Eating any kind of citrus fruit may reduce the risk of depression, according to a new prospective study.

The findings suggest that citrus alters the gut microbiota, specifically by supporting a beneficial gut bacterium called Faecalibacterium prausnitzii (F. prausnitzii), which is associated with a reduced risk of depression. The study also indicates that flavonoids—compounds found in the peel and juice that give fruits their color and flavor—play a central role in this protective effect.

Dr. Raaj Mehta, instructor in medicine at Harvard Medical School, attending physician at Massachusetts General Hospital and corresponding author of the study, told The Epoch Times via email that eating citrus boosts the abundance of F. prausnitzii, helping regulate neurotransmitters involved in depression.

“Diet matters as much for your mental health as it does for physical health,” he said. “If comfort foods make you feel happy in the short term, why can’t healthy foods such as citrus—’mood foods’—make you feel happier in the long term?”

Citrus, Gut Microbiota, and Depression Risk

The study, published in Microbiome on Nov. 14, investigated the connection between citrus consumption, depression, and gut health. Researchers analyzed dietary patterns, depression status, blood metabolites, and gut bacteria in stool samples from more than 32,000 middle-aged women in the Nurses’ Health Study 2 (NHS2), a long-term observational study tracking women’s health that was designed to investigate the relationship between various lifestyle factors and the risk of chronic diseases.

They found that those who consumed more citrus had a 22 percent decreased risk of depression. This protective effect seems specific to citrus, as other fruits, such as apples and bananas, did not demonstrate the same benefit.​

The researchers found that citrus micronutrients, which are naturally occurring compounds in citrus fruits, influence the gut microbiota. Specifically, naringenin and formononetin, two flavonoids found in citrus peels and expressed juice, affected depression.

Microbes Regulate Inflammation

Of the 144 identified gut microbial species among participants, 15 were associated with citrus intake. Citrus consumption enriched 11 microbes, such as F. prausnitzii, Clostridium leptum, and Bifidobacterium longum. These bacteria break down dietary fiber and produce short-chain fatty acids, which help regulate inflammation, support immune and metabolic function, and influence communication between the gut and the brain.

Four bacterial species associated with adverse health outcomes, such as ulcerative colitis and obesity, decreased with higher citrus intake.

Notably, many citrus micronutrients are linked with an abundance of beneficial F. prausnitzii. This suggests that citrus benefits may result from the synergistic effects of multiple compounds enriching this beneficial bacterium.

Brain Chemicals Get a Boost

Of the 15 microbial species linked with citrus intake, only F. prausnitzii had an effect on depression. Women with depression had significantly fewer of these bacteria than those without. The researchers extended their analysis to a separate cohort of men using biomarkers such as gamma-aminobutyric acid (GABA) and serotonin—neurotransmitters linked to mood regulation.

They found that higher levels of F. prausnitzii were associated with increased GABA and serotonin scores in this cohort as well, suggesting an inverse relationship with depression.

Further investigation revealed that F. prausnitzii enhances a pathway that clinicians are exploring as a potential target for depression treatment.

The S-adenosyl-L-methionine (SAM) cycle 1 pathway was associated with reduced depression when activated. A higher intake of citrus was also linked to an increase in proteins necessary for activating this pathway.

Naringenin, a flavonoid found in citrus fruits, tomatoes, and grapes, is linked to an increased abundance of this protein.

The researchers studied another group outside the NHS2 cohort. This group consisted of 132 male and female participants with and without inflammatory bowel diseases, who provided stool and gut tissue samples. The researchers found that increased microbial activity of the SAM cycle 1 pathway assisted by F. prausnitzii was associated with reduced breakdown of dopamine and serotonin in the gut, resulting in greater availability of these chemicals. Low levels of dopamine and serotonin are associated with depression.

Role of Diet in Depression Management

Recent studies have shown the mental health benefits of citrus fruits in alleviating conditions such as depression and anxiety disorders. For example, one study found that patients with chronic heart failure who consumed less citrus reported higher rates of depression.

Citrus fruits provide mental health benefits through their unique compounds. Flavonoids such as hesperidin and naringenin exhibit antioxidant and anti-inflammatory properties that promote brain health and help alleviate depression. Limonene has been shown to regulate neuron activity in the brain, helping reduce stress, anxiety, and mood disorders.

“I would love to see a clinical trial test our hypothesis,” Mehta said. “We urgently need complementary treatments for patients with depression. Medications are one important piece of the puzzle, but they often don’t work or come with significant side effects.”

Although the study focused on grapefruits and oranges, he said there is no reason to believe the benefits are limited to only these citrus fruits. The benefits also appear to apply universally, regardless of factors such as age, diet, or lifestyle.

For those looking to include citrus in their diet, Mehta wrote, “In our study, we found that the greatest possibility of depression prevention was seen at about 1 serving of citrus per day, which is about one medium orange a day.”

A medium orange provides roughly half the daily fruit intake recommended by the Department of Agriculture, which advises consuming 2 cups of fruit per day.