis. He says these foods touch off a cascade of hormonal reactions that bring blood sugar levels down, causing symptoms of depression like anxiety, irritability, fatigue, change in mood and behavior, and hunger. High GI diets are also associated with inflammation and cardiovascular disease, which also play a role in the development of depression.
"The fact that these are new cases of depression strengthens the argument that the diet contributed toward the depression, as opposed to the depression contributing toward the diet,” Gangwisch said.
What this all adds up to, said Gangwisch, is an even more compelling reason to stay away from added sugars and refined grains. Though randomized, controlled trials are needed to determine if low-GI diets could treat or even prevent depression in post-menopausal women, he says it can't hurt to adopt such a diet now.
"Most nutritionists would agree that people should try to keep to a minimum added sugars and refined grains and to eat whole, natural, seasonal fruits and vegetables, whole grains, nuts and beans that are high in fiber,” said Gangwisch. "I think [a low-GI diet] would be well worth a try for anyone suffering from depression."