What Causes Slow Metabolism?

Many of us have thrown around the word metabolism when talking about our health, particularly around discussions of weight loss and weight gain.

But there are still many misconceptions around how our metabolism works and affects our health.

The rate of a person’s metabolism, the process of providing the body with energy essential for living, is largely determined by genetics.

But there are some other factors that can slow down your metabolic rate, including age, gender, extreme dieting, and chronic health conditions. 

The most common sign of a slow metabolism is difficulty losing weight.

Keep reading to learn more about the signs and causes of a slow metabolism and which strategies can help to give you more energy and support your overall health. 

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What is Metabolism?

The term metabolism refers to a series of reactions that occur on a cellular level that are essential to our everyday functioning.

Metabolism enables our body to take the nutrients from the food we eat and convert them into energy needed for movement, growth, development, and reproduction. 

Our metabolism works around the clock, regardless of whether we’re sleeping, working out, or eating.

When talking about how quickly or slowly our metabolism runs, there are three terms to consider: basal metabolic rate (BMR), resting metabolic rate: (RMR), and total energy expenditure (TEE). 

Basal Metabolic Rate (BMR)

The basal metabolic rate (BMR) measures the minimum amount of energy your body needs for essential functions when it's at rest.

Put simply, it refers to the amount of energy needed to keep you alive.

BMR accounts for roughly 80% of the metabolic activity that occurs in the body. 

Resting Metabolic Rate (RMR)

Though BMR and resting metabolic rate (RMR) are sometimes used interchangeably, some experts note a difference between the two terms: while BMR measures the minimum number of calories required to keep the body functioning while at rest, RMR refers to the number of calories the body burns at rest.

Total Energy Expenditure (TEE) 

Total energy expenditure (TEE) refers to the total amount of energy the body burns in a day, or the sum of BMR or RMR plus the energy burned during physical activity or exercise, when digesting food at mealtimes, and when the body is in stress. 

What are the Symptoms of a Slow Metabolism?

People of all ages, genders, and body sizes can have fast metabolisms, slow metabolisms, or average-speed metabolisms. 

The metabolic process is complex and experts are still investigating how it impacts other components of our health.

But one of the most commonly-reported signs of a slow metabolism is trouble losing weight.

If you struggle to shed pounds even after making changes to your diet and physical activity, a slower metabolism may be part of the reason why. 

Causes of Slow Metabolism

There are several key, unchangeable factors that contribute to a person’s metabolic rate, including:

• Genetics: How fast—or slow—your body metabolizes food is largely determined by your genes. 

• Age: Evidence shows that our metabolism peaks at around 20 years old and starts to slow at approximately 60 years of age, although this can be a gradual process.

• Sex: In general, men tend to have faster metabolic rates than women. 

• Race: Research suggests that the BMR is affected by race. One study shows that African American men and women may have slower metabolic rates than Caucasian men and women.  

Below are some additional factors that can affect metabolic rate.

Hypothyroidism

Hypothyroidism is an underactive thyroid disorder.

People with hypothyroidism produce lower-than-average levels of thyroid hormones. 

The condition is associated with a slower metabolic rate and is a risk factor for weight gain.

The most common signs of hypothyroidism include:

• Fatigue.
• Lethargy.
• Intolerance to cold.
• Weight gain.
• Constipation.
• Change in voice.
• Dry skin.

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Extreme Dieting

It makes sense that losing weight slows down a person’s metabolic rate somewhat, given that as a person’s body size decreases so does their energy requirements.

This process is also referred to as metabolic adaptation or adaptive thermogenesis.

But research shows that more extreme attempts to lose weight, including crash or fad dieting, may have more drastic and permanent effects on a person’s metabolism.

One study from 2014 following 14 former participants on the extreme weight loss reality TV show, The Biggest Loser, found that after pursuing extreme weight loss, participants’ resting metabolic rate significantly decreased.

Their leptin levels, the hormone responsible for controlling satiety cues, had also drastically lowered, leaving people feeling constantly hungry. 

At the time of the study, one participant’s metabolic rate was reduced to such an extent that they were limiting their daily caloric intake to just 800 calories in order to maintain their weight of 295 pounds (which is not sustainable).

Poor Sleep

Sleep loss and sleep disorders, like insomnia or difficulty falling or staying asleep, can have a significant impact on metabolism.

Specifically, studies suggest that losing sleep can cause leptin levels to decrease and ghrelin levels (the hormone that boosts appetite) to increase. 

Stress

Stress can increase the body’s metabolic needs, demanding more caloric intake for the same basic functioning. 

Stress can also cause sleep loss, which can have reverberating effects on metabolism.

Low Body Temperature

One scientific paper suggests that lower core body temperatures in some people may be part of the reason why some people have slower metabolisms than others. 

However, more evidence on the effects of body temperature on metabolic rate is needed to determine this cause. 

Tips for Boosting Energy

Many of the factors that determine a person’s metabolic rate, like age, genetics, and sex, are unchangeable.

But there are some things you can do that may help to affect your metabolic rate and support your overall health.

Strength Training

Generally speaking, the more lean muscle you have, the higher your metabolic rate.

This is because muscles burn more calories for energy than fat. 

One study showed that people who engaged in strength training over a period of six months increased their lean muscle mass and improved their RMR.

Another study also found that strength training over a period of ten weeks increased RMR by 7%.

Eat Regularly

Extreme dieting can slow down a person’s metabolism, even after dieting stops.

Which is why avoiding crash or fad dieting by eating regular, balanced meals can help to keep metabolism slow downs at bay.

Prioritize Self-Care

Stress and sleep loss can negatively affect your mental health and physical health, including your metabolism.

Prioritizing mindfulness and other self-care techniques that aim to improve your sleep and stress management may also help to stabilize your metabolism in the long run. 

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Takeaway

There are several inherent factors that can affect your metabolism, like your age, sex, race, and genetics.

Though there’s little evidence that you can boost or increase your metabolism significantly, there are strategies that can help to support a healthy metabolism, including strength training, eating regularly, and prioritizing sleep and stress management.

How a Dietitian Can Help

Developing a healthy relationship with food and eating regular, balanced meals is one way to support a well-functioning metabolism.

Working with a dietitian can help you uncover new ways to feed yourself nutrient-dense and satisfying meals.

During your appointments with a Nourish dietitian, you’ll review your current dietary intake and develop a personalized nutrition care plan to help you achieve your health goals.

At every follow-up visit you’ll have an opportunity to review your progress, make modifications, and receive unconditional support as you move through your wellness journey. 

You can find a dietitian through Nourish to start improving your relationship with food.