In recent years, studies have started pointing to nuts as a way to boost heart health, but most of them were observational with a limited sample size. Now, a systematic review of clinical trials spanning 25 years has confirmed that when it comes to cardiovascular health, nuts are the go-to food.

This delicious snack may be key for heart health and healthy aging, slashing the risk of stroke or coronary heart disease.

But the benefits of nuts do not stop here; some studies suggest that a handful of nuts may help us live longer, improve our memory, and strengthen our brain.

Now, scientists led by Marta Guasch-Ferré—a research associate in the Department of Nutrition at the Harvard T. H. Chan School of Public Health in Boston, MA—have carried out a large-scale review of numerous studies covering the link between nut consumption and heart health.

These "natural health capsules," as Guasch-Ferré called them, may do wonders for our cardiovascular system.

This is the main takeaway of the new review, which has been published in the American Journal of Clinical Nutrition.

Walnut-enriched diets protect the heart

This review updates the results of a previous meta-analysis that was published in 2009. It included 13 clinical trials.

Now, Guasch-Ferré and team have assessed the trials published since that point; this amounted to 26 randomized trials, summing up 1,059 participants with ages between 22 and 75.

Among the study participants, some were living with conditions, such as high cholesterol, type 2 diabetes, metabolic syndrome, or obesity.

The scientists evaluated the benefits of a diet rich in walnuts and compared it with low-fat, Western, Mediterranean, and Japanese diets.

Walnut-enriched diets provided a more significant reduction in cholesterol levels and other markers of cardiovascular health when compared with these control diets.

More specifically, a diet rich in walnuts had a 3.25% greater reduction in total cholesterol levels, a 3.73% greater decrease in low-density lipoprotein (LDL) cholesterol, and a 5.52% greater reduction of triglycerides.

Also, levels of apolipoprotein B—which is the main protein found in LDL, or "bad," cholesterol—were lowered by 4.19% than in control diets.

"Incorporating walnuts into the diet improved blood lipid profile without adversely affecting body weight or blood pressure," conclude the authors.

Strengths and limitations of the study

Walnuts' benefits may be down to their rich polyunsaturated, or "healthful," fat content, including essential omega-3 fatty acids, as well as to their wide variety of antioxidants.

Dr. Michael Roizen, the chief wellness officer in the Department of Preventive Medicine at the Cleveland Clinic in Ohio, weighs in on the findings.

"This updated review further strengthens the case that enjoying walnuts is a great (and tasty) way to add important nutrients to your diet while supporting the health of your heart."

–Dr. Michael Roizen

But the review does have some caveats. The samples in most of the studies reviewed were fairly small, which may weaken the findings.

Also, some trials used a considerable amount of walnuts, which may be hard to stick to in a day-to-day setting, say the researchers.

Still, they highlight the fact that great benefits were noticed with even smaller amounts of walnuts—that is, fewer than 28 grams per day.