A new study from Osaka Metropolitan University has challenged conventional thinking about carbohydrates, revealing that staple foods like bread, rice, and wheat may promote weight gain and increased body fat not by encouraging overeating, but by significantly slowing down the body’s energy expenditure.
In carefully controlled experiments, researchers observed that mice strongly preferred carbohydrate-rich foods over their standard chow, eventually abandoning the regular diet altogether.
Even when total calorie intake did not increase substantially, the mice consuming bread, wheat flour, or rice flour experienced notable gains in body weight and fat mass. The effect was consistent across both normal and high-fat diet groups, suggesting the weight gain was driven by metabolic shifts rather than wheat-specific compounds.
Using indirect calorimetry and respiratory gas analysis, the team found that the mice burned less energy after switching to carb-dominant diets. Blood analysis revealed elevated fatty acids and reduced essential amino acids, while liver gene expression showed increased fat production and lipid transport. Crucially, when wheat flour was removed from the diet, both body weight and metabolic abnormalities improved quickly, indicating the effect is potentially reversible.
Professor Shigenobu Matsumura, who led the study published in Molecular Nutrition & Food Research, explained that these findings suggest weight gain from carbs may stem from a strong dietary preference combined with reduced energy use.
The research team now plans to shift focus to human studies, examining how factors such as whole grains, dietary fiber, food processing methods, meal timing, and combinations with proteins and fats influence metabolic responses.
The study offers important new insight into why carbohydrate-heavy diets common in many cultures may contribute to rising obesity rates, even when calorie consumption appears stable. It could help shape future nutritional guidance, food education, and product development aimed at balancing taste, convenience, and long-term health.