Carbohydrates like bread and rice may drive weight gain in unexpected ways.
Bread has been a dietary staple for centuries, shaping cultures and daily meals around the world. But as obesity rates continue to rise, researchers are taking a closer look at whether heavy reliance on foods like bread still fits with modern health needs.
Obesity, Diet, and the Overlooked Role of Carbohydrates
Obesity is linked to a wide range of lifestyle-related diseases, making prevention increasingly important. Much of the research on weight gain has focused on high-fat intake as the main cause, which is why many animal studies use high-fat diets.
At the same time, carbohydrates such as bread, rice, and noodles remain everyday staples for many people. Despite this, their role in weight gain and metabolism has not been studied as extensively. Common beliefs such as “bread makes you gain weight” or “carbohydrates should be limited” persist, but it has been unclear whether these effects come from the foods themselves or from broader eating patterns and preferences.
Study Examines Carb Preference and Weight Gain
To explore this question, researchers led by Professor Shigenobu Matsumura at Osaka Metropolitan University’s Graduate School of Human Life and Ecology studied how carbohydrate-rich foods affect eating behavior and metabolism in mice.
The team tested whether mice would prefer foods such as wheat, bread, and rice over standard chow, and how these choices affected body weight and energy expenditure. The animals were divided into several groups, including Chow, Chow + Bread, Chow + Wheat flour, Chow + Rice flour, High-fat diet (HFD) + Chow, and High-fat diet (HFD) + Wheat flour. Researchers tracked body weight, energy expenditure, blood metabolites, and gene activity in the liver.
Weight Gain Without Increased Calories
The results showed a clear preference for carbohydrates. Mice chose carb-rich foods and stopped eating their standard chow entirely. Even though their total calorie intake did not rise significantly, both body weight and fat mass increased.
Mice that consumed rice flour gained weight in the same way as those given wheat flour. Interestingly, mice in the High-fat diet (HFD) + Wheat flour group gained less weight than those in the High-fat diet (HFD) + Chow group.
“These findings suggest that weight gain may not be due to wheat-specific effects, but rather to a strong preference for carbohydrates and the associated metabolic changes,” said Professor Matsumura.
Metabolism, Not Overeating, Drives the Effect
Further analysis using indirect calorimetry and respiratory gas measurements showed that the weight gain was not caused by “overeating,” but by reduced energy expenditure.
Blood tests revealed higher levels of fatty acids and lower levels of essential amino acids. In the liver, fat accumulation increased, along with greater activity in genes involved in fatty acid production and lipid transport.
When wheat flour was removed from the diet, both body weight and metabolic disruptions improved quickly. This suggests that shifting away from a carbohydrate-heavy diet toward a more balanced pattern may help regulate body weight more effectively.
Future Research on Human Diets and Carb Quality
“Going forward, we plan to shift our research focus to humans to verify the extent to which the metabolic changes identified in this study apply to actual dietary habits,” stated Professor Matsumura. “We also intend to investigate how factors such as whole grains, unrefined grains, and foods rich in dietary fiber, as well as their combinations with proteins and fats, food processing methods, and timing of consumption, affect metabolic responses to carbohydrate intake. In the future, we hope this will serve as a scientific foundation for achieving a balance between “taste” and “health” in the fields of nutritional guidance, food education, and food development.”
The findings were published in Molecular Nutrition & Food Research.
Reference: “Wheat Flour Intake Promotes Weight Gain and Metabolic Changes in Mice” by Shigenobu Matsumura, Miona Marutani, Eri Nousou, Nagisa Murakami, Saki Mizobata, Miyu Fujisawa, Mizuki Fujiwara, Nanase Iki, Soyoka Horie, Yuka Yamato, Azumi Yamamoto, Mina Fujitani, Teppei Fujikawa, Chinami Ishibashi and Shigeo Takenaka, 22 January 2026, Molecular Nutrition & Food Research.
DOI: 10.1002/mnfr.70394
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2 Comments
They used white bread and white rice in the testing. I agree, the test needs to be done with whole grains instead of ultra-processed white flour and rice.
Needs to be both types, there is so much conflicting information including that white is better for you than whole grain etc. Now before you object…hence the reason to tests to include both types.