The Science of Exercise Fuels, Gels and Sports Drinks

What are they, do you need one, do they help and which one is best? Big questions for sure but do they even work is a pretty good one too! I found it a really weird concept that I would eat while I was running when I trained for my first half. It was a really intimidating actually and the whole idea made me a bit anxious for some reason. We will be focusing on the science here but there are concerns that are personal too. So I might sneak in some of my personal experiences with fueling in too or at least some considerations. At the time I did a lot of googling about fueling and the advice was thankfully pretty consistent so that was as far as I went with it at the time. But I never dug down into the science of the thing until now. But that is exactly what we are going to do today. What is the deal with eating while you’re working out? So if you don’t want to know all about it just read the first few sections for the standard stuff but if the rational, deep dive science stuff is your thing you’ll find that here too!

What are energy fuels and do you need one?

They can take a lot of forms but gels, goos, beans or sports drinks all have the same aim and that is to deliver some carbohydrates and calories in the form of sugar to you body while you are working out. However you don’t necessarily have to use a commercially produced product either. It’s been pretty well studied at this point and the idea is if your hard workout is going to last more than an hour you should start taking in energy at about the 45 minute mark and then about every 15 minuets there after. Now that is what is optimal according to science but you don’t have to do exactly that. So if your workout is going to last about 70 minutes for example you might not fuel. The longer your workout lasts past an hour the more important it is. The harder your effort the closer you should come to re-fueling every 15 minuets (Kozlowski et al., 2020). But remember most of the studies we will be referencing here today are done with highly trained athletes and even elites. That doesn’t mean that you don’t need fuel at all but rather that there are some pretty good reasons that a different schedule might work for you. For example on long runs I start fueling somewhere between 40-60 minuets in depending on what and when I last ate and about every half hour after that. I might skip a fueling point towards the end of my workout if I don’t feel like I need it.

Finding the right fuel can be an issue though both for taste and mouthfeel but most importantly because they can upset your stomach. That’s the polite way of saying diarrhea but remember it comes when you’re already a long way from home or even worse mid race. This is called gastrointestinal stress and it can also take the form of nausea, throwing up, burps or gas. If you’ve tried what feels like all of the options and your tummy is still all bubbly there’s a pretty good chance you’re not drinking enough water along the way (Williamson, 2016).

Why do we fuel workouts?

The short answer is to prevent ‘hitting the wall’ or ‘bonking’ which is when you literally just can’t anymore. You’ll notice your perceived effort goes way up while your performance goes down if you are edging up to that point. More simply a good, fast run, whatever that means to you, isn’t fun anymore and starts to feel terrible. If your workouts are getting long enough for that to happen that’s a reason to start thinking about fueling them. Biologically speaking your body has a lot of energy on board even for prolonged periods of intense exercise. First in the form of free glucose in the blood, then stored glycogen which can be quickly mobilized. After that it’s on to stored fats. When you start using stored fats for energy on the go there can be performance decreases and it can feel terrible for some athletes. For a more in depth post check out this one about the science of ketosis. I go into more depth there. It’s relevant here because long bouts of intense exercise do push you body into that state. Many athletes suffer performance decreases when they move on to primarily fatty acid metabolism. The idea of taking in carbs (made of sugars) is to replenish your stores of glucose and to some degree glycogen to prevent ‘hitting the wall.’ Science does say it works and I can personally vouch for that!

Do they work?

Yup they do and not just for running (Phillips et al., 2011), cycling (Saunders et al., 2007) and triathlons. There were lots of examples of other sports too. For example in alpine skiing athletes who had a gel hit more gates and had fewer DNF’s compared to those that were given a placebo (Seifert et al., 2012). So across the board yes fueling your workouts at a certain point is a great idea. There is this idea out there that you might have to experiment to find the one that works best for you. But aren’t they all the same? No beyond obvious things like taste, delivery method, texture and packaging they makeup varies widely. One study by Zhang et al., in 2015 looked at 31 products across 25 brands and found significant differences in serving size, energy density, the number of calories, sugar content and osmolality which is pretty much everything! The first four of those things have major implications for how much energy you’re getting and osmolality is really a big deal for potential GI issues. So that means you really might have to try a lot before you find the one that’s perfect for you. That’s also the reason so many racers (like me) opt to bring their own energy source even if the race provides an option. I’m not aware of any races that prohibit the practice but it might be worth checking for triathlons in particular. Those kids do have some pretty crazy rules!

What does the perfect energy source look like?

Optimal glucose to fructose levels have been established by several studies between 1.2:1 and 1:1 but actual elite athletes in ultra endurance events take fuels that are well outside that range (Wilson et al., 2015). I think the takeaway message here is that if the elites are straying widely outside that range (probably for good reasons) it’s totally reasonable that we can too. In other words finding something that works for you is probably more important than just sticking to an optimally balanced fuel that doesn’t suit you otherwise. Studies suggest taking in enough fluids to account for how much you are sweating and 30-60 g of carbohydrates per hour of exercise (Coyle, 2003) is the goal. Other studies have established that energy intake during exercise should optimally be equal to what you are burning however most endurance athletes do fall short of that goal (Williamson, 2016).

Other stuff to know (some of it is really important)

  • If fueling your workouts always seems to upset your tummy there were two things I found that might help you out. The first is that GI issues are more common in those that hydrate the least so try drinking a lot more water. Second energy sources with more glucose rather than fructose or sucrose were more likely to lead to issues (Wilson et al., 2015).
  • It’s important to practice your fueling strategy during training workouts and before race day. There is a theory that over time your gut gets better at dealing with ‘eating on the run’. Gut training happens naturally as you fuel your workouts while increasing distance and intensity (Williamson, 2016), so start early in training!
  • Personally I didn’t want to get reliant on commercially produced products if I didn’t have to. One it’s expensive but more importantly I live about a 40 minute drive from the nearest sports stores. I do go to the city regularly but not every day or even every week sometimes. So I didn’t want to add a whole other level of errands to my life. I ended up finding that raisins worked really well for me.
  • Watching your carb intake can also have implications in the days leading up to a workout (carb loading) and in your recovery after.
  • There are many whole foods that can work for fueling workouts and many have been tested to be just as effective.
  • Foods with lots of fats, proteins or fiber can upset your stomach which means if you are looking for a whole food you might want to watch these components.
  • That said ultra marathoners often consume very high fat foods because they are so calorie dense.
  • Past 2 hours of exercise, particularly in warm weather sodium intake also becomes a concern (Williamson, 2016).
  • Fueling workouts is important but so is proper nutrition outside the times you are working out. Athletes can see performance increases and have faster recoveries by following an optimal diet all of the time in training (Wilson et all, 2015).
  • If a particular food works well for you and you’re happy with it that’s likely good enough!

My takeaways

As intimidating or weird it may seem to eat while you are working out it’s important to do for performance and comfort at longer distances and times. There is also a great benefit psychologically and physically to fueling your workouts early in your training and not waiting until it’s absolutely necessary. There are many variations and formula differences out there even in the commercially produced products so some experimentation could be necessary. Add whole food fueling to that and there probably is the perfect option for everyone out there. Science can tell us what the perfect ratio of sugars is, how much and how often exactly we should take in energy but there is also plenty of personal variation as well. While I think that it is absolutely necessary at some point to fuel it is far from necessary that you do so in only one specific way. If you do suffer from GI stress when you fuel a commercially produced gel and more water might just make most of your problem disappear.

Did the idea of fueling your workouts make you a bit anxious at first? Does it still feel weird to eat and run even years in? What is your old reliable workout fuel? Leave it in the comments below!

Read what I read

Coyle, 2003. Fluid and fuel intake during exercise. The journal of sport sciences.

Kozlowski et al., 2020. Effects of Energy Gel Ingestion on Blood Glucose, Lactate, and Performance Measures During Prolonged Cycling. Journal of strength and conditioning research.

Phillips et al., 2011. Carbohydrate gel ingestion significantly improves the intermittent endurance capacity, but not sprint performance, of adolescent team games players during a simulated team games protocol. European journal of applied physiology.

Saunders et at., 2007. Consumption of an oral carbohydrate-protein gel improves cycling endurance and prevents postexercise muscle damage. Journal of strength and conditioning research.

Seifert et al., 2012. The Effects of a Carbohydrate-Protein Gel Supplement on Alpine Slalom Ski Performance. Journal of sports science and medicine.

Williamson, 2016. Nutritional implications for ultra-endurance walking and running events. The journal of extreme physiology and medicine.

Wilson et al., 2015. Saccharide Composition of Carbohydrates Consumed during an Ultra-endurance Triathlon. Journal of the American college of nutrition.

Zhang et al.. 2015. Extreme Variation of Nutritional Composition and Osmolality of Commercially Available Carbohydrate Energy Gels. The international journal of sport nutrition and exercise metabolism.

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