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Eating a diet designed to protect the environment might also protect the human brain from conditions like depression, anxiety, and stroke. A large study of British adults found that those who closely followed a plant-heavy, climate-friendly diet experienced a lower risk of developing several neurological and mental health conditions over a twelve-year period. The research, published in the Journal of Affective Disorders, suggests that this way of eating helps preserve brain health in part by slowing down the body’s cellular aging process.
In 2019, an international group of scientists proposed the Planetary Health Diet. This nutritional framework was designed to feed a growing global population while minimizing environmental damage. The regimen emphasizes plant-based foods, such as whole grains, fruits, vegetables, nuts, and legumes.
The planetary diet allows for modest amounts of meat and dairy but largely limits highly processed foods and added sugars. In recent years, medical researchers have linked the diet to a lower risk of heart disease, improved respiratory health, and a longer overall lifespan.
Until now, the diet’s specific impact on the brain remained relatively unexplored. Neurological and mental health conditions are a leading cause of disability worldwide, and their prevalence is rising as the global population grows older. Medical researchers are searching for accessible lifestyle interventions to help delay or prevent age-related cognitive and psychological decline.
To understand how sustainable eating habits might influence the brain, public health researchers Jue Liu of Peking University and Liyuan Tao of the Harvard T.H. Chan School of Public Health led a new investigation. They wanted to see if the climate-friendly diet could lower the risk of developing brain-related conditions. The research team also wanted to find out if the diet exerts its protective effects by altering an individual’s biological age.
While chronological age simply counts the years a person has been alive, biological age measures how rapidly their cells and organs are deteriorating. Two people born in the same year can have very different biological ages depending on genetics, environment, and lifestyle choices. A lower biological age indicates a slower rate of physical decline.
The research team analyzed data from 69,370 participants enrolled in the UK Biobank, an ongoing health study in the United Kingdom. When they entered the study, the participants were about fifty-six years old on average. Over the course of a few years, each participant completed at least two detailed surveys outlining everything they ate and drank over the previous twenty-four hours.
The researchers used these dietary records to calculate a score for each participant based on how closely their eating habits matched the Planetary Health Diet. A higher score indicated stricter adherence to the diet. The maximum possible score was 130 points.
The researchers also examined blood samples taken from the participants during the study. By analyzing various markers in the blood, such as cholesterol levels, kidney function, and inflammation, the team calculated each person’s biological age. They then compared that calculation to the person’s actual age to see if their aging process was accelerated or decelerated.
Finally, the researchers tracked the participants for about twelve years using national health records. They monitored who developed dementia, Parkinson’s disease, stroke, depression, anxiety, or bipolar disorder. They also tracked cases of multimorbidity, which occurs when a person develops two or more of these conditions at the same time.
When analyzing the data, the research team found that participants who scored in the top quarter for adhering to the environmental diet had a markedly lower risk of developing several brain disorders. Compared to those with the lowest diet scores, the top scorers experienced a 12 percent lower risk of stroke. They also had a 13 percent lower risk of depression, a 13 percent lower risk of anxiety, and a 19 percent lower risk of experiencing multiple brain conditions.
The researchers noted that the protective effect was most pronounced up to a certain threshold. For conditions like depression, anxiety, and multimorbidity, the risk dropped to its absolute lowest when participants achieved a score of about 86 points on the diet index. Scoring even higher than 86 did not offer any additional protection for those specific conditions, though the risk for stroke continued to drop as diet scores rose.
The team did not find a linear association between the diet and Parkinson’s disease or bipolar disorder. For bipolar disorder in particular, the number of cases during the study period was too low to draw firm statistical conclusions.
The researchers then looked at the blood test results to understand how the diet might be protecting the brain. They found that people who ate meals more closely aligned with the Planetary Health Diet tended to have a biological age that was younger than their chronological age.
When the researchers ran statistical models, they discovered that this decelerated biological aging accounted for a modest fraction of the diet’s brain benefits. Depending on the specific condition and the exact blood markers used, a slower biological aging process explained between roughly 2 percent and 13 percent of the reduced risk for brain disorders. This suggests that while slowing cellular aging is part of the equation, the diet likely protects the brain through several other mechanisms that have not yet been fully mapped out.
Because the study relied on observing people’s natural habits over time, it cannot prove that the diet directly caused the improved brain health outcomes. People who eat a sustainable diet often engage in other healthy behaviors that might contribute to a lower risk of neurological conditions. The researchers used statistical methods to account for factors like income, education, physical activity, and smoking, but hidden variables could still influence the results.
The reliance on self-reported dietary surveys also introduces the possibility of human error. Participants might have misremembered what they ate or altered their eating habits after the initial surveys were completed.
In addition, the participants in this dataset were predominantly white, middle-aged adults living in the United Kingdom. The relationship between this specific diet and brain health might look different in populations with different genetic backgrounds, cultural dietary traditions, or levels of access to fresh produce. Future research will need to track different populations across the globe to see if the protective effects remain consistent.
The study, “Planetary health diet benefits brain health by decelerating biological aging,” was authored by Xi Li, Zhaoyu Wang, Gram Lu, Hongguang Chen, Yi Yang, Jue Liu, and Liyuan Tao.