Metabolism and weight

You might want to blame a medical condition for slow metabolism and weight gain. But rarely does a medical condition slow metabolism enough to cause a lot of weight gain. Conditions that can cause weight gain include Cushing syndrome or having an underactive thyroid gland, also known as hypothyroidism. These conditions are uncommon.

Many things affect weight gain. These likely include genes, hormones, diet and lifestyle, including sleep, physical activity and stress. You gain weight when you eat more calories than you burn — or burn fewer calories than you eat.

Some people seem to lose weight more quickly and more easily than others. But everyone loses weight by burning more calories than are eaten. The bottom line is calories count. To lose weight, you need to eat fewer calories or burn more calories through physical activity. Or you can do both.