Don’t Blame Metabolism Changes for Your Fitness and Health Issues

Maintaining physical fitness standards is important during the holidays. (U.S. Air Force photo/ Senior Airman Jarrod Grammel)

Over the years, many have stated the obvious about the downward slide in life when saying, “Well, I am not 18 anymore.” As we have aged into our 30s, 40s, 50s and beyond, the natural understanding for our physical decline and weight gain was due to a slowing metabolism.

How many of you remember being a “hard gainer,” when no matter how hard you tried, you just could not gain weight? And how many of you became an easy gainer after you turned 30? It turns out there is a very common-sense reason for that, but that reason is not quite what we originally thought it was .

A 2021 study researched more than 6,400 people across the globe and age spectrum from infants to 90-year-olds. The results show that our middle-age spread is not necessarily caused by a decreasing metabolism. According to this comprehensive worldwide study by the Pennington Biomedical Research Center in Baton Rouge, Louisiana, there are three major changes in metabolic rate and total calorie expenditure.

Metabolic rate is also known as basal metabolic rate (BMR), which corresponds with the minimum number of calories a person needs to live. The basic life functions include breathing, circulation, digestion, growing and other life-supporting activities.

There are three major changes in BMR and total calories burned in a day during a lifetime. The first comes in infancy, then after puberty during your late teens or early 20s but not again until age 60.

This study researched people of all ages around the world and tallied the total energy spent or calories burned during a day and not just the basic living BMR. Previously, there had been very little research that has looked beyond basic living caloric needs and more into how the total daily energy requirements for day-to-day physical activities change throughout life.

Obviously, growing from an infant to a toddler requires a faster-burning metabolic rate. This rate during this time is 50% higher than it is for adults. After infancy, the study shows a steady decline of the higher metabolic rate of about 3% per year until a person finishes puberty.

Believe it or not, the metabolic rate stays roughly the same in humans from ages 20-60, but the total daily caloric expenditures and our eating habits evolve. The data says it is not the metabolic rate but our activity levels that change.

We Are Not Built to Be Still

Living organisms are incredible machines built to survive and can use energy effectively from many fuel sources. The ancient basic survival needs of fight, flight, hunting for food, building shelter and making clothing are daily activities that are rarely used in modern society. Most of us remain quite still throughout the day.

Animals (humans included) were not meant to be sedentary creatures. Once we understand that the human body’s metabolic rate does not change due to age, it puts the weight gain of the last several generations in a new light.

Most of us make the transition into a more sedentary lifestyle during our early 20s, depending on our career and education options. The problem is that we are still eating like we are hard gainers and moving far less than we did in our younger years.

We simply need to move more for starters, calories out is just one end of the caloric issue.

Processed vs. Unprocessed and Natural Foods (

The number of calories in is just as important. For the past 50 years, highly processed foods have made up more than 50% of an American’s daily diet.

Though there may be some age-related issues that affect weight gain, the primary cause is our sedentary lifestyle and the processed foods that put way too many calories in our bodies each day.

Though it is a bit oversimplified, move more, eat less (and better)” is a motto that most of us should follow. Eating more natural foods will help you consume fewer calories, chemicals and other additives that are incompatible with a healthful lifestyle.

We no longer have the excuse that older people will find it impossible to lose weight like we did in our youth. To maintain your body weight, your calories in must equal your calories out.

Hormone Changes and Hormone Imbalances as We Age

Throughout life, there are normal age and hormone-related physiological changes such as puberty, pregnancy and menopause. Those changes in hormone production can affect normal metabolic function and cause potential weight gain.

Usually, normal hormone changes are not the cause of abnormal metabolic changes, but a hormone imbalance can change how the body burns calories. Insulin, thyroid hormones, estrogen, testosterone, epinephrine and stress hormones like cortisol or adrenaline can create bodily changes as we age.

If you feel that you may have hormonal imbalances, check with your doctor and ask for a hormone blood screening test. If you are having difficulty with your weight, sleeping, energy levels, mood, strength and sex drive, you could be experiencing too much or too little of certain hormones.

Sometimes these issues can be corrected by healthful diet changes, increased activity (walking for starters) or through medical treatment supervised by a doctor.

Staying Active After Your Teens and 20s

This study highlights the fact that humans need to stop making excuses and get moving, no matter what their age. We can see improvement even with the slightest increase in activity, water consumption and smaller portions of better food.

Even though there comes a time in a human lifespan when metabolic rate decreases, we must remember that humans were not meant to be sedentary, only breathing, eating and digesting.

Your metabolism has not slowed down; you have. While you may not see the same performance levels you did in your younger, athletic days, the need for maintaining strength and muscle mass throughout life is critical to how we spend our next few decades on this pale blue dot.

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Make Change – Build New Habits

Proven Methods to Rebuild Fitness Habits

Stew Smith is a former Navy SEAL and fitness author certified as a Strength and Conditioning Specialist (CSCS) with the National Strength and Conditioning Association. Visit his Fitness eBook store if you’re looking to start a workout program to create a healthy lifestyle. Send your fitness questions to

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