Bread can cause weight gain without extra calories

Bread and other carbohydrate staples may be doing more than just filling plates–they could be quietly reshaping metabolism. In a surprising twist, researchers found that mice strongly preferred carbs like bread, rice, and wheat, abandoning their regular diet entirely. Even without eating more calories, they gained weight and body fat, not because they overate, but because their bodies burned less energy.
Bread has long been a dietary cornerstone, sustaining societies for generations. It is deeply woven into everyday life. But with obesity rates continuing to climb, researchers are beginning to question whether this reliance on staple carbohydrates still makes sense in modern diets.
Obesity increases the risk of many lifestyle-related diseases, making prevention a major public health priority. Traditionally, research has focused on high fat consumption as the main driver of weight gain. This is why many animal studies rely on high fat diets.
However, carbohydrates such as bread, rice, and noodles are consumed daily around the world, yet their role in obesity and metabolism has not been explored as thoroughly. While many people believe that “bread makes you gain weight” or that “carbohydrates should be limited,” it has been unclear whether the issue lies in the foods themselves or in how people choose and consume them.
To better understand these questions, a research team led by Professor Shigenobu Matsumura at Osaka Metropolitan University’s Graduate School of Human Life and Ecology studied how carbohydrates influence eating behavior and metabolism in mice.
The researchers examined whether mice preferred foods like wheat, bread, and rice over standard chow, and how these choices affected body weight and energy use. The animals were divided into several feeding groups, including Chow, Chow + Bread, Chow + Wheat flour, Chow + Rice flour, High-fat diet (HFD) + Chow, and HFD + Wheat flour. The team tracked changes in body weight, energy expenditure, blood metabolites, and liver gene expression.
The findings showed that mice strongly favored carbohydrate-rich foods and stopped eating their standard chow altogether. Even though their total calorie intake did not increase significantly, both body weight and fat mass went up.
Mice that consumed rice flour gained weight in a similar way to those that ate wheat flour. In contrast, mice given a High-fat diet (HFD) + Wheat flour gained less weight than those on a High-fat diet (HFD) + Chow.