AND this statistic is averaged across the usual sedentary population, so keep this in mind: the average person doesn't actively exercise to maintain their muscle mass as they age. And it's a known fact that you WILL lose muscle as you age past 20 if you don't intervene. When this is taken into account, those whopping 6 calories being lost can pretty much be accounted for by people atrophying muscle. In other words, you can maintain or even build your metabolism up as you age if you incorporate regular resistance training and consume adequate protein in your diet. No excuse to be a ham for sure.