Health and Wellness

Slow Metabolism

Why is My Metabolism Slow?

Do you feel like you’ve been gaining weight even though you haven’t changed your diet? Are you consistently tired or cold? You may have a slow metabolism.

Why does this happen? Why does your metabolism slow down?

What causes slow 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. This is called your “metabolic rate,” which is measured in calories.

Your metabolic rate is much more complicated than the outdated “calories in vs calories out” idea. Here are just a few things that can slow down your metabolism:

Examples of common reasons why you may have a slow metabolism:

  • low thyroid hormone
  • long history of dieting
  • your size and body composition
  • your activity levels
  • undereating
  • 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 the thyroid 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. But there are several things that can affect it and throw it off course. Things like autoimmune diseases and mineral deficiencies (commonly iodine or selenium) for example. Long-term stress can kill your thyroid function.

Tip: Talk with your doctor about having your thyroid hormones tested.

A history of dieting

When you eat less, your metabolic rate often slows down. his is because the body senses that food is scarce, and adapts by lowering your energy output to deal with the lack of calories.

While dieting can lead to a reduction in body fat, it unfortunately can also lead to a reduction in the amount of muscle you have. Muscle is what burns fat. The more muscle you have, the faster youe resting metabolic rate will be.

Tip: Make sure you’re eating every 3 or 4 hours, and eating enough calories overall, to fuel your body and keep your metabolism from slowing down.

Your activity levels

Sitting tanks your metabolic rate. So get up and move as often as you can! Even little things can add up — Walking a bit farther than you usually do, using a standing desk instead of sitting all day, or taking the stairs instead of the elevator can all contribute to more activity in your day.

Aerobic exercise only temporarily increases your metabolic rate. Your muscles are burning fuel to move, so they’re doing “work”. But after you’re done with cardio, you don’t get a lasting metabolic “afterburn” like you do when you train with weights.

Some research shows that your metabolic rate (i.e. your hourly calorie burn) is elevated for as long as 72 hours after a hard strength training workout. So if you want to lose weight, get off the treadmill and pick up the dumbbells instead!

Tip: Incorporate movement into your day. Also, exercise regularly with weights.

Lack of sleep

There is plenty of research that shows the influence that sleep has on your 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. Limit screen time before bed. Don’t drink too much alcohol – it drops your blood sugar, which can cause you to wake up in the middle of the night.

Your body composition

Your “body composition” means your lean vs body fat ratio. Body fat is not very metabolically active. Muscle tissue is. Muscle is metabolically “expensive”, meaning that is requires a lot of calories to maintain. Fat just sits there.

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

Tip: Do regular weight training to help increase your muscle content.


If you need help setting up a safe and effecting weight training program, contact Basics and Beyond fitness & nutrition for help! We see clients in Nashville, Brentwood, Franklin, Antioch, and Bellevue — And we have both in-home and online options if you don’t want to come to a gym!