Updated: June 12th, 2022

It’s said amongst runners, that there’s a ‘delicate art’ to figuring out the balance of how to fuel and refuel on the run, without upsetting your stomach. Gastrointestinal (GI) problems whilst running is more common than you think, so how can we keep that in check, whilst getting all that mileage in without having to run to the nearest loo? I’m so glad you asked!

What is GI distress? And why do runners suffer so much?

Exercise-induced Gastrointestinal distress isn’t entirely understood, although studies do declare women and younger runners are more prone to digestive discomfort and feeling nauseated, it’s not completely clear why. But for long-distance runners, it is a problem you’re likely to run into (like what I did there?) and something you might want to discuss with your doctor or nutritionist.

“Some of the most frequent exercise-induced GI symptoms are abdominal pain, heartburn, acid reflux, diarrhoea,” says Karen Woods, M.D and are frequent with long-distance runners. Could it be due to race nutritional factors, nerves or simply asking the body to run a ton of miles?

There is no single clear-cut answer to avoiding GI issues as a runner because nutrition is a complex topic.

So if you do suffer, know that you are not alone – It is common to feel especially nauseated before and during a race. “Anxiety and pre-competition stress may also contribute to GI symptoms, particularly Upper-GI symptoms like acid reflux and heartburn” states Jessalynn Adam, M.D., an attending physiatrist of sports medicine at Mercy Orthopedic Specialty Hospital in Baltimore.

Young runner struggling with GI stomache issues

When is it time to seek medical help?

I can tell you not to worry, that you’re not alone – all runners at some point will face stomach discomfort. But there becomes a point where that doesn’t cut the mustard anymore and it is persistent or feels like it is seriously affecting your health.

So call your doctor if you experience any of the following:

  • Blood in your stool
  • Very dark/Black stool
  • Severe Diarrhea
  • Weight loss
  • Persistent stomach-region pain that doesn’t ease after you’ve stopped running

It is rare, but in some instances, runners can face a serious intentional condition called Intestinal Ischemia.This is blood shunting away from the intestines and towards the heart and muscles to keep you running during prolonged exercise. This condition is not to be taken lightly so seek immediate medical help if any of the above symptoms occur.

Runner racing with GI issues stomach

Does running duration affect nutritional needs and the potential for GI issues?

The short answer? Yes.

But it is complex – you need to strike a balance between catering to what your body needs whilst bypassing GI upset.

Professional athletes of all varieties will work with qualified nutritionists to streamline and affect their diet, for them – no two plans will be the same. For amateur runners trying to avoid the stomach upset and/or reach for that PB, trying different gels, sweets, gum, chews, drinks and foods to see how your body reacts, is a solid substitute – trial and error at its best.

For example, I initially trialled high in sugar sweets for my ultra-marathon training runs, but suffered for it – instead I use mini chews and mini nutty-flapjacks alongside jam sandwiches and snack-size mixed bean burritos, because 1. They’re less sugar per sweet 2. Easier for me to run and chew on. 3. My body accepts them all, and honestly, you feel a boost in energy. Long gone are the tangtastic style sour-y goodness. Although, I’ve even seen ultra-runners with yoghurts and cheese, which I would never even attempt. You have to find what works for you.

Runner taking a gel whilst racing

Nutritional needs when running for up to 90 minutes:

On short to medium runs your body’s main source of energy is glycogen (energy from carbohydrates) for the first 60 minutes or so, which are the most basic to replenish. A few chews or energy gels as you go will do the trick.

Specific energy gels and chews are made from Maltodextrin rather than Sucrose (cane/beet sugar in sweets). The benefit here is that Maltodextrin gets broken down one molecule at a time, unlike sucrose, or fructose for that matter (natural sugar from fruit) which is broken down in larger bits at a time. The problem with sucrose/fructose chunks? The larger amount of sugars can cause your gut to flood with water and result in an upset stomach.

Fructose is a popular component of energy drinks though when it is mixed with Maltodextrin, the number of carbohydrates you can absorb increases. There is a limit though, 60g of functional carbohydrates per hour.

Check your chews or gels to understand how carbohydrate-rich they are to take on enough, but not overdo it. What’s the point of downing an entire packet if it’s nutritionally no use to you?

Runner sitting to eat and refuel

Nutritional needs when running longer than 90 minutes:

Hitting the two-hour mark of running or exercise, your body’s energy source starts to change. It moves away from carbohydrates (the go-to source) and begins utilising fat and protein – so you’ll want to eat these as well as your carbohydrate intake per hour. The trick? Trial and error here during your training runs. See how your body reacts to certain foods.

When replenishing on the run, ensure that about 25% of the carbohydrates with fat and protein sources too. Great natural sources (and come in handy bit size options) come in the nut variety.

Of course, this is dependent on any allergens – and professional advice would need to be sought if you do suffer.

Longer races, such as marathons and ultra-marathons do require less of an intense pace, so you can afford the time to digest solid foods on the run, as it were. Nut bars, flapjacks and sandwiches are my go-to there, and haven’t let me down yet!

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