Final answer:
BMR decreases by roughly 2 percent per decade after the age of 30 due to changes in body composition, particularly the loss of lean muscle mass. This effect can be compounded by reduced physical activity and dietary factors.
Step-by-step explanation:
Basal Metabolic Rate and Age
The Basal Metabolic Rate (BMR) tends to decrease with age. After the age of 30, the metabolic rate is known to decrease nearly 2 percent per decade. The change in BMR is primarily due to alterations in body composition, such as reduced lean muscle mass, which are mostly responsible for the decrease. This reduction in muscle mass is significant between the ages of 50 and 70. Such decrease in muscle mass leads to reduced physical activity and can create a positive-feedback cycle where less physical activity leads to even more muscle loss, further slowing down the metabolic rate.
Factors like gender also play a role, as men generally have a higher BMR due to greater muscle mass and a lower body fat percentage compared to women. Additionally, diet plays a role; starvation or drastic calorie reduction can significantly lower BMR. As for the initial question, it's important to note that the BMR decreases by about 2 percent per decade after the age of 30.