"Numerous aspects of your metabolism play a role in determining whether you lose, gain, or maintain your weight. We all have a distinctive ability to burn energy called basal metabolic rate (BMR). BMR is the minimal rate of energy expenditure the body uses in order to survive and maintain vital functions in the body. Resting metabolic rate (RMR) takes into account BMR and any additional energy used during activities of daily living such as eating, digestion, sitting, or standing. Exercise metabolic rate (EMR) refers to the energy that is expended during exercise or physical activity. A person’s metabolic rates can change throughout one’s lifespan and can be affected by puberty, hormonal changes, age, and physical activity. Unfortunately, our metabolism naturally slows down as we age, making it much more difficult to lose weight at middle age. A slower metabolism, combined with age-related muscle loss known as sarcopenia, family obligations, and long work hours, all contribute to gradual weight gain in middle-aged adults."