Scientists revealed the secret: why bread makes us fatter even if we don’t overeat
Bread is one of the oldest foods in human history, a dietary staple for billions of people. But new research by Japanese scientists calls into question its safety for our figure. It turns out that wheat flour products slow down metabolism so much that the body begins to gain weight even without increasing caloric intake. It seems that the beauty bloggers I’ve seen on social media were actually saying something useful.
What happens to weight with an excess of carbohydrates
Professor Shigenobu Matsumura and his colleagues conducted an interesting study. The scientists gave mice a simple choice: standard balanced feed or wheat flour products — baked flour and bread. Meanwhile, another group was offered rice flour.
The mice clearly preferred the carbohydrate-rich food. They almost completely abandoned the balanced feed and switched to wheat products. Within just four weeks, their body weight increased significantly and fat deposits grew noticeably. Humans would also choose bread, if only because it smells so delicious.
The most interesting part came next. It would be logical to assume that the mice simply overate the tasty bread and consumed more calories than they needed. But the researchers carefully measured the daily energy intake of all groups. The total number of calories consumed by mice eating wheat products did not exceed the caloric intake of the control group. That is, they were not overeating, but they were still gaining weight.
Why bread slows down metabolism
If the calories are the same but weight is increasing, it means the body is expending less energy than before. This is exactly what the scientists discovered.
Using metabolic gas analysis, the researchers tracked how much energy the mice were expending. The result was striking: mice on a wheat diet sharply reduced their energy expenditure. They didn’t move any less than before, but their basal metabolic rate slowed down significantly.
Imagine a car that, instead of burning fuel while driving, starts draining it into a reserve tank. The fuel arrives in the same quantity, but is consumed much more efficiently, while the surplus is stored away. This is roughly how the body works when it receives too many refined carbohydrates.
The data obtained suggest that weight gain may not be related to a specific effect of wheat, but rather to a strong preference for carbohydrates and the accompanying metabolic changes, — explained Professor Matsumura.
An important detail: mice that ate rice flour gained weight following a similar pattern. The specific type of refined flour didn’t play a decisive role — what mattered was the excess of processed carbohydrates in the diet.
How carbohydrates turn into fat in the body
To understand what exactly happens inside the body, the scientists examined the blood and liver of the mice.
Blood analysis revealed a twofold problem. The level of fatty acids in the blood increased, while the content of essential amino acids dropped sharply. This is understandable, since wheat flour is about 80% carbohydrates and contains very little complete protein. By refusing balanced feed, the mice effectively deprived themselves of a normal source of amino acids.
But the main changes occurred in the liver. Genes responsible for fatty acid synthesis and lipid transport were significantly activated. The liver was receiving a stream of simple carbohydrates and actively converting them into fat. Under a microscope, numerous fat droplets were found in liver tissue — a clear sign that the organ had switched to an intensive energy storage mode.
In effect, the body restructured its entire energy logistics: instead of burning incoming calories, it began storing them. And the trigger for this switch was precisely a diet dominated by refined carbohydrates.
Can weight gain from bread be reversed
There is good news, too. When the researchers removed wheat flour from the diet of the fattened mice, the results were swift. Within just one week, the rapid weight gain stopped, and metabolic indicators began returning to normal. This means that switching from a refined carbohydrate diet to a balanced one can quickly affect weight and metabolism.
Another curious finding concerns differences between sexes. Female mice gained significantly less weight than males on the same wheat diet. Scientists attribute this to the protective effect of the hormone estrogen — it is known to reduce susceptibility to diet-induced obesity.
However, even in the protected females, blood glucose and fat levels still increased. In other words, metabolic stress was present — it just wasn’t as visibly apparent on the outside.
Does this apply to humans or only to mice
It’s important to emphasize that this study was conducted on mice. The human body works differently, and it would be incorrect to directly extrapolate the results to people. The authors themselves understand this.
In the future, we plan to shift the focus of our research to humans in order to verify how applicable the identified metabolic changes are to real eating habits, — stated Professor Matsumura.
The team also intends to study how whole grain products, unrefined grains, fiber, as well as combinations of carbohydrates with proteins and fats, food processing methods, and meal timing affect carbohydrate metabolism.
Different types of bread, from white to whole grain, may affect metabolism differently
Nevertheless, the study raises an important question. For decades, obesity science has focused on fats — high-fat diets were used in most experiments modeling obesity. Meanwhile, billions of people consume bread, rice, noodles, and other refined flour products daily, and the impact of excess simple carbohydrates on metabolism remains far less studied.
This work does not mean that bread should be immediately eliminated from your diet. But it provides a scientific basis for what many have noticed in practice: it’s not just about the number of calories, but about how exactly the body processes them. If further research on humans confirms these findings, it could seriously change the approach to dietary recommendations — from simple calorie counting to considering which specific foods we eat and how they alter our metabolism.
