Dietary Mistakes Hampering Your Running Performance

So, you’re training for distance. Be it a 10k, half-marathon or even the whole 42km, endurance running is no joke. If you’re a first timer, or even a seasoned veteran, struggling with a plateau is incredibly frustrating. Or so, I’ve heard (I’m not a runner by any stretch). If you’ve tried all the training strategies possible – shorter runs, introducing more sprint work etc. – it may be worth considering tweaking your nutrition.

How We Fuel Distance Running

Before we get into any nutritional recommendations, it helps to know what the hell is going on in the first place.

Our body uses three main pathways to generate energy. When running, the aerobic pathway is the predominant pathway. Aerobic metabolism converts macronutrients (carbohydrates, fat and protein) into energy, using oxygen (McArdle, Katch & Katch, 2015). We convert these macronutrients into adenosine triphosphate (ATP). This is the “energy currency” of the cell, and what drives mitochondria.

 For events longer than a couple of minutes, we primarily rely on carbohydrate and fat to generate ATP. As duration and distance increase (e.g. marathons), we draw more heavily on carbohydrate for fuel.

We primarily get this from glycogen. Glycogen is stored mostly in the muscle tissue (up to 400g), but we also store smaller amounts in the liver (100g). We will use our muscle glycogen first, then our liver glycogen. In this way, the body doesn’t have to draw on our blood glucose for fuel (Hargreaves and Spriet, 2020).

However, when we are running for distance, the body cannot replenish glycogen stores fast enough to meet the demand. Depletion of liver glycogen is the main cause of fatigue in endurance exercise (Hearris et al., 2018). This is responsible for the feeling of “hitting the wall” when running. If you have ever experienced this feeling, you know what I’m talking about – knees week, arms heavy, vomit on your sweater already, mom’s spaghetti. It’s not pretty, and it can be pretty mentally taxing.

So, we want to avoid this feeling, or coming close to it. With these facts in mind, let’s talk about how we can mitigate this through diet.

You Don’t Eat Enough Carbohydrates

Training for marathons involves running for long distances repeatedly. Your ability to repeatedly put in these distances is largely dependent on sufficient muscle glycogen replenishment (Murray and Rosenbloom, 2018). This takes time and carbohydrates.

Sports nutrition guidelines recommend that endurance athletes consume anywhere from 6-12g of carbohydrate per kilogram bodyweight (Burke et al., 2012). These guidelines define endurance activity as moderate-high intensity activity of at least 1 hour per day. Obviously, if you are training for longer durations, your needs will be at the higher end of the scale. Indeed, those who eat higher amounts of carbohydrates report faster marathon running times (Atkinson et al., 2011). These were amateur athletes, so the “I’m not training for the Olympics” excuse is out, and carbohydrates are in.

However, there is a huge problem with endurance athletes failing to meet these requirements. This is evident in runners, with one study finding 73% of college-aged athletes failing to meet their carbohydrate intake (Beermann et al., 2020). When it comes to longer ultra-endurance events, the problem compounds, with many athletes struggling to meet a third of their requirements (McCowan and Edelstein, 2006)!

So, if you find your performance lagging, the first thing to do is make sure you’re getting enough carbohydrates in overall.

You Don’t Eat Intra-Workout

If you’re running distances of less than 10km (or roughly less than an hour), your performance is unlikely to be limited by running out of muscle glycogen. However, for longer runs (>90 minutes), athletes are advised to consume 30-60g of carbohydrates per each hour of exercise (Burke et al., 2012).

If you aren’t replenishing your glycogen stores during long runs, you could be selling yourself short.

Runners can benefit from including an intra-workout snack/drink during longer runs. If you haven’t started implementing this strategy, it might be helpful to try it and get yourself across the line.

Now, we don’t want you to shit yourself, so we need to make sure we are smart about this. Your intra-workout should be low fibre (too slow to release energy), portable (you’re gonna be carrying it) and easily digested (for obvious reasons). A simple sugar source is ideal (Wilson, 2016). You could consider sports drinks, gels or jellies.

Summary: Consider intra-workout carbohydrates for longer runs, but make sure you do this gradually.

You’re Training Fasted

As we discussed already, glycogen stores are the main limiting factor in endurance performance. You need to give your body the time and fuel (carbohydrates) to replenish these stores.

So, training fasted might not be the best idea for you. Training fasted in itself is not an issue, and in some cases training fasted may actually increase performance (Vieira et al., 2016).

However, you need to make sure that you are replenishing your glycogen stores after your sessions. Sports nutrition guidelines are very clear that if you have a short window between sessions (<8hrs), you need to get carbohydrates in ASAP (Burke et al., 2012). If you refuel without carbohydrate, it’s pretty much ineffective.

This largely comes down to when your sessions are structured. If you are an amateur runner, chances are you are getting your sessions in when you can. You may have to do a long run in the evening, and then another the following morning just to fit them in. If you aren’t refuelling properly, you’re started on the backfoot for the morning run. Same goes for leaving a long gap between eating and your session, e.g. going for a long run straight after work, when you haven’t eaten since lunchtime.

If possible, try and leave a longer gap between your longer sessions (>90 mins), and ensure you’re eating carbohydrate post-run to ensure you recover. Of course, if you go running in the evening, chances are it’s unlikely you want to slam a huge amount of carbohydrates in before bed. Adding in a serving of protein with your carbohydrate source can help replenish glycogen stores, even if you’re not intaking enough carbohydrate (Ivy, 2004).

Summary: Try and space your longer sessions further apart, and ensure you intake carbohydrate ASAP after your session to kickstart recovery. Consuming protein with carbohydrate can help increase glycogen stores, even if you aren’t getting enough total carbohydrate in.

You’re Too Thirsty

Being thirsty, when it comes to Instagram, or indeed endurance running, is never going to end well. Dehydration is a big performance killer for endurance runners. Proper hydration strategies enhance performance, delay fatigue and prevent dehydration-associated injuries (Von Duvillard et al., 2004).

Goulet (2012) presents the following recommendations for endurance athletes:

  • Start your session hydrated (obv).
  • Test this by ensuring urine is pale and no thirst sensation. Oh, the glamour.
  • Drink 5-10ml of water per kilo of bodyweight 2 hours before your session.

Interestingly, for sessions <1hr, dehydration is rarely a factor in reduced endurance performance (Goulet, 2012). It is recommended to consume 400-800 mL/hr during endurance events (Vitale and Getzin, 2019). Being hydrated also helps push those carbohydrates you’re slamming into your system all around your body faster (Burke et al., 2012).

HOWEVER, and this is a big cause for pause, these recommendations are individual. You don’t want to overhydrate either, which can also hamper performance and be pretty dangerous (Vitale and Getzin, 2019). Your intake depends on your bodyweight, sweat rate, kidney function and a whole host of other factors. Start smaller, and build up your tolerance.

Summary: Ensure you’re properly hydrated before your sessions.


Of course, there’s a good chance you’re doing most, if not all, of these techniques. These are recommendations, and not absolutes that must be followed to the letter. It may be simply unfeasible for you to practice some of these strategies. Eating anything close to your session may lead to you feeling sick during session, for example.

So, treat yourself like the special snowflake you are, and make sure these recommendations are tailored to work for you. And the beauty of trying out these strategies in training is that you get to see what works for you before the big day you’ve been training for!

Hopefully you found this helpful. Let me know if there’s anything else you’d like to see covered next!


  • Atkinson, G., Taylor, C.E., Morgan, N., Ormond, L.R., Wallis, G.A. (2011) ‘Pre-race dietary intake can independently influence sub-elite marathon performance’, International Journal of Sports Medicine, 32(8), pp. 611-617.
  • Beermann, B.L., Lee, D.G., Almstedt, H.C., McCormack, W.P. (2020) ‘Nutritional Intake and Energy Availability of Collegiate Distance Runners’, Journal of the American College of Nutrition, 39(8), pp. 747-755.
  • Burke, L.M., Hawley, J.A., Wong, S.H., Jeukendrup, A.E. (2012) ‘Carbohydrates for training and nutrition’, Journal of Sports Sciences, 29(1), pp. 17-27.
  • Goulet, E.D. (2012) ‘Dehydration and endurance performance in competitive athletes’, Nutrition Reviews, 70(2), pp. 132-136.
  • Hargreaves, M., Spriet, L.L. (2020) ‘Skeletal muscle energy metabolism during exercise’, Nature Metabolism, 2, pp. 817-828.
  • Hearris, M.A., Hammond, K.M., Fell, J.M., Morton, J.P. (2018) ‘Regulation of Muscle Glycogen Metabolism during Exercise: Implications for Endurance Performance and Training Adaptations’, Nutrients, 10(3), p. 298.
  • Ivy, J.L. (2004) ‘Regulation of Muscle Glycogen Repletion, Muscle Protein Synthesis and Repair Following Exercise’, Journal of Sports Science & Medicine, 3(3), pp. 131-138.
  • McArdle, W.D., Katch, F.I., Katch, V.L. (2015) Exercise Physiology 8th edition. United States: Wolters Kluwer.
  • McCowan, K.A., Edelstein, S. (2006) ‘Are Female Ultra-endurance Triathletes Getting a Sufficient Daily Carbohydrate Intake?’, Topics in Clinical Nutrition, 21(2), pp. 139-144.
  • Murray, B., Rosenbloom, C. (2018) ‘Fundamentals of glycogen metabolism for coaches and athletes’, Nutrition Review, 76(4), pp. 243-259.
  • Vieira, A.F., Costa, R.R., Macedo, R.C., Coconcelli, L., Kruel, L.F. (2016) ‘Effects of aerobic exercise performed in fasted v. fed state on fat and carbohydrate metabolism in adults: a systematic review and meta-analysis’, British Journal of Nutrition, 116(7).
  • Vitale, K., Getzin, A. (2019) ‘Nutrition and Supplement for the Endurance Athlete: Review and Recommendations’, Nutrients, 11(6), p. 1289.
  • Von Duvillard, S.P., Braun, W.A., Markofski, M., Beneke, R., Leithäuser, R. (2004) ‘Fluids and hydration in prolonged endurance performance’, Nutrition, 20(7-8), pp. 651-656.
  • Wilson, P.B. (2016) ‘Does carbohydrate intake during endurance running improve performance? A critical review’, Journal of Strength and Conditioning Research, 30(12), pp. 3539-3559.

Published by Michelle Carroll

I am an online coach (MSc Sports & Exercise Nutrition, EQF Level 4 Personal Trainer, PN Level 1) and radiographer (BSc). I believe in empowering others to make better choices for their health through education. I think that the fitness industry has created a disconnect between best practices and “evidence-based” practices. I hope by chronicling my experience as a healthcare professional and my education as a fitness professional I can assist others on the path to bettering themselves.

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