You gain weight as you get older because your metabolism slows down

This is like saying, ‘You go into debt as you get older because your pension is lower than your previous wages.’

As long as the amount of fuel you ingest is in line with the energy your body uses up, you don’t put on weight. When you start finding yourself gaining weight, it’s time to adjust either the number of calories you take in or the amount of energy your body uses, to regain the balance and put a stop to the weight gain. This is true for people in any life situation, whether the imbalance is due to a career change into a less physical job, a busier job with less time for physical exercise, or any other factor that alters the body’s energy needs.

It’s also a myth that increased age must necessarily cause the body’s metabolism to slow down. It is true that, statistically speaking, it happens, which explains why the calculated bodily energy requirements produced by some websites and apps go down as the entered age goes up. But the reason for this is not connected to any biological condition, it’s just the result of statistical observations related to the fact that, on average, most people become less active when they get older, their muscle mass is reduced, and their general lifestyle means they have a reduced energy requirement. As early as 1977, Tzankoff and Norris were able to confirm the theory that age-related drops in the body’s energy needs can be explained almost completely by the loss of muscle mass. And in 1991 Vaughan et al. once again confirmed those results with a study that compared the energy expenditures of older and younger test subjects. On average, the older subjects had less muscle mass, as well as a higher proportion of body fat and lower energy consumption. However, when seen in proportion to their body mass, their energy consumption was no lower than that of the younger subjects. And so, once more, the deciding factor was not age, but physical activity and muscle mass.

Therefore, if you build up muscle mass or maintain existing muscles with weight training later in life, there is no reason why you should necessarily require less energy than you did when you were younger. But it should be said that it becomes increasingly difficult to develop muscle mass as we get older, so it’s a good idea to build up reserves early, so that they can be maintained with increasing age.