Bread could be quietly slowing your metabolism and adding weight: Study

Bread, rice and other carbohydrate staples may be contributing to weight gain in ways that go beyond calorie intake, according to new research that points to changes in how the body uses energy.

A study led by Professor Shigenobu Matsumura at Osaka Metropolitan University found that mice showed a strong preference for carbohydrate-rich foods such as bread, wheat and rice, abandoning their regular diet when given the option. Despite consuming roughly the same number of calories, the animals gained more body weight and fat.

The findings challenge the long-held focus on high-fat diets as the primary driver of obesity. While fat-heavy diets have traditionally dominated research, carbohydrate staples remain a daily feature of diets worldwide, with limited understanding of their metabolic effects.

Researchers divided the mice into multiple diet groups, including combinations of standard chow, bread, wheat flour, rice flour and high-fat diets. They monitored body weight, energy expenditure and metabolic changes.

Results showed that mice consuming carbohydrate-rich options consistently chose these foods over standard chow. Weight gain occurred even without a significant increase in calorie intake. According to Matsumura, this suggests that “weight gain may not be due to wheat-specific effects, but rather to a strong preference for carbohydrates and the associated metabolic changes.”

Further analysis indicated that the increase in weight was linked to reduced energy expenditure rather than overeating. The mice burned less energy, while also showing higher levels of fatty acids in the blood and lower levels of essential amino acids. The liver showed increased fat accumulation and heightened activity of genes associated with fat production and transport.

Notably, removing wheat flour from the diet led to a rapid improvement in both body weight and metabolic indicators, suggesting that dietary balance may play a key role in managing weight.

The study also raises questions about modern reliance on refined carbohydrate staples, especially as obesity continues to be a major public health concern linked to chronic diseases.

The research team plans to extend its work to human subjects to examine whether similar metabolic effects occur in real-world diets. Future studies will also explore the role of whole grains, fibre-rich foods and combinations with proteins and fats, along with how food processing and timing influence metabolic responses.

The findings have been published in Molecular Nutrition & Food Research, and may contribute to future nutritional guidelines aimed at balancing taste and health.