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Can The Low-FODMAP Diet Help Endurance Athletes?

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If you’re lucky enough not to suffer from irritable bowel syndrome (IBS) then you might never have heard of the low-FODMAP diet. And even if you have heard of it, we’re betting you can’t reel off what FODMAP stands for – frankly, even after reading and writing it out several times, we can’t remember the entire acronym.

The low-FODMAP diet has been shown to be effective in helping those with IBS manage their symptoms, but recent research also suggests there might be some benefit for endurance athletes worried about gastrointestinal distress related to their exercise – an all-too-common and obviously unpleasant problem.

For more information about the low-FODMAP diet and how it might help endurance athletes, we spoke to dietitian Sasha Watkins, co-founder of Field Doctor (opens in new tab), a meal delivery service that includes low-FODMAP options.

What is the low-FODMAP diet?

It’s a bit of a mouthful! FODMAP stands for fermentable oligosaccharides, disaccharides, monosaccharides and polyols. They are fermentable short-chain carbohydrates which have been shown to trigger gastrointestinal trouble, particularly in people suffering from irritable bowel syndrome. That’s where most of the research has been done, principally through Monash University in Australia (opens in new tab).

What kind of foods are FODMAPs found in?

FODMAPs include fructose, lactose, certain digestible fibres and other undigestible compounds like inulin. You’ll find lactose in milk, galacto-oligosaccharides in legumes and fructans in wheat. Fruits are high in fructose and some vegetables are high in a range of these compounds.

What kind of symptoms can be triggered by FODMAPs?

The gastrointestinal symptoms that FODMAPs generally aggravate in certain people are stomach pain, bloating, wind, and a change in bowel habit and stool consistency. People can be constipated, or they can get diarrhoea, but I think diarrhoea is more common.

How can the low-FODMAP diet benefit endurance athletes?

There has been some research in recent years around its use in athletes, because there are certain symptoms that come around sports events, like runner’s diarrhoea and other gastrointestinal issues. We call it exercise-related gastrointestinal symptoms. I found a statistic that indicated about 70% of endurance athletes (opens in new tab) seem to suffer from exercise-related GI problems, and 22% of endurance athletes appear to have IBS.

In one review (opens in new tab) the authors looked at diets, of which the FODMAP diet is one, and in the studies they covered there was a reduction in these exercise-related problems.

There were four studies. One was a case study, with a six-day restriction. One was longer -erm, 10 weeks. In another, it was six days. And in the final one 18 endurance runners were given the FODMAP diet one day before an exertion heat stress trial. Across these four studies there was evidence that the exercise-induced symptoms did improve.

However, the caveat is that it’s just four studies, and the body of research in this area is quite new. One study had 11 people, one had 18, so they are small trials. More research definitely needs to be done, but there is some evidence that it’s going to be beneficial.

Is there any risk to following a low-FODMAP diet?

There are risks to following this diet as a long-term strategy. The first is the effect on the gut microbiome. A lot of FODMAPs are prebiotics [food for gut bacteria], so good bacteria really depend on them. There have been studies done on people with IBS who follow the low-FODMAP diet that show a reduction in total bacterial abundance, and also decreased bifidobacteria, and there is good evidence that bifidobacteria have a good impact on our health. This reduction is why we don’t want people to do it long-term.

What we also know from IBS studies is that it’s a tricky, complicated diet. It really should be done under the care of a dietitian who is trained in the low-FODMAP diet, because if not done properly people may overly-restrict, or restrict the wrong things, and there is a risk of missing out on key nutrients. Particularly in the case of endurance athletes, who have quite high requirements already, it’s best to do it with the help of a dietitian.

I also wouldn’t advise this as a diet for someone who’s at risk of disordered eating. Sometimes people get very hung up on and almost obsessive with what they eat. If they remove these foods from their diet, sometimes they may be fearful to bring them back in. You have to understand that it’s a short-term solution for you as an endurance athlete. It’s not a diet for life.

With athletes there’s also a question whether endurance athletes are maybe having too many FODMAPs. A lot of sports supplements and high-energy foods that you’re trying to consume for sports are very in FODMAPs – a lot of gels are really high in fructose, for example. Some might have sweeteners in them and a lot of those sweeteners are classed as polyols, like xylitol and sorbitol.

Foods commonly recommended for sports can be high in FODMAPs, like dry dates, which are extremely high in fructans, and honey, which is high in fructose. Some sports foods have chicory root added to them and that's an oligosaccharide, or inulin, which is a fructan.

If you are keen to try it, is there a way to do it where it’s not high risk?

Absolutely. I would say there’s absolutely no problem with doing a quick, small trial – I mean, the studies did it for one day! – whether it’s just the day before the event, or also during the event, or to do it up to six days before the event. I’ve not seen any evidence to see what happens to the gut bacteria, but I’d imagine in such a short time period, that wouldn’t be a risk.

The other question is how stringent do you need to be? Maybe you don’t have to go as low on FODMAP intake as we would normally recommend for somebody with IBS. As I mentioned, athletes often have quite high-FODMAP diets, so it might just be about toning down or swapping FODMAP ingredients. It may be that just restricting lactose and fructose does the trick. Not low-FODMAP, but lower-FODMAP.

Would using gels or similar during an event negate the benefits of following the diet beforehand?

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I think there’s a benefit in just doing it the day before because of course gastrointestinal movements that happen the next day are obviously highly dependent on the food that was put into the system 24 hours earlier.

However, it depends on what your symptoms are. If you do suffer from bloating and abdominal pain, you may want to continue to do it on the day of the event because that could happen quite quickly and might even happen during the race.

Since it is a complex diet, do you have any advice on how to follow it?

My top tip would be to look at the low-FODMAP app by Monash University (App Store (opens in new tab) and Google Play (opens in new tab)). That’s a great starting point.

Second of all, there are freelance dietitians that you can easily access and do a Zoom with. If somebody does seriously want to try this diet, I would definitely recommend they do it under supervision by a dietitian, because if you really want to see whether the diet works, it's best to do it with all the right knowledge.

You can look at the freelance dieticians website (opens in new tab) and you can search for FODMAP. There are a lot of FODMAP-trained private dietitians in the UK who you can easily have a call with.

Nick Harris-Fry
Nick Harris-Fry

Nick Harris-Fry is a journalist who has been covering health and fitness since 2015. Nick is an avid runner, covering 70-110km a week, which gives him ample opportunity to test a wide range of running shoes and running gear. He is also the chief tester for fitness trackers and running watches, treadmills and exercise bikes, and workout headphones.