New study challenges mental health benefits of calorie-restrictive diets

A recent study suggests that following a low-calorie diet may be associated with an increased risk of depressive symptoms, particularly among men and those who are overweight. The findings challenge earlier research that indicated calorie restriction might improve mental health outcomes.

“This study adds to the emerging evidence linking dietary patterns and mental health, raising important questions about whether restrictive diets that are low in nutrients considered beneficial for cognitive health, such as omega-3 fatty acids and vitamin B12, may precipitate depressive symptoms,” says professor Sumantra Ray, chief scientist and executive director of the NNEdPro Global Institute for Food, Nutrition, and Health, UK.

“But the effect sizes are small, with further statistical limitations limiting the generalizability of the findings. Further well-designed studies that accurately capture dietary intake and minimize the impact of chance and confounding are needed to continue this important line of inquiry.”  

Analyzing diets

Published in BMJ Nutrition Prevention & Health, the study analyzed data from 28,525 adults who participated in the US National Health and Nutrition Examination Survey between 2007 and 2018. Participants completed the Patient Health Questionnaire-9 (PHQ-9), a widely used measure of depression severity.

Nearly 8% of respondents reported experiencing depressive symptoms. Researchers categorized participants’ diets into four groups: calorie-restrictive, nutrient-restrictive (low in sugar, salt, or fat), established dietary patterns (such as those tailored for diabetes), and no specific diet. Most participants (87%) reported not following any specific dietary plan.

Among those who did report dieting, calorie restriction was the most common, particularly among individuals living with obesity. Analysis revealed that people on calorie-restrictive diets had higher PHQ-9 scores — indicating more severe depressive symptoms — than those not on a diet.

Calorie deficit correlations

The increase was even more pronounced in overweight individuals, where scores rose by 0.46 points. Nutrient-restrictive diets were associated with a 0.61-point increase. The researchers highlight that the observational nature means it can only correlate the two factors and makes no claim of causation. 

However, they also point out that these findings contradict previous findings suggesting that lower-calorie diets decrease depression symptoms.

“This discrepancy may arise because prior studies were primarily randomized controlled trials where participants adhered to carefully designed diets ensuring balanced nutrient intake,” the study reads. 

“In contrast, real-life calorie-restricted diets and obesity often result in nutritional deficiencies (particularly in protein and essential vitamins/minerals) and induce physiological stress, which can exacerbate depressive symptomatology, including cognitive-affective symptoms.”

The researchers also posit that another possible explanation could be unsuccessful weight loss or repeated weight cycling — losing weight and then regaining it.

Gender discrepancies

Further breakdown of the results reveals that low-calorie diets were linked to more cognitive-affective symptoms — such as negative thought patterns — while nutrient-restrictive diets were tied to increased somatic symptoms like fatigue and physical discomfort.

Men on restrictive diets experienced higher levels of both symptom types compared to women. As a possible explanation for the observed gender differences, the researchers note that glucose and omega-3 fatty acids are essential for maintaining brain health.

“Diets low in carbohydrates (glucose) or fats (omega-3s) may theoretically worsen brain function and exacerbate cognitive-affective symptoms, especially in men with greater nutritional needs,” the researchers conclude.