Fall race season is here, and training logs are closing out across the board. Whether you're toeing the line at a city marathon, a trail ultra, or a half-marathon through autumn countryside, the work is largely done. What's left is execution. And one of the most consequential execution calls you'll make happens at the dinner table, not on the road.
Race-week nutrition is where a lot of runners quietly unravel. Not from lack of effort, but from misinformation, habit, or last-minute panic. Here's what the evidence actually says, and what sports dietitians wish more runners understood before the starting gun fires.
The Carb-Loading Window Is Shorter Than You Think
The phrase "carb-loading" has been misapplied for decades. Many runners interpret it as a license to eat pasta every night starting Monday of race week. That's not how glycogen storage works, and doing it for seven days straight can leave you feeling sluggish, bloated, and heavier than you want to be on race morning.
The research is consistent: carbohydrate loading is most effective in the 36 to 48 hours before your race start. During that window, increasing carbohydrate intake to roughly 8 to 12 grams per kilogram of body weight per day allows your muscles and liver to top off glycogen stores without excessive fluid retention or GI stress.
Before that window, your nutrition should look relatively normal. Eat well, stay fueled from your training, and resist the urge to dramatically change your intake from Monday through Thursday. Consistency in the early part of race week sets a stable foundation. The actual loading phase is a short, deliberate push, not a week-long feast.
If you're unsure how to time your fueling around training sessions more broadly, the principles outlined in when and what to eat around your workouts apply here too, especially for the shorter efforts you might still be doing in early race week.
Fall Temperatures Are Hiding Your Dehydration
Summer runners have it easy in one specific way: sweat is visible and constant, so thirst cues stay active. In fall, cooler air reduces sweat rate and suppresses your thirst response, even though your body is still losing fluids through respiration, especially during longer efforts in dry autumn air.
This creates a genuine risk in the final days before a race. You might arrive at the start line mildly dehydrated without realizing it, and even a fluid deficit of 2% of body weight has been shown to measurably impair endurance performance.
The strategy for fall racing isn't about drinking more water on race morning. It's about building your hydration status intentionally in the 48 to 72 hours before the event. Aim for consistently pale yellow urine throughout race week, not just the day before. Consider including electrolytes, particularly sodium, in your hydration routine. Sodium helps retain fluid in the body and can prevent the "drinking lots but still urinating it all out" effect that plain water can cause.
Alcohol and excess caffeine both act as diuretics. Race week isn't the time to test a new coffee ritual or celebrate with drinks. Keep both moderate, or cut them out entirely in the final 48 hours if you want to be precise about your fluid balance.
Your Gut Has a Memory. Don't Confuse It Race Week
GI distress is one of the most common reasons runners have miserable race days. Studies from endurance sports medicine consistently show that a significant proportion of marathon and trail runners experience nausea, cramping, or worse during competition, and a major contributing factor is what they ate in the 24 to 48 hours before the race.
The gut is a creature of habit. It performs best when it's working with familiar foods in familiar quantities. Race week is the absolute worst time to try a new restaurant, experiment with a cuisine you don't regularly eat, or order something unfamiliar because you're in a new city for a destination race.
This applies to supplements too. Introducing a new probiotic, digestive enzyme, or gut health product in the days before a race is a roll of the dice. Even foods that are technically healthy, like fermented dairy products, can cause issues if your gut isn't accustomed to them. The relationship between gut microbiome diversity and performance is real, but dose and timing matter significantly, and race week is not the moment to experiment.
Stick to foods you've eaten regularly during training. If you've been eating oatmeal most mornings, eat oatmeal. If rice and chicken has been your go-to pre-long-run dinner, that's your race-eve dinner too. Boring is good here. Boring means predictable. Predictable means your stomach stays quiet on the course.
Cut Back on Fiber in the Final 24 Hours
This one surprises some runners, especially those who eat a wholefood-heavy diet and assume more fiber is always better. For most of the year, they're right. But in the 24 hours before a race, sports dietitians broadly agree: reduce dietary fiber intake.
Here's why. High-fiber foods increase gut motility and stool bulk. During a race, that translates directly to urgency, cramping, and the need to find a porta-potty at mile 18. Reducing fiber in the final day before your race gives your GI tract time to clear and calm down.
Practical swaps to make in those final 24 hours:
- Choose white rice, white bread, or white pasta instead of whole grain versions
- Skip raw vegetables and high-fiber salads
- Avoid beans, lentils, and legumes
- Limit cruciferous vegetables like broccoli, cabbage, and cauliflower
- Go easy on high-fiber fruits like apples, pears, and berries. Opt for bananas or melon instead
This isn't about abandoning healthy eating. It's a one-day tactical adjustment to give your gut the best possible conditions on race morning. You'll be back to your regular fiber intake the day after the race.
Protein Doesn't Disappear Race Week. It Just Takes a Back Seat
One mistake some runners make in their carb-loading enthusiasm is essentially dropping protein from their diet during race week. That's unnecessary. Protein supports tissue repair, helps maintain muscle function, and contributes to satiety so you're not overeating refined carbs out of hunger.
Lean, easily digestible proteins like chicken, turkey, eggs, white fish, and Greek yogurt are all fine throughout race week. The key is keeping portions moderate and avoiding high-fat preparations like heavy sauces, fried foods, or thick marinades that slow gastric emptying and sit heavily before a race.
There's also a lot of noise in the endurance community about protein requirements that isn't always accurate. If you want to sort fact from fiction on this, the protein myths most athletes still believe is worth a read well before your taper begins.
Race Morning: Simple, Tested, Non-Negotiable
Everything covered so far is preparation. Race morning is execution. And the cardinal rule is this: eat nothing on race morning that you haven't eaten before a long training run.
Aim to eat your pre-race meal two to three hours before your start time to allow for digestion. A meal in the range of 1 to 4 grams of carbohydrate per kilogram of body weight is appropriate, with minimal fat and fiber. Think white toast with peanut butter and a banana, or oatmeal with honey and a small amount of protein. Keep caffeine intake consistent with your normal training routine if you use it.
If your race starts very early and a full meal isn't practical, a smaller, carbohydrate-focused snack 60 to 90 minutes before the gun is a workable alternative. Again, tested in training first.
Hydrate with 400 to 600 milliliters of water or a sports drink in the two hours before the race, and try to stop drinking large amounts about 30 minutes before the start to avoid that sloshing discomfort in the first miles.
The Bigger Picture: Race Week Is Not the Time to Experiment
Fall race season is producing record participation numbers across distances, from local 5Ks to flagship marathons. Running's biggest participation surge in a decade means more first-timers and returning runners are navigating race week for the first time or after a long break. Nutrition mistakes are especially common in that group.
The thread connecting everything in this guide is consistency. Your gut, your glycogen stores, your hydration status, and your energy levels all respond better to planned, familiar inputs than to last-minute corrections. The nutrition decisions you make in the 48 hours before your race have an outsized impact on what happens in the first half of your race, when you set the tone for everything that follows.
Train your nutrition like you train your body. Whatever you plan to eat race week, practice it during your long runs. Treat the final few weeks of your training block as a dress rehearsal, not just for pacing and gear, but for the plate in front of you the night before.
Get that right, and you give yourself the best possible chance of running the race you trained for.