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Renee McGregor is a leading sports dietitian, specialising in eating disorders, relative energy deficiency in sport (RED-S), athlete health & performance, and the female athlete. She has worked with Olympic and Paralympic athletes and is herself an accomplished ultramarathon runner.

In this blog post, Renee highlights the most common nutrition mistakes made by runners and provides 5 easy-to-follow nutrition tips for runners of all abilities.



Everyone has an opinion about nutrition – why shouldn’t they? After all we all need food to survive. However, there is a difference between anecdotal nutrition advice and actual nutritional science. On social media we are exposed to the former a lot more than the latter. The issue with this is that what works for one person in a sample of n=1, is unlikely to work for another.

Just the other day I was on a group chat where someone very boldly stated that their new Vegan regime was the cause of their newly found energy and improved recovery. However, this was based on subjective information, which they had collected over a few weeks. Is this science? No, this is one individual’s personal experience with no information of what their diet had been like previously, or even if any other aspect of their life had also changed, which may have resulted in they were feeling.

Presently, there is no scientific evidence to suggest that a plant-based diet can improve an individual’s performance. In fact, if anything, there is more evidence pointing at the opposite, that a plant-based diet can be lacking in sufficient energy and also specific nutrients needed to improve performance.

Nutritional science and particularly sports specific, is actually quite complex. While many simply look at the impact of one particular nutrient or process on performance, this completely ignores the fact that the human body is run on an intricate system of endocrine, biochemical, immunological, physiological and psychological pathways that all work collectively.

Let’s take the keto diet as an example. This was a huge trend a few years ago and many still promote it with the idea that if we remove carbohydrate from our diet, then our body will use more fat for fuel and improve our performance but also our body composition.

While on the surface this may seem to have some gravitas, it kind of makes sense – take out carbohydrate and so the body will have to find another source of fuel to provide the body with energy. However, what has been completely ignored, is the importance of carbohydrate intake on the hypothalamic pituitary axis, which is necessary to get adaptation from a training response. In addition, carbohydrate has a critical role in optimising the immune function in those who are physically very active.

So, with all this in mind, here are some of the common nutrition mistakes often made by runners, broken down into three categories:




Numerous studies have demonstrated that carbohydrate is the preferred fuel used by the body and is definitely the key to optimal performance. That said, many runners still have little understanding of how much they actually need in order to meet their requirements, with many under-fuelling.

As stated above, carbohydrate availability is particularly key for the hormonal cascade needed in order to see adaptation and thus progression. This means ensuring sufficient carbohydrate before, during if your runs are over 90 minutes, and within 30 minutes of completing your session.

While everyone’s physiology is slightly different, as a rule of thumb the requirements set are 5g/Kg BW of carbohydrate if you are running for 60 minutes a day, with this figure increasing for longer or multiple training sessions.

In general, I do not encourage fasted sessions and the recommendations state that if you are going to include these, you should not do more than 2 a week and they should be no longer than 60 minutes, at an effort of no more than 6/10. More than this and at higher efforts, can potentially result in chromic stress on your body. This can lead to a depressed immune system, higher risk of injury and down regulation of your hormones, particularly your thyroid gland, oestrogen and testosterone, leading to further negative health consequences.

In practise, if you are training regularly, it is unlikely that you will ever have full glycogen stores, and so it is essential that you consume carbohydrate at meals and snacks throughout the day. Aim to include nutrient dense carbohydrates such as oats, potatoes, whole grains, fruit and yoghurts at 3 meals (about a 1/3 of your plate), as well as including 2-3 smaller carbohydrate-based snacks such as bananas, cereal bars, 2 slices malt loaf or 2-3 oatcakes with peanut butter.

One common observation I have seen is that many people view vegetables as carbohydrate, often displacing these for pasta, grains, bread and potatoes. While vegetables play a role within our diet and should be included, they are predominantly fibre which means they add bulk to the diet but not essential carbohydrate fuel.




There is a lot of hype around protein in the recovery phase, with many runners stressing about not getting enough to enhance recovery.

Protein does play a role in the response to training and should be included in addition to carbohydrate, particularly immediately after. The general recommendations are that a recovery meal/snack/choice should provide 1.2g/Kg BW carbohydrate and 0.4g/Kg BW protein.

 So, for someone who is 55Kg this would be 66g of carbohydrate and 22g protein. It looks like a medium size baked potato with a small tin of tuna.

 It is important to appreciate that the body will struggle to utilise more than 0.4g/Kg BW post training for muscle protein synthesis and adaptation. Any additional protein consumed will be used as fuel or stored as excess. Therefore, it is really important to spread your protein requirements out throughout the day. Aim for a palm-size portion of protein at 3 meals and then half this amount for snacks. This will ensure that your body always has an amino acid pool to draw from in order to repair and rebuild muscles throughout the day, as well as preventing blood sugar fluctuations.




With so much negativity around sugar, it is hardly surprising that many runners are concerned about their intake. While I would never advocate a high sugar diet, there are definitely times during training and competing, where sugar is the only option.

During endurance events, such as a half or full marathon, the body will need an easily digestible source of carbohydrate to keep stores topped up, so that running pace can be maintained beyond 60-90 minutes. Gels, jelly babies, sports drinks are all suitable options, and they all contain sugar. So, in this case, sugar actually enables and potentially enhances your performance.





  1. Don’t be drawn to the latest fad. Many runners will try almost anything to improve their performance. Focus on training and getting the building blocks of your diet correct first – this is going to have more impact than whether you are gluten free or not.


  1. After a very hard training session, and especially when training again within 12 hours, taking on something like flavoured milk is an ideal choice to start recovery as quickly as possible. The combination of added sugar to the natural milk sugar causes insulin to increase in the blood. Contrary to what you might think, this is actually really important. Only when our insulin levels are raised, can we draw carbohydrates and protein into the muscles to start the recovery process.


  1. Always practise your race day nutrition. The worst mistake you can make is to use what is available on race day without previously having tried it. This could have real negative effects on your performance.


  1. Work out what is right for you. Just because your training partner swears by a bowl of porridge every morning, this does not necessarily mean this is the right fuel choice for you.


  1. You don’t have to eat less on your rest day. For most this will fall between two training days, so it is the perfect opportunity to recover and then refuel. By being consistent with your nutrition, you will also allow for consistency with your training, which in turn allows for progression.



*Follow Renee on Instagram @r_mcgregor and check out her website

*Related blog posts: 10 Running Superfoods

*All the running photos of Renee in this blog post are courtesy of Jen & Sim Benson.



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