You would give up just about anything to be the same weight you
were when you were younger, right? Believe it or not, you need
not give up too much. But you do need to make some changes,
which may actually be easy to do. Although metabolism plays a
large role in controlling weight, it can't take all the blame.
Genetics play a role, too. But genetics are predetermined, and
cannot be changed. Lifestyle is not predetermined and can be
modified. Metabolism is the amount of energy—in this case,
calories—that the body burns to maintain itself. You're always
burning calories, even when you're sleeping. Your basal
metabolic rate (BMR) is the number of calories your body uses at
rest. How many calories you burn depends on your BMR, exercise,
and the body's muscle-to-fat ratio. Muscle cells burn more
calories than fat cells. Muscular people, with less body fat,
have a higher metabolism. Everyones BMR is different. It depends
on genetics and other factors. Changing with age After the age
of 45, it is estimated that the