If you’re on a mission to improve your muscle tone or overall health, you may have heard a little something about amino acids. But what exactly are they? And, is it necessary to take amino acid supplements to get their benefits? To find out, we asked nutritionist Jo Woodhurst, director of nutrition at British supplement brand Ancient+Brave. Read on for everything we learned. And, spoiler alert: Amino acids might just be exactly what the doctor ordered—as long as you keep a few key factors in mind.

What are amino acids?

Amino acids are absolutely essential to our health—and for life itself. They are the so-called “building blocks” of proteins. They play a key role in the growth, repair, and maintenance of almost every body tissue and system, including energy production, muscle growth, regulation of the immune system, metabolism, and mood, and the production of enzymes, hormones, collagen, and elastin.

You can think of amino acids as a bit like the letters of the alphabet, with each amino acid serving a unique role. When strung together in certain combinations, amino acids form peptides and proteins—much like letters form words and phrases. Some of these proteins and peptides support the production of hormones; some, the synthesis of neurotransmitters; others, the metabolic processes.

For example, both collagen and keratin are composed of amino acids, and are thus essential for the strength, elasticity, and structure of the skin, nails, and hair. These tissues are constantly regenerating and depend on a constant supply of amino acids to maintain elasticity and vitality.

What are essential amino acids?

Our body needs 20 different amino acids to function. Of those 20, nine are considered “essential” amino acids (EAAs) because the body doesn’t make them naturally. Instead, these nine essential amino acids must be consumed via food.

Each amino acid has different functions. When combined into a protein, the role expands further. The human body is believed to contain between 10,000 and 50,000 different proteins—each with a unique purpose, including:

• Structural materials such as muscles, skin, blood, ligaments, tendons, bones, collagen, and the walls of intestines and arteries.
• Enzymes that catalyze reactions essential for digestion, energy production, and detoxification.

The nine essential amino acids are:

• phenylalanine
• isoleucine
• histidine
• leucine
• lysine
• methionine
• threonine
• tryptophan
• valine

What foods contain essential amino acids?

Essential amino acids cannot be produced by the body and must be consumed from the foods we eat. Luckily, plenty of foods that contain essential amino acids: