body size and composition
if you weigh more or have muscle mass,you will burn more calories, even at rest. So people who weigh more are more likely to have a faster metabolic rate not a slower one because a portion of excess weight is muscle tissue
Gender
if you’re a man, you probably have less body fat and more muscle mass than does a woman of the same age,so you burn more calories.
Age
as you get older, your muscle mass decreases, which slows down the rate at which you burn calories
Genetic
Genetic also play or role in whether you have a slower or faster metabolism and some genetic disorders can also affect your metabolism.
Diet
certain aspects of your diet can also affect metabolism for instance if you don’t have enough iodine for optimal thyroid function it can slow down your metabolism.
Muscle mass
Muscle requires more energy to function than fat. so the more muscle tissue you carry the more energy you body needs just to exist. while most forms of exercise will help boost muscle,resistance or strength training is most effective
Hormonal factors
hormonal imbalances caused by certain conditions, including hypo and hyperthyroidism can affect your metabolism
Environmental factors
the weather can also have an effect on your metabolism if it is very cold or very hot your body has to work harder to maintain it’s normal temperature and that increases the metabolic rate
Health tips 