The role of age and genetics

How much a person weighs depends in large part on four things:

• Calories taken in each day.
• Calories burned off each day.
• Age.
• Genetics.

Eating and drinking more calories than you burn each day leads to gaining extra weight, including belly fat.

Getting older also plays a role. You lose muscle as you age. And muscle loss is worse if you are not physically active. Loss of muscle mass slows down how quickly the body burns calories. That can make maintaining a healthy weight harder. For example, when men are in their 50s, they need fewer calories a day than they do when they are in their 30s.

Your genes can contribute to your chances of being overweight or having obesity too. They also play a role in where the body stores fat.

Although people who smoke cigarettes tend to weigh less than people who don't, people who smoke tend to carry more of their weight as belly fat.