For some time now, the eating of walnuts has been associated with feelings of fullness. Recently, a study conducted by scientists at the Harvard-affiliated Beth Israel Deaconess Medical Center (BIDMC) uncovered what's actually going on in the brain to make this happen. The findings could lead to future treatments for obesity.
Led by Drs. Olivia M. Farr and Christos Mantzoros, the researchers recruited 10 obese volunteers to live at BIDMC's Clinical Research Center for two five-day sessions. By having them live there, the scientists could precisely track their nutritional input.
During one of those sessions, the test subjects consumed daily smoothies containing 48 grams of walnuts (the daily recommended serving, according to the American Diabetes Association). Throughout the other session, they received placebo smoothies – these were nutritionally comparable to the others, plus they tasted the same, but they contained no walnuts.
The order of the sessions was chosen randomly, meaning that the walnut smoothies came first for some of the test subjects, while the placebo smoothies came first for others. Needless to say, the volunteers weren't told which smoothies they were receiving during which session.
As has been the case in other studies, the test subjects reported feeling less hungry during the week that they consumed the nut smoothies.
Taking things a step further, however, each person was placed in an fMRI (functional magnetic resonance imaging) machine on the fifth day of each session, to have their brains scanned. While in the machine, they were shown a variety of images, including shots of neutral objects, photos of desirable foods such as hamburgers and desserts, along with pictures of less desirable but healthier foods.
When the volunteers who had been drinking the walnut smoothies saw the desirable food pictures, increased activity was detected in an area of their brains known as right insula. This region is associated with the regulation of hunger and cravings.
"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," says Mantzoros. "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."