Since "metabolism" is technically an umbrella term for a series of reactions in the body, decoding what a slow metabolism is can seem rather complex. Luckily, you don't need to know the nitty-gritty science to spot slow metabolism symptoms. 

Read on for answers to common questions about a slow metabolism, including when and if it slows with age.

Understanding Metabolism

Metabolism is the basic life process that turns food and oxygen into energy, which is vital to keeping the body functioning properly. Technically, metabolism is an umbrella term for a number of complex chemical reactions that help to break down food into more usable building blocks. 

While there are basic formulas to estimate base or resting metabolic rate, everyone’s metabolism rate differs. Becoming familiar with your body and how it responds to food, exercise, sleep, stress, and other factors can help you understand your metabolism. 

What Is a Slow Metabolism? 

The terms "slow metabolism" and "fast metabolism" may seem confusing, especially since there aren’t definitive definitions for these metabolic states. In medical settings, a "slow metabolism" is generally used to describe a resting metabolic rate that requires fewer calories to function. 

In casual conversation, when someone says they have a "slow metabolism," they likely mean that they've noticed their body processes food differently than it used to at a younger age. For example, a 40-year-old may say they have a slow metabolism because they don't feel like they can survive on fast food and next to no sleep anymore. 

On the other hand, having a fast metabolism means the body burns more calories at rest. This is a healthy goal to have, especially if you’re looking to accomplish it by maintaining healthy weight, eating well, and exercising. 

However, remember that a fast metabolism doesn't automatically equal health. At rest, obese individuals technically have a fast metabolism, since their bodies require more energy for basic functions. Essentially, the method by which you accomplish a fast metabolism is important to your overall health. 

Factors That Affect Your Metabolism 

Some aspects of metabolism are determined by genetics. However, other factors also play a role in how the body breaks down nutrients. 

Age

One of the most well-known factors that influence metabolism is age. Many people notice a loss of muscle mass and increased abdominal fat as they become middle-aged. During aging, the body begins to burn fewer calories and may not break down foods as efficiently. 

Essentially, someone aged 60 will likely have a slower metabolism than someone aged 20. Someone 95 years old will likely have a slower metabolism than someone who is 60 years old. 

Although a slow metabolism isn’t necessarily inevitable, it is a common byproduct of age. Luckily, the same tips for making metabolism faster can work whether you are 22 or 82. 

Sex & Hormones 

There may be differences in metabolism based on sex, too. Since hormone signals regulate metabolism, there can be significant differences in metabolism between men and women of the same age or life stage. Generally, men and women have differing muscle mass and reproductive hormone levels, which can impact how metabolic reactions proceed.

Disorders affecting the thyroid hormone can also have a significant impact on metabolism. Thyroid hormone is the main chemical messenger responsible for regulating the body’s metabolism. When the thyroid becomes overactive (hyperthyroidism), underactive (hypothyroidism), or experiences inflammation or injury, it can have serious metabolic consequences.

Timing of Meals 

Interestingly, skipping meals may also affect metabolism. Like other body processes, metabolism is believed to be influenced by the circadian rhythm—the body's natural sleep and wake cycle. Skipping breakfast or eating a late dinner may disrupt the body’s natural metabolic rhythm, and researchers are still studying the reasons why this may be. 

Changes in Weight 

When you lose weight, your metabolism might also be affected. Many benefits for overall wellness can result from healthy weight loss, however, metabolism does become down-regulated. 

In other words, thanks to a physiological change in hunger hormones, body size or composition, and energy expenditure, weight loss may result in the body burning hundreds of calories less than it used to at a higher weight. While this makes it more difficult to lose weight, the effort is often worth it for the overall benefits of weight loss to an individual’s wellness. 

Metabolic Disease

As the name implies, metabolic diseases impact the way metabolism works. Disorders due to taking in more calories than are burned can cause metabolic dysfunction and seriously affect the quality of life.

Examples of these types of conditions include obesity, metabolic syndrome, and type 2 diabetes. 

Does Your Metabolism Slow Down?

A slower metabolism isn't necessarily a "bad" thing. Maybe your body is being over-stressed and overworked, and slowing down is actually a part of your plan to become healthier. 

For many people, however, a slower metabolism is sidelining their health goals. During life stages when you face aging or a difficult diagnosis, it may be appropriate to reevaluate how you approach your metabolism. 

Remember, a sluggish metabolism doesn't have to be inevitable with age or life stage—like after pregnancy. Practicing healthy habits and recognizing when your metabolism slows down can help you make meaningful changes. 

Slow Metabolism Symptoms

Just as slow metabolism affects many areas of life, it can also affect many areas of the body. In general, you may feel sluggish, or you don't have enough energy to accomplish daily tasks. You may also notice that your body has difficulty accomplishing seemingly simple tasks—such as stabilizing body temperature or digesting food. 

Chronically taking in more calories without burning enough calories may also contribute to this sluggish feeling, and can ultimately lead to weight gain. As discussed above, excessive weight gain can further alter metabolic rate, making it faster (but not in a healthy way). 

Other, and potentially less noticeable symptoms, may also occur. For example, brittle nails or dry skin may indicate a nutrient deficiency. This could indicate the body is not getting the needed amount of nutrients, or that an error in metabolism prevents the body from absorbing nutrients efficiently. 

How to Remedy a Slow Metabolism 

Many ways exist to improve metabolism and live a healthy, balanced lifestyle. Try the following tips today to see if they change your metabolism over time. 

Choose the Right Exercise 

It may seem like a no-brainer that exercise impacts metabolism. However, physical activity may impact metabolism in more ways than one. While it's long been established that exercise can influence how the body metabolizes fat, recent research suggests moderate physical activity can even help upregulate metabolism in different brain regions. 

Basically, exercise can be beneficial for many different types of metabolism going on in the body. Beyond helping to burn more calories, exercise lasting beyond a couple minutes engages major metabolic pathways. 

Muscle is considered a metabolically active component of the body, meaning people with more muscle require more energy to function. Fortunately, increasing lean muscle mass through exercise can help improve metabolism.

Intensity and duration are the main determinants of up-regulating a metabolic pathway through exercise. More specifically, longer and more intense types of exercise may be better for increasing metabolic rate. For example, high-intensity interval training (HIIT) and endurance training are associated with metabolic benefits. 

Struggling with where to start? Try participating in the following: 

• Higher-impact aerobic exercises like running and jumping rope
• Intense short-term exercises, including HIIT and Tabata workouts
• Lower-impact aerobic exercise for longer amounts of time, such as 30-45 minutes of swimming or walking
• Strength training that engages all major muscle groups 

Eat Enough

While it might sound counterintuitive, eating enough calories daily is crucial to a speedy metabolism. Limiting calories can force the body into "survival mode," which can shift the body's priorities regarding metabolism. The Mayo Clinic's Calorie Calculator can give you a basic estimate of how many calories you need.

A simple way to eat enough is to listen to your body and respond to hunger cues. Eating enough when you are hungry—but before you feel "starving"—can help keep cravings at bay and may help you to avoid overeating. 

Boost your metabolism by eating smaller meals or snacks regularly every three to four hours (instead of just three big, main meals). Snacks can be especially helpful, particularly those with a balanced number of calories and containing filling nutrients like fiber, protein, and healthy fats. 

Don't Skip Breakfast

Did you know that breakfast can jump-start metabolism? Since your body's metabolic rate slows while you're sleeping, the first meal in the morning plays an important role. 

Studies suggest people who eat breakfast make healthier food choices throughout the day, further supporting a faster metabolism and better metabolic health. 

Pump Up the Protein, Fiber, and Healthy Fats 

Eating foods from different groups can involve the body in different metabolic processes. In other words, variety is good! Search for nutrient-rich foods, particularly those that contain nutrients like protein, healthy fats, and fiber, to curb cravings. 

Healthy fats are unique since they provide a sustained energy source. Fiber also takes longer to digest and break down; foods like whole grains may boost you. In fact, a recent study suggests that regularly eating whole grains may raise your resting metabolic rate. 

Protein-rich foods are also crucial for improving metabolism, especially when combined with the habit of regular exercise (namely weight-bearing exercise). Not only does protein help to support speeding up the process, but it also contributes to building lean muscle mass in the body. Basically, protein helps both the breakdown and build-up aspects of metabolism.

Whole grains containing protein and fiber have been heralded as an especially useful food for metabolism. 

Aim for Burning Brown Fat

Brown fat is a special type of fat tissue. It's primarily broken down to help create heat. This heat helps to keep body temperature at the proper levels. 

Interestingly, scientists hypothesize that participating in activities that activate brown fat may have marvelous effects on metabolism. Researchers believe tapping into brown fat may be the answer to treating metabolism-related diseases, such as obesity or diabetes. 

As you may have guessed, a common method of activating brown fat is exposing the body to cold temperatures. These temperatures don't need to be cold enough to cause a shiver, just chilly enough to activate the body’s need to burn brown fat. 

Keep in mind that cold exposure for boosting metabolism is still viewed as an alternative kind of therapy. While typically considered safe for most people, it’s recommended that you check with your personal healthcare provider before beginning a new cold exposure protocol like cryotherapy. 

In Summary on Slow Metabolism

Metabolism can be affected by many factors, making it tricky to identify exactly why you feel sluggish. Luckily, there are many solutions to help improve metabolism, and exercise and eating patterns play a major role. 

While factors like birth sex, age, and genetics can’t be changed, new approaches and therapies like cold exposure hold promise for the future.

References

Academy of Nutrition and Dietetics. Eating to Boost Energy. Eatright.org. Published July 2020. 

Cleveland Clinic. Aerobic Exercise. My.clevelandclinic.org. Published July 2019.

Cleveland Clinic. Metabolism. My.clevelandclinic.org. Published August 2021. 

Cleveland Clinic. Thyroid Hormone. My.clevelandclinic.org. Published February 2022. 

Ellis E. Metabolism Myths and Facts. Eatright.org. Published April 2019.

Hadi HE, Vincenzo AD, Vettor R, Rossato M. Food Ingredients Involved in White-to-Brown Adipose Tissue Conversion and in Calorie Burning. Front Physiol. 2018;9.

Hargreaves M, Spriet LL. Skeletal muscle energy metabolism during exercise. Nat Metab. 2020;2:817-828. 

Harvard Health Publishing. The truth about metabolism. Health.harvard.edu. Published March 2021. 

Mayo Clinic Staff. Metabolism and weight loss: How you burn calories. Mayoclinic.org. Published October 2022.

National Cancer Institute. Body Functions & Life Process. Training.seer.cancer.gov. Accessed June 2023. 

National Institutes of Health. Minding Your Metabolism. Newsinhealth.nih.gov. Published July 2015. 

Schaeffer J. Rise and Dine! — A Breakdown of Breakfast’s Benefits With Experts’ Best Meal Suggestions. Todaysdietitian.com. Published September 2011. 

Today’s Dietitian. Penn Researchers to Study How Mealtimes Influence Human Health. Todaysdietitian.com. Published November 2017. 

Warchaw H. Lifestyle Changes That Keep Pounds Off. Todaysdietitian.com. Published August/September 2020. 

Wein H. How brown fat improves metabolism. Nih.gov. Published September 2019.