Is Muscle Loss the Only Reason Your Metabolism Slows with Age?

Most of us don’t want to deal with a slow metabolism, yet we often notice gradual weight gain with age, some of which is due to a slowing metabolic rate. Your metabolic rate is the number of calories you burn. It’s divided into three components:

Resting metabolic rate:

The number of calories you burn when you’re not exercising and haven’t just eaten a meal. It’s the calories expended when you’re simply resting. This portion of metabolism represents between 60 and 75% of total energy expenditure.

Thermic Effect of Food

The extra calories your body must expend to digest, break down, and metabolize the food you eat. This component of metabolism accounts for 10 to 15% of total energy expenditure. Protein is the most complex macronutrient and meals higher in protein increase the thermic effect of food more than carbohydrates or fats.

Thermic Effect of Exercise

The extra calories you burn over a 24-hour period due to exercise. This includes structured exercise as well as NEAT (non-exercise adaptive thermogenesis). NEAT refers to the non-structured movements you make throughout the day such as shaking your leg nervously while you sit or pacing back and forth. Studies show these “extra” movements can add up to significant calorie burn over the course of a day.

Metabolism Slows with Age

It should come as no secret that total energy expenditure declines with age. This slowdown makes it easier to gain weight as you age. Over the years, as your metabolism slows, you begin to see a gradual increase in weight. Plus, weight gain speeds up in women after menopause. One reason this happens is that we lose muscle mass over the years. Muscle is metabolically active tissue that burns more calories than fat. Plus, having more muscle improves metabolic health – but this isn’t the only reason resting metabolic rate slows with age.

Other Reasons Metabolic Rate Slow with Age

As people age, they become less active and the volume of movement they do throughout the day decreases as well. Along with the decline in movement comes a slowdown in metabolic rate. Plus, older people tend to eat less food and this slows metabolism, as well as your body tries to conserve energy.

How do we know this? In one study, researchers compared older and younger subjects who did comparable volumes of exercise and ate a similar number of calories. Interestingly, there was little difference in metabolic rate between the young and old subjects when the volume of exercise and calories was equivalent.

Also encouraging is a study showing that metabolic rate didn’t slow in older women who maintained a high volume of exercise. So, one of the ways to offset a slowdown in metabolism with age is to not restrict calories and move around more. It makes sense since the thermic effect of food and exercise make up as much as 40% of your metabolic rate.

Another factor is the age-related loss of metabolic efficiency. Studies show that older adults have, on average, 20% fewer mitochondria and the mitochondria are less capable of using oxygen to produce energy. This decline in mitochondrial efficiency has repercussions for weight control and for metabolic health. Plus, a decline in mitochondrial function is linked with a higher incidence of chronic, age-related health problems. Fortunately, regular aerobic exercise helps to mitigate the loss of mitochondria.

Keeping Your Metabolism from Slowing with Age

Of course, you’d like to keep your metabolism from slowing to the point that you put on body fat as you age. The age-related gain of fat and loss of muscle tissue leads to sarcopenia, a condition linked with health problems like type 2 diabetes and frailty. So, what can you do to keep your metabolic fires burning as you age?

Strength Train

Strength training is arguably the most important thing you can do to keep your metabolism from stalling and to avoid the pitfalls of sarcopenia. No matter what your age, there is some form of resistance exercise you can do to help preserve muscle tissue. Heavier weight training helps to preserve bone density as well.

Get Enough Protein

Some studies suggest that we need more protein after midlife. One study involving people over the age of 50 found that those who ate double the RDA of protein were better able to build muscle through weight training. Building more muscle means a healthier body composition and a faster resting metabolic rate.

Don’t Skimp on Sleep

When you deprive your body of quality sleep, it increases the appetite hormone ghrelin and reduces leptin, a hormone that helps turn off appetite and speeds up metabolic rate. With less leptin release, resting metabolic rate slows. So, lack of sleep is a double whammy for weight control – it increases your appetite and slows your resting metabolic rate. There is also some evidence that exposing your eyes to light as early as possible helps keep your metabolic fires humming as well.

Don’t “Diet”

Dieting further slows your metabolism and is counterproductive to weight control. In fact, eating too little at any age is harmful to your metabolism. Upgrade the quality of what you eat by eating less sugar and processed foods rather than cutting calories to lose weight. Focus on moving more instead.

Check Your Thyroid Function

An underactive thyroid becomes more common with age, especially in women. The cause is frequently an autoimmune condition called Hashimoto’s thyroiditis. If you’re having problems losing weight, get your thyroid function checked via a blood test.

The Bottom Line

The reason metabolism slows with age is only partially due to loss of muscle tissue but it’s a factor we can control to some degree by strength training. Plus, we can maximize nutrition and try to get enough sleep as well. Weight gain with age isn’t inevitable, so make sure you’re leading a metabolism-friendly lifestyle!

 

References:

Proc Nutr Soc. 2003 Aug;62(3):621-34.
Am J Clin Nutr November 2005. vol. 82 no. 5 941-948.
Healthline.com. “Why Your Metabolism Slows Down with Age”
Muscle EVO. “Why Does Your Metabolic Rate Drop As You Age?”
American Journal of Physiology, E281, 633-639.
The Journal of Clinical Endocrinology & Metabolism, Volume 82, Issue 10, 1 October 1997, Pages 3208–3212, https://doi.org/10.1210/jcem.82.10.4268.
Sleep Med Rev. 2007 Jun; 11(3): 163–178.Published online 2007 Apr 17. doi: 10.1016/j.smrv.2007.01.002
Physiol Rev. 2013 Jan; 93(1): 107–135. doi: 10.1152/physrev.00016.2012.

 

Related Articles by Cathe:

Does Strength-Training Really Boost Your Metabolism?

5 Factors that Contribute to a Fast or Slow Metabolism

Why You Probably Don’t Have a Slow Metabolism after All

Why Metabolic Rate Calculators Aren’t Always Accurate

New Research Shows the Mineral Copper May Play Key Role in Fat Metabolism

 

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