Endurance Skating

Training, Racing & LCHF Fueling For Skating And Endurance Sports

In-Race Fueling Part 1: Is Your Ego Writing Cheques Your Body Can’t Cash?

You engine sucks and your sparkplugs are

Avoid running on empty….

One of the major competitive advantage of achieving good fat-adaptation is a lesser reliance on exogenous fuel sources during long races. However, even the most fat-adapted athletes must consider their in-race fueling strategy if the race is long enough to warrant it. A typical 3-4hr marathon race for a well fat-adapted athlete should not require too much nutritional planning, but a longer 6hr, 12hr or even 24hr race is another matter, and opens up a complex, constantly changing and hotly debated topic.

Racing Is Not Training

One of the great mistake made by many fat-adapted athletes is to neglect their carbohydrate requirement and try to maintain LCHF principles even during a race. The body uses a mix of carbs and fat during exercise – run out of either, and your Central Governor will shut your entire system down – bonk time. As fat stores are plentify even on the leanest athletes, in practice it is only carb depletion that we must be wary of.

So, ironically, while we restrict our carbohydrates intake in everything outside of racing – including training – in order to upregulate and promote fat burning, the point of a RACE is to get out there and perform at your best; it is not to train for further adaptations, and therefore our priority is to ensure a proper and adequate fuel mixture is supplied in order to *preserve* the fat burning we have and perform at our best.

Practical Considerations

In practice all that any athlete should care about when considering what to use for race fueling is this:

“What works for ME?”

This is highly individual, and is largely dictated by what you like and what your stomach can handle. Some people are fortunate enough to have a cast-iron gut and can chomp down all manner of sports drinks, sweet and savoury food, and in large quantities. Others find that almost anything will cause them to chug or eventually give them the squirts. Eww.

Too much, too soon

Too much, too soon

That is why gels, coca-cola, red-bull, and other stuff that you wouldn’t normally go near in your normal healthy eating  routine should not be ruled out as a part of your race fueling strategy. There is no standing on ceremony when it comes to racing: you do what works.

You Want The Calories…? You Can’t Handle The Calories!

The ubitqitous 'nana

The ubitqitous ‘nana

The problem we all face is that the stomach can only absorb a limited amount of food under the stress of a race. Actually, that is true even when at rest; the food you eat after a regular meal takes several hours to be fully digested and absorbed, and that process is retarded further during exercising.

Some of the other factors that can contribute to absorption and digestion are:

The individual; some people can simply digest more food and at a faster rate than others
Activity; the less jarring the sport easier it is to digest and absorb food
Intensity; the higher your level of intensity, the less blood can be diverted to stomach and intestine function
Heat & hydration; if you are hot and/or dehydrated, the less nutrition can be absorbed as the body must work harder for thermoregulation
Race duration; Your stomach typically can absorb less and less the longer the race goes on
Food preparation; liquids and less fibrous foods will be more quickly digested

Some of these factors can be trained and manipulated, others simply have to be managed.

I have heard anecdotal evidence of elite Iron-Man triathletes consuming as much 500-600kcal hr on the bike leg. However I suspect a far more realistic maximal figure for most of us mortals is probably less than half of that, especially if you are doing anything non-cycling; the fixed body position of cycling lends itself well to easier digestion, which is why Iron-Man triathletes do most of their fueling for the run on the bike leg.

This could be your lucky day

This could be your lucky day

If you guesstimate that in a best case scenario you can absorb 250kcal/hr, you can then start figuring how to fuel for a race. Think of this as your in-race fuel budget – you had better use those calories wisely. You may think that you can just eat more and your stomach will eventually digest it when it can, but this is can be fatal for your race: the consequence of trying to take on more fuel than you can manage is inevitably GI distress.

250kcal/hr may seem quite conservative if you think of that it is just 2-3 typical energy gels, and indeed you may personally be able to handle more, especially near the start of a race when all your bodily functions are still working well, but imagine consuming that much each hour, every hour during the course of a multi-hour RACE. It’s really not that easy to consume much more… hour after hour..

Fueling Priorities

Remember, during racing we can almost flip our LCHF protocol on to its head – we are fueling to perform. So from your in-race fuel budget of, say 250kcal/hr, your order of priorities are:


Your first and foremost priority MUST be to ensure that your do not risk muscle glycogen depletion. You have a starting tank of approximately 1,600kcal glycogen stored in the muscles & liver – the minimum rate at which you need to replenish depends on race duration and *how efficient a fat-burner you are*.

For example, if you’re extremely well fat-adapted and expending 700kcal/hr in race effort with only 10% of that coming from carbs (as was demonstrated by the ultra-elites fat-adapted group in the FASTER study), then you only have to worry about replenishing approximately 70kcal/hr of carbs to keep your body well stocked with glycogen. There are 4kcal/g in carbs – so that’s just 17.5g/hr of carbs you need to be ingesting.

However if you’re slightly less well fat adapted, let’s say you are relying on 30% of that 700kcal/hr coming from carbs (which is still pretty good), then you now need to worry about replenishing 210kcal/hr. You can see that doesn’t leave you with much wiggle room!

Worse, if you are a relatively poor fat burner and are utilizing, say 60% carbs (which is very typical of many high-carb athletes), you now need to worry about replenishing 420kcal/hr. But as you almost certainly cannot even absorb that much, you will be running a continual deficit (in this example perhaps as much as -170kcal/hr) and will reach complete glycogen depletion in about 9.5hrs in a very best case scenario. A typical full Ironman or 50mile age-grouper can expect to go longer than 9.5hrs, so under such a scenario they risk full glycogen depletion before the finish line. In reality it could easily be much sooner as the stomach beings to shut down and their ability to digest food diminishes under racing duress.


Bonus points if you saw this one coming. Replenishing protein becomes increasingly important if your races go much longer than about ~3hrs. Contrary to what I have written up until now, fat & carbs are NOT the only fuel that your body will metabolize for energy during exercise – amino acid oxidation from protein breakdown can account for as much as 10% of your energy output right from the get go. Interestingly, this ratio is constant and hardly changes, regardless of exercise intensity – it’s the fat/carb mix that changes, which is why we tend to focus on it so much. This makes the calculations for protein requirement pretty easy.

 Again, protein requirement must be paid for out of your 250kcal/hr total budget. 10% of our theoretical 700kcal/hr is 70kcal you need to allocate to protein intake. Protein contains 4kcal per gram, so that is 17.5g of protein/hr.

Now if you add the protein requirement (70kcal/hr) on top of the carb requirement you can see that, under a best case scenario you could be looking at a requirement of just 140kcal/hr total intake for a hypothetically uber fat-adapted athlete, or conversely it could easily be 500kcal/hr+ for a metabolically inflexible athlete – ie way over budget.

Neglect protein and the body will start to catabolize its muscle and internal organs in order to meet its energy-from-protein requirement. This is not something you want, trust me. Much worse than a simple glycogen bonk, it can lead to renal failure and a trip to A&E. I personally aim to take it a bit higher, up to 15% protein to compensate for increased muscle breakdown in ultra-style races.


If you have any spare budget, only then should you be thinking about allocating it to fat consumption. Remember that your body already has a very large fat fuel-tank, so even if you are able to digest more beyond your minimum carb & protein requirement, it may not be necessary to do so. The most effective fueling strategy is the one that provides the absolute minimum calories to sustain optimal performance, thereby minimizing non-essential work required from your stomach and digestive system.

Nonetheless, many athletes find that they do prefer to take on some savoury foods that are naturally fat-laden during the course of long races. I am certainly one of them, so I do include a good amount of fat and try to stick to real whole foods even during races. As already stated: the only thing that matters is what works for YOU!

Fuel Usage vs Duration & Intensity

It’s never that simple, of course. None of these are variables are fixed – your fat/carb usage will vary depending on race duration (and hence the intensity). I don’t care how well fat-adapted you are, a typical 10k or half-marathon race effort will see you making a fairly sizeable withdrawal from your glycogen account. However, these races aren’t long enough to seriously threaten full glycogen depletion. It’s only at [running] marathon duration (3-5hrs) and above that metabolically inflexible folks risk hitting the wall.

In long ultras of 6hrs-24hrs+, far more than willpower or technique, the effort and speed you can maintain is almost completely proportional to how much energy you can release from both bodyfat and food intake – so make use of and maximize both.

How you actually quantify how good a fat burner and therefore your exact carb intake requirement is a topic for another post altogether.

Staying properly hydrated and maintaining electrolyte balance is also essential. Hydration and electrolytes are a long and almost just as large and controversial a topic as in-race food intake, but again, that is for another discussion.

Phew. That was only meant to be an introduction to the main topic of what foods and fuels I do actually use during races, but it kinda morphed into quite a long explanatory piece by itself, so I think I’ll draw a line under it there and write part 2 when I get around to it!

Related articles:

Fat Adaptation for Athletes 101

Central Governor

DIY Energy Bars


4 comments on “In-Race Fueling Part 1: Is Your Ego Writing Cheques Your Body Can’t Cash?

  1. Pingback: In-Race Fueling Part 1: Is Your Ego Writing Cheques Your Body Can’t Cash? | runs to stand still

  2. Pingback: Race Fueling Part 2 – Carbohydrates | Endurance Skating

  3. Pingback: In-Race Fueling Part 3: Race Day | Endurance Skating

  4. Pingback: Race Report: The “9BAR 9×9” (81km Trail Ultramarathon) — 10.Oct.2015 | Endurance Skating

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This entry was posted on April 23, 2015 by in Endurance, Nutrition, Science and tagged , , , , , .

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