Walnuts may promote fullness and healthy eating habits.
Many physicians recommend that patients with obesity and type 2 diabetes consume nuts, as they are believed to discourage overeating. How nuts, including walnuts, promote fullness was previously unknown.
A new study published by Diabetes, Obesity, and Metabolism found that walnut consumption activates part of the brain that regulates hunger. The brain imaging study is the first to explore the neurocognitive effects walnuts may have.
“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,” said first study author Olivia Farr, PhD.
The authors used functional magnetic resonance imaging (fMRI) to determine how walnut consumption alters brain activity.
Included in the study were 10 patients with obesity who were recruited to live in the Beth Israel Deaconess’ clinical research center for two 5-day sessions. This controlled environment allowed the authors to keep track of the patients’ nutritional consumption opposed to patient-reported food intake, according to the study.
During a session, patients consumed daily smoothies that contained 48 grams of walnuts, which is the recommended serving by the American Diabetes Association. During another session, the patients consumed a comparable smoothie without walnuts.
The order in which patients consumed the smoothies was randomized, and both patients and researchers were unaware of when patients consumed the walnuts.
The authors found that patients felt less hungry when they consumed the walnut-containing smoothies compared with when they consumed the placebo smoothie, according to the study.
The authors conducted the fMRI tests on the fifth day of the sessions, which indicated why patients felt fuller when consuming walnuts.
While in the MRI machine, patients were shown “desirable” foods, such as hamburgers and desserts, neutral images, and “less desirable” foods, such as vegetables.
When patients were shown pictures of highly desirable foods, the fMRI showed increased activity in the right insula after patients consumed walnuts compared to when they had not, according to the study.
“This is a powerful measure,” said Dr Mantzoros. “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.”
The authors report that the right insula likely plays a role in cognitive control and salience. This led the patients to be more aware of their food choices and select the healthier food option.
The investigators plan to explore different amounts of walnuts to determine whether more will increase brain activation or if the effect plateaus, according to the study.
The future studies will also allow the authors to explore whether other compounds have comparable effects. Similar studies have shown that other foods and compounds change appetite control, according to the authors of the current study.
“From a strategic point of view, we now have a good tool to look into people’s brains—and we have a biological readout,” Dr Mantzoros concluded. “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 [excess] weight down.”