At first, aging is commonly perceived to slow your metabolism down, making weight gain easier and weight loss harder; but according to a new international study of 6,421 participants aged from 8 days old up to 95 years living across 29 countries and their total energy expenditure (TEE), their metabolic rates didn’t differ much between childhood and middle adulthood even when accounting for body size changes.
TEE (thermic energy expenditure) refers to how much fat and muscle you have on your body, along with your level of physical activity, that determines your daily calorie burn. Scientists use TEE as the main metric to assess an individual’s daily energy expenditure.
As people get older, their TEE declines slowly over time – only decreasing by around 1% annually as predicted by researchers who expected more rapid decline.
Furthermore, this study finds that as people age their muscle mass declines while fat-free mass increases. This finding contradicts popular beliefs regarding metabolism and aging.
These findings further substantiate the idea that an “aging metabolism” may be more caused by overeating and leading a sedentary lifestyle than by changing muscle mass or slow metabolic processes. As people age, their bodies become resistant to growth signals which leads to imbalanced cell growth/breakdown processes (anabolism/catabolism), leading to weight gain.