Why limiting your diet could be harming your brain

Teddy Amenabar

Older people who aren’t picky eaters appear to have better brain health than those who prefer more limited diets, according to a large study of British adults.

The research tracked the dietary preferences of nearly 182,000 older adults in Britain. The study was unusual because rather than focusing on the health effects of a particular diet, it examined the link between the foods individuals liked and disliked and their mental wellbeing and cognitive health.

After parsing the data, the researchers noticed a trend: People who liked a variety of foods and flavours reported better mental health and well-being, and did better on cognitive tests than those with limited dietary preferences.

The findings suggest that preference for a limited diet - such as a vegetarian diet or a high-protein diet - may not always be best for overall well-being. Based on the results, people “need a more balanced diet to be better off,” said Jianfeng Feng, one of the study’s lead researchers, who works at both the Institute of Science and Technology for Brain-Inspired Intelligence at Fudan University in Shanghai and at the University of Warwick in Britain.

Picky eaters vs ‘balanced’ eaters

To conduct the research, which was published in the journal Nature Mental Health, the scientists from Britain and China looked at food preferences among participants in the UK Biobank study, one of the largest and longest health research studies in the world. The UK Biobank volunteers completed a “food-liking” questionnaire, ranking their preferences for 140 foods and beverages. The rankings were measured on a nine-point hedonic scale, in which 1 represents “extremely dislike” and 9 represents “extremely like.”

The ranked foods fell into 10 categories: alcohol, beverages, dairy, flavourings (such as black pepper, curry, ketchup and vinegar), fruits, fish, meat, snacks, starches and vegetables.

The researchers found that 57 per cent of respondents showed a balanced preference across all 10 food categories, while others were more picky. One group (18 per cent) preferred starch-free or reduced starch foods, another 5 per cent preferred a vegetarian diet, while the last group (19 per cent) preferred eating more protein and less fibre.

Some of the findings contradict conventional wisdom about healthy eating. For instance, individuals who preferred fruits and vegetables more than protein-rich foods - suggesting a more vegetarian diet - “exhibited a heightened susceptibility” to symptoms of anxiety, depression and other forms of mental distress, said Wei Cheng, a professor in the Institute of Science and Technology for Brain-Inspired Intelligence at Fudan University.