The Final 72 Hours: What You Eat and Do Before Your Marathon

Three days to go. No workout left on the calendar is going to make you fitter than you already are. What can happen in these 72 hours is that you undo weeks of training with a last-minute decision at the dinner table — or you show up Sunday with full tanks, a calm stomach, and a clear head.

This week isn't for experimenting. It's for executing a plan you already tested during your long runs. If anything you read here is new to you, don't try it for the first time on Saturday. Test it in your next race, not this one.

The Golden Rule: Nothing New

I repeat this every season because every season I watch someone break it. Your last hard workout is behind you. Sunday's race gets run on what your body already knows: the gel you've already used, the breakfast you've already tested, the clothes you've already worn. The 72 hours before race day aren't the moment to "improve" anything — they're the moment to leave alone whatever is already working.

There's a physiological reason behind this, not just a psychological one: the digestive system, the cardiovascular system, and the thermoregulatory system all work under accumulated stress on race day. Introducing a new variable — a supplement, a different kind of fiber, a caffeine dose you've never tried — adds a risk factor to a system that's already pushed to its limits [PMID:41922043]. Exercise biomarker research confirms something I see constantly on the ground as a coach: the body responds better to the predictable than to the theoretically optimal.

Carb Loading: The Real Numbers

Forget the myth of "eating pasta the night before." Effective carb loading starts 48-72 hours out, not the evening before.

The dose that actually works:

• 36-48 hours out: 8-10 g of carbohydrate per kg of body weight per day.
• The last full day before the race: maintain that 8-10 g/kg, emphasizing easy-to-digest carbs (white rice, potatoes, white bread, ripe fruit) and reducing fiber (more on why below).
• Race morning, before the start: 1-4 g/kg in the 3-4 hours before the gun, depending on how well each runner tolerates eating early.

For a 70 kg runner, that's 560-700 grams of carbohydrate per day in the 48 hours leading in. It sounds like a lot, and it is — which is why most recreational runners don't load enough. It's not necessarily "eating more," it's shifting the ratio: less protein and fat, more carbohydrate, with roughly the same total calories or only slightly more.

This tops off muscle and liver glycogen stores. And here's a detail a lot of runners overlook: the more sustained intensity you're going to ask of your body for more than 2-3 hours, the more performance depends on those stores — not just on cardiovascular capacity. Training periodization built the engine [PMID:35418513]; carb loading fills the tank. Both are necessary, and neither replaces the other.

Hydration and Sodium: Start Early, Not on Race Day

Marathon hydration doesn't get solved by chugging water Saturday night. That just gets you up three times overnight and standing at the start line short on sleep.

Hydration script:

• Thursday and Friday: normal hydration, but mindful — urine should be pale straw, not clear (that's overhydration) and not dark yellow (that's a deficit).
• Saturday: slightly increase intake of fluids with sodium — a broth, water with a pinch of salt, an electrolyte drink — without overdoing it. The goal is optimizing plasma sodium and water retention, not "loading" water like filling a tank.
• Sunday, race morning: 400-600 ml of fluid with electrolytes in the 2-3 hours before the start, leaving time for a bathroom stop before the gun.

Sodium matters more than most race plans give it credit for. Heavy sweaters or runners racing in hot, humid conditions can lose 500-1000+ mg of sodium per hour. Without replacement, that contributes to cramping and, in extreme cases, hyponatremia. If your long runs have already told you you're a "salty" sweater — white marks on your clothes, recurring cramps — this week is for making sure sodium is dialed into your diet, not for solving it with a brand-new pill you've never tried.

Coffee: Keep Your Dose, Don't Change It

Coffee on race day improves performance — that's well established. But the key move this week isn't "drink more coffee," it's not changing your relationship with caffeine.

If you drink coffee every day, keep drinking your normal dose through race week. Some protocols suggest a caffeine "taper" a few days out to boost sensitivity on race day — but that's highly individual, and if you've never tested it during a long run, this week is not the place to experiment with your neurotransmission and your mood three days before running 26.2 miles.

What you should plan with precision: the exact timing of your race-day coffee, the amount, and whether you'll repeat it with a caffeinated gel during the race. That decision should already be locked in from your long runs over the past few weeks.

Fiber: The Variable Nobody Controls and Everybody Pays For

This is the part that gets talked about the least and ruins the most races. Fiber is good for your general health — and it's a bad idea in excess in the 48 hours before a marathon.

High-fiber foods (legumes, cruciferous vegetables, whole grains, fruit with skin in excess) hold water in the gut and can cause bloating, gas, and GI urgency during the race — right when there isn't a bathroom every mile.

My practical recommendation:

• 72-48 hours out: gradually reduce fiber. Swap whole wheat bread for white bread, brown rice for white rice, raw vegetables for well-cooked or peeled ones.
• 24 hours out: minimal fiber. This isn't forever — it's a 24-48 hour window, not a permanent diet change.
• Race breakfast: zero new fiber. No oatmeal loaded with seeds "because it's healthy." Save the healthy oatmeal for Monday.

This doesn't contradict eating healthy — it contradicts eating healthy on that specific day. Long-term gut health and microbiota composition are built over months of consistent habits, not defined by 48 hours of lower fiber [PMID:38233990]. Don't worry about your microbiome Saturday night — worry about it on Monday.

Sunday's Breakfast, With Exact Timing

Here's the full script. Adjust the times to your race's start time, but keep the sequence and proportions the same.

If your race starts at 7:00 AM:

• 3:30-3:45 hours before (3:15-3:30 AM): wake up, drink 300-400 ml of water with electrolytes.
• 3 hours before (4:00 AM): main breakfast. 1-2 g/kg of easy-to-digest carbs: white bread with jam and banana, or white rice with honey, or whatever combination you've already tested on long runs. Avoid fat and fiber. Coffee, at your usual dose, if that's your routine.
• 90-60 minutes before (5:30-6:00 AM): if you tolerate eating closer to the start, a small snack — half a banana, a gel diluted in water, a handful of raisins.
• 30-15 minutes before the start: one last sip of water with electrolytes or a gel if that's your tested protocol. No more than 150-200 ml of fluid at once.
• At the start: stomach comfortable, neither empty nor heavy. If you feel hungry in the corral, that's a sign you miscalculated the timing — note it for next time, don't fix it by eating something new right then.

This sequence gives the body enough time to digest, empty the stomach of anything heavy, and arrive at the start with glucose available in the blood without feeling "loaded." The 3-4 hour window between main breakfast and start is what most runners tolerate best — but if your long runs have taught you that you need more or less time, respect that over this generic guide.

A Note on Stress and the Heart

Worth mentioning something that rarely gets connected to pre-race nutrition: the cardiovascular stress of prolonged effort is real, and it's more pronounced in master's runners. Evidence on the cardiac effects of prolonged endurance exercise shows that both younger and older athletes experience acute changes in cardiac function during and after long efforts [PMID:40667749]. That's not cause for alarm — it's cause for respect. Arriving well hydrated, with adequate sodium and no digestive surprises, isn't a cosmetic detail — it's part of how you give your heart the best possible conditions to do demanding work.

What I Want You to Take Away

• Real carb loading: 8-10 g/kg/day over 48-72 hours, not a plate of pasta the night before.
• Sodium starting Saturday, not scrambled together on Sunday morning.
• Coffee: your usual dose, at your usual time.
• Low fiber the last 24-48 hours — it's temporary, not your new diet.
• Sunday breakfast on a fixed schedule, tested on your long runs, executed without improvising.

All of this sounds simple because it is. The challenge isn't understanding the plan — it's having the discipline not to change it at the last minute because you read something new Thursday night. This week is about trusting what you've already practiced, not chasing last-minute perfection.

References

• Siebers M, Bizjak DA. Exercise biomarkers. Adv Clin Chem. 2026. [PMID:41922043]
• Frandsen J, Aaroe M. Cardiac Effects of Prolonged Endurance Exercise in Young and Older Athletes. Scand J Med Sci Sports. 2025. [PMID:40667749]
• Couvert A, Goumy L. Effects of a Cycling versus Running HIIT Program on Fat Mass Loss and Gut Microbiota Composition in Men with Overweight/Obesity. Med Sci Sports Exerc. 2024. [PMID:38233990]
• Casado A, González-Mohíno F. Training Periodization, Methods, Intensity Distribution, and Volume in Highly Trained and Elite Distance Runners: A Systematic Review. Int J Sports Physiol Perform. 2022. [PMID:35418513]