Walnuts and the gut, leafy greens and the brain


Readers are probably aware that trillions of bacteria in our intestinal tract can protect us from infection if they are the beneficial kind. These bacteria are nourished by a diet high in plant fiber, such as that found in vegetables, whole grains and fruit. Now, research from Louisiana State University School of Medicine found that eating walnuts can change the makeup of bacteria in the gut in a beneficial way. The findings were published this year in The Journal of Nutritional Biochemistry. 

“Walnuts have been called a ‘superfood’ because they are rich in the omega-3 fatty acid, alpha-linoleic acid and fiber, and they contain one of the highest concentrations of antioxidants,” Dr. Lauri Bylerly, the chief author on the paper, wrote. “Now an additional superfood benefit of walnuts may be their beneficial changes to the gut microbiota.”

The research team worked with rodents, adding walnuts to the diet of one group but not the other. They measured the types and numbers of bacteria in the descending colon in both groups. “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. Walnuts increased several bacteria, like Lactobacillus, typically associated with probiotics, suggesting walnuts may act as a prebiotic.” 

Probiotics are foods containing beneficial bacteria; these include yogurt, kefir and fermented foods such as sauerkraut and kimchi. Prebiotics are foods that promote the numbers of beneficial bacteria; some examples are garlic, onions, leeks, dandelion greens, asparagus, bananas and, now, walnuts. “Researchers are finding that greater bacterial diversity may be associated with better health outcomes,” the study found. The research was supported by the American Institute for Cancer Research, a non-profit organization that funds research to help people prevent and survive cancer, and the California Walnut Commission, which is funded by mandatory assessments of growers. The commission represents growers and handlers of California walnuts and conducts health research.

In previous studies, eating walnuts was found to be associated with reduced cardiovascular disease risk, slower tumor growth in animals and improved brain health.


Leafy greens may help your brain

New research from the University of Illinois found that men and women ages 25 to 45 are aided in decreasing brain aging by including green vegetables in their diet. The nutrient known as lutien, found in leafy green vegetables, avocados and eggs, was measured in the eyes of research subjects. People with higher levels of lutein had brain responses similar to people of a younger age.

Lutein is a nutrient that must be obtained through what you eat–the body can’t make it on its own. It is found in brain tissue and in the eye. The researchers were able to measure levels in subjects’ eyes by looking at an area in the back of the eye, the retina, where the pigment containing lutein is found. They also used electro-encephalograms to measure the subjects’ speed at completing various tests.  

The researchers said that most previous studies of brain function and aging have focused on older adults. This study looked at young to middle-aged people to see if lutein made a difference in their thinking processes. 

Dr. Anne Walk, the first author of the recent paper in Frontiers in Aging Neuroscience, wrote: “The neuro-electrical signature of older participants with higher levels of lutein looked much more like their younger counterparts than their peers with less lutein. Lutien appears to have some protective role, since the data suggest that those with more lutein were able to engage more cognitive resources to complete the task.” Others have pointed out that lutein also gives some protection against a type of blindness called macular degeneration. 

Researchers on this study are continuing to study the effects of lutein on learning and memory, as well as how more dietary lutein may increase lutein in the eyes. In the meantime, we should all take advantage of the summer’s bounty of spinach, kale, chard, lettuces and avocado, which have many health benefits in addition to those cited in this article.  


Dr. Sadja Greenwood is a retired physician formerly active at the University of California, San Francisco. She lives in Bolinas.