It is a well established fact that in the general population, body weight and body mass index (BMI) increases during adult life, with the peak BMI reached around 60 years of age.
So why do we tend to carry more excess weight as we get older? Does metabolism slow down as we age?
The short answer to this question is, Yes.
The long answer: Yes – and the decrease in metabolism may start sooner than you think.
In fact, after age 20-30, lean body mass (muscle tissue) starts to decrease, which is partly due to the natural aging process, and also due to the fact that adults tend to become less and less physically active with time.
All three components of energy burn decrease with age:
- Resting Metabolic Rate (RMR), which is the calories we burn for maintenance of bodily functions (at rest) decreases 2-3% per decade after age 20. For a 70kg individual, this results in a 50 kcal per day decrease in energy expenditure per decade, which equates to about 5 pounds (about two and a half kg) of weight gain per year.
- Physical activity markedly declines for most adults, and may account for as much as half of the decrease in total energy expenditure.
- The energy we burn digesting food (called the Thermic Effect of Food) decreases as we age as well.
(Sidebar: After age 60, body weight and BMI in general begins to decline, due to a combination of a progressive decrease in muscle mass, decrease in appetite, and concomitant illnesses, amongst other factors.)
So, how can we combat the age-related decrease in metabolism that starts in early adulthood?
Well, the most important thing we can do is to stay active – both in our daily life activities (eg walk instead of driving), and also in focussed exercise. Studies show that while both are important, it may be easier to maintain daily life activities over the long term (vs focussed exercise) – for example, if you build it in to your life that you take public transit to work (which almost always involves walking) instead of driving, that is something that is more likely to be maintained in the long term (eg if you haven’t built a parking pass into your budget, you just don’t have one, and you have to take transit to work).
Focussed exercise is still very important, however, and should be a combination of aerobic activity as well as muscle strengthening – remember that a pound (or kg) of muscle on your body burns 2-3 times more calories at rest than a pound (or kg) of fat. Studies show that accessibility to exercise equipment is an important predictor of long term adherence to an exercise program – in particular, having the ability to exercise at home rather than having to go to a gym to sweat it out. This can be as complex as having a home gym, but can also be as simple as having a pair of sneakers and a safe place to go for a walk every evening (though in some communities, this can unfortunately be a challenge).
Be sure to talk to your doctor before embarking on any new activity/exercise program.
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