What is Metabolism?

If you have been working out or working on improving your nutrition, you will come across the term metabolism. Typically though, metabolism is spoken in the context of being fast or slow. But what does that mean anyway?

What is metabolism?

Before we move on, let's get the definition straight. Metabolism in textbook definition is a chemical process that occurs in living organism to maintain life. Therefore, everything that happens in our body, whether is insulin secretion, digestion and absorption of food, protein synthesis and so on are a part of metabolism.

Metabolic rate is the way for us to numerically understand how much energy has been used by the body. So if you are bigger individual, you will have higher metabolic rate than someone who is smaller.

Think of the car engine for an example If you had 200 horse power engine versus 500 horse power engine, which has bigger engine size? Obviously 500 horse power right? Which requires more fuel? Also 500 horse power car. Although this analogy is similar to how human metabolism works but our body is little more complex than a car.

Two metabolism theories

To explain metabolism there are two different theory. Thermodynamic theory, where focusing on energy being stored or used. This is where energy in/ energy out or calorie in/ calorie out came. This theory believes that the weight gain or fat gain is due to excess energy or calories. But there is a problem. This theory ignores hormonal function, which is part of the definition of metabolism.

Second theory is hormonal dynamic, where excess fat gain is due to excess insulin. It is not replacing thermodynamic theory but it is adding better understanding of what metabolism actually does.

Insulin and Glucagon

Metabolism is dictated by the two hormones and depending on what hormone is predominant, the metabolic rate changes. Those hormones are insulin and glucagon.

Both insulin and glucagon are secreted by pancreas. They are like my kids where one does one thing and another does the complete opposite.

Main function of insulin is to store energy from food in a form of fat. This is very important because without insulin, we would never have survived. When insulin is predominant, protein synthesis and glycogen creation happens in muscles, fat and glycogen creation will occur in liver and in fat cells. So when we eat, despite what food source we eat, our insulin level will spike. Of course, higher the glucose level is the higher the spike of insulin will be.

When glucagon is predominant on the other hand, is use or waste energy. It does not have any affect in muscles, thank goodness, but does break down and use fat in fat cells, and in liver break down fat, create glucose, and create metabolites called ketones. Glucagon can be secreted more when we are fasted or follow a diet with very low carbohydrate intake.

Hormonal Function and Metabolism

From metabolic perspective, when insulin level is high our metabolic rate is decreased. This is shown on the study on diabetic patients comparing metabolic rate of before and after the insulin therapy. This makes sense because the role of insulin is to store. Therefore the metabolic rate cannot be high when the insulin level is high. It is not very surprising to see 20lb increase in diabetics with insulin treatment event when calorie intake is low.

When glucagon is high, opposite will happen. Because glucagon's role is to spend energy, metabolic rate increases. When we are fasted, our metabolic rate goes. This also make sense because your body is using and wasting regardless of what you are doing. Of course, the rate of usage will increase when activity level and muscle mass is greater.

Whether insulin or glucagon is high or low is based on ratio. As mentioned in characteristics of insulin, whether you eat low carb or high carb diet, the body will secrete insulin unless you are type 1 diabetic. However, depending on content of your meal, ratio of insulin to glucagon will be different. When you meal leads to high in insulin to glucagon ratio, then your metabolism will be slow and tend to store more fat or in muscle to promote protein synthesis. When insulin to glucagon ratio is low then you will have higher metabolism and will use fat.

What other factors contribute to metabolic rate?

Metabolic rate is depended on what hormone, insulin or glucagon, is predominant. However, other factors that can change the metabolic rate is muscle mass and activity level. When you have more muscle mass, despite the age, the body will be requiring more energy to survive. In other words the energy requirement to live has increased.

It is not necessary to bulk up like body builder, however, the physical activity level of the individual must increase.

Biggest benefit of increasing muscle mass is the body will have more insulin receptors, or place for body to send insulin too. Therefore, more insulin can be distributed to more cells than without more muscle mass, when we consume food. The body can also use more energy when we are in low carb or fasted state.

Age can contribute to metabolic rate, however, for those who are physically active and being mindful about insulin and glucagon ratio can have higher metabolic rate even at elder age.

Can you break metabolism?

By now you should understand basics of metabolism. When you are conversing with others, you may hear interesting comment like "my metabolism is broken" or " my metabolism is messed up". But it is never messed up or broken. What is broken and messed up is their daily habit of eating and physical activity. Yes, the metabolism will be lower when you have insulin resistance, but that doesn't mean it is broken.

Metabolism or metabolic rate can be changed based on your lifestyle. Physiology may be complicated yet application is quite simple. Apply metabolic rules below based off of what health and fitness goal you are pursuing.

Remember, both metabolic pathways, insulin or glucagon, are important. It is just a matter of how you utilize it that matters.

Metabolic Rule

1. To gain muscle or weight, insulin and glucagon ratio should be high.

2. To lose fat or weight, insulin and glucagon ratio should be low.

3. Glucagon can be predominant by low carb diet or fasting.

Kota Shimada