You may feel tired, cold, or that you've gained weight. 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 your metabolism?

Metabolism includes all of the biochemical reactions in your body that use nutrients and oxygen to create energy. 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 that 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 doctor can test this easily to rule it out)

• 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 - and usually it does. 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. Talk with your doctor about having your thyroid hormones tested. Don't fret - this is easily fixable with medication.

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 amount of fat, it, unfortunately, can also lead to a reduction in the amount of muscle you have. More muscle means faster resting metabolic rate. When you are losing weight, make sure you're eating enough food to fuel your body without overdoing it and that you are including strength training in your exercise routine.

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. This means that the amount of energy your body uses depends partly on the amount of lean muscle mass you have. That means it's critical to do weight training to help increase your muscle mass.

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, 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. Incorporate movement into your day and exercise regularly.

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. Try to create a routine that allows at least 7 hours of quality sleep every night.