Starting at age 35, losing weight can become more challenging due to changes that occur in the body over time. A study published in the journal Science, with 6,421 participants from 29 countries, aged between eight days and 95 years, showed that the adjusted metabolic rate remains relatively stable between 20 and 60 years. During this period, however, changes in body composition, especially the reduction of muscle mass, can influence the way the body uses energy and responds to the weight loss process.
Body fat distribution also reorganizes with aging. Researchers at City of Hope, in the United States, identified in a study released in 2026 a type of stem cell that begins to produce new fat cells in the abdominal region in midlife. The finding helps understand why the waist tends to grow even when total weight varies little.
The topic gains relevance as obesity is recognized as a disease.
