Anabolic vs Catabolic

Written by Ben Bunting: BA, PGCert. (Sport & Exercise Nutrition) // British Army Physical Training Instructor // S&C Coach.

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Anabolic and catabolic refer to the two prominent types of chemical reactions present in your body.

In this article we shall cover how these reactions work and how they can be beneficial or detrimental to your fitness goals.

We shall cover the following points:

• Metabolic actions
• Anabolic reactions
• Catabolic reactions
• Anabolic pathways and muscle
• What does catabolism do?
• How to increase anabolism
• Summary

Read on to gain insight into how the human body works twenty-four-seven, making and breaking things to keep you strong and efficient. 

Metabolic Actions  

Whether you're sleeping or running outside, your body carries numerous catabolic and anabolic reactions every day.

Understanding these fantastic biochemical performances is an excellent way to figure out how your body transforms into various shapes and how it sustains itself for years.¹ 

While they might sound like some terms only relevant to scientists, anabolism and catabolism concepts are used by dieticians, doctors, and bodybuilders to achieve various goals.

This article will highlight how anabolism and catabolism differ and what are the different ways you can reach either.

Specifically, we will discuss how anabolic pathways work to increase muscle mass in the body.  

Metabolic Meaning

Metabolism refers to the set of chemical reactions that occur in each body cell to produce energy.

Simply, the process of converting food into energy in the body is termed metabolism.

This energy is then used to carry out various functions, e.g., building muscles or breaking down fat.

Making sure that your body is functioning correctly requires constant repair.

Thus, anabolic and catabolic reactions help the body build and repair all its tissue to ensure longevity and health.^2,3

If a person is not growing or shrinking, the dynamically working anabolic and catabolic pathways work equilibrium.

It means that the number of products being broken down is equal to the number of products being made. ⁴

You may hear of the term, ‘resting metabolic rate’ (RMR) or 'basal energy expenditure' (BEE). This is your bodies calorific needs to function and is based on a few factors such as body mass, height, gender and activity levels.

You can calculate your RMR/BEE by using a simple calculation based on anthropometric data (measurements of the human body).

By calculating your RMR you can establish whether you require more calories (for growth), fewer calories (to lose weight) or maintain your current calorie intake to maintain weight.

Anabolic Reactions

Anabolic metabolism or anabolism is a set of reactions that use energy to build or synthesize various compounds, e.g., muscle proteins from amino acids.

You can think of it as building a wall with bricks, which is the opposite of catabolism. An example can be your body trying to heal a wound you encountered while playing football.

During anabolism, a team of different types of cells with several enzymes works together to form compounds from glucose, amino acids, and fatty acids.

Combining these smaller molecules, your body then creates new cells, making new tissues, for example, a healed scar.⁵ 

Another way anabolism works is when you're fed, or your caloric intake is more significant than your caloric expenditure.

Like every other living organism, humans are programmed to strive for survival. For physical survival, we need food.

The human body is always striving to store food that can be used in times of need, e.g., a starving state.

To accomplish this goal, your body breaks down the food you eat and develops similar but different compounds that can be stored for future use. An example is glycogen stored in your muscles.

Every time you drink orange juice, the carbohydrates (starch, fructose) are broken down into glucose and transformed into glycogen to be stored in the muscles. ^3,4

Your body can store about 900g of glycogen within the muscles and liver which is the preferred fuel source for exercise.

However, these stores can be depleted within just 90 minutes of intense activity. Once depleted it can lead to huge feelings of fatigue and lethargy, this is sometimes known as ‘hitting the wall’.

Catabolic Reactions

Catabolic metabolism or catabolism is a term used for the set of reactions that aid in the breakdown of various substances in the body.

You can think of it as digestion. This breakdown is carried out by special biological machines called enzymes.

Enzymes target specific compounds like fat, protein (muscle protein), and carbohydrates (glycogen) and chop them down into simple molecules like fatty acids, amino acids, and glucose.

On days you are fasting, your body digests the glycogen stored in the liver to provide you with energy. 

Anabolic and Catabolic Hormones 

You might know that hormones (chemical messengers) are required to initiate and regulate reactions at every level in the body.

Certain hormones push the responses into catabolic pathways while other hormones activate anabolic pathways. 

The anabolic hormones stimulate growth, e.g., muscle growth after working out. They consist of:

• Testosterone (T) and other androgens
• Human growth hormone (HGH) and insulin-like growth factor (IGF) 1
• Insulin 
• Estrogen

On the other hand, the catabolic hormones are related to times of stress, e.g., when you are working out or running away from a bear. They consist of:

• Glucagon
• Adrenaline or Epinephrine 
• Cortisol or stress hormones^6,7

How do anabolic pathways help build muscle?

Every outcome needs a stimulus.

To begin with, we need to look at how your muscles get stimulated through a different mechanism and how your body reacts (results) to these stimuli, i.e., anabolism.

Once the general idea of how that happens is familiarized, it gets easy to manipulate your body into anabolism or catabolism - bulk up or shred.

The moment you start exercising, your muscles and other organs receive exertion stimuli.

Stimuli are of different scales and categories, and the best incentive for muscle growth proven by science is resistance training.

Resistance training refers to doing exercises against a form of stress, e.g., lifting weight against gravity via your muscles.

Loading your body around 70-80% of your rep max (1-RM) is optimum to generate growth signals in the muscles.

The signals generated via exercising or training initiate a cascade of events that require two things. Hormones and food.

For anabolic reactions, insulin and growth hormone/IGF-1 (most crucial) along with testosterone are released, which stimulate the muscles to do the following:

1. Increase their uptake of food, e.g., glucose (from baked potatoes), amino acid (from fish), and fatty acids or cholesterol (from an avocado). 
2. Signals the cell nucleus to initiate growth, i.e., produce new proteins. We will shortly discuss how that happens.
3. Manufacture new proteins
4. Incorporate these new proteins in the muscles, tendons, and joints.

These processes are carried out so that your quadriceps, for instance, can get better at lifting weight during squats exercise.

As you can have guessed, this series of processes focus on building new tissues instead of breaking down previously formed tissue. This is anabolism in essence. 

The mTOR Signaling and IGF-1

The most well-known mechanism related to skeletal muscle growth by science is the mammalian target of rapamycin (mTOR) and its activation or upregulation by the hormonal stimulus of IGF-1/insulin.

High amounts of IGF-1/insulin are released following exercise and intake of food. As per much research, after a bout of loading training or resistance training, the mTOR signals are upregulated for up to 36 hours.

This occurs partly due to the IGF-1 mediated signaling of the skeletal muscles. 

The skeletal muscle, sensing a rise in IGF-1/insulin, initiates a chain of chemical reactions that instantly raise mTOR levels.

To date, numerous studies have shown that mTOR regulation of muscle protein is of prime importance.

Another anabolic pathway that may determine the rate of protein synthesis is the beta-catenin/c-Myc signaling.

Summing this up, these signaling mechanisms enhance the rate of protein synthesis and decrease the protein turnover (breakdown) following adequate external stimulation through exercise and food.^7,8

An essential concept to keep in mind here is that anabolism requires energy surplus.

Apart from the stimulus provided by training, your caloric intake, i.e., calories from the food, should be higher than the caloric expense.

The caloric expense depends on burning calories while exercising or due to basal metabolic rate (energy required to keep vital organs working during rest, e.g., breathing).

In fact, research has shown that protein intake is essential for the anabolism of skeletal muscle protein.

Many studies recommend that athletes consume an average of around 1.6 – 2.4 grams of protein/kg every day for an adequate protein anabolism.⁹

At the end of the day, if you have a positive energy balance (with enough protein intake), that energy will be utilized to build new tissue.

If added with the adequate muscle forming stimulus, you'll experience muscle growth and increased strength.

We will discuss how to boost your anabolism shortly so you can make the most out of this information. 

What does catabolism do?

Catabolism works counter-anabolic. During rest, your body needs a minimum amount of energy to keep the vital organs alive.

This is known as the basal metabolic rate or resting metabolic rate and averages around 2000 – 2500 kilocalories/day for a person.

On days when your caloric intake is lower than BMR, your body starts catabolizing the stored food compounds in the body for a continual supply of energy. 

Low glucose levels usually reveal a decrease in energy, and it is the earliest marker of decreased energy in the body.

Similar to the anabolic pathway, sensing this decrease in glucose (a stimulus), the body releases various hormones.

The earliest one is glucagon, followed by epinephrine or adrenaline and cortisol or glucocorticoids. 

Collectively, these hormones inhibit the effects of anabolic hormones, i.e., insulin and IGF-1, thus stopping the synthesis of new compounds.

Simultaneously, these hormones act on many tissues in the body and initiate the cascade of compound breakdown.

Glucagon acts on the liver and muscle cells to digest glycogen into glucose. It also serves to inhibit fat storage and increases lipolysis (fat breakdown).

Additionally, Adrenaline and cortisol have similar functions and help maintain glucose levels at an optimum level for survival.²

Over more extended periods, i.e., weeks of starving or undernourishment, the continuously elevated cortisol or the stress hormone results in the breakdown of muscle protein for fulfilling the body's energy requirement.

This eventually manifests as loss of muscle mass and progressive weakness. It also increases fat mobilization, causing thinning of the limbs and truncal obesity, translating into a growing waistline. 

It should be noted that when the body is predominantly in the state of catabolism, you'll lose weight instead of gaining.

It is undoubtedly helpful when you are trying to cut down the excess fat to look leaner, but it is not optimum for muscle growth.

Moreover, a high caloric deficit diet with inadequate rest keeps the cortisol elevated, leading to protein breakdown and a decline in lean muscle mass.

How to Increase Anabolism

There are several evidence-based methods and techniques that you can incorporate into your daily routine to shift your balance towards anabolism.

These tips mainly include dietary modifications, routine modifications, and training regimens.

However, being consistent in several pro-anabolic habits will guarantee growth, especially muscle growth. 

• Eat enough calories with adequate amounts of protein – this is one of the fundamentals regarding muscle anabolism, especially for people looking to grow their muscles. As mentioned earlier, having an ample supply of protein is crucial for an effective anabolic drive in the skeletal muscles. For athletes, it is also imperative to choose the protein options that deliver all the essential amnio-acids (EAAs) required for protein synthesis. Lastly, it would be best to aim for a caloric surplus, i.e., 200-300 kcals above your daily requirement (RDA) to stay anabolic. 
• Resistance Training – studies have shown that this resistance training or high force muscle contraction significantly affects skeletal muscle hypertrophy (growth). Interestingly, training can directly activate the mTOR pathway even in the absence of IGF-1 or other hormonal signals. Hence, resistance training is one of the cornerstones of muscle protein anabolism. 
• Ensure your body is getting the micronutrients (vitamins/minerals) - your body needs micronutrients to develop, recover and maintain optimum testosterone secretion. This can be from nutritionally rich food sources, or a science backed supplement.
• Getting adequate rest – you'll find this advice in every fitness-related article, and it is so because of its importance. Rest is vital for tissue growth and repair. When it comes to training and increasing skeletal muscle growth, resting becomes necessary. Whenever you tax your muscles with a training session, the metabolic and mechanical stress your muscles encounter is only cured by resting. Inadequate rest also impairs the body's ability to regulate hormones and thus locate the food properly. Resultantly, your body becomes ineffective in growing muscles.^5,10

Summary

Anabolic and catabolic reactions are two opposing reactions that occur throughout the day in our body.

Anabolic reactions or anabolism work to increase the production of new compounds and tissues in the body, such as the skeletal.

On the other hand, catabolism is primarily responsible for reducing large complex molecules and tissues, e.g., fat, around your body.

To increase your anabolism, you should aim to have a good diet, training regimen, and sufficient rest.

We hope this article helps you embark on your very own muscle-building journey. 

References:

1. Anabolism and Catabolism: Definition and Examples. Accessed April 9, 2022. https://www.thoughtco.com/anabolism-catabolism-definition-examples-4178390
2. Berg JM, Tymoczko JL, Stryer L, Gatto GJ. Biochemestry. Published online 2011:1224. https://silo.pub/biochemistry-seventh-edition.html
3. Ramsey KM, Marcheva B, Kohsaka A, Bass J. The clockwork of metabolism. Annual Review of Nutrition. 2007;27:219-240. doi:10.1146/ANNUREV.NUTR.27.061406.093546
4. Nava ASL de, Raja A. Physiology, Metabolism. StatPearls. Published online September 20, 2021. Accessed April 8, 2022. https://www.ncbi.nlm.nih.gov/books/NBK546690/
5. Catabolism vs. Anabolism: What’s the Difference? – Cleveland Clinic. Accessed April 11, 2022. https://health.clevelandclinic.org/anabolism-vs-catabolism/
6. Demling RH. The Role of Anabolic Hormones for Wound Healing in Catabolic States. Journal of Burns and Wounds. 2005;4:e2. Accessed April 9, 2022. https://pubmed.ncbi.nlm.nih.gov/16921407/
7. McCarthy JJ, Esser KA. Anabolic and catabolic pathways regulating skeletal muscle mass. Curr Opin Clin Nutr Metab Care. 2010;13(3):230. doi:10.1097/MCO.0B013E32833781B5
8. Miyazaki M, Esser KA. Regulation of Protein Metabolism in Exercise and Recovery: Cellular mechanisms regulating protein synthesis and skeletal muscle hypertrophy in animals. Journal of Applied Physiology. 2009;106(4):1367. doi:10.1152/JAPPLPHYSIOL.91355.2008
9. Hector AJ, Phillips SM. Protein Recommendations for Weight Loss in Elite Athletes: A Focus on Body Composition and Performance. Int J Sport Nutr Exerc Metab. 2018;28(2):170-177. doi:10.1123/IJSNEM.2017-0273
10. Moore DR. Maximizing Post-exercise Anabolism: The Case for Relative Protein Intakes. Frontiers in Nutrition. 2019;6:147. doi:10.3389/FNUT.2019.00147