You may have heard that building muscle requires eating endless protein.

This macronutrient certainly enjoys a strong reputation in fitness, and performs key roles in bodily function.

Including helping you build strong quadriceps, of course.

Read on to learn why protein matters.

What is a protein?

Chemically, a protein is a macromolecule made of amino acids. There are 20 main amino acids, joined by peptide bonds in different sequences to form different proteins.

What do proteins do?

Have you wondered what proteins are for?

They have structural roles, including maintaining and repairing organs and muscles, and regulatory roles controlling metabolic pathways.

When carbohydrate and fat availability is limited, they can also provide an energy source.

What types of protein are there?

There are several ways to classify them:

By origin:

Proteins may be animal, plant or microbial in origin, with the latter produced by bacteria or single-celled fungi.

Microbial proteins are less widely used than conventional sources but may offer future opportunities because of cost and biological value.

By biological activity:

Proteins perform many different functions.

They include enzymes and structural, transport, storage, motor, regulatory, signalling, sensory and defence proteins, receptors and hormones, as well as antibodies.

A macronutrient with plenty of roles!

By solubility:

Proteins may be water-soluble or insoluble. Transmembrane proteins have hydrophilic and hydrophobic regions suited to their position in cell membranes.

Plant or animal protein?

Different diets can work when well planned and tailored to your needs.

The balance of animal and plant protein proposed here is around 50:50, as both sources can provide useful nutrients.

Consider the accompanying foods: plant protein sources often supply fibre with relatively little fat.

Animal protein foods often contain less fibre and more fat.

Their amino acid profile also matters. Essential amino acids must come from food because the body cannot make them.

With plant foods, combining different protein sources is particularly useful for covering the full essential amino acid profile.

Protein in an athlete’s diet

This macronutrient has a key role in normal bodily function, whether or not you exercise.

It is particularly relevant to weight training, running or swimming, especially with a goal of gaining muscle.

Proteins supply the building blocks of muscle.

Eating protein after training supports muscle repair. A large protein-rich meal immediately before exercise may slow digestion and cause gastrointestinal discomfort.

The appropriate amount depends on goals and individual needs. A range of 1.6–2.2 grams per kilogram of body weight is discussed here. More does not automatically build more muscle, because the muscle protein synthesis response is limited.