The Best Pre-Race Meal for Runners with Sensitive Stomachs (What the Research Actually Says About Low FODMAP)

One of our triathletes finished a full-distance race last weekend. Great bike split, solid swim, and then she spent the entire 26.2 mile run nauseous because she had to take Imodium in T2. If you have ever raced with a sensitive stomach, you know exactly how that feels. You trained for months, and on the one day it counts, your gut decides it is running a different race.

Here is the thing: she is not an outlier. Depending on the study, somewhere between about 30% of marathoners and up to 60 to 90% of ultra runners report gastrointestinal symptoms during racing (Costa et al., 2017). In our coaching practice, “what do I eat before the race so my stomach doesn’t blow up” is one of the most common questions we get on client calls. Just in the last two weeks I have talked through race week nutrition with an ultrarunner prepping a mountain 50 miler, a triathlete recovering from that Imodium marathon, and a cyclocross racer testing her supplement timing so it doesn’t wreck her gut.

So let’s talk about what actually works, because the internet is full of confident advice on this topic and most of it is wrong.

The influencer version vs. the research version

If you ask Instagram, the answer to race day stomach problems is usually some version of “cut out gluten and dairy” or “just eat clean.” Whole grains, big salads, fermented everything, more fiber. Forever.

The research tells a very different story.

When researchers actually tested the gluten theory, it fell apart. Dana Lis, Trent Stellingwerff, and colleagues put competitive non-celiac endurance athletes on a short-term gluten-free diet in a blinded crossover trial and found no difference in performance, gastrointestinal symptoms, inflammation, or overall wellbeing compared to a gluten-containing diet (Lis et al., 2015). These were trained adult endurance athletes, so if you have celiac disease or a diagnosed sensitivity this obviously does not apply to you, but for everyone else, gluten was not the villain.

So why do so many athletes swear they feel better when they ditch bread and pasta? Most likely because when you cut gluten, you also accidentally cut a bunch of FODMAPs. That is the real lead in this story.

FODMAPs: the actual suspects

FODMAPs are fermentable carbohydrates (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) found in foods like wheat, onions, garlic, apples, beans, honey, and some dairy. They pull water into the gut and get fermented by your gut bacteria, producing gas. In everyday life, that is mostly fine and even good for your microbiome. Put a race on top of it, with blood flow shunted away from your gut for hours, and it becomes a recipe for bloating, cramping, and emergency porta potty stops.

Two studies are worth knowing here.

First, Lis, Stellingwerff, and colleagues took 11 recreationally competitive runners with persistent exercise-associated GI symptoms and ran them through short low FODMAP and high FODMAP diet blocks in a crossover design. Nine of the eleven, so 82%, reported meaningfully lower daily GI symptoms during the low FODMAP block (Lis et al., 2018). Caveat: this was a small group of trained runners who already had GI issues, the diet blocks were only about six days, and the biggest improvements showed up in daily symptoms rather than symptoms during the running sessions themselves, possibly because the prescribed training wasn’t hard enough to provoke the gut.

Second, Wiffin and colleagues ran a similar crossover in 16 recreational runners, average age around 44, with a week on each diet. IBS-type symptom scores dropped by more than half on the low FODMAP week, and 69% of participants rated the low FODMAP period as positive for their symptoms (Wiffin et al., 2019). Caveats again: small sample, mostly recreational runners rather than elites, free-living conditions, and total carbohydrate intake drifted lower on the low FODMAP week, which is exactly what you do not want in race week. Responses also varied a lot between individuals.

Notice what neither study says. Neither says FODMAPs are bad for you, and neither says you should eat this way permanently. Long-term strict FODMAP restriction can alter your gut microbiota and reduce production of short-chain fatty acids that your gut actually needs, which is why researchers in this space consistently recommend using it as a short, targeted tool, on the order of one to three days before a big event, not as a lifestyle (Lis, 2019).

That is the hot take, honestly: the influencers selling you permanent elimination diets are prescribing a lifetime of restriction for a problem the research solves in 48 to 72 hours.

What we actually do with clients in race week

This is roughly the playbook we use with our one on one athletes, and it maps closely onto the evidence.

1. Carb load earlier than you think, then eat boring the day before. Race week is not the time to abandon carbs, since a pre-event meal in the range of 1 to 4 grams of carbohydrate per kilogram of body weight in the 1 to 4 hours beforehand is standard guidance from the joint position stand co-authored by Louise Burke (Thomas et al., 2016). With several of our athletes racing on Saturdays, we now run the big carb load on Thursday and keep Friday totally normal and familiar. One of our ultrarunners heading into a 50 miler this fall is doing a single-day load of nearly 600 grams of carbs two days out. That timing means the heavy digestive work happens while there is still time to process it, and race eve dinner can stay small, low fiber, and familiar.

2. Go low FODMAP for one to three days pre-race, not forever. Swap the high FODMAP carbs for low FODMAP ones: white rice instead of beans and lentils, ripe bananas and oranges instead of apples and watermelon, sourdough or gluten-free bread instead of regular wheat bread, maple syrup instead of honey, and go easy on onion and garlic. You are not eating less carbohydrate, you are choosing carbs that ferment less. This is the exact window the athlete studies used, and it sidesteps the microbiome concerns of chronic restriction.

3. Audit your race products, not just your meals. The pre-race meal gets all the attention, but products matter too. One of our ultrarunners kept having lower GI urgency during long efforts, and the culprit turned out to be her highly caffeinated energy drink, not her food. We moved her to gels she tolerates plus a lower-dose caffeine source and the urgency problem resolved. Same story with supplements: sodium bicarbonate is famous for causing GI chaos, so when one of our racers upped her dose we split it into capsules spread over time before the start, which is the standard trick for keeping it stomach-friendly.

4. Train your gut like you train your legs. Costa and colleagues showed that two weeks of repeated gut challenge, meaning practicing race-level carb intake during training runs, reduced malabsorption and GI symptoms and improved running performance compared to placebo (Costa et al., 2017). This lines up with something I find myself saying to clients all the time. One of our cyclists was worried that finishing long rides slightly heavier than he started meant something was wrong. It usually means the gut is holding fluid and food it has not processed yet, and repeatedly asking it to handle that load is literally how you build tolerance. That reframe, that the gut is trainable tissue, changes how athletes think about every practice fueling session.

5. Do not trust every hydration signal in unusual conditions. Race environments mess with the usual cues. An athlete racing at altitude in the cold asked me whether all her peeing meant she was well hydrated and could back off fluids. Cold and altitude cause vasoconstriction, which increases urine output regardless of hydration status, so frequent urination in those conditions is not proof you are topped up. She is keeping her hyperhydration protocol, gloves and all.

The one week test

If race day GI distress is your pattern, here is the simple experiment: pick a hard long session two to three weeks out from your goal race, eat low FODMAP for the two days before it while keeping your carbs high, and log your symptoms. The research above suggests most sensitive-stomach athletes will notice a real difference, and doing the trial in training tells you whether you are one of them before you bet a race entry on it.

And if you want someone to build the whole race week plan around your gut, your sweat rate, and your actual race, that is literally what we do. Check out 1 on 1 coaching or grab our free nutrition guides and downloads to get started.

References

1. Lis DM, Stellingwerff T, Kitic CM, Fell JW, Ahuja KDK. Low FODMAP: A Preliminary Strategy to Reduce Gastrointestinal Distress in Athletes. Medicine and Science in Sports and Exercise. 2018;50(1):116-123.
2. Wiffin M, Smith L, Antonio J, Johnstone J, Beasley L, Roberts J. Effect of a short-term low fermentable oligosaccharide, disaccharide, monosaccharide and polyol (FODMAP) diet on exercise-related gastrointestinal symptoms. Journal of the International Society of Sports Nutrition. 2019;16(1):1.
3. Lis DM, Stellingwerff T, Shing CM, Ahuja KDK, Fell JW. No Effects of a Short-Term Gluten-free Diet on Performance in Nonceliac Athletes. Medicine and Science in Sports and Exercise. 2015;47(12):2563-2570.
4. Costa RJS, Snipe RMJ, Kitic CM, Gibson PR. Systematic review: exercise-induced gastrointestinal syndrome. Implications for health and intestinal disease. Alimentary Pharmacology and Therapeutics. 2017;46(3):246-265.
5. Costa RJS, Miall A, Khoo A, Rauch C, Snipe R, Camões-Costa V, Gibson P. Gut-training: the impact of two weeks repetitive gut-challenge during exercise on gastrointestinal status, glucose availability, fuel kinetics, and running performance. Applied Physiology, Nutrition, and Metabolism. 2017;42(5):547-557.
6. Thomas DT, Erdman KA, Burke LM. Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. Medicine and Science in Sports and Exercise. 2016;48(3):543-568.
7. Lis DM. Exit Gluten-Free and Enter Low FODMAPs: A Novel Dietary Strategy to Reduce Gastrointestinal Symptoms in Athletes. Sports Medicine. 2019;49(Suppl 1):87-97.