June 23, 2024

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Could eating nuts daily help lower the risk of depression? A study suggests there may be a link. Image credit: Grace Cary/Getty Images
  • A new study shows eating a handful of nuts daily is linked to a 17% lower risk of depression.
  • Nuts contain phytochemicals that could be associated with anti-inflammatory and antioxidant properties, which are linked to improved mental health.
  • Numerous studies demonstrate the impact of diet on mood.
  • Lifestyle changes to help a person manage depression include limiting alcohol intake, increasing consumption of fruits and vegetables, getting enough sleep, and exercising regularly.

Growing evidence demonstrates the impact of diet on mood. In fact, eating just 30 grams of nuts every day is associated with a 17% lower risk of depression, according to a recent study published in the journal Clinical Nutrition.

Researchers analyzed data from the UK Biobank, a database of health information from approximately half a million United Kingdom citizens. They examined data from more than 13,000 middle-aged and older people with an average age of 58 years between 2007 and 2020.

Participants were given questionnaires to measure nut intake and during the study, depression symptoms or antidepressant use was noted. Those who participated did not report having depression at the beginning of the study.

Results showed that middle-aged and older adults who ate 30 grams of nuts — almonds, walnuts, cashews, hazelnuts, pistachios, and Brazil nuts — per day had a decreased likelihood of taking antidepressants or developing depression.

Researchers discovered this result was the same despite other variables such as medical issues and lifestyle that could impact mental health.

“Nuts provide a rich variety of bioavailable phytochemicals that might be associated with anti-inflammatory and antioxidant activities; which in turn has been associated with improved mental health,” Dr. Lokesh Shahani, assistant professor of psychiatry at UTHealth Houston, not involved in this study, told Medical News Today.

Additionally, “the anti-inflammatory (downregulation of proinflammatory cytokine expression) and antioxidant (neutralization of reactive oxidative species and enhancement of endogenous antioxidant defenses) effects associated with the nutritional composition of nuts could play an important role in reducing the risk of depression,” he added.

Nuts are rich in amino acids, which may benefit mood regulation. “These include arginine, glutamine, serine, and tryptophan, and lower levels of these amino acids have been associated with depression,” said Dr. Shahani.

“The metabolites produced along the tryptophan-kynurenine pathway — i.e., kynurenic acid as neuroprotective and quinolinic acid or 3-hydroxykynurenine as neurotoxic — are vital neurobiological mediators in depression,” he told us.

Nuts also contain antioxidants, including vitamin E and omega-3 fatty acids.

Registered dietitian Natalie Rizzo, founder of sports nutrition blog Greenletes, not involved in the research, explained more about how nut-derived nutrients may influence brain health:

“These nutrients prevent inflammation throughout the body, including the brain. Researchers believe that inflammation in the brain is the cause of many illnesses, such as dementia and depression. This study shows a correlation between nut consumption and lower incidences of depression, but it does not show causation.”

In other words, although the researchers believe the nuts may be the cause of the lower levels of depression, they cannot establish causality beyond any doubt since they did not feed the participants nuts and see how the oxidation levels in the brain increase or decrease, Rizzo explained.

But, in general, nuts have been shown to be associated with lower incidences of cognitive decline.

“In my clinical practice, I often leverage the nutrient-dense power of unprocessed nuts, such as plain almonds, walnuts, macadamia, and Brazil nuts to help support our brain health,” said Dr. Uma Naidoo, a nutritional psychiatrist, professional chef, and nutrition specialist, also not involved in the current study.

“While reasons [behind the link between nut consumption and better brain health] may be multifactorial, including that people who eat more nuts may also engage in otherwise healthy behaviors, these nuts are also rich in: fiber, which nourishes the gut and promotes healthy elimination, [and] omega-3 fatty acids, which reduce brain inflammation and are shown to reduce depressive symptoms,” she also emphasized.

Numerous studies have found an association between a diet high in refined sugars and saturated fats and impaired cognitive function. In some cases, this type of diet can also worsen symptoms of mood disorders, including depression.

In one study, when comparing the Mediterranean diet to a typical Western diet, findings indicated the Mediterranean diet could reduce the risk of depression whereas the Western diet could increase the risk of depression.

“Scientists account for this difference because traditional diets like the Mediterranean diet tend to be high in vegetables, fruits, unprocessed grains, and fish and seafood, and to contain only modest amounts of lean meats and dairy,” said Dr. Shahani.

Rizzo agreed that foods that are associated with the Mediterranean diet are beneficial. And research confirms it.

However, it is important to note that “you can’t eat a certain food and expect it to increase your mood immediately,” said Rizzo.

“Most of these studies look at people’s diets over time and see how their moods change. Like most everything in the nutrition world, a well-balanced diet with plenty of plants is beneficial for a variety of things, including mood,” she emphasized.

In general, a poor diet does not benefit a person’s mental health and can become a negative cycle.

“If you eat poorly — for example, processed foods for every meal — then your inflammatory markers are raised, and you feel more depressed and anxious, which leads you to eat more nutrient-less foods,” Dr. Nicole Avena, nutrition consultant, assistant professor of neuroscience at Mount Sinai School of Medicine, and visiting professor of health psychology at Princeton University, stated. Dr. Avena was not involved in the current study.

Dr. Naidoo explained that the foods we consume have a major impact on our mental health and cognitive function due to the connection between our gut and our brain.

“Throughout life, these two organs remain connected via the vagus nerve, which connects nerve endings in our guts to nerve endings in our brains. Through this gut-brain connection, our gut (digestive tract) and our minds quite literally speak to each other,” she said.

Further research is needed to corroborate the findings of the current study. Dr. Shahani explained there are several limitations:

First, the study cohort is not representative of the general population, which could affect the magnitude, direction, and generalizability of the results.

Second, the high proportion of participants lost to follow-up could lead to selection bias. Third, nut consumption data were self-reported, and some degree of measurement error is expected.

Fourth, the highest nut consumption category only includes a few cases of depression. Therefore, the lack of associations may be due to limited statistical power.

Finally, this study assessed self-reported depression, which may affect the prevalence and incidence estimates.

“One limitation is that outside factors were not controlled, in which participants in the study only had one guideline- to eat 30 g of nuts,” said Dr. Avena. “Many other overall nutritional factors can attribute to overall mental well-being, and including nuts may have influenced the participants to eat healthier in general. Overall, including nuts in a healthy diet is a great thing to do anyway.”

Dr. Naidoo agreed that self-selection for participation was a limitation, meaning that perhaps already health-motivated individuals participated in the study.

In addition, this study measured self-reported nut consumption and depression symptoms, which may not correlate directly with objective measures. However, the results of this study are promising, and they provide a further basis for the foundational role of a healthy diet in mental health, Dr. Naidoo added.

Experts note that many different lifestyle changes can improve a person’s ability to handle depression.

Dr. Shahani said a few to highlight include smoking cessation, reduced alcohol consumption, increased intake of fruits and vegetables, increased physical activity, adequate sleep duration, and reduced loneliness.

“Information from the foods we eat is communicated to our brain and impacts our overall mental health,” Dr. Naidoo stated.

“More than 90% of the receptors for the neurotransmitter serotonin, which is responsible for mood and cognition, are located in the gut, highlighting just how powerful this food-mood connection is. Eating patterns high in healthy, wholesome foods are correlated with positive mental health while diets higher in processed, sugary foods are associated with symptoms of poor mental health, such as depression and anxiety.”

– Dr. Uma Naidoo

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