Do you remember the days when you could eat and drink anything you wanted and still not put on weight? Then sometime in your thirties, things changed and you seemed to be able to put on weight just by thinking about food. What happened? For starters, you probably became less active in general so you burned less energy on a daily basis than before, but more importantly, you started to lose muscle. As we age, we have a natural tendency to lose muscle, a process called sarcopenia. In the absence of any resistance training, we will lose roughly 0.5-1% of our muscle mass per year after the age of 25. So, if you were a fairly trim 65kg in your early 20s, by the time you reached 35, assuming you hadn’t been doing much strenuous activity, you would have lost around 3 kilograms of muscle.
Who cares, you say, I didn’t really need all that muscle in the first place. But the problem is that muscle is incredibly metabolically active. We use between 60 to 200 calories per day just to keep one kilogram of muscle alive. So if you lose 3 kilograms of muscle, even using conservative estimates, your daily calorie requirement would have declined by around 180 calories. And if you kept the same diet (and calorie intake) which was keeping you trim in your 20s, you would now be putting on one kilogram of fat every two months. Bummer.
Putting on muscle is not easy. Your ability to put on muscle is determined primarily by your hormone levels, particularly testosterone and human growth hormone. But more importantly, putting on some muscle (assuming we can achieve this) is the only way to counteract the natural process of sarcopenia and restore metabolic rates to youthful levels, which is the real key to long-term sustainable fat reduction.
Why not just use cardio exercise, like jogging, to burn off a few hundred extra calories per day? Well, you could do that, and it may have some short-term benefits, but the problem with an exercise programme which is dependent purely on cardio is that it may actually accelerate muscle atrophy and reduce your metabolic rate further. Cardio training can produce an increase in the size of your slow-twitch muscle fibres (the fibres in your muscles responsible for low-intensity steady state exercise). But, the minimal recruitment of the fast twitch muscle fibres combined with the fact that cardio training tends to involve prolonged periods of exertion can result in a breakdown of your fast-twitch muscle fibres (the fibres responsible for explosive, powerful movements) – your body effectively sees these muscle fibres as dead weight which can be used for fuel instead.
Lifting weights is not just for meatheads. There are sound physiological reasons why everyone should engage in some resistance training in order to prevent the natural wasting of muscle as we get older. The good news for people who don’t enjoy lifting weights is that it need not even take up much time in order to be effective (a 15-minute resistance workout per week is sufficient to maintain or even slightly increase muscle mass provided it is of sufficient intensity). Not a bad return on your time investment considering the benefits!