A diet plan that suits one’s lifestyle, body type and background is good for physical health. Notably, diet affects depression risk, too. Until now, healthy diets were thought to reduce depressive symptoms, while unhealthy diets were linked to worsening them. However, a new study in BMJ Nutrition, Prevention and Health suggests that dietary patterns extend beyond a simple ‘healthy’ versus ‘unhealthy’ distinction. The study finds that stressful adherence to diets, especially low-calorie diets, may be associated with depressive symptoms.
The Mediterranean diet—rich in heart-healthy fats and centred on fruits, vegetables, whole grains, legumes and herbs—is widely regarded as one of the healthiest eating patterns. Previous research has linked it to reduced depressive symptoms. The new study points out that little is known about the more varied and often restrictive diets people follow in real-world settings and how they affect mental health.
In reality, people often experiment with various diets in pursuit of better health. Common approaches include calorie restriction, nutrient-specific diets (like low-fat or low-sugar) and established plans designed for conditions such as diabetes or hypertension. However, researchers point out that the impact of these diets on depression remains underexplored and often inconclusive.
To address this gap, a team analysed data from 14,329 women and 14,196 men in the US between 2007 and 2018, comparing their dietary habits with responses to the PHQ-9 questionnaire, which measures depressive symptoms. Participants were grouped into four dietary categories: calorie-restricted, nutrient-restricted (low fat, sugar, carbs or sodium), condition-specific diets (like DASH or diabetic) and no specific diet. Findings showed that most people did not follow any structured diet. Only 8 per cent reported calorie restriction, 3 per cent followed nutrient-restricted diets and about 2 per cent adhered to an established medical diet. Roughly 8 per cent of all respondents showed signs of depression.
The study found no significant link between nutrient-restricted or condition-specific diets (like diabetic diets) and depressive symptoms. However, individuals on calorie-restricted diets, particularly men and those who were overweight but not obese, had higher PHQ-9 scores, indicating more severe depression.
Overweight individuals on nutrient-restricted diets also showed higher depressive symptoms. Men in this group had elevated somatic scores (related to physical distress and anxiety) and higher cognitive-affective scores (reflecting negative thoughts and emotions) compared to women not on any diet.
The study suggests that dieting may worsen depression if calorie cuts come at the cost of essential nutrients. Inadequate calorie intake and poor nutrient diversity can trigger deficiencies and physiological stress, potentially deepening depressive symptoms.
The study also found that men were more prone to worsening depression on restrictive diets. Researchers suggest this may be due to men's higher nutritional needs—deficiencies in mood-regulating nutrients like omega-3s and B vitamins could intensify depressive symptoms.
For those on low-calorie diets for weight loss, behavioural therapy would be beneficial, according to researchers. The study also notes the key takeaway is to ensure that one’s diet is nutritionally balanced and not overly restrictive. And weight loss, the researchers stress, is not just a physical process but an emotional and psychological journey as well.