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Over 30? Here’s What’s Happening To Your Metabolism (It Isn't What You Think)

By Sportitude

You undergo many physiological changes as you age. When you reach 30-something, you may find it more challenging to maintain a healthy weight compared to when you were a teenager or in your early 20s. This can leave you wondering, how do I get a quicker metabolism?

However, a recent study suggests what's happening to your metabolism isn't what you think. Shifting your focus from your metabolism to your muscle mass (along with a nutrient-rich diet and increased physical activity) may be key to supporting your future physical fitness.

Even if you haven’t been lucky enough to win the genetics lottery, you can make healthy lifestyle choices to love your body deep into your 40s, 50s, 60s and so on with a little know-how about your muscle mass, your metabolism and their role in your health.

What is metabolism?

Metabolism refers to the thousands of biochemical processes that continuously occur in your body to sustain life. Every cell in your body relies on your metabolism to function and survive.

Your metabolism is responsible for converting the food and drink you ingest into a usable source of energy to power literally everything you do – from cell repair, hormone regulation, blood circulation and digestion to thinking, breathing and singing your heart out as you listen to your headphones.

Most of us use the term metabolism in the place of what’s more accurately known as ‘metabolic rate’ – a measurement of how much energy (kilojoules in food/drink) your body burns off over a period of time. 

What is your basal metabolic rate?

Your basal metabolic rate (BMR) is a measurement of how much energy your body requires to support basic, life-sustaining functions at rest.

The higher your BMR, the easier it is to maintain a healthy weight without significant physical effort. In fact, the energy you use simply by being alive - from the beating of your heart to your breathing and brain function, contributes to a significantly high percentage (around 65 to 80%) of your overall energy usage, or the total calories burned each day by your body.

Beyond your BMR, there's two other key reasons your body burns up calories, adding up to your total expenditure. For the majority of us, 10 - 30% of your calories burned is to support physical movement, whether you're walking, running, strength training, enjoying yoga, running errands or gardening.

The final 10% (approximately) of calories burned is used to digest, absorb and metabolise your nutrition, referred to as the thermic effect of food.

What are the factors affecting your metabolism?

Your metabolism is complicated and unique to you. There are many factors that affect your metabolism including genetics, diet, hormones, sleep, activity levels and body mass.

Surprisingly, age may not have as strong an influence on your metabolism as once believed. Hitting the big 3-0 isn’t a magic flip switch slowing down your metabolic rate.

A 2021 study suggests that your metabolism peaks when you reach 1 year old, gradually slows as you approach your 20s, then stays relatively stable in your adult life from your 20s to the age of 60. It then gradually declines during your senior years.

Your metabolism may therefore have been wrongfully blamed for weight changes that correspond with aging starting in your 30s or 40s, with age-related muscle mass decline (and potentially a reduction in activity) a more likely culprit.

How does muscle mass change with age?

In your 30s, your pituitary gland in your brain starts decreasing its production of human growth hormone (HGH). It’s particularly important when you're young and developing but also necessary for building and maintaining muscle mass.

After the age of 30, you lose about 3 - 8% of muscle mass per decade. Men’s testosterone levels gradually decline, but usually it’s not until reaching your 40s or 50s that you’ll experience noticeable symptoms including this decrease in muscle mass and increase in fat storage.

For women, reaching menopause in your 40s or 50s triggers one of the most significant hormonal shifts during your life - as oestrogen levels decline, muscle mass decreases and muscle quality drops.

Even though your metabolism may not significantly change during this time, this decreased ability to build new muscle (muscle protein synthesis), along with hormonal shifts that stimulate fat storage are at play. Healthy lifestyle changes may be needed to adapt and stay healthy during these age-related physiological shifts now and in the years ahead.

How is muscle related to metabolism?

Your muscle-to-fat ratio is a key influencer of your metabolic rate. Muscle tissue requires about 3 times more energy to sustain than fat, so the more muscle you have the greater the kilojoules expended at rest and the less likely your body is to store fat in excess.

The increased ability of men to develop and maintain lean muscle mass due to naturally higher testosterone levels, is a key biological difference why men tend to be able to initially lose weight faster than women.

But to keep it in perspective, when weighed up against your life-sustaining organs like brain, heart, liver and kidneys that are constantly functioning to keep you alive, your muscles at rest only burn up a small portion of your daily kilojoules. A combination of positive lifestyle choices in your nutrition and activity levels are key for long-term health.

Quick fix tips to boost metabolism are short term

There's plenty of small lifestyle changes you can make that can increase your metabolism, but it can be challenging to quantify their effectiveness.

This includes turning down the air conditioning to burn calories for temperature regulation in the cool air, enjoying smoothies that are green and lean, or getting your metabolism-boosting caffeine with a morning coffee, green tea or high quality dark chocolate, just to name a few. 

These little changes may help marginally in the short term but let’s look at the big picture to improve your health and mobility as you age.

Muscle mass & metabolism: How to stay healthy as you age

Strength train to build & maintain muscle

Seeing as muscle mass deteriorates with time and inactivity, strength training like dumbbell exercises and kettlebell training are particularly valuable in maintaining muscle mass as we age, even if there is no magic, one-size-fits-all way to dramatically boost metabolism.

You don’t have to be a regular gym goer to do these exercises either. Although heavy lifting and compound movements that activate multiple muscle groups like weighted squats and deadlifts may add to faster muscle gains, more meditative exercises like yoga allow you to apply your own body weight as a strength training tool. Being low-intensity in nature, these exercises help promote strength and flexibility, without excess stress to your joints.

Diversifying your strength training workouts is beneficial to avoid overworking and overtraining particular muscle groups, helping achieve balance in your training. However, the secret to supporting a healthy muscle mass as you age is to find a strength training exercise that you enjoy, whether it's beginner-friendly resistance band exercises or lifting heavy weights.

Does cardio exercise like running speed up your metabolism?

Is it time to say cardio, smardio? No, the advantages of strength training shouldn't mean retiring from fat-burning, heart-friendly cardio exercises like walking, running or cycling.

They won’t result in building as much lean muscle mass compared to strength or resistance training, but performing cardio exercise, particularly those that require higher effort acts as a temporary metabolism booster.

Cardio exercises at lower intensity like slow running or walking won’t continue to speed up your metabolism as long or as effectively compared to HIIT (high-intensity interval training) workouts in the hours post-workout. Therefore, the best way of enjoying the metabolism-boosting benefits of running at a slower pace is to do so regularly.

However, an increase in your metabolism certainly isn't the only reason to enjoy slow running, which makes the benefits of running accessible to everyone. This includes increasing your lifespan, heart health and your mental health.

HIIT – Your #1 time-saving workout to increase metabolism

You may benefit from occasionally trading in your steady, long distance runs that improve your endurance for HIIT workouts (high-intensity interval training).

High-intensity interval training involves short periods of exercise nearly or at the full capacity your body is capable of (e.g. sprinting) broken up by brief recovery periods (e.g. recovery jogs or walking) and can be applied to both your gym sessions and on your runs. You can enjoy HIIT as part of your hill repeats to increase the calorie-burning benefit - sprinting uphill and then walking or jogging downhill to recover.

With these all-in workouts, even after you’ve stopped huffing and puffing your ‘oxygen debt’, or the amount of oxygen and energy required to fuel recovery and return your body into a normal, pre-workout state is considerably higher than it would be for longer, but less physically demanding workouts.

It’s called EPOC (excess post-exercise oxygen consumption), which has a direct relationship with the ability of high-intensity exercise to prolong the metabolism-boosting or ‘afterburn’ effect of your workout. This means that even in the hours after you’ve unlaced your running shoes post-workout, your body continues to burn calories during recovery from the physical activity.

The wrap up

A more muscular, fitter body maintained with regular strength training and cardio exercises like running has multiple benefits beyond increasing metabolism, including keeping your bones strong and heart healthy later in life. Feeling happy and healthy in your body as you age is empowering - whether you're exercising your furry buddy without running out of breath, or lifting up your little athlete confidently and comfortably.

However, it's important to remember when it comes to our metabolism that everybody is different and multiple factors are in play, including those you can control like staying hydrated and eating lean muscle-building protein as part of a balanced, nutrient-rich diet, and those you can’t like genetics.

Your body is unique, but we can all benefit from staying active and committing to healthy lifestyle choices now and in the future – so sweat it up and have fun!

Happy running!

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