Despite the arrival of spring, you may still 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 my metabolism?
Metabolism includes all of the biochemical reactions in your body that use nutrients and oxygen to create energy. Given this ENORMOUS scope of actions, there are lots of factors that affect how our metabolism functions (your metabolic rate).
It’s a complicated subject – entire programs and industries are dedicated to studying metabolism. So, 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 or hypothyroidism
Your thyroid is the master controller of your metabolism, involving several major steps and hormones. In a nutshell, when the thyroid produces fewer hormones (TRH, TSH, T3, T4) or if there is a problem with the conversion of T4 to T3 in your body tissues, your metabolism slows down.
The current "upper limit of normal" measurement for TSH in Canada are 5.0. The American College of Endocrinology has lowered their limit of "normal" to 3.0. From a holistic perspective, we like TSH numbers to be lower than 2.0.
In an ideal world, the hypothalamus, pituitary and thyroid gland work together on a negative feedback loop so that you produce optimum levels. But there are several things that can affect your thyroid function and throw it off course, causing you to either produce less than optimal thyroid hormone or have problems with conversion in the tissues.
Consider these risk factors and influences:
Chronic physical or emotional stress (the body prioritizes inflammation resolution over maintaining a perfect thyroid balance)
Autoimmune or auto-inflammatory disease (i.e., celiac, rheumatoid arthritis)
Poor bowel health (yeast overgrowth)
Estrogen dominance (fibroids, heavy menstrual cycle)
Diet low in iodine or meat (two precursors to thyroid hormones)
Poor digestion (you need stomach acid to absorb key amino acids to build healthy thyroid hormones)
Vitamin and/or mineral deficiencies: selenium, zinc, iron, vitamin A, C, B2, B3, B6
Poor kidney or liver function
Toxins and heavy metals: pesticides, mercury, cadmium, lead, flourine
Medications: lithium, naproxen
Symptoms of hypothyroidism:
Dry skin, hair
Low blood pressure
Hives, skin issues
TIP: If you have any of these symptoms and risk factors, and are concerned about thyroid, talk to your doctor about having a full thyroid panel tested (T3, T4, Reverse T3, antibodies, the works). If tests come back "normal" or "low normal" and you STILL have symptoms, consider also doing a basal body temperature test or looking at adrenal fatigue (cortisol is required in the T4 / T3 conversion). Undiagnosed, sub-clinical hypothyroidism and adrenal fatigue are so incredibly common (I have/had them!). Often, some simple supplements and a supportive meal plan can correct the issue.
Your history of dieting
When people lose weight, their metabolic rate often slows down for two reasons.
First, the body senses that food may be scarce. It adapts by trying to continue with all the necessary life functions and do it all with less food. You may lose weight initially, but then you plateau. That’s because your body switches to “survival” mode.
Second, while dieting can lead to a reduction in amount of fat, it can also lead to a reduction in muscle if you don't exercise on a regular basis. As you know more muscle means faster resting metabolic rate.
TIP: Don't drastically cut calories. Ensure you get enough quality food to fuel a regular 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 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.
Tip: Do some weight training to help increase your muscle mass.
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.
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.
Tip: Incorporate movement into your day.
Lack of sleep
There is plenty of research that shows the influence that sleep has on your metabolic rate. It allows for “recovery and repair” hormones to get to work, while our inflammation quells. Growth hormone is most active while we sleep - and growth hormone is responsible for an increase in muscle mass! 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.
Metabolism is a very complex subject – we are all different
Thyroid health is a key influencer of metabolism and many factors can impact it’s actions: stress, bowel health, protein, vitamins and mineral deficiency, toxins, autoimmune conditions, infections, inflammation
If your thyroid levels are normal, but you STILL have symptoms, do a basal body temperature test. You may have subclinical hypothyroidism which can be addressed through a supportive diet and some select supplements
A history of dieting can negatively impact metabolism. Ensure you eat enough food to fuel your daily activities
Weight training builds muscle, which can help increase metabolism
Aim for 7 – 9 hours sleep per night