About 2% to 3% of people in the U.S. and Europe are underweight, and some of them struggle to gain weight no matter how much they eat.

In addition to genetic factors, high basal metabolic rate (BMR) is one of the main reasons why it is difficult to gain weight.

Even if you lie still, the body needs to consume calories to maintain blood circulation, breathing, heartbeat and other basic physiological activities, which is the basal metabolism.

The energy consumed by basal metabolism accounts for 60% to 75% of the total body energy, while the energy consumed by physical activity only account for 10% to 30% of the overall.

The Higher the Basal Metabolism (BMR), the Less Likely It is to Gain Weight.

Studies have shown that 1 kg of human muscle can consume 90 to 100 calories per day, while 1 kg of fat can only consume 5 to 10 calories.

For example, I have 10 pounds more muscle than you, which means I can eat one more burger a day than you without gaining weight.

In short, the higher the proportion of muscle in the body, the higher its basal metabolic rate. Some people's basal metabolic rate may be 40% to 50% higher than the average person, and these people are not prone to gain weight.