A bunch of macadamia nuts, which are a type of tree nutShare on Pinterest
Consuming tree nuts such as macadamia nuts may have cardiovascular benefits. Flavia Morlachetti/Getty Images
  • A new study suggests that tree nuts may reduce certain risk factors for cardiovascular disease by modifying the metabolism of L-tryptophan, an amino acid.
  • In a controlled parallel trial, people with obesity or overweight who snacked on tree nuts as part of a 24-week weight loss and weight maintenance program experienced increased levels of serotonin, which can enhance mood.
  • Tree nuts are rich in nutrients, and eating them instead of other snacks was not associated with gaining weight.

The authors of a new study recently established a link between the consumption of tree nuts — almonds, cashews, hazelnuts, macadamia, pecans, pistachios, and walnuts — and a reduction in blood pressure, an important risk factor for cardiovascular disease (CVD). They’ve just published a new study that may explain the connection.

The researchers found that tree nuts increased levels of cardio-protective L-tryptophan metabolites in plasma and stool samples collected from study participants.

The study was a randomized, controlled, parallel study that involved 131 people with obesity or overweight over the course of a 24-week weight loss and weight maintenance program.

The diet of all participants included a daily 1.5-ounce snack. Of the 95 people who completed the study, 39 individuals snacked on pretzels as a control, while 56 other people ate tree-nut snacks of the same caloric value instead. At the end of the study period, the researchers analyzed fecal and blood plasma samples from each participant to ascertain the effects of their different snacks.

People who ate tree nuts experienced significant increases in levels of blood serotonin at week 12 (60.9%), and week 24 (82.2%), compared to their baseline levels. Those who ate pretzels experienced an increase in blood serotonin levels during the maintenance phase of the study, between weeks 12 and 24.

Tryptophan is the body’s only precursor of serotonin, which is credited with supporting a range of body functions, including mood, sleep, and digestion.

The study is published in the journal Nutrients.

The research was funded by the International Tree Nut Council Nutrition Research & Education Foundation, along with the U.S. Department of Defense, VA Merit Review, and VA Career Development Award.

According to the Institute of Food Technologists (IFT), Americans eat 2.7 snacks a day, with an increasing number of young adults consuming as many as five or more.

Children get about 27% of their daily calorie intake from snacks, according to Harvard’s T.H. Chan School of Public Health.

Snacking can lead to unwanted weight gain, and unhealthy snacks often wind up replacing more nutritious foods in one’s daily diet.

Tree nuts contain substantial amounts of tryptophan, which is an essential amino acid that helps support growth and overall health.

Tryptophan is metabolized via three pathways, the kynurenine and serotonin pathways in body cells, and via the indole pathway in gut bacteria.

Disrupted tryptophan metabolism has been linked to metabolic diseases, including obesity and CVD.

The study’s corresponding author, Dr. Zhaoping Li, said the new study at least partially answers the question posed by her group’s earlier research: “One of the possible mechanisms is through [a] change of tryptophan metabolism.”

Dr. Li said in a press release issued by the International Tree Nut Council Nutrition Research & Education Foundation:

“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.”

“Gut microbiome and their metabolites can contribute to the regulation of our metabolism and mood,” she told Medical News Today.

There are other reasons the study makes sense, said Michelle Routhenstein, cardiology dietitian and preventive cardiology nutritionist at EntirelyNourished:

“[The authors’ interpretation of t]his study’s findings that tree nuts encourage CVD protective tryptophan metabolites and heart health makes sense due to its ability to help reduce inflammation, one of the main causes for atherosclerosis and heart disease.”

Dr. Li explained the connection between eating and emotions.

“Emotional eating is a significant factor [that contributes] to obesity. Nuts may improve mood through an increase of serotonin that is one of the key neurotransmitters to regulate mood,” she said.

The researchers were surprised to find an increase in serotonin levels in the tree nut group during the weight loss and maintenance sections of the study. Only the tree-nut group experienced increased levels of fecal serotonin.

By the end of the study, both groups had higher blood serotonin levels.

The authors speculate this final increase in blood serotonin for all participants may be evidence of the body’s response to weight loss.

“An increase in serotonin levels may be beneficial for people who are overweight or obese trying to achieve weight loss because of its role in energy expenditure and appetite suppression,” Routhenstein also noted.

According to the study “Tree Nuts and Peanuts as Components of a Healthy Diet”:

“One and one-half ounces of tree nuts or peanuts provides [greater than] 10% of the adult male recommended dietary allowance for protein, iron, magnesium, phosphorus, zinc, copper, thiamin, and vitamin E. In addition, 1.5 oz (42 g) of tree nuts provides [greater than] 10% of the adult male RDA for vitamin B-6 and selenium.”

By way of example, Routhenstein listed some significant nutrients associated with a few tree nuts:

  • Pistachios contain phytosterols, potassium, and carotenoids that promote good blood vessel health and blood lipids.
  • Brazil nuts contain selenium, which helps combat oxidative stress and boost heart health and immune health.
  • Pecans are rich in copper, which helps with blood sugar metabolism and may help maintain a healthy thyroid gland.

Almonds are high in antioxidants, fiber, and protein. A single Brazil nut delivers 100% of the recommended daily amount of selenium. Although nuts are rich in energy, concerns about them being linked to weight gain appear unwarranted. Studies have shown that higher nut intake is associated with reductions in body weight and body fat, suggesting they do not contribute to weight gain.