Many people try to lose weight more than once in their lives. They diet, lose weight, then slowly gain it back. This pattern is often called the “yo-yo effect.”
A new study from Brazil now suggests that this repeated cycle may have lasting effects on women’s metabolism, even at a young age.
The research shows that the real problem may not be weight change alone, but the slow buildup of body fat over time and the damage it may cause to the body’s ability to burn energy.
The study was carried out by researchers at the State University of Campinas, also known as UNICAMP, in São Paulo. It was conducted at a research center that focuses on metabolism and diabetes and was published in the journal Nutrition Research.
The team studied how repeated dieting affects something called brown fat, a special type of body fat that helps burn calories and supports healthy blood sugar and fat levels.
Most people are familiar with white fat, which stores extra energy and increases body weight when it builds up. Brown fat works very differently. Instead of storing energy, it burns sugar and fat to produce heat. This process helps the body use more energy and supports metabolic health.
Brown fat contains many mitochondria, which are tiny structures inside cells that produce energy. These mitochondria give brown fat its darker color and its powerful ability to burn fuel.
For many years, scientists believed brown fat only existed in babies and helped keep them warm. That idea changed in 2009, when studies showed that adults also have brown fat.
In adults, it is mainly found in areas such as the neck, above the collarbone, and near the spine. Since then, scientists have been very interested in brown fat because of its possible role in protecting against obesity, diabetes, and heart disease.
In the UNICAMP study, researchers examined 121 women between the ages of 20 and 41. The women had different body weights and body mass index levels. They were divided into two groups. One group had no history of repeated dieting.
The other group, called “cyclers,” included women who had gone through at least three cycles of planned weight loss followed by unplanned weight regain of more than four and a half kilograms over the past four years. This pattern often happens after strict or restrictive diets.
The researchers chose to study only women for several reasons. Women and men differ in how much brown fat they have and how active it is.
The study also focused on women who had not reached menopause to avoid the effects of hormonal changes on fat distribution. In addition, women often face stronger social pressure about body shape and weight, which makes repeated dieting more common.
To measure brown fat activity, the women took part in a carefully controlled cold exposure test. Cold is known to activate brown fat. First, participants stayed in a warm room.
Then they moved to a cooler room set at 18 degrees Celsius. This temperature was cold enough to activate brown fat but not cold enough to cause shivering, which would increase energy use in other ways.
While the women were in both environments, researchers used a special infrared camera to measure heat changes in the neck and upper chest area. Warmer colors in these images showed higher brown fat activity.
The researchers also measured body fat percentage, visceral fat around the organs, blood sugar levels, blood fats, and blood pressure.
The results showed clear differences between the two groups. Women with a history of repeated dieting had more total body fat, more fat around their internal organs, and worse markers of metabolic health.
They also showed lower brown fat activity. At first, it appeared that the yo-yo effect itself directly reduced brown fat function. However, deeper analysis revealed something more important.
The researchers found that repeated dieting harmed brown fat mainly by increasing body fat over time. Each cycle of weight loss and regain made the body more likely to restore fat instead of muscle.
The body reacts to restrictive dieting by lowering energy use, changing hunger hormones, and becoming better at storing energy. When weight returns, it comes back mostly as fat. Over time, this extra fat is linked to lower brown fat activity.
From a medical point of view, this study shows that focusing only on weight loss may not be enough. Losing weight quickly and repeatedly without preserving muscle may slowly worsen metabolic health.
The findings suggest that long-term strategies should aim to reduce body fat in a steady way while keeping muscle mass and supporting healthy habits.
Although brown fat cannot be measured in routine medical exams, its activity is closely linked to better control of blood sugar and fats in the blood. The researchers stress that brown fat should not be seen as a magic solution for weight loss. Its main value lies in protecting against diabetes and heart disease.
When reviewing and analyzing these findings, the study adds strong evidence that repeated restrictive dieting may quietly harm metabolism even in young women. The research highlights that the true risk lies in gradual fat accumulation rather than short-term weight changes.
It also reinforces the idea that sustainable, balanced approaches to weight management are safer and more effective than repeated cycles of strict dieting. While the study focused only on women in Brazil, its message is widely relevant and supports a growing shift in obesity care toward long-term health rather than quick results.
If you care about weight loss, please read studies about orange that could help obesity, and a berry that can prevent cancer, diabetes and obesity.
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