Mar 22, 2025 12:00:00

Research shows that eating one orange a day reduces depression risk by 20%, with gut bacteria the key

It is known that the relationship between diet and the brain is close, and previous studies have shown that

the time of day you eat , a meat-free vegan diet , and sugary junk food are associated with the risk of depression. A new study conducted by Harvard Medical School and others has found that eating oranges regularly can help balance the gut bacteria and improve mental health.

F. prausnitzii potentially modulates the association between citrus intake and depression | Microbiome | Full Text
https://microbiomejournal.biomedcentral.com/articles/10.1186/s40168-024-01961-3

Eating citrus may lower depression risk — Harvard Gazette
https://news.harvard.edu/gazette/story/2025/02/eating-citrus-may-lower-depression-risk/

According to a research team led by Raaj Mehta of Massachusetts General Hospital and Harvard Medical School, 280 million people worldwide suffer from depression. Despite this, the exact cause of depression is unknown, and 70% of patients face problems such as not responding to initial treatment with antidepressants or experiencing strong side effects.

Mehta and his colleagues, who noted that a Mediterranean diet rich in fruit and citrus fruits may help prevent depression, extracted data from 32,427 participants in the Nurses' Health Study II (NHS2), a long-term study of female nurses, who had sufficient data from dietary questionnaires and other sources, and analyzed the relationship between diet and depression risk.

When the research team looked at participants' frequency of grapefruit and orange and their juice consumption and their risk of depression, they found that those in the highest citrus fruit consumption group had a 22% lower risk of depression than those in the lowest citrus fruit consumption group. The amount consumed by people in the high citrus fruit consumption group was equivalent to eating one medium-sized orange per day.

This result remained unchanged even after adjusting for various confounding factors, such as age, BMI, and lifestyle factors such as smoking and drinking habits. The research team also analyzed the total intake of whole fruits, vegetables, apples, and bananas, but found no significant association. This suggests that the reduced risk of depression cannot be explained simply by a healthy diet rich in fruits and vegetables, but is an effect specific to citrus fruits.

Commenting on the results, Mehta said: 'We found evidence that nurses who eat a lot of citrus fruits have a lower risk of developing depression in the future than nurses who don't.'

What's notable about this study is that the NHS2 included data from stool sample donors. The team analyzed the DNA sequences in the samples to look for associations between citrus consumption and the types of gut bacteria. They found that non-depressed people had more of

the gut bacteria F. prausnitzii than depressed people, and that people who ate a lot of citrus fruits had more of this bacteria.

F. prausnitzii is a bacterium that metabolizes dietary fiber to produce short-chain fatty acids. According to the research team, data from another study examining the lifestyle of men also showed that having more F. prausnitzii in the intestines was associated with a lower risk of depression.

'One answer to the question of why F. prausnitzii improves people's mood is that the bacteria affects the levels of serotonin and dopamine produced by human cells in the intestine through a metabolic pathway called the S-adenosyl-L-methionine cycle I pathway,' Mehta explained.

The research team analyzed various nutrients contained in citrus fruits and found that while vitamin C intake was not related to depression, two compounds found in citrus peels and juice, naringenin and formononetin, which are types of polyphenols, were associated with a lower risk of depression. These two compounds were also correlated with the number of F. prausnitzii, so experts believe that these nutrients in oranges may increase gut bacteria and affect the production of neurotransmitters that improve mood.

'Our findings indicate a potential protective role of citrus fruits against the development of depression and suggest that F. prausnitzii and its metabolic activity may modulate the effects of citrus fruits and flavonoids on human mood,' the research team wrote in their paper. 'These data support the idea that gut microbiota may be useful for improving dietary habits to prevent depression and for developing new molecular-based biomarkers.'