A new study has found that individuals who eat more unhealthy plant foods (such as fruit juices, potatoes, refined grains, and high-sugar foods) have higher risks of depression and anxiety compared to individuals who eat less of such foods. Eating healthy plant foods (such as healthy vegetables, whole grains, fruits, nuts, legumes, vegetable oils, and tea/coffee) was not associated with changes in risks of these disorders. The study was published in PLOS One.
Recent studies have indicated that diet plays a significant role in mental health. Researchers have examined various dietary patterns, with plant-based diets receiving particular attention. However, a meta-analysis reported that vegetarian and plant-based diets may increase the risk of depression. This suggests that not all plant-derived foods are healthy and some may even contribute to various diseases.
Researchers have developed plant-based diet indices to categorize different dietary patterns. The healthy plant-based diet index (hPDI) measures the consumption of healthy plant foods, while the unhealthy plant-based diet index (uPDI) measures the consumption of unhealthy plant foods. These indices can be combined to create an overall plant-based diet index.
Study authors Fahimeh Haghighatdoost and his colleagues wanted to explore how values of the plant-based diet index are associated with depression and anxiety. They also wanted to know whether tendencies to consume healthy and unhealthy plants (i.e., hPDI and uPDI) may be differently associated with these disorders. They conducted a survey.
The study involved 2,456 healthy participants aged 18 or older from five cities in Iran: Isfahan, Birjand, Bandar Abas, Kerman-shah, and Shahrekord. Data collection took place between February 2018 and July 2019. Participants were required to be free from serious medical conditions specified by the researchers and to consume between 800 and 4,200 kilocalories per day on average.
Participants completed a questionnaire regarding their age, sex, socioeconomic status, and smoking habits. Dietary intake was assessed using a food frequency questionnaire administered by interviewers. The questionnaire asked about the frequency and quantity of different food items consumed. The researchers used these answers to calculate the average intake of each food item for the entire sample, as well as energy and nutrient intakes.
Nutritionist IV software adjusted for Iranian food was utilized for this purpose. The questionnaire classified food items into 21 groups, which were further categorized into animal food, healthy plant-based food, and unhealthy plant-based food. The plant-based indices were based on the latter two groups.
Participants also completed the Iranian version of the Hospital Anxiety and Depression Scale (HADS) to assess their anxiety and depression symptoms.
The results showed that younger participants tended to consume more plant-based food overall, including unhealthy plant-based food (higher uPDI and PDI values). In contrast, older participants tended to consume more healthy plant-based food (higher hPDI values). Higher consumption of healthy plant-based foods (higher hPDI) was associated with lower energy intake, lower macronutrient consumption, and lower consumption of several other food items.
Participants who reported consuming more unhealthy plant-based food (higher uPDI) were more likely to experience symptoms of depression and anxiety, indicating a higher risk of these disorders. However, there was no significant association between the consumption of healthy plant-based foods (hPDI) or the overall plant-based diet index and the risk of depression and anxiety.
“In conclusion, our results suggest that the greater adherence to an unhealthy plant-based diet, the higher the risk of depression and anxiety. However, neither plant-based diet index nor healthy plant-based diet index were pertinent to depression and anxiety. Though an unhealthy plant-based diet in our study population is a risk factor for depression and anxiety, overall plant-based diet or healthy plant-based diet cannot be protective factors against them,” the study authors concluded.
The study, “The relationship between a plant-based diet and mental health: Evidence from a cross-sectional multicentric community trial (LIPOKAP study)”, was authored by Fahimeh Haghighatdoost, Atena Mahdavi, Noushin Mohammadifard, Razieh Hassannejad, Farid Najafi, Hossein Farshidi, Masoud Lotfizadeh, Tooba Kazemi, Simin Karimi, Hamidreza Roohafza, Erika Aparecida Silveira, Nizal SarrafzadeganI, and Cesar de Oliveira.
