What Are Amino Acids? A Detailed Explanation


There are lots of terms related to diet and nutrition that are commonly used, even in everyday conversations, but that many people don’t fully understand. 

Examples include macronutrients (the three primary types of nutrients: proteins, carbohydrates, and fats), micronutrients (vitamins and minerals), and antioxidants (powerful compounds that reduce oxidative damage in the body by combating free radicals).

Another frequent dietary term is amino acids. You might hear additional terms such as essential amino acids and non-essential amino acids.

But what is an amino acid? How many amino acids are there? Do you need non-essential and essential amino acids?

In this article, we will answer the questions what are amino acids, how many amino acids there are, the differences between essential and nonessential amino acids, and the roles of amino acids in the body.

We will cover: 

  • What Are Amino Acids?
  • How Many Amino Acids Are There?
  • Essential Amino Acids vs. Non-Essential Amino Acids
  • What Are BCAAs?
  • What Foods Contain Amino Acids?

Let’s get started!

A chalkboard that says amino acids and foods surrounding.

What Are Amino Acids?

Amino acids are a specific type of biological molecule that get linked together to form proteins. In this way, amino acids are typically considered to be the “building blocks“ of protein molecules.

Amino acids are considered organic compounds because they contain a backbone of carbon atoms bonded together with hydrogen atoms.

Every amino acid has certain structural components that are identical to one another, but then there is a side chain of this basic structure. The side chain, termed the R-group, is what differentiates each different amino acid and determines the unique properties of that particular amino acid and how it bonds and interacts with other molecules.

Amino acids link together by peptide bonds and can form long linear chains, or three-dimensional structures, depending on the complexity and type of protein molecule.

A list of what the amino acids are.

How Many Amino Acids Are There?

 The human body breaks down all the protein contained in the foods we eat into 20 unique amino acids, whether the protein source of dietary protein is meat, beans, dairy, eggs, fish, vegetables, etc. 

These amino acids can then be used by the body to manufacture all the various structural and functional proteins we need.

Similar to the concept of the 26 letters in the alphabet that can be arranged in different combinations and patterns to form every single word in the English language, the 20 amino acids are like “letters” that can be strung together in different combinations to form any of the hundreds of proteins the body needs for various functions.

Although we often just think of proteins forming muscle tissue in the body, proteins are actually involved in tons of different structures and physiological processes in the body as well.

Proteins form constituent components in DNA, hair, nails, enzymes, neurotransmitters, and hormones, among other biological structures help produce energy to fuel white blood cells, digest food, etc.

Essential Amino Acids vs. Non-Essential Amino Acids

Of the 20 amino acids our body needs, there are nine essential amino acids (EAAs), which means that they must be consumed in the diet or in supplement form because our body cannot manufacture them endogenously. 

The 9 essential amino acids, along with the recommended daily intake of each essential amino acid per the Cleveland Clinic, include the following:

Histidine written on a piece of graph paper.

#1: Histidine

Histidine is an essential amino acid that supports the immune system, digestion, sleep, and sexual and reproductive functions and helps form a neurotransmitter called histamine. 

The recommended daily intake of histidine is 14 mg/kg of body weight.

#2: Isoleucine

Isoleucine is considered a branched-chain amino acid (BCAA), so it helps produce energy and support muscle tissue growth. It also is involved in helping the body manufacture hemoglobin, the protein molecule that helps carry oxygen through the blood.

The recommended daily intake of isoleucine is 19 mg/kg of body weight.

#3: Leucine

Leucine is a BCAA that is critical for muscle repair, wound healing, blood sugar regulation, and the manufacturing of proteins and growth hormones.

The recommended daily intake of leucine is 42 mg/kg of body weight.

#4: Lysine

Lysine helps produce hormones and energy and plays a role in immune and calcium function.

The recommended daily intake of lysine is 38 mg/kg of body weight.

Methionine on a tablet.

#5: Methionine

Methionine is required for the absorption of certain essential minerals such as zinc and selenium; it also is involved with tissue growth, energy metabolism, and detoxification of the body.

The recommended daily intake of methionine is 19 mg/kg of body weight.

#6: Phenylalanine

Phenylalanine helps produce other amino acids that the body can manufacture on its own. It’s also required for the production of neurotransmitters such as dopamine, norepinephrine, and epinephrine.

The recommended daily intake of phenylalanine is 33 mg/kg of body weight.

#7: Threonine

Threonine forms a component of collagen and elastin, which are two structural proteins found in the skin and connective tissue. This essential amino acid is also involved in the blood clotting process and helps metabolize fat.

The recommended daily intake of threonine is 20 mg/kg of body weight.

#8: Tryptophan

Tryptophan helps form a neurotransmitter called serotonin, which has numerous roles in the body, including regulating digestion, sleep, and mood. Tryptophan also helps maintain the proper nitrogen balance in the body.

The recommended daily intake of tryptophan is 5 mg/kg of body weight.

BCAA, valine, leucine and isoleucine written next to a test tube of powder.

#9: Valine

Valine is one of the BCAAs. It supports muscle growth, tissue regeneration, and energy generation.

The recommended daily intake of valine is 24 mg/kg of body weight.

There are also 11 amino acids termed nonessential amino acids because your body can manufacture them naturally. 

The nonessential amino acids include alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, and tyrosine. 

It is important to note that some of these nonessential amino acids are sometimes classified as conditional amino acids, which means that they become essential amino acids under certain circumstances, such as with chronic illnesses, pregnancy, or in times of high stress.

Some nonessential amino acids are classified as conditional.

This means they’re only considered essential when you’re ill or stressed. Although different sources cite slightly different lists, conditional amino acids typically include arginine, cysteine, glutamine, tyrosine, glycine, proline, and serine.

Powder and pills.

What Are BCAAs?

As mentioned, three of the essential amino acids are classified as branched-chain amino acids BCAAs (leucine, isoleucine, and valine), all of which are essential amino acids. BCAAs are so named because they have a branched-chain structure. 

This unique chemical structure enables them to bypass digestion in the liver and go straight to the muscles, where they can be immediately used for energy. BCAAs may reduce fatigue during exercise. 

For example, studies show BCAAs can reduce the level of perceived exertion, preserve glycogen stores during endurance exercise, and decrease lactate production, increasing the time to exhaustion, which is why BCAAs are often found in pre-workout supplements for athletes.

Finally, BCAAs have also been shown to support muscle protein synthesis, helping repair and build muscle after exercise.

A variety of foods such as proteins and grains.

What Foods Contain Amino Acids?

Any food that provides protein inherently contains amino acids, but the specific breakdown of which amino acids, and how much of each is in a given food depends on the type of food.

Animal proteins, such as meat, poultry, fish, seafood, and eggs, are typically complete proteins, which means that the food provides all nine essential amino acids. 

Many plant-based proteins, such as beans, vegetables, and rice, are considered “incomplete” proteins because they lack at least one or more of the nine essential amino acids. 

There are some complete plant-based sources of protein, such as soy, seitan, and nutritional yeast.

You can also pair sources of incomplete proteins to make the sum total protein of your meal a complete protein. For example, eating rice and beans together gives you a decent amount of all nine essential amino acids.

Amino acid foods such as meat, chicken, potatoes, eggs and beans.

However, according to the National Institute of Health, you do not need to pair incomplete proteins in the same meal for your body to have all the amino acids it needs; rather, it’s ultimately the total amino acid profile provided to the body over the course of the day.

Generally speaking, even if you are following a plant-based diet, if you eat a wide array of legumes, vegetables, nuts, seeds, and whole grains and aim to meet the recommendations for protein for adults, you should be getting an adequate amount of amino acids in your diet.

However, animal-based foods, including dairy and eggs, are also excellent sources of amino acids. 

The Academy of Nutrition and Dietetics and the National Academy of Medicine recommend that for general health, the average adult should strive for a daily protein intake of 0.8 grams of protein per kilogram of body weight.

The American College of Sports Medicine recommends that athletes consume at least 1.2–2.0 grams of protein per kilogram of body weight per day. 

Protein powders, and BCAA supplements, may also be recommended for people who cannot meet their amino acid needs through their diet. Here are some of the best protein powders to check out, if you need to add them to your diet.

A person holding a clock that says amino acids.
Photo of author
Amber Sayer is a Fitness, Nutrition, and Wellness Writer and Editor, as well as a NASM-Certified Nutrition Coach and UESCA-certified running, endurance nutrition, and triathlon coach. She holds two Masters Degrees—one in Exercise Science and one in Prosthetics and Orthotics. As a Certified Personal Trainer and running coach for 12 years, Amber enjoys staying active and helping others do so as well. In her free time, she likes running, cycling, cooking, and tackling any type of puzzle.

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