Walnuts: appetite control by activating certain brain regions
The consumption of walnuts is associated with numerous health benefits, particularly in terms of metabolism and the cardiovascular system. In a recent study, US scientists have now shown that walnuts can also help you lose weight by giving you a feeling of fullness.
In their current study, the scientists at the Beth Israel Deaconess Medical Center (BIDMC) were able to demonstrate the neurocognitive effects of walnut consumption for the first time. They found that consuming walnuts activates a region in the brain that controls hunger and cravings. The researchers published their results in the journal "Diabetes, Obesity and Metabolism".
Brain activity examined when consuming walnuts
To determine exactly how walnuts work in the brain, the scientists used the imaging technique of functional magnetic resonance imaging (fMRI). They were able to observe the activity in the brain and determine which brain regions are activated when the walnuts are consumed. Ten obese volunteers were transferred to the clinic for two periods of five days each, where they received strictly controlled food. This meant that the scientists did not have to rely on the test persons' information about their food consumption, but were able to understand it exactly.
Subjects received walnut smoothie or placcebo drink
During a five-day session, subjects received 48 grams of walnuts daily (recommended by the American Diabetes Association). During a second investigation period, they received a walnut-free but nutritionally comparable placebo smoothie, which was modeled on the taste of the walnut smoothie. The order of the two examination periods was chosen at random, so that some participants consumed the walnuts first and others the placebo. "Neither the volunteers nor the researchers knew in which session they received the nutty smoothie," explains the BIDMC in a press release on the current study results.
Less feeling of hunger after consuming walnuts
As in previous observational studies, the subjects in the current study reported that they were less hungry during the week when they received the walnut smoothies. According to the scientists, an unequivocal reason for this could also be determined in the examination using functional magnetic resonance imaging on the fifth day of the experiment. After consuming walnuts, the test subjects showed a significantly increased activity in the brain region, which is referred to as the insula, when looking at pictures with tasty, rather unhealthy foods and less tasty, rather healthy foods.
Activation of the insula
According to the researchers, the activated area of the insula is probably involved in the cognitive control of the decision for certain foods. The participants paid more attention to the choice of dishes and opted for healthier, less tasty options. The researchers emphasize that there is no ambiguity about the study results. “When the participants eat walnuts, this part of their brain lights up, and we know that this corresponds to what the test subjects report: They are less hungry and feel more comfortable,” says study leader Christos Mantzoros.
Influence of food on brain activity
"We don't often think about how what we eat affects brain activity," says lead author Olivia M. Farr of the Endocrinology, Diabetes and Metabolism Department at BIDMC. The current study clearly shows here that there is also evidence of brain activity for the feeling of well-being and the lower feeling of hunger after consuming walnuts. In other words, the food consumed has direct neurocognitive effects in the brain, which in turn have a significant impact on eating behavior.
In a next step, the researchers plan to test different amounts or dosages of walnuts to see whether more nuts lead to more brain activation or whether a maximum effect is achieved after a certain amount. In addition, the neurocognitive effects of other foods should also be examined. (fp)