So what causes downwards trends in your Metabolic Rate:
Children’s per body weight kilo metabolic rate is about 200% that of adults. Because they have a much higher proportion of their body composition made up metabolically active tissue (heart, lungs, kidneys, brain etc) in comparison to adults, are undergoing the demands of growth and simply having a more active lifestyle kids have a much higher metabolism than grownups.
However as growth finalises getting and we get older the proportion of metabolic active organs to our body composition drops. This alone means that our RMR decreases. Your RMR drops round about 25% between the ages of 6 and 18 as your adult proportions are reached and growth slows and eventually halts.
After age 18 your RMR decreases at least 2-3% for each decade that follows. (Many researchers put this figure even higher if you live the typical Western lifestyle.) By the time you have hit 40 your RMR is usually more than 40% less than it was as a child.
So this drop in RMR is coupled with an increasing loss of fat-free lean body mass as we take on adult, ‘real life’ responsibilities and move less, exercise less, eat metabolism slowing foods and eat more than our slowing RMR demands. Usually we eat more ‘on the go’, less regularly and the wrong foods with a lower TEF – so this compounds the RMR dropping effect.
So as we age we experience a lower RMR, lower TEF, and less TEA – these all combine to create a less lean, fatter, less metabolically active environment for our bodies. Even worse because these changes are gradual our bodies accept them and then strive to maintain them via a state of homeostasis.
Face it – by the time we are in our 40’s, if not before, most of us are well on the way to a future of not moving well, having larger fat stores than is good for our health and in fact be starting to experience firsthand some of the myriad health issues that our Western lifestyle is rife with.
So does Metabolism slow down or do we?
The answer is both.
As we age we certainly move slower as the ability to contract our muscles lessens and undertake less physical activity.
The slowing of your metabolism is real. Our cells have miniature ‘furnaces’ in them called mitochondria. These mitochondria burn the fuel supplied to them and as we get older they become less & less efficient at burning fuel and recent research suggests that their numbers also decline as we age. This leads to a slower metabolic rate not just at rest but also for all activity.
Next we have a delightful process called sarcopenia, which is a fancy name for muscle wasting. Once past the age of 50 our ability to retain muscle tissue in the face of poor nutrition and lack of exercise diminishes rapidly. Again since muscle burns more energy than fat, this means the metabolism slows down. This means it is harder to burn off a cupcake when you are in your twenties than it is in your sixties!!
Lastly being overweight slows metabolism because overweight people burn fat even less efficiently. Add these together as the years go by, and it is little wonder that we get fatter, less lean and that the inches start to get more & more numerous around your waist.
Take Away: Your Metabolism slows as you age – especially if you follow the typical Western lifestyle & diet.
Part 9 next week!! Don’t forget to browse the blog backlog – lots of good info hiding there!!