- Previous research has indicated that daily consumption of walnuts can boost heart health.
- Now, researchers are saying those benefits are likely the result of changes in the gut microbe that walnuts produce.
- They note that walnuts contain omega-3 fats, antioxidants, and protein.
The heart-healthy benefits of eating walnuts could come from changes to the gut microbes.
That’s according to research presented today at DiscoverBMB – the annual meeting of the American Society for Biochemistry and Molecular Biology.
The study, which was funded by the California Walnut Commission, hasn’t been published yet in a peer-reviewed journal.
Researchers at Texas Tech University used metatranscriptomics, the study of gene expressions of gut microbes, to monitor changes that might occur when someone alters their diet.
Specifically, the scientists looked at how cardiovascular health could be affected.
Their findings indicated that eating walnuts could alter the gut microbiome by increasing the body’s production of the amino acid L-homoarginine. In turn, this might lower the risk of developing heart disease.
How the walnut study was conducted
The researchers used samples from a previously performed controlled-feeding study.
There were 35 participants with a high risk of cardiovascular disease.
Participants were put on a two-week standard Western diet and then were randomly assigned to one of three study diets:
- A diet that incorporated whole walnuts.
- A diet that included the same amount of omega-3 fatty acids and polyunsaturated fatty acids as the walnut diet but without walnuts.
- A diet that partially substituted the fatty acid, oleic acid, for the same amount that would be derived from walnuts, but the diet did not include walnuts.
Participants followed each diet for six weeks, with a break in between.
How walnuts help heart health
The diets were designed to explain how walnuts affect cardiovascular health due to bioactive compounds, alpha-linolenic acid, or ALA, content, or whether walnut ALA could substitute for dietary saturated fats.
The researchers collected fecal samples shortly before the participants completed a diet.
Those on a diet of whole walnuts had higher levels of:
- Gordonibacter bacteria in their gut – metabolites that exert anti-inflammatory activity
- Gene expressions for the increase of the body’s production of the amino acid L-homoarginine
The researchers concluded that changes to the gut microbiome induced beneficial pathways that could reduce cardiovascular risk factors. They noted that further research is needed to confirm their observations.
“This study suggests that walnuts might promote positive changes in the gut microbiome (friendly bacteria) that can help your body absorb and use certain antioxidants linked to reduced heart disease risk,” said Anne Danahy, a Scottsdale, Arizona-based registered dietitian and integrative nutritionist specializing in the Mediterranean diet and healthy aging. “It’s a small study, and the participants were at risk for heart disease, so it’s impossible to say whether larger groups of healthy people would have the same benefit.”
“It’s always important to consider bias with industry-funded research, but there’s also a substantial body of evidence that supports various health benefits of walnuts,” Danahy told Healthline. “And many of the studies have not been industry-funded. Hopefully, small industry-funded studies like this will open the door for much larger, high-quality, independent studies in the future.”
What you need to know about walnuts
Past research has indicated that walnuts are a healthy addition to diets.
They contain omega-3 fats and antioxidants and are high in fiber.
A one-ounce serving of walnuts has about seven whole walnuts (the study used a diet with about 28 walnuts per day).
A one-ounce serving of walnuts contains about 185 calories as well as the following nutrients:
4.3 grams of protein
3.9 grams of carbohydrates
0.74 grams of sugar
1.9 grams of fiber
18.5 grams of fat
Despite walnuts being high in fat and calories, researchers in one study reported they did not significantly increase weight or obesity risk.
“Walnuts are particularly high in fiber and omega-3 fatty acids — two nutrients that we know already have a positive influence on cardiovascular disease risk,” said Caroline Thomason, RD, CDCES, a Virginia-based dietitian who helps women stop dieting and find confidence with food. “Fiber is associated with decreasing cholesterol, and omega-3s are associated with many disease processes that reduce inflammation.”
“The serving size tested in the study is 2 to 3 ounces of walnuts per day over six weeks,” Thomason told Healthline. “This is a large serving of walnuts — about 28 halves — but you could incorporate one serving for your morning snack and one in the afternoon. Alternatively, I think it could be helpful to consider other nuts that offer a similar nutrition profile. For example, chia, flax, and pumpkin seeds are all sources of omega-3s.”
This isn’t the first study that showed that walnuts are a beneficial addition to diets, but it is the first that explained how that works due to improved gut microbiome.
“Many previous studies have shown a link between walnut consumption and reduced heart disease risk, which might provide one possible mechanism for the benefits,” Danahy said. “Research on the gut microbiome is in its infancy, but over time, we’ll see that the bacteria living in our gut and throughout our body play a vital role in regulating many aspects of our health, including heart disease risk.”
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