On average, 1 pound of muscle would burn between 7 and 10 calories, while 1 pound of fat can only burn 2 or 3 calories. As we get aged, the loss of muscles also leads to a decrease in our body’s calorie-burning power. At the age of 70s, the resting metabolism might be around 15% slower than it was in your 30s. This means you would consume fewer foods without gaining weight. Though building new muscles could help reverse this trend, it is also significant to engage the muscles that you currently have.