The Importance of Amino Acids in Muscle Gain and Fat Loss

You’ve probably seen new gym-goers, gym bros, and advanced lifters adding powdered BCAAs into their shakers before, during, and after workouts. You’ve also probably seen amino acid jargon printed on the label of your go-to protein powder. Everyone has heard of them, but few people truly know the importance amino acids have in helping you achieve your fitness goals

What Are Amino Acids?

Amino acids are the building blocks of protein and muscle tissue. They play a major part in physiological processes relating to our energy, recovery, mood, brain function, muscle and strength gains, and even in our quest for fat loss.

There are 20 amino acids, and 9 of these are classed as essential or indispensable amino acids (IAA) that must be obtained from our nutritional intake. The others are termed dispensable amino acids (DAA), or non-essential, due to the body being able to synthesize them from other amino acids.

Graphic of the structures of the 20 amino acids.

Different Ways to Consume Amino Acids

Amino acids are found in the food you eat and the supplements you take. Protein-rich foods such as lean meats, non-fat dairy products, and protein drinks are the most common ways that we get our amino acids. We can also obtain amino acids from vegetables and legumes. Additionally, protein drinks and amino acid supplements can serve as a convenient means to supplement our dietary needs.

Many of us don’t consider the amino acid content and balance of our food, but the amino acid content of our meal is an important factor in supporting maximum muscle growth; however, it is not the only factor to take into consideration. You also have to factor in the extent that the amino acids are delivered to the tissues where they are needed. This brings us to the bioavailability, digestion, and absorption of amino acids by the body. 

Bioavailability, Digestion, and Absorption of Amino Acids


From pre-packaged amino acid workout and recovery drinks to powdered amino acids in the gym bags of fitness enthusiasts across the world, it is safe to say that the popularity of amino acid supplements has dramatically increased over the past several years. The main reason we use supplements is the bioavailability of the amino acids. Bioavailability is the measure of a substance’s ability to be absorbed by the body. Two factors determine amino acid bioavailability:

  1. How much fat is contained in the protein source
  2. The length of time it takes for the amino acids to be available for use by the body

Digestion and Absorption

The good thing about supplements, like powdered or capsuled BCAAs, is that they don’t require digestion like food does. Most supplements contain free-form amino acids meaning they are free of chemical bonds to other molecules and move quickly through the stomach into the small intestines where they are very rapidly absorbed into the bloodstream.

When absorbed, amino acids are processed by the liver. However, the liver can only process so many amino acids at one time. If you consume a dose of amino acids that exceeds the liver’s capacity, the amino acids will be redirected to the muscles. A dose of 3-4g of amino acids is enough to achieve this result.

Several factors contribute to the absorption rate of amino acids:

  • Cooking of foods
  • Whether the food is a solid, liquid, powder, or even tablet
  • The extent to which the amino acid is chemically pre-digested
  • Fillers and binders present in the food/supplement
  • Digestive system health

Muscle and Strength model wearing a blue M&S tank and black shorts scooping supplement powder into shaker cup.

Benefits of Amino Acids

Provides Source of Energy

A lot of misconceptions exist about the use of energy substrates during heavy, high-intensity weight training. When performing your training with repetitive, power workouts, a substantial portion of your energy comes from non-carbohydrate sources. When your muscles contract, they use stores of adenosine triphosphate (ATP, a substance vital to the energy processes of all our living cells) for the first few seconds. These stores are immediately replenished by creatine phosphate (CP). This biological process is how the supplement creatine became so popular with bodybuilders and strength-trained athletes.

Creatine is made from three amino acids: arginine, methionine, and glycine. To keep our CP and ATP levels high, these amino acids must be kept elevated in our bloodstream. The amino acids in creatine supplements can be supplied by foods in our diet, but the process of elevating these amino acids takes a great deal of time in digestion and also would be accompanied by fats and carbohydrates. So, the use of free form amino acids, either alone or in combination with creatine supplements, can provide a direct source of energy for power and strength.

Related: Creatine Supplements Guide

Prevents Muscle Breakdown

Our body has the ability to break down our muscle tissue for use as an energy source during heavy exercise. This is part of a bodily process called gluconeogenesis, which means producing or generating glucose from non-carbohydrate sources. The part of this reaction that is important to us as bodybuilders is known as the glucose-alanine cycle. In this process, the BCAAs are stripped from the muscle tissue and parts of them are converted to the amino acid alanine, which is then transported to the liver and converted into glucose. If we consume supplemental BCAAs, the body does not have to break down our muscle tissue to gain extra energy. Studies have concluded that the use of up to 4g of BCAAs during and after training can result in a significant reduction of muscle breakdown during training. Catabolism of muscle can cause shrinkage of our muscles and muscle soreness and may also lead us to injury.

Muscle & Strength model wearing grey M&S t-shirt doing cable tricep pushdowns.

The Importance of Amino Acids in Muscle Growth

Muscle growth is caused by exercise, hormones, and nutrients. Resistance training generally stimulates both protein synthesis and protein degradation in exercised muscle fibers. The normal hormonal environment (e.g, insulin and growth hormone levels) in the period following resistance training stimulates the muscle fibers’ anabolic processes while blunting muscle protein degradation. Dietary modifications that either increase amino acid transport into muscles or increase anabolic hormones should augment the training effects by increasing the rate of muscle anabolism and/or decreasing muscle catabolism. Either effect will create a positive body-protein balance for improved muscle growth and strength.

Supplementation of free form amino acids that are high in the branch chain amino acids (BCAAs)  Leucine, Isoleucine, and Valine will also assist in muscle growth. The ideal time to consume amino acids is immediately after training when the muscle is especially receptive to nutrients and blood flow to the exercised muscles still remains high. After training, muscle growth and recovery can be optimized with a meal consisting of a fast-digesting protein and both simple and complex carbohydrates. Whey protein is a great option for fast-digesting protein.

The Role of Amino Acids in Fat Loss

In fat loss, two major processes must occur:

  1. The mobilization and circulation of stored fats in the body must be increased
  2. Fats must be transported and converted to energy at the mitochondria (the powerhouse site of cells)

Several nutrients can assist in the conversion of fat to energy including the amino acid methionine, which in sufficient amounts can help improve the transport and metabolism of fat. When attempting to keep your total calories down during dieting, amino acid supplements, including BCAA’s and glutamine, can also help to keep our food volume down but still provide support directly to the muscles, liver, and immune systems, which are critical to optimizing our body composition.


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