High metabolism across the ages

Written adaptation of episode #82 of Fit Body, Happy Joints: How to keep your metabolism high as you age by Dr. Shannon Ritchey, PT, DPT

How often do we hear someone in their 30’s, 40’s and beyond tell someone in their 20’s:

“What I would give to have my old metabolism back and eat whatever I want”

Or something that I heard over and over when I was younger:

“Enjoy that donut while your metabolism is high.” 

I think we could have an entirely different conversation about those comments and our trained thoughts about food. Let’s focus on metabolism as you age, and what current science is saying that metabolism as you age. 

The belief that a declining metabolism is an inevitable part of adulthood causes people to feel helpless and that they can’t do anything about it.

But what does the current evidence say?

Emerging evidence shows that a decrease in metabolism isn’t an inevitable part of adulthood, at least in early adulthood from ages 20-60ish. 

A study released in August 2021 by Herman Pontzer demonstrated that when you account for lean mass, metabolism:

• stays stable from ages 20-60, and
• declines about .7% each year after the age of 60. 

Let’s go over this study a little deeper. 

The researchers studied over 6,000 participants, 64% of them female, between the ages of 8-95. 

They used the doubly labeled water method, a technique that is considered the gold standard for measuring how many calories one burns throughout their day. This includes all the activity of their cells, otherwise known as their total daily energy expenditure (metabolism). 

This accounts for:

• digestion
• thinking
• fidgeting
• moving around
• exercise
• any other process your cells have to do to keep you alive

This study found that TDEE was:

• highest before the age of one
• slowly declined throughout childhood
• plateaued and stayed steady from the ages of 20-60ish
• slowly declined about .7% per year after the age of 60-ish

But people DO tend to gain weight as they age. This study demonstrates that it’s not because of a decrease in metabolism. 

This study kept lean mass constant. So if a 60 year old had the same lean mass and body size of a 20 year old, their metabolic rates would be roughly the same. 

I can hear you asking

“but what about menopause?” and 

“what happens after the age of 60?” 

Hang tight until the end for your answers!

So what might contribute to this weight gain?

The researchers still have things to uncover. But there can be some pretty convincing reasons why you seem to gain weight as you age. Let’s talk about the potential reasons for age-related body composition changes.

One hypothesis is because of sarcopenia. A second is because of a tendency to decrease activity as you age. Another points to changes in stress levels and/or nutrition that affect lifestyle and body composition. A different hypothesis is that weight gain can creep up slowly (it isn’t hard to gain a couple of pounds/year).

Sarcopenia

Let’s focus on sarcopenia, or age-related muscle loss. Because fighting against sarcopenic changes is one of the most powerful things we can do for ourselves. Counteracting sarcopenia can help improve longevity and keep our bodies super healthy and aging well. 

We tend to lose between 3-8% of muscle mass per decade after the age of 30.

When you have less muscle, your metabolic rate declines. You may find that as each decade goes on, your body composition changes. A large reason for this could be because you aren’t consciously trying to build or maintain muscle.

Let’s talk about the power of muscle as it relates to your metabolism.

Muscle is very metabolically active. So the more muscle we have, the more we burn. 

Focusing your sessions on building muscle, regardless of the calories you burn in the workout itself, is the best way to facilitate glucose transport, avoid gaining fat, and improve your insulin sensitivity. This improves your body’s ability to use fat as fuel.

It also helps prevent age-related diseases that seem to be associated with insulin resistance like dementia, Alzheimer’s, diabetes, heart disease, PCOS, and much more. 

I interviewed Dr. Ben Bikman, a metabolic scientist, on my podcast. In our conversation, he emphasized the importance of being insulin sensitive because insulin affects every cell in our bodies. So logically, being more insulin sensitive will improve the health and longevity of our entire system. 

There are obviously nutritional aspects to improving insulin sensitivity, but a powerful way to improve insulin sensitivity is to build muscle. 

Fitness culture obsesses over what we are BURNING, instead of focusing on what we are BUILDING. And we are potentially setting ourselves up for long-term issues.

Constrained Total Energy Expenditure and its effect on metabolism

Research shows that exercise does not significantly increase caloric deficit due to a phenomenon called constrained total energy expenditure, coined by the same researcher, Herman Pontzer. 

We used to think that energy expenditure was additive; the more exercise we do, the more we burn, the quicker our fat loss. 

But in reality our bodies adapt to our routines, stabilize our energy expenditure, and keep us within a narrow window of calories burned within a week period. 

So if you burn more in your workouts, you aren’t significantly contributing to your deficit. Your body is downregulating other energy, using processes like fidgeting, digestion, and more, to keep you within this narrow window. 

In fact, exercising just to burn calories may be DECREASING our muscle mass, since your body will break down unused tissue for energy, regardless of if it’s muscle or fat. 

We’ve been looking at exercise all wrong.

And potentially doing our population a disservice by teaching people to burn, burn, burn. Not only are they losing muscle due to natural aging, but they are accelerating that muscle loss with lots of cardio and exercise that isn’t intentionally loading and causing muscles to increase in size and strength.

What CAN exercise do for our metabolism?

The act of exercising isn’t great for fat loss in the sense that we shouldn’t focus on what we are burning. But what exercise CAN do is improve metabolic processes like your glucose transport and regulation and insulin sensitivity, ultimately improving your metabolism.

Let’s discuss how this can affect your body.

You store the food you eat via glucose or energy in three storage units. 

• Liver
• Muscle
• Fat

When you eat, food breaks down into glucose and travels to the tissues of your body via your bloodstream (aka blood sugar). 

An increase in blood glucose triggers insulin, which is a hormone that you can think of like a key. Insulin is the key to unlock the storage units (liver, muscle, fat) to let glucose in and save it for later to power your movements, fuel digestion, keep your brain sharp, etc. 

Liver

The liver is the first place that glucose is stored. It has a limited storage capacity, and to my knowledge, you cannot increase the storage unit size.

When the liver is full, the next storage site is muscle. 

Muscle 

You can build MORE muscle, which means you can increase the amount of storage sites for glucose.

Fat 

When the storage units are full in the muscles and liver, glucose is stored as fat. 

But how does exercise and building muscle affect how your body uses the food you ingest?

When you exercise and use your muscles hard, you empty the stored glycogen in the muscles, then the liver, allowing room for NEW glucose to enter after your next meal. New glucose can now be refilled into the liver and muscle, and if you aren’t over consuming, you don’t gain fat. 

So the act of exercising can help prevent weight gain, but having more muscle mass can help prevent fat gain as well, since having more storage units available for glucose means there are more places for glucose to be stored, and less likelihood it is stored as fat. 

So yes exercise has a role in fat loss/maintenance, but it’s not in the way that conventional wisdom taught us (that we need to use it as a tool to burn).

“Ok, if it’s not my metabolism slowing down, why have I noticed weight gain as I get older?”

As noted earlier, if we are not doing something about it, we lose between 3-8% of muscle mass each decade after the age of 30. But if we aren’t changing our diet during that time, we are reducing the storage units for glucose in the muscle, which means that glucose is slowly being stored as fat. 

So no, it’s not just “age,” and yes, you can do something about it! Even if you’re over the age of 60, there is no reason why you can’t gain muscle and have an amazing metabolism.
But what many people do is they put themselves on what we call the downward spiral.

Downward spiral

You notice a little fat gain over a decade or so, so you decide to do something about it. You start running/doing cardio in an attempt to “burn more fat,” and you cut calories. 

And this may work at first, but what you don’t realize is that unless you are strength training and eating enough protein, you’re losing both fat AND muscle. This spirals the problem.

Because now you have less storage sites for glucose in the form of muscle, and you have to continue to cut calories and add more exercise to lose weight and/or maintain. 

Your system also adjusts to increase efficiency and decrease caloric expenditure, as I touched on before with the constrained total energy expenditure model. So some weight loss may happen initially, but it quickly plateaus. 

The upward spiral, on the other hand, is the opposite.

Upward spiral

This is where maybe you notice some weight gain over the years, even though you haven’t really changed your diet. 

You decide to change to a protein-dense diet and start resistance training. 

You slowly gain muscle and increase the storage units in the muscle for glucose. Now you can eat MORE, knowing that there is more room for glucose in the muscle, rather than shuttling it to fat. 

You may even be able to take more time off from exercise for vacations, sickness, etc. and not notice too much of a difference in how you feel and look. 

This is because muscle sticks around for longer, and you aren’t depending on your workouts to “burn off” anything. So you can take a break here and there, and your body is much better prepared for that break.

How can Evlo play a role?

Evlo is not a weight loss program, we are a muscle building program. 

We want to educate that it’s not about how MUCH you do or how many calories you burn. It’s about the quality of work to the muscle. 

Because putting yourself on that upward spiral can help delay age-related changes in your body and make you feel so much more vibrant, avoid health issues later, be flexible in your life as far as what you consume, and honestly usually feels better in your joints as well because cardio tends to be super repetitive. 
I’m not saying “don’t do cardio”. Cardio is important for your heart health. 150 min/week-ish of light-to-moderate intensity and optional short HIIT sessions are all you need. But I am saying that cardio or any workout isn’t about burning calories. I recommend ditching that fitness watch so you aren’t even concerned about it at all.

Let’s talk about menopause

Does your metabolism change during menopause? 

Even during menopause, when equating for lean mass, metabolism did not change. Now, there are a whole host of other changes during menopause which could be affecting body composition; but it doesn’t seem to be TDEE that is affecting body composition. 

This is yet another reason for women to focus on building muscle from an early age- before, during, and after menopause. 

Before menopause so you can be prepared for the process. During and after menopause so you can mitigate symptoms.

But what is happening after the age of 60 where the researchers saw the decline in metabolism?

The theory is that cell maintenance starts to decline around this time, which decreases metabolic rate, but further investigation needs to be done.

Here is my thought on the matter: if we can maintain as much muscle mass as possible, potentially BUILD muscle mass in your 60s and beyond (which Evlo members over the age of 60 are doing every day!!), perhaps we can continue to improve cellular processes like insulin regulation and mitochondrial health. 

But if you’re 60 and beyond, it may be a time to really focus on your nutrition and strength. If you’re noticing issues, I’d highly recommend seeing a registered dietitian or physician for a personalized evaluation.

My plan is (as of now) when I get to that age

I’m going to build as much muscle as I can up to that point. I’m going to remain curious and not take “aging” as an excuse to not do everything I can to stay healthy, strong, and vibrant. 

It seems like there is more to uncover here, and I apologize that I don’t have all the answers. But hopefully we will continue to learn more. And in the meantime, I hope this post gives you yet another reason to shift your focus from burning calories and destroying your body in your workouts, to building your body up.

References:

Daily energy expenditure through the human life course

FBHJ episode: How to keep your metabolism high as you age

Constrained total energy expenditure and metabolic adaptation to physical activity in adult humans