Lysine, tyrosine and beans, oh my! Amino acids explained

Written by Martin Ebner
Updated October 2026

Amino acids have the sort of names that make a straightforward subject sound far more scientific than it needs to be. Add BCAAs, EAAs and a neon tub to the conversation and suddenly lunch appears to require a chemistry degree.

Luckily, it doesn’t. Lysine matters, tyrosine has several useful jobs and beans are a perfectly respectable source of protein. For most people, though, eating enough varied protein covers the lot without having to micromanage individual amino acids.

WHAT ARE AMINO ACIDS GOOD FOR?

Amino acids are the building blocks your body uses to make proteins. Those proteins help build and repair muscle, but they’re also involved in enzymes, hormones, neurotransmitters, skin, organs and connective tissue.

Your body is constantly breaking proteins down and building new ones. Food supplies the amino acids needed for that process, although eating one particular amino acid doesn’t send it directly to your biceps. The body is clever, but it isn’t taking supplement-label instructions.

Twenty amino acids are commonly used to build proteins in the human body. Nine are considered essential because your body can’t make them in sufficient amounts, so they have to come from food: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine.

The remaining amino acids can usually be produced by the body. Some may become conditionally essential during severe illness or other unusual circumstances, but that’s quite different from needing an amino-acid supplement because you trained legs on Tuesday.

LYSINE AND TYROSINE AREN’T INTERCHANGEABLE

Lysine is an essential amino acid, which means it has to come from your diet. Meat, fish, eggs, dairy, soy, beans and lentils can all contribute useful amounts.

Tyrosine is different. Your body can normally make it from phenylalanine, another amino acid found in protein. Tyrosine is involved in producing compounds including dopamine, noradrenaline and thyroid hormones, but that doesn’t turn it into a general energy or muscle-building supplement.

If you arrived here wondering whether lysine or tyrosine is better, they aren’t rivals. They perform different jobs and one doesn’t replace the other. A varied protein intake usually provides both without requiring a nutritional showdown.

WHY BEANS MADE THE TITLE

Beans and other legumes are relatively rich in lysine, which is often the amino acid found in lower amounts in grains. Legumes tend to contain less methionine, while many grains provide methionine but less lysine.

That’s why rice and beans work so well together nutritionally, although they don’t have to arrive on the same plate. Your body maintains a circulating pool of amino acids, so eating a varied diet across the day matters more than attempting to complete every meal like a protein jigsaw.

Lentils, chickpeas, kidney beans, black beans, peas, soybeans and edamame all contribute protein and amino acids. They also provide fibre, carbohydrates and micronutrients, which is considerably more useful than treating them as vehicles for lysine alone.

“COMPLETE” PROTEIN ISN’T A PASS OR FAIL TEST

A complete protein contains all nine essential amino acids in adequate proportions. Meat, fish, eggs, dairy and soy are familiar examples, but the label can make incomplete proteins sound useless when they aren’t.

Most plant foods contain all the essential amino acids. They may simply be lower in one or two of them. Eating different foods across the day fills those gaps without any need for obsessive protein pairing.

A varied plant-based diet can support muscle and strength perfectly well when total protein is high enough. In one 12-week resistance-training trial, soy and whey protein matched for leucine produced similar improvements in lean mass and strength.

My guide to building muscle on a vegan diet covers the practical side in more detail.

THE BEST FOOD SOURCES OF AMINO ACIDS

Meat, fish, eggs, milk, Greek yogurt and cheese provide all nine essential amino acids in useful amounts. They also make it relatively easy to build a meal around a meaningful serving of protein.

Plant sources include soy foods, beans, lentils, peas, chickpeas, quinoa, seitan, nuts, seeds and whole grains. Soy is particularly useful because it offers a strong essential-amino-acid profile, while a mixture of legumes, grains, nuts and seeds can cover the same ground across the day.

Protein powder can help when food alone isn’t convenient. Whey, casein, soy and a well-formulated plant blend all provide a broader amino-acid profile than a standalone BCAA product. My guide to the best protein powders for building muscle explains the differences without pretending everyone requires a tub.

WHAT ABOUT LEUCINE, BCAAS AND EAAS?

Leucine is one of the nine essential amino acids and one of three branched-chain amino acids, alongside isoleucine and valine. It plays an important role in switching on muscle protein synthesis, which explains why supplement companies became rather excited about it.

The switch still needs something to build with. BCAAs supply only three of the nine essential amino acids, so they can’t support the full process alone.

A controlled resistance-training study found that BCAAs stimulated muscle protein synthesis compared with a placebo, but the response was smaller than researchers commonly see with complete protein containing all the essential amino acids.

EAAs provide all nine, so they make more sense than BCAAs if you specifically want an amino-acid supplement. Even then, a complete protein source often does the job just as well. Another controlled study found that complete whey protein sustained the post-exercise muscle-building response better than a small amount of whey fortified with leucine or other essential amino acids.

DO YOU NEED AN AMINO-ACID SUPPLEMENT?

For most people eating enough protein, probably not. I’ve never looked at a client’s diet and thought the missing piece was a brightly coloured BCAA drink. The usual issue is much less glamorous: too little protein overall, meals built mostly around carbohydrates, or trying to survive on coffee until dinner.

An EAA supplement might be convenient when appetite is low, a full protein serving feels uncomfortable around training or food options are limited. That makes it a practical alternative, not something everyone needs to add on top of an already adequate diet.

BCAAs are harder to justify. If you enjoy drinking them and the cost doesn’t bother you, fine. Just understand that adequate protein has already supplied those same three amino acids alongside the other six your body needs.

COLLAGEN HAS A DIFFERENT JOB

The old version of this article promoted collagen as an easy way to increase protein and amino-acid intake. I wouldn’t use it that way now.

Collagen provides plenty of glycine, proline and hydroxyproline, but it’s low in leucine and doesn’t contain all nine essential amino acids. That makes it a poor replacement for whey, soy or another complete protein when muscle growth is the goal.

It may still have a role when someone is specifically interested in connective tissue, joints or skin. My comparison of collagen and whey explains where each one fits.

HOW TO COVER YOUR BASES WITHOUT COUNTING AMINO ACIDS

Start with enough total protein. Build several meals around a decent protein source, include some variety and let the amino acids look after themselves.

Animal products make that straightforward, but they aren’t compulsory. A plant-based diet can do the same job with a little more planning and, if useful, a soy or blended plant protein powder.

Your body responds to the complete diet, not the most impressive ingredient on a label. My guide to how much protein you need gives you the useful numbers without requiring a spreadsheet for every bean.

EAT THE PROTEIN, NOT THE ALPHABET

Lysine is essential. Tyrosine performs several important jobs. Beans are useful, BCAAs aren’t magic and EAAs are an option rather than an obligation.

Eat enough varied protein and you’ll almost certainly cover what you need. If a supplement genuinely makes that easier, use one. If it merely adds three more letters to your kitchen cupboard, the cupboard was probably doing fine without it.

If you’ve ever bought a tub of three letters because the label made it sound indispensable, Check It Oot is where I separate useful evidence from supplement theatre. One email once or twice a month, written by me and delivered straight to your inbox.