What is metabolism anyway?

 When you think of “metabolism” you probably think of that person you know that can eat anything and never gain weight. Metabolism is actually more than this. A person’s metabolism refers to all the chemical reactions within the body¹. Specifically, let’s address energy metabolism, which narrows the broader topic down to the ways in which the body makes energy. The strength of your energy metabolism comes down to the number of and health of your cells’ mitochondria and the availability of fuel for them to convert into ATP (the body’s energy currency). Despite what you may have been led to believe, metabolism is more than a matter of just having lucky genes.

Real influences on your metabolism include: your food choices, how often and how much you eat, stress load, sleep, environmental exposures, gut health, the performance of your liver, adrenals, and thyroid gland, hormonal balance, and your cells’ ability breathe. When your metabolic rate is robust you have a warm body temperature, smooth digestion, clear skin, balanced blood sugar, restful sleep, strong hair and nails, regular menstrual cycles, strong libido, and sustained energy throughout the day. When it slows down it can cause problems like adrenal fatigue, hair loss, cold hands and feet, frequent respiratory infections, migraines, constipation, bloating, eczema or acne, weight gain, infertility, PMS, irregular menstrual cycles, blood sugar dysregulation, and a whole host of other undesirable issues. If you’re struggling with any of the negative symptoms listed, gaining a better understanding of how energy is made may help you begin working toward increasing your own energy production and metabolic rate.

 How Do We Make Energy?

You may be aware that our bodies use the food we eat to create energy, but did you know that our cells contain tiny organelles called mitochondria that make it happen?

When we consume carbohydrates, proteins, and fats, they are broken down into smaller molecules that our bodies separate and utilize in the creation of energy. While all foods can be used for energy production, carbohydrates are favored for the job because it takes fewer steps to turn them into the raw material (glucose) that our mitochondria can use to create adenosine triphosphate (ATP), the body’s main energy currency. While this can be accomplished by converting amino acids from proteins and glycerol from fat sources into glucose, carbohydrates quickly break down into the glucose needed to attach to ATP compounds. When ATP is broken apart, it releases energy that the body uses for its necessary functions as well as for body movement and activity.² The goal is to make abundant ATP for abundant energy production, and in doing so, the creation of energy also creates heat. According to the late endocrinologist, Dr. Broda Barnes, an ideal basal body temperature upon waking is between 97.8-98.2 degrees Fahrenheit.³ By using this as a guide, you can start building an understanding of the strength of your own metabolic rate.

Carbs are our Friends

“Wait!,” you may be thinking, “I thought carbs are bad and I should be using fat for fuel.” I know. I was you once, too. The problem with this scenario is that it stresses the body, and a stressed body gets in the way of itself, causing the metabolism to slow down and allowing its fine-tuned systems to slip out of balance. For example, the brain, nervous system, red blood cells, and retina cells rely on glucose for energy ^2,3. If the body doesn’t have glucose coming in by way of food, it turns to the process of gluconeogenesis, where it breaks down and converts tissues like lean muscle into the glucose it needs.² Conversely, building muscle tissue through proper protein consumption and exercise increases your overall metabolism by increasing the number and health of your cells’ mitochondria, and thus your ability to generate energy.

Not feeding the body what it needs creates stress in other ways that may affect our energy metabolism. We’ve covered how providing the body with glucose allows it to make ATP with its preferred material. Another benefit of using carbohydrates to make energy is that it creates carbon dioxide as a byproduct, where using fatty acids creates more oxygen, which leads to oxidative stress.

The Thyroid (and Sometimes the Adrenals) Run the Show.

The thyroid gland affects most systems and functions of the body, but it is the main driver behind the body’s metabolic rate.⁵ The thyroid is a small butterfly-shaped gland, sitting at the front of the throat. It regulates how our body uses oxygen, how well our organs function, and how quickly our body uses food for energy.⁴ Thyroid hormones are also directly linked to the mitochondrial process of making cellular energy and maintaining the body’s resting metabolic rate (how much energy is needed to fuel your most basic bodily needs).⁷ If the thyroid begins to lag and can’t keep us running at our prime, it causes problems—not just in the way we feel, but for the needs of the body to function. If our main metabolic manager can’t keep up, the body has a built-in back-up: the adrenal glands step in to keep us going.

The adrenal glands sit on top of the kidneys where they help manage stress responses through the release of hormones like cortisol and adrenaline.¹ Under normal circumstances, these hormones are used in moments of acute stress. A classic example of this is being chased by a sabretooth tiger. In this sort of survival scenario, your body needs glucose. Small amounts are stored in the muscles and liver for just this occasion. This is usually enough fuel to move quickly for a short time, but for more than that, the body needs to begin mobilizing more sugar with the output of cortisol. This is called the fight or flight response. In normal times of stress, you escape the tiger and your nervous system responds by coming back to a calm state. This calm state is also known as rest and digest, where your body redirects energy and nutrients back to its core, and it resumes normal functions like digestion instead of breaking down its own tissue to make blood sugar.

If thyroid function slows down, the body leans on the adrenals to make up for the energy and heat deficit that the thyroid cannot. You can think of the adrenals like a back-up generator you might store in the event of power loss.³ Much like the body might start outsourcing glucose during a stressful event, the body will break down tissue, like muscle, in order to meet the energy needs of the metabolism. In her book, How to Heal Your Metabolism, It has been hypothesized that this long-term compensation for the thyroid may actually be the source of what is commonly referred to as “adrenal fatigue” or “adrenal burnout,” and not in fact, a standalone issue in the adrenal response.³ Whether it is contributing to a burden on the adrenals or any of the other symptoms we may experience with an underperforming thyroid, suboptimal thyroid health leads to numerous imbalances and dysregulation in the body and it starts by impacting the rate of our energy metabolism.

When Problems Arise and How to Begin Addressing Them

Just as a strong metabolism can lead to overall health and wellbeing, a slow metabolism is associated with a laundry list of symptoms and in some cases, serious illness. If the thyroid is underperforming, you may experience things like constipation and digestive issues, problems with skin, thinning hair and eyebrows (especially the outer edges), imbalanced hormones and blood sugar, weakened immune system, feeling cold, weight gain, irregular menstrual cycles, brain fog, and fatigue.⁴ Many people today experience at least some of these symptoms. While thyroid testing is a fairly common practice, lab results may not always correlate with what the body is communicating. According to Dr. Ray Peat, the current lab values used to check for thyroid health may be excluding a large percentage of people who may still be suffering from the effects of low metabolism.⁶ This is often referred to as subclinical hypothyroidism. Labs may come back “normal” but a person can still be struggling with symptoms of a slow thyroid. It is important to talk to your doctor about running a comprehensive thyroid panel if you are considering testing your thyroid health with your health care provider. Another method of gathering data on thyroid function is to test your basal body temperature at home. As mentioned before, Dr. Broda Barnes associated optimal thyroid health with a waking body temperature between 97.8-98.2 degrees Fahrenheit. To get an accurate reading, he had his patients remain lying in bed while holding a thermometer under their tongue for several minutes before taking a temperature reading.

If you find that your waking basal body temperature is lower than 97.8 degrees, here are some simple changes that may start warming you up:

• Eat breakfast within an hour of waking
• Make sure to combine carbohydrates with protein and fats at every meal
• Eat whole food carbohydrates like fruits and root vegetables
• Eat every 3-4 hours to avoid low blood sugar

References

1. Tortora GJ. Introduction to the Human Body.; 2017.

2. Sharon Rady Rolfes, Pinna K, Eleanor Noss Whitney. Understanding Normal & Clinical Nutrition. Cengage Learning; 2018.

‌3. Deering K. How to Heal Your Metabolism : Stop Blaming Aging for Your Slowing Metabolism! : Learn How the Right Foods, Sleep, the Right Amount of Exercise, and Happiness Can Increase Your Metabolic Rate and Help Heal Your Broken Metabolism. Createspace Independent Publishing Platform; 2015.

‌4. Barnes BO, Galton L. Hypothyroidism : The Unsuspected Illness. Crowell; 1976.

‌5. Hyman MMD. Ultrametabolism. Scribner; 2006.

‌6. Peat, PhD R. TSH, temperature, pulse rate, and other indicators in hypothyroidism. raypeat.com. Published 2007. Accessed April 13, 2022. http://raypeat.com/articles/articles/hypothyroidism.shtml

7. Goglia F, Silvestri E, Lanni A. Thyroid hormones and mitochondria. Biosci Rep. 2002;22(1):17-32. doi:10.1023/a:1016056905347