George, who is 60, couldn't understand why he was slowly gaining weight. he was eating the same amount of food that he had each day since he was 20 and he exercised regularly. what could explain his weight gain

The reason why George, who is 60, gain weight despite the fact that he was eating the same amount of food that he had each day since he was 20 and he exercised regularly is his metabolism. George's metabolism slowed down by a third between emerging and late adulthood. The metabolism is the rate at which the body burns calories. Slower metabolism means that the body burns the calories slower which lead to weight gain. 

Ithink our serving sizes are larger.