A decrease in calorie intake could cause an increase in depression, new research has discovered.

The journal BMJ Nutrition, Prevention & Health published a new study on Tuesday, June 3, sharing findings from the National Health and Nutrition Examination Survey. The study collected data from the survey’s examination of more than 28,500 adults’ diets and depression symptoms.

Although several previous studies have found that low-calorie diets improve depressive symptoms, the latest study shows the opposite. It found that calorie-restrictive diets result in more pronounced mood changes, especially in men and overweight people. 

Researchers for the new study noted that previous studies included regimented balanced diet plans for the participants, which may not be an accurate assessment of people’s everyday habits. 

The 28,525 participants completed a health questionnaire relating to depressive symptoms, which gave them a score based on severity.

The BMJ Nutrition Prevention & Health researchers then found that 7.79% of individuals reported depressive symptoms, while 33% were overweight and 38% were obese. Out of the entire study, 87% said they were not following a specific diet. However, 2,206 were restricting calories; 631 were on regimented diets for conditions such as diabetes; while 859 were on a “nutrient-restrictive” diet, low in fat, sugar, salt, fiber or carbohydrate.

Researchers discovered that low-calorie diets were more common among obese and overweight patients. Additionally, those with restrictive calorie diets reported higher numbers of depressive symptoms, including low mood, low energy and sleep disturbances. Their results were higher compared to those who reported not being on a diet.

“Numerous studies have consistently focused on ‘healthy’ versus ‘unhealthy’ diets,” the study read. Healthy diets include fresh fruits and vegetables, whole grains, nuts, seeds, lean proteins and fish, which have “been linked to a lower risk of depression.” Whereas the unhealthy diet, is “dominated by ultra-processed foods, refined carbohydrates, saturated fats, processed meats and sweets is associated with an increased risk of depressive symptoms.”

“This dichotomy fails to capture the complexity of real-world eating habits,” the study explains. Noting that restrictive caloric intake can lead to deficiencies in protein, vitamins and minerals, which can put the body under stress.

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Researchers emphasize that previous studies were controlled tests that required participants to eat based on designed balanced diets, which “overlook the diversity of dietary patterns.”

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

Despite the recent findings, researchers emphasized that the study has several limitations. However, it provides an understanding of how these types of diets can cause depression, especially in men and obese patients.

Professor Sumantra Ray, chief scientist and executive director of the NNEdPro Global Institute for Food, Nutrition and Health, which co-owns BMJ Nutrition Prevention & Health with BMJ Group, acknowledged that “the effect sizes are small.” However, she proposed, “Further well designed studies that accurately capture dietary intake and minimise the impact of chance and confounding are needed to continue this important line of inquiry.”