A new study shows that when a person eats walnuts on a daily basis, a part of the brain linked to food cravings becomes more active. The brain area, called the insula, is tied to appetite suppression and feeling full.
The study, performed by a group of researchers from Beth Israel Deaconess Medical Center, may lead scientists to develop drugs that give a person a feeling of satisfaction after eating, say the researchers.
“We don’t often think about how what we eat impacts the activity in our brain,” said lead author Dr. Olivia M. Farr, an instructor in medicine in the Division of Endocrinology, Diabetes and Metabolism at BIDMC.
“We know people report feeling fuller after eating walnuts, but it was pretty surprising to see evidence of activity changing in the brain related to food cues, and by extension what people were eating and how hungry they feel,” added Farr.
To assess the power of walnuts on a person’s diet, the researchers monitored 10 volunteers who agreed to live at the medical center for two periods of time, each five days in length. Having the volunteers eat, sleep and otherwise spend all of their time at the center allowed the researchers to control every detail of their diets during the experiment.
Over one five-day period, the researchers gave half of the study participants a smoothie containing 48 grams of walnuts, while the other half consumed a smoothie without walnuts. During the second five-day stretch, the researchers switched roles – those who previously didn’t get walnuts now got them, and those who had walnuts went walnut-free. None of the study participants knew when they received a smoothie with walnuts.
Those who consumed nut-containing smoothies every day of the experiment reported experiencing less hunger than those who didn’t eat walnuts. Interestingly, when the researchers used an imaging machine to look at the volunteers’ brain activity, they discovered some key differences.
Specifically, people who ate walnuts and were then shown pictures of “desirable foods” – a hamburger or dessert, for example – had more activity in their insula compared to people who hadn’t consumed walnuts. The authors believe the insula is tied to “cognitive control,” which they think allows people to overcome cravings for high-fat or bad foods.
“This is a powerful measure,” said Dr. Christos Mantzoros, director of the Human Nutrition Unit at Beth Israel Deaconess Medical Center and professor of medicine at Harvard Medical School.
“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 or more full,” added Mantzoros.
The study authors add that their new findings may lead to a greater understanding of the complex topic of appetite control and dietary preferences.
“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,” said 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.”