A Complete Guide to your Triathlon Run Nutrition

Eating during a marathon is the definition of “easier said than done.” What are you supposed to eat, how much, how often, and what about water versus electrolytes?

We’re going to answer all those questions and more in this article. Let’s dive in!

Marathon Nutrition Timing

The fueling begins 15-30 minutes before the race starts. Depending on the marathon’s start time, you don’t necessarily need to consume a full breakfast before the race. Assuming you have carb-loaded the day before the race, your body can store up to 2000-2500 calories overnight.

You should still have a carb-based breakfast on race morning to make sure that your carbohydrate stores are completely topped off. Ideally, you should have this carbohydrate-based breakfast four hours before the race to give your body plenty of time to digest the food. For an 8:00 am race, that means having breakfast at 4:00 am. Many runners will go back to bed or even take a nap between their early morning breakfast and the start of the race.

Having breakfast before a marathon creates a buffer – like nutrition insurance – which provides you with some extra carbohydrates if you under-fuel during the race.

How Often to Eat During a Marathon

Once the race has started, your nutrition window – or how often you eat or drink – comes in 17-30-minute increments. Studies have shown that carbohydrates in liquid form are the best food to consume during a marathon for most runners. 

The amount and frequency of carbohydrate fueling depend on the length and intensity of the event, as well as the runner’s body weight. An average marathon runner, for example, may target 30-60 grams of carbohydrates consumed per hour during a marathon. 

Highly-trained runners may consume even higher amounts of carbohydrates 80-100 grams per hour.

How Many Calories the Average Runner Burns

The longer you run, the more calories you will burn. An average runner will burn anywhere from 400-600 calories per hour during an easy-to-moderate run.

The harder you run, the more calories you burn, and the fastest runners in the world can burn over 1000 calories per hour. Adjusting your fueling based on your run intensity in training is essential. For an easy 10-mile run, you may only need a gel or two. But if you go out and do 10 miles at a race pace, you might need 4-6 gels to fuel your workout. 

Lastly, body weight significantly affects how many calories you burn while running. The lighter you are and the less body weight you have, the fewer calories you will burn. Conversely, larger and heavier runners will burn more calories than smaller runners

What to Eat During a Marathon

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Liquid sources of calories are best for marathon training and racing because of the pounding effects of running. It can be hard to stomach solid food on the run, and it may take longer for your body to absorb the calories. 

Gels are one of the most common sources of carbohydrates during a marathon. They are small, easy to use, and can be consumed in two seconds. There’s no chewing required, and in a matter of seconds, you will have another 20-30 grams of carbohydrates flowing into your bloodstream.

Many runners consume sports drinks, electrolyte mixes, or sodas during a marathon. Each drink has its own mixture, which can be watered down or made even more concentrated. Electrolytes are vital on hot days, while the carbohydrates from a sports drink or soda help keep your energy levels full.

In most cases, runners should separate their fluids from their calories. If you start experiencing stomach distress, yet all your calories are coming from liquids and bottles, the risk becomes two-pronged. 

On the one hand, if you continue drinking your fluid calories, you could seriously upset your stomach and experience cramps, GI stress, or worse. But on the other hand, if you stop taking in your liquid calories, you risk emptying your calorie tank and bonking. 

The best solution is to separate your fluids from your calories. For most runners, the best marathon fueling strategy is to consume their calories in liquid gels while also consuming water or a low-calorie electrolyte mix. 

Sports Nutrition or Real Food?


Getting most, if not all, of your fuel from pre-packaged sports nutrition is a no-brainer for short to moderate endurance events, where taking in palatable, simple carbohydrates is the key to success. Whatever format you prefer – drinks, gels, chews or bars – they all generally work well if your total carb intake is about right.

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This fits with the narrative that glycogen depletion is a major cause of fatigue in these events and that increased dosing of simple carbohydrates tends to correlate with improved performance.

But, when things get really, really long, taste fatigue, hunger levels and morale all benefit more from including some carefully selected ‘real foods’ to supplement your energy products.

What to go for in terms of real foods is more of an art than a science, because it’s critical that you really enjoy eating them and food preference is a very personal thing. But, here are some decent general rules to help define if foods will be good or bad choices.

Good real foods for ultras should:

  • Travel well and be durable enough to survive a few hours in a pocket or pack
  • Be easy to wrap/open and consume on the move (ideally with one hand)
  • Be relatively carb dense, even if they also include significant amounts of fat and protein
  • Be thoroughly tried and tested in a climate (and at an intensity) similar to those you expect to experience in the race
  • Have a high calorie/weight ratio (especially if you have to carry them on you)
  • Some will be very salty, so you can develop a taste for whether your body is craving salt at a given point in time

Good real foods for ultras should not…

  • Be too messy, crumbly to handle, or dry in the mouth
  • Be very high in fibre
  • Present a choking hazard if eaten in a hurry on the move
  • Melt or degrade in the heat
  • Freeze easily or go totally solid in the cold

The list is not supposed to be exhaustive but gives you some sensible criteria on which to base your trial and error.

Avoiding GI distress

Gastrointestinal (GI) distress is a leading cause of ending with a dreaded DNF (Did Not Finish) in an ultra. A 2015 study reported that GI issues were the reason 35.6% of non-finishers dropped out of a 161-km ultra, with nausea being the most common symptom (90.5%).

The reasons underlying GI distress are many and varied, but an amazingly common contributor is simply overwhelming your gut with an excessive amount of calories, or a single macronutrient (often carbs), causing a back-up in the system, bloating and (if it gets bad enough) sickness or diarrhoea as your body tries desperately to clear itself out.

The classic way of overwhelming your gut with carbs is to combine the use of gels/chews/energy bars or real food with lots of sugary isotonic or hypertonic sports drinks.

Whilst isotonic sports drinks like Gatorade or Lucozade can be a useful tool for shorter endurance events, if they’re used excessively in longer, hotter races, it’s a recipe for disaster.

Using water and hypotonic (lower calorie) electrolyte drinks alongside solid foods is a much more flexible and low-risk approach for ultras. 

What about hydration?

Olympic Take: 7 Tips for Marathon Fueling & Hydration - Mile High Run ClubWe’ve written a great deal about hydration and sodium intake for long – and especially for hot – races and there are links to relevant articles distributed throughout this next section if you want to get into the detail on any specific aspect of this topic.

Of particular interest to anyone doing an ultra is perhaps this piece on how much dehydration you can tolerate before your performance starts to suffer.

Suffice it to say that hydration needs are both highly individual in terms of fluid and sodium requirements, as well as being heavily influenced by environmental factors and pacing.

It’s also important to point out that whilst there’s something of a ‘more is the better mantra when it comes to energy intake in an ultra, this is definitely not true when it comes to hydration. Too much fluid (especially plain water or weak sports drinks) can lead to hyponatremia – a dangerous condition that has taken the lives of a few unfortunate ultra athletes over the years, as well as ruined the races of countless more.

To give you an idea of the range of fluid intake levels we’ve seen work with athletes in ultra events, these can start as low as 200-300ml (~7-10oz) per hour in colder conditions and/or when intensity and sweat rates are low. They can climb to 1,000ml (~34oz) or more in hot and humid climates and with athletes who exhibit very high sweat rates.

Optimal sodium (the key electrolyte when it comes to staying hydrated) intakes also vary significantly from between ~200mg per hour up to around 1,500mg per hour. As well as being very individual based on (mainly genetic) differences in how salty your sweat is (i.e. your sweat sodium concentration), sodium needs tend to roughly track your overall fluid requirements, so are much higher in the heat and humidity than when it’s cold and dry (as you might expect).

A mismanagement of your fluid and sodium intake can have a knock-on effect on fueling because reduced blood volume (one of the main consequences of dehydration) can reduce the blood flow to your gut and negatively impact the ability of your body to absorb nutrients. The general level of fluids and electrolytes in your stomach and gut can also impact GI issues and absorption rates further, so keeping the hydration plate spinning nicely is a huge deal in an ultra.

Pro Tips for Marathon Nutrition

You know what they say about the best-laid plans… Marathon nutrition is not as simple as writing a plan and executing it. There are lots of things that could go wrong – the weather might change, you might forget a packet of gels, or you might start bonking with 7 miles to go. 

But if something goes wrong, that’s no reason to give up – there are several things that you can do to get back on track. Here are our pro tips for marathon nutrition: 

  • If your stomach starts to go awry, switch to drinking water instead of any electrolyte or flavoured mix. This will change the osmolality in your stomach – once your stomach feels better (which it will), then you can switch back to drinking electrolytes
  • Osmolality is the measure of the number of dissolved particles in a fluid. You can also think of it as the concentration of a fluid. Drinking water during a marathon changes the osmolality in your stomach by lowering the concentration of electrolytes
  • If you are beginning to fade, have a soda such as a Coke which will provide you with a quick caffeine shot and a boost of energy
  • Once you have your first Coke, stay on it. Don’t go back to your previous nutrition strategy or you’ll run the risk of losing energy, upsetting your stomach, or feeling erratic from going on and then off of caffeine.

What to Do if Things Go Wrong

  1. Stay calm. Try to think rationally and avoid getting too down on yourself about it. Ultras are, by definition, long events and in most scenarios, time can be gained back later once you’re back on track.
  2. Focus on defining what the issue is (e.g. lack of energy – a bonk, thirst/dehydration, GI distress, cramping etc) as this will point towards the best remedy.
  3. Slow down. Reducing your pace is often helpful on its own. Act on your best instinct of whether you need to take in more of something (e.g. sugar, fluid, sodium) or whether you may have taken in too much and need to hit the brakes for a while to give your body a chance to process what it’s dealing with.
  4. If you think you need ‘more’ of something, don’t overdo your intake in a short time, as that will just worsen things. Treat your body with respect and aim to coax it back rather than bullying it into behaving!
  5. If possible and safe to do so, keep moving whilst you rectify the problem. As long as you’re moving, you’re progressing towards the line. Stopping dead for a rest should be a last resort, as getting going again is tough. Sitting down is like putting one foot in the DNF grave, so only do so if entirely necessary!


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