A Daily Peanut Habit Altered a Brain Response in Elderly People

Peanuts may be a humble legume, but a new study suggests that a few handfuls could potentially do wonders for the aging brain.

In September, researchers from Maastricht University Medical Center in the Netherlands published a study in the journal Power and function showing that daily consumption of unsalted, roasted peanuts with the skin on for 16 weeks can change the way insulin affects the memory centers of older adults.

To see what happens when a person consumes peanuts daily, the team recruited 31 healthy volunteers (none had diabetes or heart disease, which is important for a study measuring insulin) aged 60 to 75.

The researchers had each participant eat 60 grams of peanuts per day (a little more than 2 ounces, or about two servings) for 16 weeks, followed by an eight-week break and an additional 16 weeks without peanuts. Participants could either finish the peanuts in one sitting or snack on them throughout the day, as long as they ate them whole, with the skin on.

At the end of each phase, participants received a dose of insulin via nasal spray, followed by an MRI that tracked changes in blood flow in the brain over the next 30 minutes. The researchers found that a group of regions on the right side of the brain, including parts of the hippocampus (a key memory center) and the lingual gyrus (involved in verbal memory), responded differently to insulin after participants ate peanuts. There, blood flow increased less in response to insulin, which the authors say could reflect more efficient handling of the hormone by brain cells.

“The hormone insulin plays an important role in the brain, where it supports memory and other cognitive processes. As people age, the brain may become less responsive to insulin, which has been associated with age-related cognitive decline,” Peter Joris, the study’s lead author, said in a press release. “Our study found that daily peanut consumption had a beneficial effect on insulin responsiveness in memory-related brain regions in older adults. These results suggest that enhanced regional brain insulin responsiveness may contribute to the cognitive benefits of consuming unsalted, roasted peanuts with the skin.”

Not everything changed after the participants ate these peanuts. The researchers observed no changes in liver fat, fasting blood sugar, insulin levels, cholesterol or inflammation. Although the brain findings are promising, the study cannot show that they lead to more accurate memory. This is also a small study conducted only in healthy older participants. It is therefore not clear what effect this would have on younger people or those with chronic illnesses.

Additionally, participants ate peanuts alongside their usual diet, so researchers can’t say for sure whether the effects came from the peanuts themselves or from a broader dietary change, which included extra calories. (The study was funded by the Peanut Institute Foundation, although the authors say the foundation had no role in how the research was conducted or reported.)

Joris also noted that he suspects no single nutrient is responsible for improving brain health. “Multiple nutrients found in peanuts, including unsaturated fats, dietary fiber, vitamins and minerals, and bioactive phytochemicals, could contribute to the observed brain benefits,” he said. “Peanuts are also a good source of plant protein and are particularly rich in L-arginine. L-arginine is a key precursor of nitric oxide, which is thought to facilitate learning and memory performance.”

If you want to test the science at home, all you have to do is pop some peanuts – just make sure they’re unsalted and have skins. We’re pretty sure honey roast won’t count.