News Release

New study shows snacking on mixed tree nuts may impact cardiovascular risk factors and increase serotonin

New findings From UCLA published in Nutrients in Partnership with The International Tree Nut Council Nutrition Research & Education Foundation

Peer-Reviewed Publication

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Credit: INC NREF

In a paper[1] published online this week in the journal, Nutrients, researchers found that consuming mixed tree nuts (almonds, Brazil nuts, cashews, hazelnuts, macadamias, pecans, pine nuts, pistachios and walnuts) had a positive effect on the metabolism of the essential amino acid, tryptophan, in overweight and obese individuals. Specifically, there was an increase in both cardioprotective tryptophan metabolites and in the neurotransmitter, serotonin.


In a previous study[2], researchers at UCLA demonstrated that consuming 1.5 ounces of tree nuts per day (versus pretzels) during 24 weeks of weight loss and weight maintenance, resulted in weight loss, increased satiety, decreased diastolic blood pressure and decreased heart rate. Tryptophan (found in tree nuts) has been indicated as an important factor in cardiovascular disease (CVD). It is metabolized in the gut, producing many bioactive metabolites that are important in immune regulation affecting chronic diseases such as diabetes and CVD. The current study looked at whether tree nut snacks, as part of a hypocaloric diet, could modify the gut microbiome, resulting in increased levels of cardio-protective tryptophan microbial metabolites.


Plasma and stool samples were collected from 95 overweight or obese participants and were evaluated in the current study for tryptophan metabolites and for gut microbiota. “We’ve known for a long time that tree nuts can help decrease CVD risk, and these findings provide some possible explanations,”


Tree Nuts as Healthy Snacks

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stated lead researcher, Zhaoping Li, MD, PhD, Professor of Medicine and Chief of the Division of Clinical Nutrition at UCLA. “We discovered some new associations between tryptophan metabolites and blood pressure, heart rate, and satiety in overweight/obese subjects, suggesting a broader impact of tryptophan metabolism in overall health, including cardiovascular health.”


Another interesting finding was the significant increase in blood serotonin levels (60.9% and 82.2% increase from baseline at week 12 and 24, respectively) in both the weight loss and weight maintenance phases, in the those who consumed mixed tree nuts. “This is the first time we’ve seen mixed tree nut consumption associated with an increase in serotonin levels in the body,” explained Dr. Li. “While more research is needed, this is exciting since serotonin can have an important impact on mood and overall mental health.”


Research has shown that people get about 25% of their calories each day from snacks and a large proportion come from desserts, sugar-sweetened beverages, sweets and salty snacks.[3] “Replacing just one of those snacks with 1.5 ounces of tree nuts may help improve overall health and reduce the risk for various chronic diseases,” stated Maureen Ternus, M.S., R.D.N, Executive Director of the International Tree Nut Council Nutrition Research & Education Foundation.

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The International Tree Nut Council Nutrition Research & Education Foundation (INC NREF) is a

non-profit, non-governmental organization dedicated to supporting nutrition research and education for consumers and health professionals throughout the world. Members include those associations and organizations that represent the nine tree nuts (almonds, Brazils, cashews, hazelnuts, macadamias, pecans, pine nuts, pistachios and walnuts). For more information, please visit our website at


[1] Yang, J., R. Lee, Z. Schulz, A. Hsu, J. Pai, S. Yang, S.M. Henning, J. Huang, J.P. Jacobs, D. Heber, Z. Li, 2023. Mixed Nuts as Healthy Snacks: Effect on Tryptophan Metabolism and Cardiovascular Risk Factors. Nutrients. 15, 569;


[2] Wang, J., S. Wang, S.M., Henning, T. Qin, Y. Pan, J. Yang, J. Huang, C.-H. Tseng, D. Heber, Z. Li., 2021 Mixed tree nut snacks compared to refined carbohydrate snacks resulted in weight loss and increased satiety during both weight loss and weight maintenance: a 24-week randomized controlled trial. Nutrients. 13(5), 1512;


[3] Dunford, E.K., B.M. Popkin, 2017. Disparities in snacking trends in US adults over a 35-year period from 1977 to 2012. Nutrients. 9(8), 809;


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