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How important is protein intake for runners?

Updated: Oct 11, 2023

written by, Louisa Maslaveckas

Most people associate high protein intakes with muscle building, resistance training, hypertrophy and high intensity sports. Within the endurance world and most commonly amongst runners, there is only a minimal focus on dietary protein. It is common knowledge that endurance athletes favour carbohydrates as the optimal source of fuel. But what if I told you that protein can also be used for fuelling endurance performance. In fact, protein is just as important for recovery in runners, as it is for high intensity exercise or weight training.

First, let's take a little look at why we need protein. Protein provides the body with around 10-15% of its dietary energy. It is made up of small molecules called amino acids and all 20 of these are the building blocks for everything in your body. They form the structure of our DNA, keep our bodies functioning through building muscles and supporting our organs. These essential amino acids are divided into two categories, which you may be familiar with, essential and non-essential amino acids. Non-essential amino acids are created naturally by the body while the 9 essential amino acids are available through the food we eat. Without ingesting these essential aminos, our body would begin to break down our available protein starting by affecting our muscles and potentially (in very extreme conditions) your organs and heart. So now we understand just HOW important protein is, let's have a look at how much you really need.

The recommended daily intake of protein for inactive adults (aged 19-70) is around 0.8g per kg of body weight. In athletes and recreationally trained people, the intake requirements are increased up to 1.2-2.0g per kg of body weight. These requirements will differ depending on the intensity and volume of training. Runners previously used to shy away from protein, assuming there was little need. However, the opposite is true. Unlike carbohydrates and fats, proteins contain nitrogen. When we exercise, we break down proteins in the body and deplete nitrogen. Maintaining a positive nitrogen balance is essential for the repair and maintenance of muscles. If nitrogen and protein stores are limited, the muscles enter a catabolic state, meaning they begin to waste away and break down.

There is a subset of amino acids known as the branched chain amino acids (BCAAs)which represents a group of essential amino acids which I am sure you will have seen available in a range of sport nutrition foods or supplements. These specific BCAA’s are: leucine, isoleucine and valine. They are popular in the sport industry promoting factors for increasing muscle growth, decreasing muscle breakdown and fatigue as well as reducing muscle soreness. These aminos are primarily used as a source of fuel during exercise, because they can be used directly within the muscle. If you are using these as fuel for exercise you won't be able to replenish these in the body naturally, therefore you have to replace them through your diet. Protein requirements are elevated for endurance athletes that are using these amino acids as fuel for exercise. This high demand of protein for fuel can occur during periods of low carbohydrate availability when, for example, you are running with low muscle glycogen either at the end of a session or following a low carbohydrate diet. Energy expenditure from protein might actually increase up to 10% in situations where glycogen is low.

If you are running for a long period of time at a high intensity, working at 75% of your Vo2 max for about an hour, you might burn through the equivalent of 12g of protein.

What is your Vo2 max?

Your Vo2 max is essentially the maximum amount of oxygen you can utilise during exercise. It is used to measure aerobic endurance or cardiovascular fitness. The units are measured in millilitres of oxygen per minute per kilogram of body weight. A strong Vo2 max is therefore a good thing, it means you can take in more oxygen and deliver it to your muscles faster and more efficiently. The fastest way to improve your Vo2 max is exercising at a high intensity, training in stop/start intervals e.g. sprint for 20 seconds, jog for 5 mins, walk for 2 mins and repeat. Combine interval training with continuous training and keep pushing yourself to run further or faster.

The previously mentioned subset of amino acids - branched chain amino acids, are primarily used as a source of fuel during exercise, because they can be used directly within the muscle. If you are using these as fuel for exercise you won't be able to replenish these in the body naturally. You have to replace them in the diet. Protein requirements are elevated for endurance athletes as high or higher than for resistance training athletes. Athletes use these amino acids as fuel for exercise. Increased demand for protein for fuel can also occur during periods of low carbohydrate availability and where muscle glycogen is low. This typically happens at the end of a session or following a low carb diet. Energy expenditure of protein might actually increase up to 10% in those situations. So, I think we can agree it probably makes sense that you consume protein and replenish these losses.

But when is the best time to consume protein?

There is quite an obsession with protein timing, with special attention on this ‘protein window’ of golden opportunity which comes with a frantic frenzy to inhale your protein shake post workout. Protein synthesis actually works in a cycle, balancing the breakdown and building of protein in the body. If one side increases, so does the other, naturally. This cycle takes up to 48 hours, therefore you have plenty of time to nourish. In a 24-hour period, the most efficient way to achieve metabolic stability is to space your protein evenly throughout the day. If you over consume protein in a single meal, your body only takes what it needs and the rest, because we cannot store protein in the body, will be used as energy. The desired amount of protein consumption in and around training primarily depends on the goals for training. There is no magic window, but the sooner you can get protein the quicker your body will begin to recover. Protein cannot necessarily improve performance but can essentially assist you in recovering faster.

It is important to note that after exercising is a perfect time to consume carbohydrate along with protein in order to replenish all the muscle and liver glycogen you have burnt during training. This carbohydrate intake is usually 1g-1.2g per kg of body mass per hour trained. This will maximise the access of muscle glycogen. If you include protein in this meal you can actually increase your rate of muscle glycogen synthesis, meaning you recover quicker. 3:1 carbohydrate:protein ratio is recommended.

Lastly, when it comes to plant versus animal-based protein, which one is truly best?

Focus on the protein quality and how easily the protein is digested and absorbed. Animal based protein is typically considered high quality from a standpoint that it has a good balance of amino acids (meaning a complete profile of all the amino acids) and is fairly easily digested. However, animal-based protein may not be the best choice for a variety of reasons. All essential amino acids that are required for an optimal protein synthesis originate in plants. When you consume animal-based proteins you are actually taking it from a secondary source. The animal you eat either consumes the plants containing these aminos first or has previously eaten an animal that eats plants. Get that? So, when people say that plant proteins are incomplete, that is not necessarily true. Plant based proteins contain different ratios of amino acids than animal proteins. However, by consuming two complementary plant protein sources, e.g from pulses and beans, you can create a full amino acid profile. Plant proteins may be harder to digest, but this is actually due to the higher fibre content which is incredibly beneficial for a healthy gut. Training the gut is essential to avoid unnecessary bloating and gas when switching to a plant-based diet. Wholefoods should be the primary vessel of your protein intake. The top plant-based proteins to look out for are legumes (beans, peas, lentils, chickpeas) including tofu and tempeh. Other great sources include chia seeds, hemp seeds, quinoa, nuts, spirulina, brown rice, nutritional yeast, oats and amaranth.

To summarise, yes protein is very important for running. There's no need to overcomplicate it, just aim for a refuelling of around 20-22g protein at a minimum along with your carbohydrates and fat, post workout. Whether this is from a protein smoothie or a high protein meal, be realistic for what works for you. Most importantly, don’t panic if this meal is 20 minutes after exercise or an hour later. I hope this blog helps.

Until next time,

Lou X


Gui, Z., Sun, F., Si, G. and Chen, Y., 2017. Effect of protein and carbohydrate solutions on running performance and cognitive function in female recreational runners. Plos one, 12(10), p.e0185982.

McLeman, L.A., Ratcliffe, K. and Clifford, T., 2019. Pre-and post-exercise nutritional practices of amateur runners in the UK: are they meeting the guidelines for optimal carbohydrate and protein intakes? Sport Sciences for Health, 15(3), pp.511-517.

Moore, D.R., 2020. One size doesn't fit all: postexercise protein requirements for the endurance athlete. The American Journal of Clinical Nutrition.

Phillips, S.M. and Van Loon, L.J., 2011. Dietary protein for athletes: from requirements to optimum adaptation. Journal of sports sciences, 29(sup1), pp.S29-S38.

Williamson, E., Kato, H., Volterman, K.A., Suzuki, K. and Moore, D.R., 2019. The effect of dietary protein on protein metabolism and performance in endurance-trained males. Med Sci Sports Exerc, 51(2), pp.352-60.


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