Just like apples, eating a handful of walnuts helps improve a person's overall health to the point that some nutrition experts also recommend the walnut diet for the obese, diabetics, and colon cancer survivors. However, researchers have yet to fully understand what walnuts do to the body that makes it so effective — at least until now.
In order to determine how exactly walnuts affect the body, a team of researchers from the Beth Israel Deaconess Medical Center enlisted obese volunteers to undergo a walnut diet, and they found that eating walnuts increases brain activity in the area that controls the appetite.
"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," lead investigator Olivia Farr expressed.
Walnuts And The Brain
As previously mentioned, the researchers recruited 10 volunteers with obesity in order to find out just how exactly walnuts are able to satiate the appetite and curb cravings. The 10 volunteers were required to live in the BIDMC's Clinical Research Center (CRC) for two five-day periods wherein their diets were monitored and they were given either a walnut packed smoothie or a placebo smoothie bearing the same taste.
Volunteers were not aware of which smoothie they were taking to ensure that their choices would not be affected.
Researchers then used functional Magnetic Resonance Imaging (fMRI) to detect any increase in brain activity on the fifth day of the session. During this time, participants were shown photos of various desirable (less healthy food like hamburgers) and undesirable (vegetables and other healthy choices) food to see any changes in the brain activity. What the team found was that there was more activity in the right insula for walnut smoothie drinkers when they saw unhealthy food.
Just so it's clear, the right insula is that really tiny part of the brain that helps in the awareness of body state and, by extension, feelings of hunger and satiety.
So What If The Right Insula Lit Up?
Now researchers know that brain activity in the right insula lights up when walnuts are involved, but what does that have to do with appetite and cravings?
In a very simple explanation, the fact that the right insula lights up when seeing unhealthy food basically means that the brain it is telling the body that it may be too full for the fatty food at that time. This led the participants to make healthier choices because, after all, most diet plans get derailed when dieters feel hungry no matter how much healthy food they eat.
"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," BIDMC Human Nutrition Unit director and senior study investigator Dr. Christos Mantzoros said. Dr. Mantzoros is also a professor of medicine at Harvard Medical School.
Now that the researchers figured out that there is a legitimate biological response to walnuts, they hope to develop medications that can help people keep their weight at a healthy level.
The findings of the study have been published in Diabetes, Obesity, and Metabolism.