A hormone released by the body during fasting may discreetly safeguard some women from gaining weight after menopause—but that natural protection may fade once early metabolic problems occur, according to new research from the United States. Scientists say the discovery underscores a critical "window of opportunity" for women to prioritise metabolic health before the body's natural weight-regulating machinery fails. 

Researchers at the University of California, Irvine, discovered that greater levels of the hormone asprosin were associated with considerably decreased long-term weight gain in metabolically healthy postmenopausal women. The study, published in the Journal of Nutrition, suggests that the hormone may play a significant role in helping the body maintain weight balance in the years following menopause. 

The researchers looked at health data from more than 4,000 women who took part in the Women's Health Initiative, which is one of the biggest long-term studies of women's health in the world. Researchers studied people between the ages of 50 and 79 for several years to find out how hormones affect weight fluctuations after menopause, a time when many women gain weight quickly and are more likely to get type 2 diabetes.

Menopause can cause weight gain because hormonal changes reduce metabolism and alter how the body stores fat. This increases the risk of illnesses including heart disease and diabetes. Scientists have long assumed that hidden biological signals throughout the body influence this process, although the precise mechanisms remain unknown. 

The current study focuses on asprosin, a hormone produced mostly by adipose tissue when the body is fasting. In layman's terms, it functions as part of the body's internal communication system, signalling the liver to release sugar into the bloodstream for energy and sending instructions to the brain that affect appetite. 

To determine whether asprosin influences weight gain over time, researchers examined hormone levels in blood samples acquired between 1993 and 1998 before tracking changes in body weight, body fat, and muscle composition over a three-year period. Some participants got enhanced body fat scans, allowing scientists to precisely assess fat and lean muscle. 

The findings indicated a striking pattern. Among women without obesity or diabetes at the start of the research, those with the highest asprosin levels gained significantly less weight over three years than those with the lowest levels. In fact, they were 43% less likely to gain substantial weight and 83% more likely to lose significant weight. 

However, only women with intact metabolic health showed the protective effect. When problems, such as insulin resistance—a situation in which the body stops responding correctly to insulin—develop, the hormone's signalling system appears to deteriorate. 

"Our findings show that asprosin may help us track and potentially treat weight changes in postmenopausal women," said Simin Liu, head and distinguished professor of epidemiology and biostatistics at the University of California, Irvine's Joe C. Wen School of Population and Public Health. "Understanding the hormonal factors that influence weight after menopause may help us develop more precise strategies for lifestyle management or pharmacologic interventions that prevent obesity and related metabolic disorders while preserving healthy muscle mass." 

Researchers identified an important nuance: some of the weight loss reported in women with greater asprosin levels was from lean muscle mass rather than fat, emphasising the need for strength-building activity as women age. 

The National Institute of Diabetes and Digestive and Kidney Diseases, as well as the National Heart, Lung, and Blood Institute, sponsored the study. 

According to scientists, the discovery could potentially lead to novel hormone-based treatments for obesity, similar to how medications that target appetite hormones are now used to lose weight. However, they caution that the study's most important lesson is preventive. 

When early diabetes or severe metabolic disorders develop, the body's natural hormonal signals may stop functioning properly. That means that the first few years after menopause may be essential, as maintaining a healthy weight, diet, and physical activity may assist in protecting the body's natural metabolic defences. 

Further research will look into whether altering asprosin levels could one day be used as a targeted method to avoid obesity and diabetes in older women.