Adding roughly half a cup of walnuts to the diet each day for two years lowered LDL cholesterol, the "bad" kind, by an average of 4.3 mg/dL in healthy older adults. Total cholesterol fell by 8.5 mg/dL.
The findings come from the Walnuts and Healthy Aging study, published in the American Heart Association journal Circulation. It was a randomized trial of 708 adults aged 63 to 79 in Barcelona and Loma Linda, California.
Small, dense LDL particles, the subtype most closely tied to heart disease risk, dropped by 6.1 percent in the walnut group. Total LDL particles fell 4.3 percent.
Men saw a larger LDL reduction than women (7.9 percent versus 2.6 percent). No weight gain was seen despite the extra calories from the nuts.
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"Eating a handful of walnuts every day is a simple way to promote cardiovascular health," said study co-author Emilio Ros, M.D., Ph.D., Director of the Lipid Clinic at Hospital Clínic of Barcelona.
What the FDA has said
Walnuts carry a rare distinction on the U.S. food label. In April 2004, the FDA approved a qualified health claim allowing packages to make a heart-related statement about walnuts.
The approved wording states that "eating 1.5 oz of walnuts per day, as part of a low saturated fat and low cholesterol diet, and not resulting in increased caloric intake may reduce the risk of coronary heart disease."
The claim is deliberately hedged. The FDA requires the phrase "supportive but not conclusive research." Even so, its willingness to permit any heart-related statement on a whole food is unusual.
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A 1.5-ounce serving is roughly a small handful. It supplies plant-based omega-3 fatty acids, specifically alpha-linolenic acid, along with polyphenols and unsaturated fats that have been tied to lower LDL in repeated trials.
What happened in the brain
The same walnut cohort also underwent a battery of cognitive tests. The results, published in the American Journal of Clinical Nutrition in 2020, were more modest.
Daily walnuts had little overall effect on cognitive function among the mostly healthy volunteers over the two years. A benefit did emerge in one subgroup, participants who had smoked more and started with lower baseline test scores.
"While this was a minor result, it could lead to better outcomes when conducted over longer periods of time," said principal investigator Joan Sabaté.
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Walnuts are not a treatment for cognitive decline. But higher-risk brains may respond over longer horizons.
What happened in the gut
A separate Penn State trial adds a third layer. In a 2020 study in the Journal of Nutrition, 42 adults with cardiovascular risk factors added 2 to 3 ounces of walnuts daily to their diet for six weeks.
Fecal analysis showed enrichment of several beneficial gut bacteria, including Roseburia, Eubacterium eligens, Butyricicoccus and members of the Lachnospiraceae family. Higher Lachnospiraceae counts were linked to reductions in blood pressure, total cholesterol and non-HDL cholesterol.
"The findings add to what we know about the health benefits of walnuts, this time moving toward their effects on gut health," said Penny Kris-Etherton, distinguished professor of nutrition at Penn State.
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What a daily portion actually looks like
The evidence lines up on a portion between 1.5 and 2 ounces a day, roughly a handful, or the amount the FDA claim rests on.
Walnuts are calorie-dense, but the trials consistently found no weight gain when the nuts replaced other snacks or fats in the diet.
Walnuts are not a substitute for medication or medical advice. Anyone weighing changes to a treatment plan or worried about their cholesterol should talk to a doctor. As a daily food choice, though, the evidence points to a small but real benefit.
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This article is made and published by Jesper Bengtson, who may have used AI in the preparation.