Gastro problems in Endurance Athletes

Posted on April 1, 2008 by


About the author: William Sichel is a leading world-class endurance athlete. His achievements in Ultra-Running include being the World # 1 for the Six Day event (2006) and the current Scottish 48 Hour Record Holder. In 2007 his world rankings were : Six Day Event – World # 3 and 48 Hour Event –  World # 12. William has had a lifetime interest in nutrition for sport and years of personal experience as a world class ultra endurance competitor. Whilst William is a Science Honours Graduate he has no formal qualification in sports nutrition or as a health professional. The following information is based on his years of practical experience in his chosen sport.

It’s well known that large numbers of athletes suffer some form of gastro-intestinal (GI) disturbance during endurance events.  In some long events GI problems can affect over 50% of the competitors. While this article has been written mainly for the benefit competitors in Endurance Sports and Ultra-Distance Events, it may be useful to anyone undertaking extreme forms of physical training and competition. We will look at some of the common GI complaints faced by those involved in endurance training and competition, consider a series of easy to implement strategies to assess and control such problems and then ask how GI complaints arise and most importantly, look at what we can do to solve these issues and improve performance.  

Do you suffer from GI problems in training or competition?

Athletes suffering GI complaints may not at first even realise they have a GI problem. The symptoms can range from mild wind, bloated feelings and diarrhoea through to indigestion, stomach cramps, nausea and vomiting.  Any GI problem – even just a minor symptom – can spoil and at worst ruin a performance, even when an athlete may have spent months preparing for an event.

The motivated athlete will want to diagnose what went wrong, as quickly as possible and then attempt to rectify the problem and try again in their next event.

Unfortunately due to the complexity of long endurance events and the many variables involved – including different courses, varying weather conditions, different states of fitness and changing intakes of calories and fluids – it can be very difficult to pin point exactly what went wrong in any situation.

This article isn’t going to try and provide an ‘off the shelf’ solution because quite simply there isn’t one, due to the infinite number of variations in physical, physiological and biochemical make-ups.

However, what I am going to do is give some kind of framework for investigating GI problems in endurance events, garnered from my own problematic and lengthy but eventually successful experience.

It took me eleven years of painstaking trial and refinement to solve my stomach problems which mainly manifested themselves as debilitating nausea and vomiting in ultra endurance events.  I had no such problems away from the stress of ultra racing.

Some Important Steps That Everyone Can Take:

ü  Write race / training reports. Record as much detail as possible – this may help diagnose the reason for problems.  Include such things as weather and course information; start and finish time; and record – in as much detail as possible – everything you ate and drank (including solution strengths and amounts of food) and when you consumed it – if you can find a willing helper this can make the job much easier and more accurate rather than trying to do it from memory after the event.

ü  Try things out in training but remember that you can easily get ‘false positives’ during training.  Often you need the stress and duration of a proper event to truly test your nutritional strategy.  So use low key events as a test bed, not major competitions. Consider getting advice from a sports nutrition advisor – sometimes they can give you pointers in the right direction, although event-specific advice may be beyond them.

ü  Speak to your doctor in order to eliminate underlying medical conditions that may be exacerbating your GI problems in races.

ü  Consult with others in your sport and/or watch what others do – you may get some ideas to analyse and cautiously experiment with, that may help.

ü  Scour the internet for sources of knowledge and ideas which may help. I found key pieces of information by doing this.

ü  Consider just changing one thing at a time, as this helps pin-point what is an effective change and what isn’t.

Remember that it can take considerable time to find practical solutions – it may not be easy but real improvements only come with time and effort.

 These Are The Important Questions To Ask:

Q – Are you trying to take in too many calories?

The golden rule is to only take the calories that you can absorb, whether they are in liquid or solid form.

Taking in too many calories too quickly can slow the emptying of your stomach causing a build up of fluid in the stomach and resulting in cramps, nausea and vomiting.  

Don’t be fooled by scientific research carried out in laboratories on treadmills or exercise bikes lasting probably 2 or 3 hours at most and then recommending 60g of carbohydrate (240 kCals) an hour. 

Many sportsmen and women extrapolate these results for multihour events with disastrous consequences.

By comparison, the first time I ran in the 153 mile Spartathlon – the world’s longest point-to-point race – I consumed just 100kcals/hr and still finished the race strongly.

So if you have problems try reducing your caloric intake a bit and try to take your energy in liquid form if possible.  It is easier to swallow, easier to digest and easier to know what you are taking in.  Solid food takes more time and energy to digest and when you are operating at your limit, the GI system, often, just doesn’t want it and can’t cope with it.

Make your drinks up to no more than 6% carbohydrate concentration.  The general recommendation is 6-8% but if you are having problems it’s best to stick to the lower limit at the most.

Q. Are you taking in too much fluid?

Once again the golden rule is only drink what you are can assimilate and no more.   Very few athletes can take in more than 600-800mls an hour, at the most, when pushing themselves to the limit in hot weather.  Most of the time, the volume is 400-600mls an hour.

In my own case, even during the hottest part of the world’s hottest race – the Badwater Ultramarathon through Death Valley in California, where temperatures reached 54°C – my maximum hourly fluid intake was 840mls (I’m 59kgs/9 stone 2lbs/128 lbs and 1.63m/5’ 5” tall).  I didn’t get dehydrated and I set a British record for the event.  The fluid included a good electrolyte level (see below).

Taking in too much fluid can result in ‘stomach sloshing’ and a build up of fluid in the stomach and small intestine resulting in nausea and vomiting.

Q.  Do you have the correct electrolyte content in your drinks?

Most commercially available sports drinks are too low in their electrolyte content and don’t have a correct balance of sodium and potassium.  The sodium:potassium ratio in sweat is about 3-5:1 – your drink should reflect this.  The GI system is highly dependant on the correct supply of electrolytes to maintain proper motility so this is an area you need to get right – especially in hot conditions when you a losing a lot of electrolytes in sweat.

Be sure to try a good mineral mix in your drinks such as the one produced by and you won’t go too far wrong.  I use this mix at 4% of the electrolyte powder (4g/100g of powder).  This provides approx 1050mg of sodium and 300mg of potassium per kilo of formula mix.

Q. Is your drink ‘simple’ enough?

Many commercially available sports drinks just have too many different ingredients in them for those with delicate stomachs. These may include caffeine, individual amino acids and complete proteins.  These may all have a role but when you are having problems it’s best to leave them out.  You can always consider adding them back in once you have a reliable nutritional plan worked out.

Everything that’s added to the drink increases its concentration and may exacerbate problems with, for example, stomach emptying.

If you’re having problems consider diluting the drink powder much more than recommended – this may weaken the flavour too much but this can be corrected by using the MyProtein range of powdered flavouring.

Another factor to be aware of is that carbohydrate sources that contain resistant starch, may contribute to symptoms of gas, bloating, cramps, nausea and diarrhea.  Resistant starch is derived from amylose often used to make maltodextrin which is widely used in sports nutrition products.  There is only one variety of corn grown that has no amylose, and that is ‘waxy maize’ corn.  Consider using MP’s waxy maize starch in your drink mix. It is very light on the stomach but doesn’t dissolve as well as some other carbohydrate sources, so just give it a good shake before drinking.

Give serious consideration to the idea of making up your own simple, clean mixture of just carbohydrate powder and a balanced electrolyte mix.  Because taste varies so much between individuals and can even change during events, I suggest using a powdered flavouring system so you can flavour to suit your personal tastes.  Myprotein have an excellent facility to allow customers to design their own custom formulasuse it!  They also have an excellent range of powdered flavourings with something to suit everyone.

Q. Is your drink too acidic?

During exercise, excess stomach acid is produced and with little food being eaten this can cause nausea and vomiting in some athletes – especially when they are pushing hard.  In effect they are suffering from ‘acid stomach’ – probably without realizing it.

It took me 10 years of research before I realized that I was suffering from too much acid.  Simple remedies include taking antacids such as Gaviscon (although the taste may be too much for many), crunching a TUMS or similar alkaline tablet or eating some solid food.  However, with regard to what’s been said before, these options may not be practical or convenient. 

Remember that many sports drinks are quite acidic – largely caused by the flavourings.  In order to work properly flavours are usually acidic.  If you are suffering from an acid stomach the last thing you want to be drinking is a large quantity of an acidic liquid.

Consider raising the ph (the measure of acidity and tested with litmus papers) of your drinks to very slightly alkaline (ph8) using sodium bicarbonate powder – about 1.5g/L should be about right.  Be aware that for some people the sodium bicarbonate itself may be a GI irritant – it isn’t for me and has really done the trick. 

Remember that the sodium in the sodium bicarbonate should be factored in when calculating your total sodium intake.

Q. Do you have an undiagnosed medical condition?

Remember that there may an underlying medical condition that is causing or exacerbating your symptoms of GI distress.  It is always a good idea to consult your doctor to rule out anything like this.

There are also a range of medications, which may also be permissible for use in sporting competitions, that could help with diarrhoea, vomiting, wind, excess stomach acid and slow stomach emptying.  Once again consult your doctor for advice and guidance.  Check with your national athletic federation regarding the legitimacy of any medication – it is your responsibility to be sure of the legality of anything you take.

Summing Up

We have seen that GI problems are very common in endurance sports, even among the very top athletes, so if you suffer from one of these complaints you are far from alone – in fact you are in very good company. The first thing to do is to analyse the issue as clearly as possible and if necessary, to seek help and advice on how to solve your problem. Look closely at your training and your diet –exactly what you eat and drink and when you eat and drink it. Many problems may be solved my making very small changes to what you eat and drink or when and how you take food and fluids. Some supplements, medicines or even something as simple as bicarbonate-of-soda may help – but often the best solution to a problem is not to add a new substance but rather to try to reduce or dilute something – like reducing acidity, calories, or cutting out unnecessary ingredients. Balance is important – for example, getting the right amount of fluids, the correct levels of sodium and potassium – this will achieve far better results than just drinking more ready-mixed preparations. Consider just changing one thing at a time as this helps pin-point what is an effective change and what isn’t.

By working your way through these suggestions you may well come across a solution.  If I had read an article like this in 1996, when I first experienced problems, my future experiences would have been very different and my difficulties much more quickly solved.

Good luck.

William Sichel


(1) “A Pain in the Gut” Dr. Douglas W. Stoddard
“The Road to Kona-Supplement to Inside Triathlon”

(2) “Proton pump inhibition prevents gastrointestinal bleeding in ultramarathon runners: a randomised, double blinded, placebo controlled study”

M Thalmann, G H Sodeck, S Kavouras, A Matalas, K Skenderi, N Yannikouris, H Domanovits

British Journal of Sports Medicine 2006;40:359-362