Unlocking Muscle Growth Through Optimized Carbohydrate Metabolism

There are so many benefits in exercising or stimulating the muscles. Some of them are obvious, like looking good, feeling better, and getting stronger. There are other benefits that are not spoken frequently, such as improving our immune system, brain health, secreting enzymes that have anti-inflammatory response, and fat metabolism (1).

As much as we want to take full advantage of benefit we can gain from building muscles, but how can we effectively do so, without gaining fat in a process? The answer is understanding and manipulating insulin.

First Law of Thermodynamics

First, let’s talk about how our body uses energy. To understand this, we will need to understand we’ll need to understand the first law of thermodynamics, which states that “energy can be transformed from one form to another but cannot be created or destroyed”.

What does this mean? It means that our body can store energy or use energy that is from our food sources, however, our body itself cannot create energy. When we eat food, depending on what we are doing, the body can either use or store energy for later use.

Therefore, macronutrients, micronutrients, supplements, or drugs cannot ignore this law.

However, depending on the type of macronutrients (carb, fat, and protein) and how our body uses those energy or calories, although they follow the law, it is different.

Way Our Body Use Food as Energy

Food sources only have 2 ways to use our body. 1.) immediate use and 2.) stored for later usage. When exercising, for example, we do want the energy immediately which can be used from stored calorie in a form called glycogen or a larger storage form called fat.

Ideally, we all want all our consumed and stored energy to be used for recovering muscles and promoting muscle growth and not storing body fat. Whether the body would use the energy to restore muscle or store as body fat is all depending on insulin and metabolic profile.

How Body Convert Food into Energy

The body must convert food sources to energy.  To understand this, I need to share something called mitochondrial respiration, which refers to how mitochondria produce energy from fat and glucose for our daily performance.

We have two energy sources that can be converted into energy, fatty acid, and glucose. Glucose can also be converted into two molecules called pyruvate and lactate.

The ideal primary energy source is fat. Stored fat or triglyceride can break up into 3 fatty acids and glycerol by the enzyme called hormone sensitive lipase (HSL). Fatty acid, then, with the help of the amino acid called carnitine, it enters mitochondria through the CPT1 transporter. Once fatty acid enters the mitochondria, the process called Beta-Oxidation starts. This is the process where mitochondria further break down into acetyl-CoA. After the breakdown into acetyl-CoA then enters the last phase called Kreb cycle then to electron transport. Through this process mitochondria can generate 129 ATP from fatty acids.

Glucose has 2 pathways. The first pathway is glucose breakdown to pyruvate through a process called glycolysis, then enter mitochondria convert into acetyl-CoA then enter Kreb cycle and electron transport like fatty acids. This process creates 32 ATP.

ATP stands for Adenosine Triphosphate. Think of it as currency for the cells. By consuming meat, vegetables, fruits, rice, the body does not know how to use it, so they need to convert it into ATP so that the body knows what to do with it. Just like when you travel to foreign countries. You cannot use US dollars in Japan so you will need to exchange the dollar to yen to make any purchases.

As we exercise, regardless of how fit you are, energy demand will increase. We do normally produce some amount of lactate, however, as energy demand increases, we create more lactate through glucose. Therefore, the second pathway for glucose is after broken down to pyruvate with decrease in cellular oxygen, then convert into lactate. If there’s enough MCT1 transporters in mitochondria, the lactate enters mitochondria then convert back to pyruvate.

Pyruvate converts into acetyl-CoA and enters Kreb cycle and electron transport. In this process 32 ATP are created. You may see 2 ATP is created; however, studies have shown that lactate pathways can generate 32 ATP.

Basics of Insulin and Insulin Sensitivity

All dietary carbohydrates will be converted into glucose in small intestine and absorbed into blood stream. For immediate use glucose will be stored in the liver and muscle as glycogen. For later use, glucose will be converted into triglycerides and stored as fat. Whether the glucose to be use as immediate energy or stored energy is determined by insulin level.

When we consume food, insulin level rises, and we always store food energy in the form of glycogen or triglycerides. For healthy individuals, muscle accounts for more than 80% of insulin stimulated glucose disposal and fat accounts for less than 15%.

The reason why the obesity population is growing is because people are consuming too much carbohydrate or wrong types of carbohydrates than the liver and muscles can store. Therefore, all excess carbohydrates or glucose will be converted to triglycerides and stored as body fat.

This fact can also lead to another fact to be true. Because people are less active or avoid building muscles for whatever reason, capacity to store glucose in muscles decreases, which will also lead to more glucose is sent to body fat.

In both cases, insulin sensitivity is decreased which also means that insulin resistance is starting to happen. This also means that an increase in muscle stimulation to build muscles and lowering (not eliminating) carbohydrate consumption can help restore insulin sensitivity.

Carbohydrate Intake for Muscle Growth

While restoring the insulin sensitivity, muscle growth will also become essential, and we do need carbohydrate along with protein in our diet. Of course, there are not any carbohydrates but vegetable type carbohydrates such as cruciferous vegetables, potatoes, and fruits.

Overall, it is good practice to limit carbohydrate intake because it is easy to overconsume carbohydrate which leads to decrease in insulin sensitivity. Decrease in insulin sensitivity or insulin resistance means there are more insulin floating in bloodstream.

It is very important to remember that when insulin is present in bloodstream, the body will not metabolize fat as an energy source. The only time stored energy of fat is utilized is when the insulin level is low. This higher insulin level will ultimately slow down the metabolic rate because the body is receiving the input from insulin to store rather than use. Whenever you feel like the metabolism is low or slow, it is possible that the insulin level is increased in the blood stream.

This is not ideal for those who are working out to build muscle and want to burn off fat because not only you cannot utilize fat as energy source, but you may also not have enough energy to complete the workout which will slow down the muscle building process.

The best timing to consume carbohydrates is immediately after the workout. The biggest reason is to restore glycogen in muscles that has been used during the session and able to replenish protein more efficiently. Although insulin inhibits fat metabolism, insulin can activate protein and glycogen synthesis which are essential for muscle growth. However, these two synthesis processes do not happen without physical activities.

Amount of carbohydrate is different from person to person; however, suggestion is ranging from 50-300g. Amount may vary due to the exercise intensity, body size and metabolic profile. Individuals with insulin resistance or diabetes may need to keep the carbohydrate intake lower around 50-150g per day.

Conclusion

Although I am sharing information on the function and effect of insulin and carbohydrates, this information does not mean that insulin and carbohydrates are good or bad. Excessively consumed carbohydrate which leads to decrease in insulin sensitivity which leads to high blood insulin concentration is bad. When you consume at proper timing, especially after your exercise, will have better benefit towards recovery.

Carbohydrates, with proper amount, timing, and quality, are important to our health especially when building muscles and restore energy for immediate use. Insulin plays an important role in storing protein, glucose and other nutrients to our body to restore and repair for the body to become stronger. Use them wisely and you can maximize the benefits of muscles.

Kota Shimada

Reference:

1. Bay, M. L., & Pedersen, B. K. (2020, September 9). Muscle-organ crosstalk: Focus on immunometabolism. Frontiers in physiology. Retrieved November 4, 2021, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7509178/#!po=81.5789.