What Does Protein Do for Your Body? A Beginner’s Guide

A typical diet contains three types of macronutrients. These are carbohydrates and fats as main energy sources and proteins, that serve as building material. But when it comes to protein, there’s much more than meets the eye. Why does the body need protein, and how much should you eat?

Protein – What Is It?

First of all, let’s look at protein as a macronutrient. Proteins are large molecules, built of long chains of amino acids. These amino acids serve as building blocks for different kinds of tissue, as well as material for enzymes – chemical catalysts that speed up thousands of biochemical reactions.

As a last resort, proteins can serve as an energy source through gluconeogenesis, when glycogen stores are sparse and oxidation of fats is not effective enough. This process is far from efficient and can result in muscle tissue degradation. To avoid muscle catabolism, try to add BCAA as an intra-workout and protein powder with fast kinetics immediately after workout (e.g. whey protein hydrolysate).

While protein can be turned into glucose, this reaction won’t come the other way around. Your body can’t synthesise amino acids from glucose, no matter how complex carbohydrates you eat. That’s why in a well-balanced diet, a solid portion of protein should be supplied and divided equally between meals.

Protein sources can be divided into two main groups – animal-based protein (e.g. beef protein) and plant-based protein (that is vegan plant protein). The first family of products is made of whey, eggs and meat derivatives. The second one is produced from a mix of different sources like brown rice, soy or pumpkin seeds. Both groups contain all 20 amino acids, but in case of plant protein, they are unequally divided. For example, pea protein has low levels of methionine, cysteine and tryptophan. On the other hand, plant sources of protein are rich in nutrients such as vitamins and minerals. Read more about differences between whey protein and vegan protein.

Why Do We Need Protein?

Do you know how protein synthesis works? Putting it simply, there are two stages of this reaction. Firstly, DNA genetic code is copied into messenger RNA. Secondly, this ‘message’ is read by ribosomes and through translation in cytoplasm, a specific protein chain is made of assembled amino acids. To better understand why we need protein, it is important to look at different functions of this macronutrient.

Building and Repairing Tissues

All food you eat is being broken down into essential nutrients, amino acids among them. Through the bloodstream amino acids are transported to the places where they are needed for repair or growth of organs and muscles. These building blocks are reassembled and made anew into proteins.

For athletes especially important is Muscle Protein Synthesis (MPS), a cycle of processes that fires up when muscles produce signals through micro-tears and damage, usually from resistance training. The opposite side of MPS is Muscle Protein Breakdown (MPB), when amino acids are released from existing muscle tissue as an energy source (amino acids) or material for repair. The amount and types of amino acids determine which one will be a winner, MPS or MPB. You can stimulate muscle growth by supplementing with, e.g. creatine powder or mass gainer.

Properly combined balanced diet, training regimen (and MPS induced by exertion), and rest can lead to supercompensation. This is a temporary increase in fitness level, strength and endurance, which can be used as a means for further adaptation of the body. It’s one of the main pillars of physical shape development, no matter the sport discipline.

Producing Enzymes and Hormones

Protein is not only a building material, but also an important chemical component used for enzymes and hormone synthesis. Why do we need protein in our diet? It produces peptide hormones, which are e.g.:

• insulin and glucagon – responsible for blood sugar regulation,
• growth hormone – promotes cell repair and muscle growth,
• leptin – regulates the feeling of fullness in the stomach,
• calcitonin and parathyroid hormone – hormones connected with bone mass density and bone mineralisation.

Among many other proteins, amino acids are used up for hemoglobin synthesis. It’s the crucial protein in red blood cells, which transport oxygen from lungs to all cells in the body. Higher levels of haemoglobin may improve results in endurance-based disciplines, such as running or cycling. When reading blood tests, focus on parameters MCV, MCH and MCHC, which describe haemoglobin concentration.

Source of Energy

The other reason why we need to eat protein is to supply the body with a substitutive energy source when carbs and fats are low. The energy yield of protein is similar to carbs (circa 4 kilocalories per gram), but a much higher thermic effect creates a less effective energy source. However, it can be useful during prolonged effort, such as running a marathon or taking part in a triathlon at Ironman distance.

The process of synthesising glucose from protein is called gluconeogenesis and can be carried out from glucogenic amino acids, e.g.:

• alanine,
• asparagine,
• cysteine,
• glutamine,
• glycine,
• histidine,
• methionine.

Making use of protein as an energy source may be an effective strategy at the beginning of a ketogenic diet, when glycogen stores are low and ketone body oxidation is far from effective. To further enhance body physical capabilities, you can combine branched-chain amino acids with beta-alanine (for endurance) or arginine (for better blood flow and muscle nourishment).

How Does Protein Influence the Immune System?

Protein is also important for proper functioning of the immune system. It produces different kinds of immune cells, like T-cells that fight-off pathogens or immunoglobulins (e.g. IgG, IgA). It’s also responsible for synthesising cytokines, signalling molecules that guide immune cells and trigger immune response.

While the most prominent radical scavengers come from fruits and vegetables, protein also presents antioxidant properties. Key amino acids in this field are cysteine, methionine, tryptophan, and histidine. Oxygen radical scavengers protect the body from inflammation.

A Beginner’s Guide to Protein Sources

There are a lot of different high-protein foods. Let’s look at the most popular ones:

• meat – chicken, turkey, beef, pork, lamb,
• fish and seafood – salmon, tuna, trout, shrimp,
• dairy – milk, cheese (white, hard or cottage),
• eggs,
• soy products – tofu, tempeh, seitan,
• legumes – beans, lentils, chickpeas, soybeans, peas.

To achieve the best and most complete profile of amino acids, try to mix different types of protein into your diet.

Is It Worth Choosing Protein Shakes or Bars?

During the high-intensity part of the season or when maintaining a balanced diet is problematic, consider supporting it with protein powder. Depending on your needs, you can choose different kinds of supplementation. For people with lactose intolerance, lactose free protein would be a good choice. If you are chasing muscle mass and want to refuel muscle during a night's rest, choose micellar casein. There are also protein bars, indispensable during long trips or hikes.

Remember that supplements are only an addition to natural food, which can’t be replaced. It’s the easiest way to fill the gaps in your diet or supply the body with proteins or carbs if you train a lot. Although, if you notice that drinking protein shakes or gainers is an integral part of the diet, consider consulting a sports dietitian, who can help you to better adapt meals caloric density and composition to your needs.

Complete vs. Incomplete Proteins – What’s the Difference?

Proteins are often divided into complete and incomplete. While both groups contain all 20 amino acids, there's a vital difference when it comes to the content of essential amino acids (EAA). These are nine amino acids the human body can’t produce, so they have to be eaten with food or supplemented. On the EAA list are:

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

Three of them (leucine, isoleucine and valine) are classified as branched-chain amino acids. However, you may not just replace BCAA with an EAA supplement because for optimal muscle growth your body needs more BCAA than other types of EAA. A good idea would be to drink branched-chain amino acids during and after a workout and EAAs throughout the day.

Complete sources of proteins are mostly meat, fish and eggs. When it comes to plant protein sources, grains are low in lysine and legumes in methionine. But that’s not always the case. Soybean, quinoa and buckwheat are all complete sources of protein.

What can you do to change an incomplete plant protein source into a complete one? Try to mix food to complement the amino acid profile. Beans and rice, as well as grains with nuts or seeds, are just a few examples. Being on a vegan or vegetarian diet doesn’t mean you have to sacrifice muscle growth or endurance. Your meal plan just has to be well-organised.

How Much Protein Do You Really Need?

Now you know why we need to eat protein. It’s time to answer how much protein is enough. There’s no straight answer to how much protein you do need because it depends on your goal, activity level, body composition and numerous other factors.

According to scientists, protein intake between 1.4 and 2.0 grams per kilogram daily for physically active individuals is not only safe, but may also improve the training adaptations to exercise training.

It can be safely said that people with a sedentary lifestyle need less protein than athletes. Recommended Dietary Allowance of protein for a healthy adult with minimal physical activity is currently 0.8 gram of protein per kilogram of body weight per day, which can be provided by a balanced diet. The heavier you exercise, the more important increased protein intake becomes – not only for muscles, but for the body as a whole.