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By Stephen Beech
Low-calorie diets can trigger depression, warns new research.
And men are particularly "vulnerable" to the negative effects of restrictive eating, according to the findings.
The study, published in BMJ Nutrition Prevention and Health, shows that following a low-calorie diet is linked to a heightened risk of depressive symptoms.
Scientists explained that a "healthy" diet rich in minimally processed foods, fresh fruits and vegetables, whole grains, nuts, seeds, lean proteins and fish is generally associated with a lower risk of depression.
But an "unhealthy diet" - dominated by ultra-processed foods, refined carbs, saturated fats, processed meats and sweets - is generally associated with a heightened risk.
However, people follow several different types of diets for health or medical reasons.
The study looked at data from more than 28,500 American adults who had completed the Patient Health Questionnaire-9 (PHQ-9), which assesses the severity of depressive symptoms.
Thought Catalog
Just under 8% reported depressive symptoms, 29% had a healthy weight, 33% were overweight, and 38% were clinically obese.
The participants were asked if they were following any particular diet, either to lose weight or for other health reasons, and if so, which of nine diet options they were on.
Most participants (87%) said they weren’t on any specific diet, while 8% followed a calorie-restrictive diet, 3% a nutrient-restrictive diet, and 2% an established dietary pattern.
A greater proportion of men (90%) than women (85%) said they weren’t on a diet.
Calorie restriction was most commonly reported by obese participants (12%) and those who were overweight (8%), while nutrient-restrictive and established dietary patterns were less common, with the highest proportion of established dietary pattern users among obese participants (3%).
PHQ-9 scores were 0.29 points higher in those on calorie-restrictive diets than in those not on any specific diet.
The scores were higher among those who were overweight and following a calorie-restrictive diet. Their PHQ-9 scores were 0.46 points higher, while a nutrient-restrictive diet was associated with a 0.61 point increase in PHQ-9 scores.
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The researchers said calorie-restrictive 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.
Study author Dr. Venkat Bhat, of the University of Toronto, said: "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.
"And people living with obesity following an established dietary pattern had higher cognitive-affective and somatic symptom scores than those of a healthy weight not on a diet."
Dr. Bhat says the findings contradict those of previously published studies suggesting that low-calorie diets improve depressive symptoms.
He said: “This discrepancy may arise because prior studies were primarily randomized controlled trials where participants adhered to carefully designed diets ensuring balanced nutrient intake.
“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.”
Dr. Bhat says another possible explanation might be a failure to lose weight or "weight cycling" - losing weight and then putting it back on.
Joshua Rawson-Harris
He said a possible explanation for the observed gender discrepancies may be down to glucose and the fatty acid omega-3, which are critical for brain health.
Dr. Bhat added, "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."
Professor Sumantra Ray, Chief Scientist and Executive Director of the NNEdPro Global Institute for Food, Nutrition and Health, welcomed the findings:
He 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."
Ray added: "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.”
