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Understanding the Science Behind Metabolism

By | September 19, 2016 | fitness, nutrition

Metabolism is related to weight loss and weight loss resistance, but how?

It can be frustrating if you’re having trouble shedding pounds, even though you are eating correctly and exercising. Maybe even more frustrating when there’s that one person that eats everything but doesn’t gain weight. We might say they have a “fast metabolism” and chalk up our own weight-loss failure to a “slow metabolism” — but what does that even mean?

To take control of your body, start with the basic science behind metabolism. When you understand the chemical processes that is your metabolism, you can manipulate it to your advantage — whether you’re trying to take the weight off or put it on.

The five factors of fat metabolism

The word metabolism is thrown around without definition. So let’s begin with what metabolism is. Breaking it down, metabolism is a chemical process that occurs at the cellular level. At it’s most basic, cells are converting chemicals (from the things you eat and drink) into energy. This energy is used by your organs to function. Typical fat metabolism uses proteins, carbohydrates, and lipids from the food we eat.

So let’s look at the factors that contribute to metabolism and can influence weight loss and weight loss resistance:

  1. Insulin and glucose
  2. Caloric intake
  3. Thyroid gland function
  4. Basal metabolic rate
  5. Exercise and activity

Clearly, there are factors that are within your control — what you eat and your activity level — and there are biological factors that may be a little bit more nebulous. But by understanding these factors, you can make more informed lifestyle decisions to hit your target weight, or whatever is right for you. Now, let’s explore the factors that contribute to your metabolism.

Insulin and glucose

Insulin, produced by the islet cells of the pancreas, is responsible for transporting glucose from the bloodstream and turning it into cellular fuel. Those suffering from type 2 diabetes and those who are overweight could be experiencing a form of insulin resistance, which means cells are starved of the fuel needed for proper metabolism.

Caloric intake

What is a calorie? It’s actually a measure of energy. The scientific equation is one calorie is the energy it takes to raise one gram of water by one degree Celsius. (Hint, “calorie” on our food labels is actually a kilocalorie). Calories — the food we eat — fuel our basic bodily functions and anything in addition. So to maintain a certain weight, you need to maintain energy in and energy out. If we consume more energy (calories) than we use, it is stored as fat for later use.

Thyroid gland function

The thyroid is a butterfly-shaped endocrine gland located in front of your windpipe. It produces hormones essential for turning on cellular metabolism. Low thyroid conditions can result in feelings of sluggishness. With these conditions, metabolism of the cells decreases and calories from protein, carbohydrates and fats more rapidly turn to fat. This can result in weight gain and an increase in the percentage of fat-based body weight. People with hypothyroidism, where the thyroid is low producing, often experience fatigue, slower heart rate, slower bodily functions, difficulty with weight loss and dry skin.

Basal metabolic rate

Basal metabolic rate, exercise and caloric intake go hand-in-hand when it comes to fat metabolism. The basal metabolic rate determines how many calories you can take in before gaining weight. Any calories you take in beyond that need to be burned off through regular exercise, otherwise those nutrients are turned into fat and stored as fat cells in the body. Basal metabolic rate will change with age and size.

Exercise and activity

Now that we understand how our body consumes, converts, and stores energy, we can then factor in how exercise and activity can help with weight control. Surprisingly, it doesn’t take marathon training to maintain a healthy weight if you are managing your caloric intake. Again, “calories in, calories out” is a good place to start. Track what you eat along with your activity level (a fitbit or smartwatch can help). Talk to a nutritionist if you have questions on how to adjust your diet to support your lifestyle.

Take control of your metabolism

There is some more chemistry to help understand the role metabolism plays in weight gain, muscle development, and weight loss. Simply eating less isn’t always the best solution. Severely restricting calories may decrease your metabolism and cause you to lose muscle mass That’s because there are two types of metabolic processes: catabolic and anabolic.

Anabolic versus catabolic metabolism

The difference is crucial if you are trying to slim down and build muscle. That’s because catabolism is when the body breaks down larger molecules to release energy. So a strict diet might lead your body to feed off of fat or muscle tissue for energy. This may counter efforts to build muscle. Anabolism is taking energy to build up larger molecules. Caloric reduction and increased exercise may seem like a straightforward equation to lose weight. But if you are trying to maintain or build lean muscle it is important to commit to a program that includes proper nutrition, resistance training, and adequate recovery time.

Find the right lifestyle for your body type and your fitness goals

Ultimately, we are all built a little different. Not all of us are mesomorphs that put on muscle like a pair of pants. And not all of us want to bulk up. It’s important to be realistic about what your body is capable of, while also designing a lifestyle that works for you. A good place to start is with a self-assessment of the five factors of fat metabolism.

Are you trying to lose or gain weight, but having a hard time doing so? Tell us about it in the comments section below.


  1. Metallo, C., & Vander Heiden, M. (2013). Understanding Metabolic Regulation and Its Influence on Cell Physiology. Molecular Cell, 49(3), 388-398. doi:10.1016/j.molcel.2013.01.018
  2. Brady, B., MD. (n.d.). Thyroid Gland, How it Functions, Symptoms of Hyperthyroidism and Hypothyroidism. Retrieved September 11, 2016, from http://www.endocrineweb.com/conditions/thyroid-nodules/thyroid-gland-controls-bodys-metabolism-how-it-works-symptoms-hyperthyroi

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