Basics of ultra marathon nutrition and hydration (2024)

The key issues are under feeding, developing Gastro-Intestinal (GI) issues, dehydration, and (occasionally) over-hydrating. In this article we will cover some of the key things you can do to minimise the risks of your gut letting you down on race day.

First some numbers. You need to be able to consume around 250 calories an hour whilst on the move, of which you should be aiming for around 90 grams of Carbohydrate (CHO) with a 2:1 glucose to fructose mix.

These are not absolute numbers, we are all different, but they are a great place to start (and note in most research athletes rarely achieve the 90g/hr of carbs, normally hitting nearer 60).

But nutrition planning and training must be a central part of your overall training plan if you are to be successful.

• First, your gut needs to be trained to work effectively whilst you are exercising. This takes time and like all training the more you do it the better it gets. You should be practicing your nutrition plan (more later) on every long run.
• Second, working out which foods work for you, and which don’t, can take a lot of trial and error. Doing this early will reduce the chances of stomach issues derailing your event.
• There are many who have become used to getting their nutrition during an event just from gels and other such supplements. This is possible up to a marathon distance – but trust us you won’t want to take this approach on anything over 50km; it is not a recipe for success on an ultramarathon

You must practice eating the food for your event in training. Different foods will have an adverse effect on you and your gut when you start adding exercise into the mix. Whilst a rapid visit to the bush isn’t necessarily an event ending scenario, chronic stomach ache, vomiting and diarrhea can be!

What about fat and protein you cry…yes you need both(!) At around Ultra pace you will be taking about 50% of energy from CHO and the other 50% from fat. Yep, you are an Ultra athlete, so you will be fat adjusted…no fancy diets required.

So how do you develop your nutrition plan? Simply start at expected duration, add 15%, and multiply by 250 (or 90)! e.g. 50 miles, I’m expecting to complete in 8 hours, so I’ll plan for 10. That means I need at least 2500 calories, of which I’ll need 900g of CHO. And you need a mix of foods. Not only the numbers above but you should aim for a protein intake of 0.25g per kg of body weight per hr.

OK, that’s the easy bit. Now what foods will you use. As already stated, although gels are tempting they become sickly at some point for most people. We favour a mix of sweet and savoury, as well as ensuring we have some ‘real’ food thrown in the mix. This can include cold pizza (one of our favourites!), mini pies, sandwiches, fruit and nut trail mix, as well as specialist bars and gels. But note that bars and gels aren’t cheap and they aren’t essential as long as you hit your numbers!

If your event is a series of picnics with a run between (!) ensure you find out what food is available beforehand and train with it. But caution, we have seen many event where the ‘menu’ has changed on the day; I suffered my worst ever ‘bonk’ on a 150 mile cycle ride where this happened and the feed stops only had a brand of gel I knew made me sick…and I foolishly was reliant on them, not myself (lesson learned!).

Ideally, build in your own options. Your palate will change significantly over the duration of an Ultra and you need to have the ability to ‘switch it up’ and keep the nutrition going in.

You should be training with event food twice a week, try overloading your gut and getting even more calories in. And make note of what doesn’t work so you can adapt your plan.

As an example, here’s my (zero aid stations) menu for 50 miles, expected duration around 9 hours (calories in brackets):

• Savoury Bars x3 (900).
• Gel flask (300). With three gels decanted in. Used if I needed an instant boost if/when I got behind on nutrition plan.
• Trail mix (1000) – fruit and nut mix with chocolate M&Ms; grabbed a handful on most uphills where I slowed to a walk. This is my go to.
• Luchos Dillitos x3 (300) cut into 1/4s in with trail mix.
• KMC Kendal Mint Bar x1 (340)
• Mountain Fuel Chia gel (400) – spare if I needed a real kick.
• Mini Pork Pie x2 (200)

How much water you need will depend on the weather, and how much you sweat. But you should be aiming for between 400 and 800 ml an hour.

Under hydrate and you will suffer. So, if you are thirsty, drink. If your pee is orange, drink. If you can’t pee, drink (quite a lot!).

We prefer to stay on top of our hydration by calculating desired consumption (see below) and sipping regularly (every 10 minutes for example).

However, over hydrate and you can be very ill (Hyponatremia) – Damian Hall’s infamous leans at the end of his record breaking UK coast-to-coast could have been much worse. He had overcompensated for the heat, ended up with hyponatremia and could have ended up in a lot of trouble.

The best way of knowing how much water you need to take on is to conduct multiple sweat tests in various temperatures, as follows:

1. Weigh yourself nude prior to your run – doesn’t have to be nude but at the end your clothing may retain an amount of fluid that can skew the results.
2. Run for 1 hour at Ultra Run intensity (note the temperature)
3. After the run, weigh yourself (nude) again
4. Subtract your post-run weight from your pre-run weight.
5. Convert your weight loss to litres, 1 kg = 1 litre (or 1 pound = 16oz). This equates to your hourly sweat rate for a given temperature.
6. Perform this test in various temperatures – ideally in 10 degree differences.
7. Aim to replace 90-95% of fluids lost, not 100%.

Obviously on a long event in the heat that can be a lot of fluid. There is a balance to be struck between how much fluid you carry and how much you can source either from aid stations, filtering from natural water sources, or from shops. And factor in the forecast and recent weather, expecting to filter water from a stream that’s dried up can quickly become a challenge you don’t need. Equally, under-carrying on a hot day can end your event way too quickly!

Again, we are not nutritionists but…

There’s enough sodium, electrolytes etc in the food you’ll be carrying for the average person; the average slice of pizza has about 500mg of salt. If you think you are an extreme sweater(!) there are companies that will conduct sweat tests on you and provide a bespoke electrolyte plan. Salt tablets aren’t recommended (but we’ve used them) as they can lead to over drinking and subsequently Hyponatremia.

Caffeine can be used in the second half of a 50 (KM or mile) to give you a ‘boost’. 50mg/hr (half a cup of coffee) has been shown to improve performance in the latter half of an Ultra. For longer events, save the caffeine until you are tired. This gives you a double benefit of keeping you more alert and improving performance.

Once you have your nutrition plan, have decided what foods you’ll take and how much water you need to carry…go and practice!

You should have your plans done early and start working with different foods from at least 12 weeks before an event. Aim to have a complete plan with enough time to rehearse it 3 or 4 times pre-event.

Up to 40% of DNFs are down to GI issues. Train your gut just as well as you train your legs!