And you'll make better food choices when you eat them, research shows.
Beth Israel Deaconess Medical Center researchers asked 10 volunteers, diagnosed as obese, to submit to observation for two five-week sessions. During one session, participants drank smoothies with 48 grams of walnuts—which is the daily serving size recommended by the American Diabetes Association. During the other session, participants drank smoothies, too—but these beverages, while nutritionally comparable, were walnut-free.
Then, the researchers used functional magnetic resonance imaging (fMRI) to observe how eating walnuts was changing the participants' brain activity.
It wasn't exactly surprising to hear the participants report they felt less hungry when they drank the smoothies that included walnuts, the researchers say. (Another recent study had already proven that point.) But the participants also weren't experiencing cravings for junk food—and with the fMRI tests, the researchers could see, for the first time, why.
While they were in the fMRI, participants who had eaten the walnuts were shown images of food: desirable food—aka, junk food such as hamburgers and desserts—and less desirable food, like vegetables. (They were also shown neutral objects, such as flowers and rocks, as a control for the test.) The researchers were surprised to observe that the participants' right insula—the part of the brain that is linked to cognitive control and salience—lit up as they saw images of the less desirable foods. In other words, after noshing on the nuts, they were paying more attention to the food and making healthier (perhaps subconscious) choices.
"This is a powerful measure," said lead study author Christos Mantzoros, MD. "We know there's no ambiguity in terms of study results. When participants eat walnuts, this part of their brain lights up, and we know that's connected with what they are telling us about feeling less hungry." Next, Mantzoros said, the researchers will test to see if eating more walnuts increases their healthy, craving-cutting effect or if the positive effect plateaus.
"From a strategic point of view, we now have a good tool to look into people's brains—and we have a biological read out," Mantzoros explained. "We plan to use it to understand why people respond differently to food in the environment and, ultimately, to develop new medications to make it easier for people to keep their weight down."