Many things make walnuts one of the best go-to snacks for people of all ages: They’re low in carbs, taste great on their own, provide plenty of essential nutrients and are good for your heart and gut.

According to studies, eating walnuts is an excellent way to keep your blood vessels clear of cholesterol buildup and your blood pressure within the normal range. A reduced-calorie diet that includes walnuts was also found to promote weight loss in overweight and obese individuals, suggesting that this superfood can also help you manage your weight.

When it comes to digestive health, German researchers found that eating walnuts regularly can not only improve your blood cholesterol levels, but also influence the composition of your gut microflora. After eight weeks on a walnut-enriched diet, they reported an increase in the number of good bacteria in the guts of healthy individuals, specifically bacteria that produce short-chain fatty acids (SCFAs) like butyrate. Butyrate helps strengthen your intestinal barrier and supplies energy to the cells of your colon.

Experts often attribute these favorable effects to either the healthy fats, dietary fiber or bioactive compounds present in walnuts. To find out which of these components are truly responsible, researchers at the Pennsylvania State University (PennState) and Juniata College (JC) decided to examine the effects of a walnut diet on gut microbiota. They discovered a surprising link between walnuts’ heart and gut benefits.

How walnuts improve heart health

In a randomized controlled feeding trial, PennState and JC researchers recruited 42 adults at risk of heart disease. They first asked the participants to spend two weeks on a standard Western diet — which included high amounts of red meat, refined grains and high-fat and processed foods — before switching to three different isocaloric diets (moderate-fat, moderate-carb) for six weeks.

After the “run-in” Western diet, the researchers randomly assigned the participants to three groups. The first group replaced the saturated fats in their diet with whole walnuts (57-99 grams, g per day), while the second group replaced saturated fats with alpha-linolenic acid (ALA), an essential omega-3 fatty acid found in walnuts. The third diet required participants to replace saturated fats with oleic acid, an omega-9 fatty acid found in vegetable oils.

The researchers collected fecal samples from the participants after the run-in and study diets to evaluate any changes in their gut microbiota composition.

After the two-week Western diet, the researchers noted that the participants’ body mass indices (BMI) were higher than what is considered healthy. The participants also had high blood pressure and low-density lipoprotein (LDL) cholesterol, or bad cholesterol, levels.

But after six weeks on their assigned diets, the researchers discovered that those who ate whole walnuts every day had increased numbers of good commensal bacteria, such as Roseburia, Eubacterium eligens, Lachnospiraceae UCG001, Lachnospiraceae UCG004, Gordonibacter and Leuconostocaceae.

Those who consumed ALA in place of saturated fats also had an increase in Roseburia and E. eligens bacteria. Meanwhile, the participants who included oleic acid in their diet had increased populations of the Clostridiales vadin BB60 group in their gut.

According to studies, Roseburia species, Lachnospiraceae species and E. eligens bacteria all produce SCFAs and support healthy immune function. Leuconostocaceae species and the C. vadin BB60 group also exert beneficial effects on gut health. Meanwhile, Gordonibacter bacteria are known for producing urolithins, which have anti-inflammatory, anti-aging, anti-cancer and lipid-lowering properties.

But what the researchers found interesting was that the number of E. eligens and Lachnospiraceae species in the gut is inversely correlated with blood pressure and blood lipid levels. Since eating walnuts increased the populations of these good bacteria, those on the walnut diet experienced significant reductions in their blood pressure and blood lipid levels. This suggests that walnuts’ heart benefits stem from a positive change in gut microbial composition.

“Foods like whole walnuts provide a diverse array of substrates — like fatty acids, fiber and bioactive compounds — for our gut microbiomes to feed on. In turn, this can help generate beneficial metabolites and other products for our bodies,” explained Regina Lamendella, an associate professor at JC and one of the study authors.

Walnuts are a great source of essential nutrients, including healthy fats that support good heart and gut health. To experience the benefits of this incredible superfood, eat a handful of walnuts every day or add this versatile culinary ingredient to your recipes for a delicious nutrient boost.

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