They are rich in the omega-3 fatty acid, alpha-linolenic acid and fibre.
A walnut-enriched diet may improve your digestive health by significantly increasing the amount and diversity of beneficial bacteria in the gut, a study claims.
Eating walnuts has been associated with reduced cardiovascular disease risk, slower tumour growth in animals and improved brain health, researchers said.
The study suggests a new way walnuts may contribute to better health by boosting the amount of probiotic-type bacteria in the gut, they said.
"Walnuts have been called a 'superfood' because they are rich in the omega-3 fatty acid, alpha-linolenic acid and fibre, and they contain one of the highest concentrations of antioxidants," said Lauri Byerley, Research Associate Professor at Louisiana State University (LSU) in the US.
"Now, an additional superfood benefit of walnuts may be their beneficial changes to the gut microbiota," said Byerley, who led the study published in The Journal of Nutritional Biochemistry.
Working in a rodent model, the research team added walnuts to the diet of one group.
The diet of the other group contained no walnuts. They then measured the types and numbers of gut bacteria in the descending colon and compared the results.
The researchers found that there were two distinct communities of bacteria in the groups.
In the walnut-eating group, the numbers and types of bacteria changed, as did the bacteria's functional capacity.
The researchers reported a significant increase in beneficial bacteria like Lactobacillus.
"We found that walnuts in the diet increased the diversity of bacteria in the gut, and other non-related studies have associated less bacterial diversity with obesity and other diseases like inflammatory bowel disease," said Byerley.
Prebiotics are dietary substances that selectively promote the numbers and activity of beneficial bacteria.
"Walnuts increased several bacteria, like Lactobacillus, typically associated with probiotics suggesting walnuts may act as a prebiotic," said Byerley.
"Gut health is an emerging research area, and researchers are finding that greater bacterial diversity may be associated with better health outcomes," she said.
The study, supported by the American Institute for Cancer Research and California Walnut Commission, concludes that the reshaping of the gut microbe community by adding walnuts to the diet suggests a new physiological mechanism to improve health.