The thing I Stopped doing 48 hours before my marathon was deceptively simple: I stopped eating high-fibre foods. No more leafy salads piled with raw vegetables, no lentil soup, no handful of mixed nuts as a mid-afternoon snack. And the difference on race day was, frankly, startling. For years I had been running through a low-grade fog of GI discomfort in the final miles, blaming my pace, my fitness, my shoes. The real culprit had been sitting on my dinner plate all along.
Key takeaways
- One simple dietary change 48 hours before the race can eliminate the GI issues that plague your final miles
- Everything you think is ‘healthy’ nutrition becomes a liability in the final 48 hours of marathon prep
- The most powerful performance strategy isn’t about doing more—it’s about knowing exactly what to stop
Why the 48-hour window matters more than you think
Most marathon preparation advice focuses on the big stuff: the training block, the long runs, the taper. And rightly so. During marathon training, muscle power diminishes, stores of glycogen deplete, and overall muscle fatigue accumulates. The taper exists to reverse that damage. But the final 48 hours before the gun fires operate on a different logic entirely. You cannot add fitness. You cannot correct months of suboptimal training. What you can do is avoid sabotaging the body you have spent 16 weeks building.
You can’t add Fitness in the taper, but you could do too much and affect your race. That principle applies just as much to food and drink choices as it does to extra training miles. The 48-hour window is where small decisions compound quickly, for better or worse.
The fibre mistake (and the other dietary traps)
Here is something most training plans bury in a footnote: as you taper down your miles, you will also want to taper down your fibre intake. While fibre is an essential part of any Healthy diet, too much fibre can slow down digestion and cause GI issues on race day. Foods like white rice and potatoes are perfect in the two days leading up to the race to ensure they are easily digested. That means the virtuous bowl of mixed grains and roasted vegetables you might normally consider “good nutrition” becomes a liability when your gut has 26.2 miles of sustained stress ahead of it.
The pasta party phenomenon is its own trap. Excessive pasta parties are not necessarily the answer: of course you have to fill up your carbohydrate reserves before a run, but first and foremost it is all about balanced nutrition, both during training in general and in particular during the tapering phase. Carb loading, done properly, is not an excuse to eat vast quantities of anything carbohydrate-shaped. There is an optimum way for each person to carb load, and it is individual based on your size and your food preferences. Carb loading doesn’t just mean stuffing your face with as many calories as possible. Focus on foods you like eating and reduce protein and fats while increasing carbs.
Alcohol is another item that quietly disappears from the pre-race checklist of experienced runners. It disrupts sleep architecture, increases inflammation, and impairs glycogen synthesis, three things you cannot afford in the 48 hours before you ask your body to perform at its absolute ceiling.
The new-activity trap: why curiosity can cost you minutes
There is a particular type of pre-race anxiety that manifests as sudden enthusiasm for self-improvement. You book a sports massage you have never had before. You try a yoga class because someone in your running club swears by it. You decide the race expo is the perfect moment to spend an hour on your feet exploring stands. All of this is well-intentioned. Much of it is quietly catastrophic.
Avoid deep, aggressive stretching in the final 48 hours, and avoid trying Pilates or yoga for the first time during your taper. These activities can engage muscles you may not be used to using, which could leave you with DOMS (delayed onset muscle soreness). Keep it gentle and restorative, the goal is to feel loose and calm, not to challenge yourself. The same logic applies to footwear: the final 48 hours is emphatically not the moment to break in new trainers, however compelling the technology.
Avoid any new foods or activities that could potentially upset your routine and impact your Performance on the big day. Routine is your armour in the days before a race. Anything that departs from it carries risk, however benign it looks.
Sleep, stress, and the cortisol problem
Sleep is where the body does its most productive recovery work, and the nights directly before a marathon are often the most compromised. During tapering, sleep plays a vital role in allowing the body to recover, repair, and adapt. The body releases growth hormones that promote tissue repair and muscle growth during sleep; less sleep means less growth hormone release and therefore less tissue repair. Poor sleep can also increase levels of the stress hormone cortisol, which can negatively affect immune function, mood, and cognitive performance.
The reassuring counterpoint: barely anyone sleeps well the night before race day, but one night of poor sleep does not impair performance. You may feel tired and think you are going to have a bad run but, physiologically, performance is not impaired. This is genuinely one of the most liberating facts in endurance sport. Protect the sleep two nights out, and you give yourself a buffer.
Hydration follows a similar logic to food. Dehydration can significantly impair performance, but it is preventable with adequate hydration in the days and hours leading up to the race. Sipping on fluids throughout the day is the approach to aim for. Over-drinking in the hours immediately before the start, on the other hand, creates its own discomfort.
The real lesson of that 48-hour window is not about adding anything. No supplement, no special food, no last-minute protocol will meaningfully improve what months of training have already built. You can’t add fitness in the final days, but you could ruin your chances of a good race by doing too much. The runners who seem to have magical race-day transformations are usually just the ones who Finally learned to get out of their own way. Perhaps that is the most counterintuitive performance strategy of all: sometimes the discipline is not in what you do, but in what you stop doing.
Always consult your GP or a qualified sports medicine professional before making changes to your nutrition or training approach, particularly if you have any underlying health conditions.