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If there’s one thing I hear most about, it would be complaints of a slow metabolism. Is it to blame for weight gain? What affects it? How can I speed it up? Transitioning back-to-routine after quarantine has indeed catapulted the topic into the spotlight. Learn what affects your metabolic rate and how to boost your metabolism, according to science.

Woman athlete exercising with kettlebell indoors

Slow metabolism symptoms typically hit as we age, though some lifestyle habits and underlying medical conditions can also impact metabolism. Common symptoms include tiredness, unexplained weight gain, and feeling cold. In some cases, slow metabolism symptoms present as “sluggish” digestion. 

But before we dive into plausible reasons why your metabolism may have hit a speed bump, let’s cover the basics because, to be honest, “metabolism” gets thrown around a lot.

Simply put, metabolism represents all of your body’s biochemical reactions: how you take in nutrients and oxygen and utilize them to fuel and “service” your body. You may be surprised to hear that this incredible biochemistry enables your body to heal, grow and function.

So, metabolism comprises how your body’s cells:

  • Support activities under your control (e.g. physical movement, etc.).
  • Support activities not under your control (e.g. heartbeat, wound healing, digestion, absorption and processing of nutrients and toxins, etc.).
  • Allow storage of excess energy for later use.

As you can imagine, when we connect all these complex processes under the parasol of metabolism, they can either work too quickly, too slowly or perfectly as they should.

All this is related to your “metabolic rate.” 

What Is Meant By Metabolic Rate?

You can think of metabolic rate as how fast your metabolism operates. It’s measured in calories. 

Calories from the food you eat are utilized for:

  • Carrying out work (i.e. exercise and other physical activity).
  • Producing heat (i.e. from biochemical reactions in your body).
  • For storage (i.e. excess “unburned” calories are stored as fat).

Interestingly, the more calories you burn carrying out “work” or creating heat – the easier it is to lose weight. This is because there will be fewer “unused” calories to store for later use.

There are a few different methods to measure metabolic rate. For example, “resting metabolic rate” (RMR) is how much energy your body uses when you’re not physically active. On the other hand, “total daily energy expenditure” (TDEE) takes account of both the resting metabolic rate as well as the energy used for “physical activity” over 24 hours.

Healthy yogurt with raspberry and mint, selective focus image

Factors That Slow Metabolism

Consider this: metabolic rate is much more complicated than the age-old maxim “calories in-calories out”! In fact, it’s so complex that I’m only going to dive into a few of the everyday things that can slow it down.

Examples of common reasons why metabolic rates can slow down:

  • low thyroid hormone (underactive thyroid)
  • history of dieting
  • body size and body composition
  • activity level
  • lack of sleep
  • genetics

Let’s briefly touch on each one below, and I pledge to offer more helpful advice than simply “eat less and exercise more.”

Low Thyroid Hormones

The thyroid gland is at the front of your throat and releases hormones telling your body to “rev up” your metabolism. When it produces fewer hormones, this can cause your metabolism to slow down. I like to think of the thyroid as the motherboard of your metabolism. 

Specifically, your thyroid hormones (T3 & T4) signal your body when to use more energy (become metabolically active). In an ideal scenario, your thyroid should work optimally to keep your metabolism in check. However, several issues can affect it and throw it off course. Problems like autoimmune diseases and mineral deficiencies (e.g. iodine or selenium), for example. If you’re concerned about your thyroid, talk with your doctor about having your thyroid hormones tested. 

Low thyroid hormones aren’t the only reason to throw your metabolic rate out of whack. Body size and body composition also matter.

Body Size And Body Composition

Generally speaking, larger bodies have more active or “faster” metabolic rates. This is because it takes a greater amount of energy to fuel a larger body than a smaller one. 

It goes without saying that gaining weight is seldom the best strategy for boosting your metabolism. What matters is your muscle mass. Muscles that actively move and perform “work” require energy. In fact, even muscles at rest burn more calories than fat. This means that the amount of energy your body uses depends somewhat on the amount of lean muscle you have. The good news is that weight training can help increase your muscle mass, and therefore—your metabolic rate.

History Of Dieting

Surprised? The thing is, when you lose weight – especially through crash diets, your metabolic rate often slows down. This is because the body senses that food may be scarce and adjusts by carrying on with all the necessary life functions—and does it all with less food. 

While “dieting” to achieve weight loss can reduce the amount of body fat, it, unfortunately, can also cause some degree of muscle loss. This isn’t ideal because, as we learnt earlier, the more muscle you have, the faster your resting metabolic rate. The key is to make sure you’re eating a sufficient amount of food to fuel your body. And that includes listening to your body’s hunger and appetite cues and practicing mindful eating.

Green dumbbells and jump rope on vintage background. Top view.

Activity Level

Any type of aerobic movement could help to raise your metabolism. This is because your muscles burn fuel to move and do “work.” And picking up the pace doesn’t have to mean sweating at the gym 7 days a week. Even small things can help; walking a bit farther than you ordinarily do, working on a standing desk rather than sitting all day, or choosing to take the stairs instead of the elevator. These alternatives will help to add more movement to your day. 

It’s a good idea to pick exercises you love when it comes to a more formal exercise routine. That way, they’re pleasurable, and you’re more likely to continue with them. Consistent action truly creates consistent results.

Lack Of Sleep

The amount and quality of sleep can cause your hunger and appetite cues to go haywire. There is a plethora of research that links the influence sleep has on your metabolic rate. While some self-proclaimed gurus swear by less sleep, experts advise 7-9 hours of uninterrupted sleep every night. Read tips on better sleep here.


Your metabolism may be hard-wired in your DNA. According to this University of Cambridge study, researchers were able to show genetic variations among “thin” people versus those of significantly higher weights. Based on their findings, scientists were able to generate a genetic risk score to develop “obesity” later in life. 

Then, there is the theory of “set-point.” It suggests that your body strives to maintain your weight within a specific range, and seems to be influenced by your genetic makeup. Bear in mind: your actual weight within that set point is affected by your lifestyle. In other words, diet, exercise, drug use, head injury and certain brain conditions will influence this set point.

How To Fix A Slow Metabolism, According To Science

Build Muscles

Because muscle is more metabolically active than fat, you want to build muscle as a strategy to help boost your metabolism. Generally speaking, the more muscle you have, the higher your metabolism. However, building and preserving muscle requires strength training to be a consistent part of your exercise strategy, alongside diet and lifestyle changes.

Do Quick Bursts Of Activity

Aerobic exercise has been shown to temporarily increase metabolic rate. Your muscles are burning fuel to move, so they’re doing “work.” According to research, a high-intensity workout, like HIIT (High-Intensity Interval Training), can rev up your metabolism. Remember to vary up your exercise routine to counter boredom and stay physically challenged.

Just Stand Up

Encouraging, isn’t it? It turns out that simply standing is good for your health; people who sit for extended periods have a higher risk of developing diabetes, heart disease, hypertension and other related lifestyle diseases. Standing “actively” engages your leg, back and abdominal muscles. According to this study, standing burnt 174 calories greater than merely sitting. Even intermittent standing while working has been shown to modestly burn calories compared to sitting. Perhaps you should stand up while reading this.

Recognize the Mind-Body Connection

An abundance of research shows the influence of stress and sleep on your metabolic rate.


Sleep is usually the most overlooked reason. Studies have noted that sleep deprivation and sleep disorders cause metabolic dysfunction. This occurs through multiple pathways involving hormonal imbalances, inflammation and overstimulation of your sympathetic nervous system. Plus, we know that inadequate sleep can increase food cravings and reduce appetite control. Read tips to get a handle on food cravings.

Coffee cup and coffee beans on rustic background

Foods That Increase Metabolism

Your body actually burns calories to absorb, digest, and metabolize your food. This is termed the “thermic effect of food” (TEF) and could offer a metabolic advantage. According to science, here are the types of food that increase metabolism.


Fats, for example, increase the TEF by 0-3%; carbs raise it by 5-10%, and protein can result in increases as high as 20-30%. By swapping some of your fat or carbs for lean protein, you could slightly boost your metabolic rate. What’s more, your working muscles need protein to grow. Grab 32 plant sources of protein here.

Frequently Asked Questions:

Does Caffeine Decrease Metabolism?

The opposite may be the case, in fact! Interestingly, some research indicates that coffee may burn fat through a thermogenic effect (caffeine increases heat production) and by making the body use fat for fuel. This golden milk turmeric coffee is health in a cup; milk infused with turmeric, ginger, cinnamon and coffee to create a spicy, warm, and creamy brew.

Remember, go easy on coffee, as caffeine can have a disruptive impact on sleep. According to Mayo Clinic, 400 mg of caffeine per day seems to be safe for most healthy adults.

Do Hot Peppers Increase Metabolism?

Capsaicin, found in peppers, may stimulate metabolism; however, I’m not convinced. The required dosage to achieve this effect is not tolerable for most people. Plus, the effect is short-lived.

I’d love to hear from you! What have you tried to boost your metabolism? Leave me a comment below.

Desi~liciously Yours, Shahzadi

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