Low-calorie diets may increase risk of depressive symptoms, study finds

Following a low-calorie diet is linked to a heightened risk of depressive symptoms, particularly among men and individuals who are overweight, according to new research.

The study, which analysed data from 28,525 adults, found that people on calorie-restrictive diets scored higher on measures of depressive symptoms than those not following any specific dietary plan.

Men and those classified as overweight appeared especially vulnerable to the mental health effects of restrictive eating, the analysis showed.

Professor Sumantra Ray is chief scientist and executive director of the NNEdPro Global Institute for Food, Nutrition and Health.

Ray said: “This study adds to the emerging evidence linking dietary patterns and mental health, raising important questions about whether restrictive diets which are low in nutrients considered beneficial for cognitive health, such as omega-3 fatty acids and vitamin B12, may precipitate depressive symptoms.

“But the effect sizes are small, with further statistical limitations limiting the generalisability of the findings.

“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.”

Researchers used data from 28,525 adults who took part in the US National Health and Nutrition Examination Survey (NHANES) between 2007 and 2018.

All participants completed the Patient Health Questionnaire-9 (PHQ-9), a widely used tool that assesses depressive symptoms based on nine questions relating to mood, sleep and daily functioning.

Just under 8 per cent of participants reported experiencing depressive symptoms.

Of the full sample, 29 per cent had a healthy weight (7,995 participants), 33 per cent were overweight (9,470 participants), and 38 per cent were classified as obese (11,060 participants).

Participants were divided into four dietary categories: those following calorie-restrictive diets, those on nutrient-restrictive diets (limiting intake of fat/cholesterol, sugar, salt, fibre, or carbohydrates), those adhering to established dietary patterns (such as diabetic diets), and those not following any specific diet.

Most respondents (87 per cent) reported not following any particular dietary approach.

Specifically, 25,009 participants were not on any specific diet, 2,026 (8 per cent) followed calorie-restrictive diets, 859 (3 per cent) followed nutrient-restrictive diets, and 631 (2 per cent) adhered to established dietary patterns.

People on calorie-restrictive diets scored 0.29 points higher on the PHQ-9 depression scale than those not on any diet.

Among overweight individuals following a calorie-restrictive diet, the increase was 0.46 points. Those following nutrient-restrictive diets saw a 0.61-point increase.

The study also examined specific types of depressive symptoms.

Calorie-restrictive diets were associated with higher cognitive-affective symptom scores, which measure the relationship between thoughts and feelings.

Nutrient-restrictive diets were linked to higher somatic symptom scores, indicating excessive distress and anxiety about physical symptoms.

These scores also varied by sex: a nutrient-restrictive diet was associated with higher cognitive-affective symptom scores in men than in women not on a diet, while all three types of diet were associated with higher somatic symptom scores in men.

Additionally, people living with obesity who followed established dietary patterns had higher cognitive-affective and … 

The findings contrast with earlier studies that suggested low-calorie diets might help reduce depressive symptoms.

The authors explained that many prior studies were conducted under controlled conditions with carefully designed, nutritionally balanced diets.

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

They also suggested that unsuccessful weight loss attempts or cycles of weight loss and regain (known as weight cycling) may contribute to poorer mental health outcomes.

To account for the gender differences, the researchers highlighted the role of nutrients like glucose and omega-3 fatty acids in supporting brain function.

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,” they noted.

The authors noted that, as an observational study, their research could not establish causation.

They also acknowledged the possibility that some participants may have inaccurately reported their dietary habits.