Sports Nutrition Basics - Protein

If there’s one topic in sports nutrition that causes the most confusion, rumours, urban myths and products marketed to athletes it’s protein. Protein is an essential part of an athletes diet, however with all the “advice” out there it’s hard to work out how much we need, what type we need and when we need it. Today we’ll look at the basics of protein and try and sort out the myths from the facts.

Protein – a specific combination of amino acids

Proteins in our diet (and in our body) are built from specific combinations of amino acids. When we eat protein, we digest it down into individual amino acids (or combinations of 2 or 3 called peptides) and these are absorbed across the wall of the small intestine and into the blood. These amino acids can then be used in the body for either creating new proteins in the body, or used as a fuel source to provide energy.

There are 20 different amino acids, which can be arranged in a massive variety of ways to form proteins in the body. If DNA is the blueprint of your body, then amino acids are the bricks that do the building. Every cell in our body contains a cast array of proteins that have coded by our DNA, and all have different purposes. Some form the structure of our cells, including muscle fibres, blood cells, brain cells, and so on. Some are used to create enzymes that control chemical reactions in the body – including digesting food and producing energy from carbs, fat, protein and alcohol.

Proteins in the body have a limited lifetime

All the proteins in our body have a limited lifetime before they are replaced. For example, red blood cells are turned over roughly every 120 days. When proteins are replaced, the body can recycle some of the amino acids and re-use them to make new proteins. It can also make some of the amino acids without getting them from food. These are known as the non-essential amino acids. However those that can’t be made in the body must come from food, and are called essential amino acids. The protein that can’t be recycled forms urea, a waste product that exits the body in your urine.

How does protein affect my training?

Every time we exercise the body responds by rebuilding (or building more) proteins that allow the body to adapt to exercise and get fitter and stronger. Some muscle proteins can also be damaged during exercise and are replaced. For example after weight training the body goes to work building more muscle fibre proteins in the muscles that were worked during the session. After endurance training proteins are also built, but these are different proteins, the ones that allow us to improve our cardio fitness such as mitochondrial proteins (that allow us produce energy from fat and carbs together with oxygen). Remember though that proteins in the body are also broken down and recycled, so only when you build more protein than you breakdown do you see an improvement. This is the balance of protein synthesis (building new proteins) and protein breakdown.

Let’s look briefly at muscle protein balance during weight training. Every time you train you will get an increase in muscle protein synthesis in the hours afterwards. Every time you eat protein you also get a small increase in muscle protein synthesis. If you haven’t eaten or exercised for a while, then you get some muscle protein breakdown. Normally, the synthesis and breakdown are balanced, so you don’t gain nor lose muscle

Muscle protein is constantly either building up (protein synthesis) or breaking down (protein breakdown). Eating protein increases synthesis and fasting increases breakdown. Training also increases synthesis and breakdown. But combining training and protein gives increased synthesis and reduced breakdown, causing a gain in protein over time. From Burd N et al. J Appl Physiol 106:1692-1701, 2009.

But training combined with protein from food increases the protein synthesis and reduces protein breakdown. Over time this causes a gain in muscle. It’s expected that a similar process happens in endurance training, however there is not enough research in this area to say for sure whether the process is exactly the same as with resistance training.

Muscle protein growth (synthesis) responses to endurance & resistance training in trained and untrained athletes. The top two graphs show muscle fibre protein synthesis (that is enhanced by doing resistance training) and the bottom two graphs show mitochondrial protein synthesis (which increases after endurance training). From Wilkinson S et al. J Physiol 586.15 (2008) pp 3701–3717.

Foods that provide protein

Foods that provide a good source of protein include:
 

• Meat, seafood and poultry
• Eggs
• Legumes (eg. chickpeas, kidney beans, lentils, soy beans and soy products such as tofu)
• Milk, yoghurt and cheese
• Nuts (be careful = because nuts also contain a lot of fat and therefore calories)
• Most protein powders are based on processed milk powder, soy or egg protein
  

Does the type, timing and amount of protein matter?

A lot of marketing hype about protein supplements centres on the type of protein in the product, and the way it is manufactured. We know from research is that it’s the essential amino acids (especially Leucine) that are needed in our diet after exercise to build muscle, but you don’t need special supplements to get them because they exist in everyday foods. Of the regular food sources, dairy proteins seem to be the most efficient way of getting the required amount.

There has also been a lot debate about whether some types of protein are better for building muscle after exercise compared to others. The differences between sources of protein can be summarised in two ways:
· The amount of essential amino acids and Leucine in the food
· How quickly or slowly the protein from the food is digested absorbed

Some people also believe that the type of protein influences the way amino acids are absorbed through the bowel wall (ie. specific combinations of 2 or 3 linked amino acids). They believe that some combinations are “bioactive peptides” and are beneficial for athletes. However this is very little research in this area, and we don’t know enough to say whether this works or not.

However research has shown whey protein (one of the two main groups of proteins in milk) is superior to casein (the other type in milk) and soy proteins for enhancing muscle growth as a result of training. This is likely to be because whey contains more Leucine, or because whey is digested and absorbed more quickly. Future research will hopefully answer this question.

One thing that is clear from research is that the timing of protein is important. Studies consistently show that taking protein in the first hour or so after exercise helps maximise the response to training. Protein before and during exercise makes little difference. So exactly how much protein do we need after exercise, and in one or multiple doses? This still isn’t clear – the AIS are currently conducting a study looking at exactly this. But we do know that the required dose of protein is fairly small, around 20-30g when good quality protein (egg protein was used in the research) is eaten. Excess protein is simply used as a source of energy.

This graph shows that once protein intake (from egg protein) goes above 20g, there is no extra increase in the muscle building response. The extra protein is simply used up as an energy source - from Moore D et al. Am J Clin Nutr 2009;89:161–8.

Summary

Despite what supplement companies claim, there’s still a lot we don’t know about protein and training. We do know that after every training session your body adapts to get better, by building specific proteins that will help achieve this. These are built from amino acids, using DNA as the blueprint. We know that eating protein after exercise is required to get produce a net gain in muscle proteins in response to training, that whey protein seems to be ideal for building muscle size and strength, and the amount required is not that great (20-30g in the hour or so after exercise). But it will be some time before we can say for sure exactly what dose to take, when and how often.