A new study in mice finds that walnut consumption alters the gut microbial community in ways linked to good health, both increasing the overall diversity of bacteria and shifting the level of different types. The study, partially funded by AICR, offers insights into how these nuts may play a role in lowering cancer risk and health. It was published in The Journal of Nutritional Biochemistry.
This study builds on previous research that has linked walnuts to lower cancer risk. Ongoing studies are also pointing to the important role of gut microbes — our microbiome — in health.
The human gut contains trillions of bacteria and other microbes. These microbes are helping digest food, communicating with the immune system and providing healthful compounds. Research is also increasingly drawing links between the microbiome and cancer protection.
“Gut health is an emerging research area, but we are seeing that greater bacterial diversity may be associated with better health outcomes, whereas low diversity has been linked to conditions such as obesity and inflammatory bowel disease,” said lead researcher Lauri Byerley, PhD, RD, Associate Professor of Research in the Physiology Department at Louisiana State University in a statement.
In this animal study, rats were randomly assigned to a diet containing ground walnuts, equivalent to about 2 ounces (one-half cup) per day in humans, or a diet without walnuts for up to 10 weeks. Calorie and nutrient intake was similar between the two diet groups. Compared to those that did not consume walnuts, rats that ate a walnut-enriched diet saw an increase in beneficial bacteria including, Lactobacillus, Roseburia, and Ruminococcaceae.
Animal research is provided as background and used to inform future studies needed to understand the effect on humans. More research is needed to understand how these outcomes translate to humans.
Walnuts contain several compounds that may be responsible for these microbial changes in the animals. Walnuts contain a significant amount of alpha-linolenic acid (ALA), the plant-based omega-3 fatty acid and also offer protein (4 grams per one ounce) and fiber (2 grams per one ounce).
Nuts overall contain protein, fiber, minerals and phytochemicals. Folate, copper, vitamin E and magnesium are a few of the nut compounds studied for their role in cancer prevention. They also have unsaturated mono- and polyunsaturated fats, a healthier alternative to the saturated fats in red meats.
The specific nutrients and fat content depends upon the nut. Walnuts, for example, contain relatively high amounts of omega-3 fats. Brazil nuts are packed with selenium – containing the entire Recommended Daily amount in one Brazil nut. Almonds and hazelnuts contains high amounts of vitamin E.
Serving size is important when consuming nuts because weight management is key to cancer protection. The serving size is generally an ounce, a small handful.
Previous research on walnuts, nuts and cancer risk -- both in animals and people -- suggests regular moderate consumption of nuts may offer protection. Last year, for example, another study in mice linked walnuts to lower risk of colon tumors. And a study in people found that eating nuts at least four times a week linked to lower risk of cancer overall compared to those eating nuts less than once a week. This research is ongoing and not yet conclusive.
Along with AICR, the study by Dr. Byerley and her colleagues was funded by the California Walnut Commission.
Source: Byerley LO, Samuelson D, Blanchard E, et al. Changes in the Gut Microbial Communities Following Addition of Walnuts to the Diet. J Nutr Biochem. 2017. DOI: https://doi.org/10.1016/j.jnutbio.2017.07.001.