How Your Metabolism Changes with Age

Like so many other things in the body, metabolism undergoes some serious changes as we get older. Don’t panic! It’s normal, manageable and totally not the end of the world, with just a little understanding of a) what your metabolism is and b) what happens to it over time.

First off, the fear instilled in your kid-self by your great aunt about never being able to eat carbs after the age of 25 isn’t true. You are not doomed to a life of muumuus and carrot sticks from middle age and beyond just because your body will no longer burn calories efficiently.

How Your Metabolism Changes with Age

(But if you love muumuus and carrot sticks, by all means, go for it.)

So what is your metabolism, anyways, apart from that thing we’ve learn to stress over endlessly (or blame for all kinds of things)? Here’s a quick run-down so we’re all on the same page:

What is metabolism?

Metabolism is the process by which the body converts the energy from food into useable energy for cells, which power everything in the body from thinking to organ function to movement to respiration. The energy derived from food is what we refer to as calories (one calorie is equivalent to the amount of energy required to raise the temperature of water one degree).

Metabolism involves both breaking down chemical bonds in food to release energy (“catabolism”) and storing energy as chemical bonds, like those in carbohydrates and fat, for later use (“anabolism”). We eat, the food is broken down, energy is extracted, energy is used, energy is stored as fat and so on.

The rate at which we burn through energy and the rate at which we accumulate storage relies on a number of factors, from body composition to the types of food we eat to how active (and what kind of active) we are.

So how does this process change as we get older (and what does that mean for our bodies)?

Your metabolism in your 20s

Typically, your metabolism through your mid-twenties should be about the same as your late teenage years. With growth and muscle development characteristic of this time, we have more cells actively burning calories: the more muscle mass and “less metabolically active fat” we have, the more calories we burn in a day. Plus, we continue to build bone until the age of 25, which requires additional energy.

As you approach your late 20s, roughly a decade out from your late teens, you may start to notice that how you eat and how you exercise change how your body feels, especially energetically. By your late 20s, you may undergo up to a 2% decrease in metabolic activity.

The reason for this? Even this early in life, we start to lose fat free mass (muscles and organs) and gain incremental amounts of that less metabolically active fat. This means we have fewer cells burning as efficiently, so the rate at which we utilize food energy decreases a tiny bit while the rate at which we store it increases a tiny bit.   

To combat this, it’s important to work strength and resistance training into your workout routines. Weighted movement helps build muscle, increasing the number of high-powered muscle cells in your body, thereby increasing your basal metabolic burn. Plus, strength training is a terrific complement to any fitness regimen (and ClassPass has tons of options to keep it interesting and varied).

Your metabolism in your 30s

The typical human body will start to reduce muscle mass around the age of 35 (eek!). Because body composition plays such an important role in how quickly and efficiently the body uses energy, the decrease in muscle mass common to the mid-30s years can noticeably change your metabolism. With less muscle and more fat comes the sad truth that the body requires fewer calories to maintain the same weight.

According to experts, when you don’t use and develop muscular strength, you’re effectively telling your body you don’t need to use those cells to burn energy and instead the body will store that potential energy as fat.

Plus, by the time you’re in your 30s, you’re no longer producing as high of levels of Human Growth Hormone (HGH) as you were in your 20s, which further decreases metabolism.

Good news, though: strength training will help maintain (and increase) muscle mass and bone health, as well as increase your HGH levels, all of which will contribute to raising metabolism. Ensure, too, that you get enough rest to allow your body to regenerate and utilize excess energy.

Your metabolism in your 40s

By 40, your cells aren’t regenerating as quickly, which could mean that even with all of your great efforts to build muscle by strength training, you might not be getting as intense returns for your efforts (sigh). But never fear! Training is still valuable: you should definitely keep it up!

Know, too, though, that the ongoing decrease in super-powered-muscle-and-organ-cells has continued for twenty years and that will further impact your caloric needs. To maintain the same weight you saw on the scale at 25 when you’re 40, it’s likely you’d need to adjust your food intake (around 200 calories less per day) and up your workouts (up to 2-3 times more minutes each week). The exercises that worked for you 15 years ago might also be different at this point, so experiment with a combination of cardio, strength and HIIT to see what works best for your unique body.

As you approach menopause, you may also notice more body fat settling around your middle: this is entirely normal and a response to changing estrogen levels, but these added fat cells slow down metabolism even more.

To avoid sending your metabolism into panic mode, it’s key to avoid yo-yo dieting and to remember to eat every 4-5 hours to keep your blood sugar levels stable. Keep moving. Lift things. Rest. Don’t stress out. Just do the best you can for your body and pay attention to what keeps you feeling best.

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