Counting calories and yo-yo dieting could increase your risk of depression, new research suggests. A study published in BMJ Nutrition Prevention & Health found that following a low-calorie diet is linked to a heightened risk of depressive symptoms, contradicting previous studies that suggested low-calorie diets improved depressive symptoms.
The study analyzed data from 28,500 Americans who took part in the US National Health and Nutrition Examination Survey (NHANES) from 2007 to 2018 and had completed a health questionnaire relating to depressive symptoms, which gave them a score based on severity. Among those studied, 2,508 people—just under 8%—reported depressive symptoms.
Participants were asked if they were following any particular diet either to lose weight or for other health reasons, and if so, which of the nine diet options set out in all six cycles of NHANES they were on. Dietary patterns were categorized into four groups: calorie-restrictive; nutrient-restrictive (low in fat/cholesterol, sugar, salt, fiber, or carbohydrates); established dietary patterns (adapted for diabetes, for example); and not on a diet.
Most participants (25,009, 87%) said they weren't on any specific diet, while 2,206 were restricting calories. Additionally, 859 participants (3%) followed a nutrient-restrictive diet Low in fat, sugar, salt, fiber, or carbohydrates. Another 631 participants were on diets tailored for conditions like diabetes, with 2% following an established dietary pattern.
Among the participants, 9,470 (33%) were overweight, and 11,060 (38%) were obese. Calorie restriction was most commonly reported by obese participants (1,247; 12%) and those who were overweight (594; 8%). Of the total participants, 14,329 were women and 14,196 were men, with a greater proportion of men (12,772; 90%) than women (12,237; 85%) reporting they weren't on a diet.
Questionnaire scores for depressive symptoms—such as low mood, low energy, and sleep disturbances—were higher among those restricting calories compared to those who reported not being on a diet at all. The PHQ-9 scores, which measure the severity of depressive symptoms, were 0.29 points higher in those on calorie-restrictive diets. The scores were also higher among overweight people following low-calorie diets, with PHQ-9 scores being 0.46 points higher in this group. A nutrient-restrictive diet was associated with a 0.61 point increase in PHQ-9 scores, indicating the negative impact of such diets on depressive symptoms.
These findings contradict previous studies which found that low-calorie diets improved depressive symptoms. Researchers argue that prior trials included tailored and balanced diet programs that may not reflect the calorie-counting diets people realistically follow in everyday life, which often contain processed foods. "The discrepancy may arise because prior studies were primarily randomised controlled trials (RCTs) where participants adhered to carefully designed diets ensuring balanced nutrient intake," the researchers explained, according to the Mirror.
"Restricting calories can lead to deficiencies in protein, vitamins, and minerals, which puts the body under stress," the researchers suggested, as reported by the Mirror. They added: "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."
"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," said Professor Sumantra Ray, chief scientist and executive director of the NNEdPro Global Institute for Food, Nutrition and Health, according to Medical Dialogues.
Experts suggest that eating healthy whole foods rather than processed foods might be more important than focusing only on cutting down on calories. The study notes that an "unhealthy diet" dominated by ultra-processed foods, refined carbohydrates, saturated fats, processed meats, and sweets is associated with a heightened risk of depression.
Another possible explanation for the findings might be a failure to lose weight or weight cycling (losing weight and then putting it back on), the researchers suggest. They also point out that glucose and the fatty acid omega-3 are critical for 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 said.
"The reported effects are small and some are scarcely statistically significant, so may well be due to chance. Even if it is the case that people who are dieting have more depressive symptoms, I don't see why we should assume that it is the dieting which causes this," said Professor David Curtis, honorary professor at University College London, who was not involved in the research, according to the Mirror. "To me it seems plausible that this observation could be accounted for by the fact that people who are more unhappy with themselves, and with their weight in particular, may be more likely to go on a diet in an attempt to change their situation."
The researchers acknowledge that the study has a number of limitations and that it is observational, so no firm conclusions can be drawn about causality. They stressed the study gives insight into how diets recommended by healthcare professionals should be considered for risk factors for depression, especially in men and obese patients.
"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," added Ray, according to Medical Dialogues. The research team said a focus on "idealised diets" can "overlook the diversity of dietary patterns." They explained: "Therefore, individuals must adopt a perfectly healthy dietary pattern to reduce the risk of depressive symptoms. The dichotomy fails to capture the complexity of real-world eating habits," as reported by the Mirror.
The preparation of this article relied on a news-analysis system.