Is a Slow Metabolism Inevitable as We Age?

I am sure you have heard the excuse of a slow metabolism as a reason for putting on weight as people get older.

I remember being pretty thin as a teenager and older relatives telling me to “enjoy it while you can”.

They would say things like, “I was thin just like you until I hit 30, then my metabolism slowed down”.

I was told, “just wait until you are 30, then you will understand what we are talking about”.

So I am rolling up on 50 and didn’t put on any weight in my 30’s and 40’s. 

I waited for that big metabolism slow down to hit me, but it never really happened.

Was I just lucky or is something else going on here?

It is True That Young People Have Less Body Fat on Average

According to the book Exercise Physiology college-aged men carry 15% body fat, while older men carry around 25% body fat.

Women are closer to 25% body fat at a younger age and move up to 35% as they reach age 50.

I also have read elsewhere (can’t remember where) that men on average put on one pound of fat per year from the age of 35 to the age of 60… and that women put on less than one pound per year, but more in proportion to their overall weight.

Fat-Free Mass Burns the Same Amount, Regardless of Age

In 1950, Dr. Ancel Keys led a study with several other researchers called “Energy Requirements of Adults”.

They found that regardless of age, the daily energy requirements (calories burned) per pound of fat-free mass was the same.

So a 20-year-old and a 65-year-old will burn roughly the same amount of calories if they are of the same height, weight, and body fat percentage.

So it isn’t that the body is slowing down the calorie burning process… it is due to another factor.

Maintain Your Muscle to Maintain Your Metabolism

This is as simple as it gets.

As adults become less physically active, their muscles shrink due to not being used.

The combination of less fat-free mass and less activity leads to inevitable weight gain (unless they reduce their calorie intake over time).

The only reason why older people on average tend to burn fewer calories than younger people of the same weight is that the older people have less lean body mass.

Is It Extremely Difficult to Maintain Lean Body Mass?

Honestly, maintaining muscle is really easy to do and doesn’t take much effort at all.

Maintaining the muscle you have is as simple as doing just about any type of resistance training a couple of times per week.

It doesn’t require a perfect diet and it doesn’t require a massive amount of time in the gym.

“Your Metabolism Won’t Slow Down if You Don’t”

This quote is from Clarence Bass, who I believe is in his 60’s or 70’s now…is still at a 6-8% body fat level.

This quote from Clarence is one of the best mottos I have heard for staying lean for a lifetime.

This is why exercise is so important…

You can get lean with diet alone, but you will have a tough time staying lean if you don’t exercise.

If you just diet, you will eventually lose lean body mass and in a few decades your metabolism will eventually slow down.

For long-term health as well as looking and feeling great as you age, exercise is extremely important.