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Metabolism Truths and Myths: Not So Fast or Not So Slow?

Reading time: 5 minutes

Are you gaining weight in recent years? Do you notice less muscle tone? Do you find it not only hard to lose weight but hard to avoid weight gain?

You’re not alone. But don’t throw in the towel or blame your metabolism just yet. A study published in 2021 disproved the myth that metabolism slows in adulthood. It showed that between ages 20 and 60, it remains stable, even for pregnant women.1

What is metabolism?

Even as much as we use the word, a quick review of metabolism is warranted before we dive in. Metabolism is the set of chemical processes that occur in the body to maintain life. This is resting metabolism. The more active you are, the more you also boost your metabolism during exercise and, as we’ll discuss, immediately after exercise.

Does metabolism really slow with age or because of midlife hormonal changes? Let’s unpack the two biggest factors we often blame for a slow metabolism.


During menopause, when estrogen (and other hormones) declines, muscle mass can more easily decline.

One study shows lower estrogen levels also interfere with the ability to regulate blood sugar, insulin and leptin, in mice.2 That causes greater fat storage, especially around the abdominal area, and a greater risk of type 2 diabetes and cardiovascular disease. The result of increased fat storage is, again, a slower metabolism.


What we learn is that, for every decade we age, we need to reduce the number of calories we consume to avoid weight gain.3 This is because basic body processes require less energy when there is a decline in physical activity and loss of muscles.

But why?

Because collectively as humans, we’ve been less active as we age. The mistake many make is thinking when they retire, they’ll take the time to exercise and do all the activities they’ve missed while juggling their family and careers. But often, disease, degeneration, and disinterest results such that by the time they have the time, many adults don’t have the energy or health.

There’s no argument that muscle is lost easier than it is gained and even maintained during aging. At least until now. This is a gentle reminder that few adults in their 90s or even 80s have been exercising in a way that will help them gain muscle consistently as a part of their lifestyle. Nor have they led the significantly active lives they started with. Over the lifetime of a 90-something, life tends to become less and less active. Gone are the days of doing chores on the farm or planting and harvesting our own food. We don’t even get up to change the TV channel, make dinner or go to the office. Yet most of this generation missed the cultivation of regular fitness routines.

The example of aging that exists right now does not have to remain the only option. You can reject the model of growing weaker, sicker and fatter with age. A quick look around provides data showing that weight gain is not inevitable either with aging or with menopause. If that were true, every mature adult and postmenopausal woman would be overweight, but they aren’t.

The common denominator: muscle

Muscle is the only metabolically active tissue. That is, it requires calories to function, unlike fat. So, when you lose it, you lose some metabolic flexibility, meaning you gain weight more easily because your body is less adaptive to ups and downs of calorie intake and expenditure. When calories drop too low, the metabolism slows. When calories go too high, your body is more likely to store them.

The real cause of metabolism slowing with age and with midlife hormone decline is a change in behavior that results in a loss of muscle mass. During menopause, factors contributing to reduced activity include common signs and symptoms of hormone fluctuation or loss. Insomnia, hot flashes, depression and anxiety, just to name a few, don’t inspire motivation to exercise.

Muscle mass peaks at around age 25. By age 30, the loss of muscle begins unless something is actively being done to counter it. We tend to lose 3–8 percent of our muscle mass per decade starting at age 30, and even more after the age of 60.4 By age 80, most adults have lost about 30 percent of their muscle mass.

When I interviewed renowned nutrition expert Dr Joel Fuhrman about metabolism and aging on my podcast The Flipping 50 Show, he shared this: “Exercise is the only way to speed metabolism without accelerating aging.”

The free and pharmaceutical-free answer

There’s an answer to the tendency toward a slower metabolism: gain muscle. Muscle is a sponge for blood sugar, it’s metabolically active, and it’s free.

In case you’re asking, no, it’s not too late.

The right type of physical activity and adequate fuel, particularly protein, are two potent answers to sustaining lean muscle tissue.

Resistance training, in combination with an adequate nutrient-dense diet high in high-quality protein, has been proven to improve muscle at any age.5 Adults in their 90s can gain strength, even when muscle mass gains haven’t been documented for the oldest old.

There are two ways muscle positively impacts metabolism. First, it uses your blood sugar as fuel during exercise.6 The more regularly this occurs, the more your body will store blood sugar in muscle as a reserve for you. This is a much healthier place for blood sugar to go and a faster way to remove it from the bloodstream. Blood sugar spikes that naturally occur after meals are minimized.

Second, with muscle mass increases from the size and number of muscle fibers, the positive body composition change increases metabolism around the clock.7 This is a distinguishing factor in the power of strength training vs cardio where metabolism is concerned. Do you want to burn more calories for 30 minutes or for 24 hours?

In other words, as you sit comfortably reading this, you’ll burn more calories if you lift weights regularly (with enough stimulus) than someone of your same weight and age who is not lifting weights as part of an exercise routine.

What also is notable is referred to as EPOC, excess post oxygen consumption, that occurs following exercise. For strength training as opposed to cardio, EPOC is higher and lasts longer.8 In fact, for up to 38 hours after resistance training, your metabolism enjoys a significant bump as your body repairs tissue and restores physiology. Although the popular high-intensity interval training (HIIT) also provides a bigger boost than a steady cardio session, it does not give aging muscle the round-the-clock bump in resting metabolism that comes from increasing lean muscle mass. Interval training is a “What have you done for me lately?” exercise friend when it comes to metabolism.

But what if . . .

You may have limitations. You may not be able to lift weights for certain body parts. Do what you can. Focus on that. Muscle is required for every movement you make all day. When you have more muscle, you will have more energy and desire to move more.

Metabolism-boosting benefits can occur with both more and stronger muscle throughout the lifespan. Increase the amount and strength of your muscle to positively change your metabolism, your health and your life.

What do you think? Start a conversation over on the... WDDTY Community

  1. Science, 2021; 373(6556): 808–12
  2. Diabetes. 2019; 68(2): 291–304
  3. US Dept of Agriculture, “Dietary Guidelines for Americans, 2020–2025,” Dec 2020,
  4. Curr Opin Clin Nutr Metab Care. 2004; 7(4): 405–10.
  5. Eur Rev Aging Phys Act, 2020; 17: art. 11
  6. Diabetol Metab Syndr, 2020; 12: art. 14; Diabetes, 1985; 34(10): 1041–8
  7. Eur J Clin Nutr, 2015; 69: 831–6
  8. Res Q Exerc Sport, 2015; 86(2): 190–5; Eur J Appl Physiol, 2002; 86:411–417
  Author: Debra Atkinson, MS, CSCS, is CEO of Flipping50 and creator of the Flipping50 Menopause Fitness Specialist course for trainers and health coaches. She is a medical exercise specialist with nearly four decades experience. Her career has included teaching Kinesiology at Iowa State University, giving international presentations to fitness professionals for major fitness associations, and serving as a subject matter expert for the American Council on Exercise. She’s a sought-after speaker for reframing aging and teaching how to do it, and her TEDx talk is “Everything Women in Menopause Learned about Exercise May Be a Lie.” She will host “What, When and Why to Exercise for 40+ Women,” an online event, in May 2023.
Article Topics: ageing health, Metabolism
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