Why You Have A Slow Metabolism

Do you feel tired, cold or that you’ve gained weight even though there’s been no change to your eating habits?  Maybe your digestion seems a bit more “sluggish”.

You may be convinced that your metabolism is slow.

Why does this happen? Why do metabolic rates slow down?

What can slow my metabolism?

Metabolism includes all of the biochemical reactions in your body that use nutrients and oxygen to create energy. And there are lots of factors that affect how quickly (or slowly) it works, i.e. your “metabolic rate” (which is measured in calories).

But don’t worry – we know that metabolic rate is much more complicated than the old adage “calories in calories out”!  In fact, it’s so complicated I’m only going to list a few of the common things that can slow it down.

Examples of common reasons why metabolic rates can slow down:

  • low thyroid hormone
  • your history of dieting
  • your size and body composition
  • your activity level
  • lack of sleep

We’ll briefly touch on each one below and I promise to give you better advice than just to “eat less and exercise more”.

Low thyroid hormones

Your thyroid is the master controller of your metabolism. When it produces fewer hormones your metabolism slows down. The thyroid hormones (T3 & T4) tell the cells in your body when to use more energy and become more metabolically active. Ideally, it should work to keep your metabolism just right. But there are several things that can affect it and throw it off course. Things like autoimmune diseases and mineral deficiencies (e.g. iodine or selenium) for example.

Tip: Talk with your doctor about having your thyroid hormones tested. Ask for a full thyroid panel which includes TSH, total T4, free T4, total T3, free T3, T3 uptake and thyroid antibodies (TPO and anti-thyroglobulin). At the bare minimum, get your TSH, including free T3 and T4 tested to see if they are in desirable ranges. If not, then request further testing. Doctors need to stop relying on the TSH blood test as the only way to test for hypothyroidism. You can read about those flaws here. Patients can feel terrible for years before the TSH starts to reflect what’s going on. Also note: when it comes to lab work, there is “normal” and there is “optimal”. Would you rather feel average or amazing?

Your history of dieting

When people lose weight their metabolic rate often slows down. This is because the body senses that food may be scarce and adapts by trying to continue with all the necessary life functions and do it all with less food.

While dieting can lead to a reduction in the amount of fat it, unfortunately, can also lead to a reduction in the amount of muscle you have. As you know more muscle means a faster resting metabolic rate.

Tip: Make sure you’re eating enough food to fuel your body and don’t become a chronic dieter. Learn how to stop the yo-yo dieting and eat in a way that supports your health, lifestyle and personal preferences so you can maintain your weight for life. Shameless plug: nutrition education and behavior change is what I do. If you’re interested in working with a coach please check out our programs here.

Your size and body composition

In general, larger people have faster metabolic rates. This is because it takes more energy to fuel a larger body than a smaller one.

However, you already know that gaining weight is rarely the best strategy for increasing your metabolism.

Muscles that actively move and do work need energy. Even muscles at rest burn more calories than fat tissue. This means that the amount of energy your body uses depends partly on the amount of lean muscle mass you have.

Tip: Do some weight training to help increase your muscle mass. I’m a huge advocate of strength training for women. It stimulates testosterone which drops as we age, it increases muscle mass, helps to improve or maintain bone density, and burns fat. The physical and mental benefits are countless!

Which leads us to…

Your activity level

Aerobic exercise temporarily increases your metabolic rate. Your muscles are burning fuel to move and do “work” and you can tell because you’re also getting hotter. 

Even little things can add up. Walking a bit farther than you usually do, biking to work, or taking the stairs instead of the elevator can all contribute to more activity in your day.

Tip: Incorporate movement into your day. Incorporating some form of cardio can stimulate your metabolism, improve your mood, and keep your heart muscle strong. It is recommended that healthy adults get at least 150 minutes of moderate activity or 75 minutes of vigorous activity a week.

Lack of sleep

There is plenty of research that shows the influence that sleep has on your hormones and metabolic rate. The general consensus is to get 7-9 hours of sleep every night.

Tip: Try to create a routine that allows at least 7 hours of sleep every night. If you want 14 actionable tips on how to get a better sleep, please read this post.



(Because the majority of women with hypothyroidism actually have Hashimoto’s Disease.)

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So, which one of these tips do you want to get started on? Let us know in the comments section below. We’d love to hear from you!

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