Repeated cycles of intentional weight loss followed by weight regain are linked to poorer metabolic health in young women, according to a new study from researchers at the State University of Campinas.
The study, published in Nutrition Research, examined 121 women ages 20 to 41 with a wide range of body mass index values. Researchers compared women with no history of weight cycling with those who reported at least three episodes of intentional weight loss followed by unplanned regain of 4.5 kg or more within the previous four years, a pattern often associated with restrictive dieting.
Women with a history of weight cycling had higher overall body fat, greater accumulation of visceral fat and less favorable cardiometabolic indicators, including blood glucose and lipid measures. They also showed lower activity of brown adipose tissue, often referred to as brown fat, which plays a role in glucose and lipid metabolism.
Brown fat differs from white fat in that it burns energy to generate heat rather than storing it. For many years, it was thought to exist only in newborns, but research over the past decade has shown that adults also retain brown fat, particularly in areas such as the neck and upper chest.
To assess brown fat activity, participants underwent controlled cold exposure while researchers used infrared thermography to measure temperature changes in the supraclavicular region. Higher temperatures in this area indicate greater brown fat activation.
At first glance, the results suggested that repeated weight cycling directly reduced brown fat activity. However, when researchers performed more detailed statistical analyses, that relationship changed. The reduction in brown fat activity was largely explained by higher levels of body fat rather than weight cycling itself.
“The yo-yo effect probably acts indirectly,” said Ana Carolina Junqueira Vasques, who supervised the study. “Over successive cycles of weight loss and regain, there’s a progressive worsening of body composition, with recovery predominantly of fat and not muscle mass.”
The findings help explain why repeated dieting can have lasting metabolic consequences. Each period of restrictive weight loss can trigger biological adaptations that reduce energy expenditure, alter hunger and satiety hormones and favor the regain of fat rather than lean tissue. Over time, this pattern may contribute to higher visceral fat levels, which are closely linked to metabolic risk.
The researchers emphasized that brown fat should not be viewed as a weight loss tool.
“Its most relevant role is improving glucose and lipid metabolism and helping protect against diabetes and cardiovascular disease,” Vasques said.
The study was observational and relied on self-reported dieting history, meaning it cannot establish cause and effect. The sample size was modest and limited to young, premenopausal women, so the findings may not apply to men or older adults.
Still, the results add to a growing body of research suggesting that obesity treatment strategies should focus less on repeated short-term weight loss and more on long-term body composition, muscle preservation and sustainable behavioral change.
This research was supported by public research funding agencies in Brazil, including the São Paulo Research Foundation and the National Council for Scientific and Technological Development. Additional institutional support was provided by research centers at the State University of Campinas.