A new study has found that following a low-calorie diet could increase the risk of developing symptoms of depression.
The researchers found that the effects of calorie restriction on mood were more pronounced in men and overweight people.
These findings stand in contrast to previous studies which claim low-calorie diets improve depressive symptoms.
However, the researchers noted that prior trials included tailored and balanced diet programmes that may not be the same as what people realistically follow in everyday life.
For the study, published in BMJ Nutrition Prevention & Health, researchers in Canada used data from the 28,525 people who took part in the US National Health and Nutrition Examination Survey (NHANES) and had completed a health questionnaire relating to depressive symptoms, which gave them a score based on severity.
Of the total, 14,329 were women and 14,196 were men.
A little under 8 per cent had reported depressive symptoms, while 33 per cent were overweight and 38 per cent were obese.
The majority of the group (87 per cent) said they were not on a specific diet, while 2,206 were restricting calories.
Some 859 were on a “nutrient-restrictive” diet, low in fat, sugar, salt, fibre or carbohydrate, and 631 were on diets tailored for the likes of diabetes.
Researchers found low-calorie diets were more common among obese patients and those who were overweight.
Questionnaire scores for depressive symptoms, such as a 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 scores were also higher among overweight people following low-calorie diets.
Researchers said: “Numerous studies have consistently focused on ‘healthy’ versus ‘unhealthy’ diets.
“They have shown that ‘healthy’ diets rich in minimally processed foods, fresh fruits and vegetables, whole grains, nuts, seeds, lean proteins and fish have been linked to a lower risk of depression.
“In contrast, an ‘unhealthy’ diet dominated by ultra-processed foods, refined carbohydrates, saturated fats, processed meats and sweets is associated with an increased risk of depressive symptoms.
“Therefore, individuals must adopt a perfectly healthy dietary pattern to reduce the risk of depressive symptoms. This dichotomy fails to capture the complexity of real-world eating habits.”
Restricting calories can lead to deficiencies in protein, vitamins and minerals, researchers suggest, which puts the body under stress.
The findings also contradict previous studies showing low-calorie diets improve depressive symptoms.
Researchers highlight that these studies were controlled trials, with those taking part following carefully designed and balanced diets.
The team said a focus on “idealised diets” can “overlook the diversity of dietary patterns”, adding: “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.”
Researchers stressed the study has a number of limitations, but gives an insight to how diets recommended by healthcare professionals should be considered for risk factors for 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, added: “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.”
