Low-calorie diets are associated with an increased risk of depressive symptoms

A low-calorie diet may increase the risk of depressive symptoms, according to research published in the journal ' BMJ Nutrition Prevention & Health '.

According to this work, overweight people may be especially vulnerable to the effects of restrictive eating.

A healthy diet rich in minimally processed foods, fresh fruits and vegetables, whole grains, nuts, seeds, lean protein, and fish is generally associated with a lower risk of depression, while a less healthy diet, dominated by ultra-processed foods, refined carbohydrates, saturated fats, processed meats, and sweets , is generally associated with a higher risk, the researchers explain.

But people follow many different types of diets for health or medical reasons, including those that restrict calories or particular nutrients, and it's unclear whether these other dietary patterns might be associated with a risk of depressive symptoms, they add.

To explore this further, the authors of this paper drew on data from 28,525 adult respondents (14,329 women and 14,196 men) from the nationally representative US National Health and Nutrition Examination Survey (NHANES) for the years 2007–2018, who had completed the Patient Health Questionnaire-9 (PHQ-9) for depressive symptom severity.

In total, 2,508 people (just under 8%) reported depressive symptoms, and 7,995 participants (29%) were at a healthy weight; 9,470 (33%) were overweight, and 11,060 (38%) were obese.

Participants were asked whether they were following any particular diet, either for weight loss or other health reasons, and, if so, which of the 9 diet options established over the 6 survey waves they were following.

Dietary patterns were classified into four groups: (1) calorie-restricted; (2) nutrient-restricted (low in fat/cholesterol, sugar, salt, fiber, or carbohydrates); (3) established dietary patterns (adapted for diabetes, for example); and (4) no diet.

The majority of participants (25,009, 87%) stated that they did not follow any specific diet, while 2,026 (8%) followed a calorie-restricted diet, 859 (3%) a nutrient-restricted diet, and 631 (2%) a set dietary pattern.

When stratified by sex, a higher proportion of men (12,772; 90%) than women (12,237; 85%) reported not following a diet.

Obese and overweight people reported following calorie restriction guidelines more frequently (1,247; 12% and 594; 8% respectively).

Calorie-restricted diets were also associated with higher cognitive-affective symptom scores (a measure of the relationship between thoughts and feelings), while nutrient-restrictive diets were associated with higher somatic symptom scores (excessive distress and anxiety about physical symptoms).

These scores also varied by sex: a nutrient-restricted diet was associated with higher cognitive-affective symptom scores in men than in non-dieting women, while all three diet types were associated with higher somatic symptom scores in men.

And people living with obesity who followed a set dietary pattern had higher scores on cognitive-affective and somatic symptoms than those with a healthy weight who did not follow a diet.

The authors acknowledge that this is an observational study, so no firm conclusions about causality can be drawn.

Furthermore, the findings also contradict those of previously published studies suggesting that low-calorie diets improve depressive symptoms . However, the researchers explain: "This discrepancy could be because previous studies were primarily randomized controlled trials (RCTs) in which participants followed carefully designed diets that ensured a balanced nutrient intake."

In contrast, low-calorie diets and obesity often cause nutritional deficiencies (particularly in essential proteins, vitamins, and minerals) and induce physiological stress, which can exacerbate depressive symptoms, including cognitive-affective symptoms. Another possible explanation could be the inability to lose weight or weight-loss cycles (losing weight and then regaining it), they suggest.

To explain the observed gender discrepancies, the researchers point out that glucose and omega-3 fatty acids are crucial for brain health. "Diets low in carbohydrates (glucose) or fats (omega-3) could, in theory, worsen brain function and exacerbate cognitive-affective symptoms, especially in men with greater nutritional needs," they suggest.

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