A handful of peanuts a day for four months changed how older brains responded to insulin, in memory regions in particular

Insulin is best known for managing blood sugar, but the brain responds to it too. In healthy brains, insulin helps regulate blood flow to areas that are working hard, and researchers think that a blunted brain response to insulin, sometimes called brain insulin resistance, may play a part in age-related memory decline. A team at Maastricht University Medical Center in the Netherlands wanted to know whether an everyday food could shift that response. Their answer was published in the journal Food & Function on 30 September 2026.

The trial enrolled 31 healthy men and women aged 60 to 75 (average age 67, average BMI 26.7). Each person went through two 16-week periods in random order, separated by a washout of at least eight weeks: one in which they ate 60 g of unsalted, skin-roasted peanuts every day, and one in which they ate none. At the end of each period the researchers measured blood flow in the brain with an MRI technique called arterial spin labelling, before and after giving a spray of insulin into the nose, a route that lets insulin reach the brain without changing blood sugar much. How much blood flow changed after the spray was used as the measure of the brain's insulin responsiveness.

After the peanut period, the response to insulin was better in one cluster of the right side of the brain that takes in parts of the lingual gyrus, the hippocampus, the parahippocampal gyrus and the posterior cingulate gyrus, areas involved in memory and visual processing. Liver fat and the metabolic blood markers the team measured did not change. An earlier report from the same trial, published in Clinical Nutrition in 2025, found that the peanut period raised overall brain blood flow by 3.6%, improved delayed verbal recall by 5.8% (about 1.4 more words remembered) and lowered systolic blood pressure by about 5 mmHg, while other tests of thinking speed and planning did not change.

The authors suggest that the mix of unsaturated fats, fibre, vitamins, minerals and plant compounds in peanuts, and their high content of L-arginine, which the body uses to make the blood-vessel relaxant nitric oxide, could explain the effects. The trial was small, short and done in healthy, mostly well older adults, the brain finding was limited to one region rather than the whole brain, and participants knew when they were eating peanuts. It was funded by The Peanut Institute Foundation, an industry-backed body. Whether the change in brain insulin responsiveness translates into better memory over years, or into lower dementia risk, was not tested.