The 72-Hour Marathon Nutrition Countdown: What to Eat From Thursday to the Start Line

You have done the training. You have run the long runs, practised your gels, and dialled in your goal pace. Now your marathon is 72 hours away, and a new kind of anxiety kicks in: what exactly should you eat between now and the start line?

Most nutrition guides tell you to "carb load" and leave it at that. But the 72-hour window before a marathon is where your race-day fueling plan is won or lost. Get it right and you show up on the start line with full glycogen stores, stable hydration, and a calm stomach. Get it wrong and you are bloated, dehydrated, or running to the porta-potty before mile 3.

This guide breaks down exactly what to eat, drink, and track from Thursday morning through Sunday's gun — whether you are racing Chicago, NYC, or any fall marathon.

Why 72 Hours Matters More Than the Pasta Dinner

Here is a fact that surprises most runners: a single large pasta dinner the night before your marathon cannot fully top off your glycogen stores. Your muscles can store roughly 1,800 to 2,200 calories of glycogen, and filling those tanks takes two to three days of elevated carbohydrate intake combined with reduced training volume.

This is why taper week matters nutritionally, not just for your legs. The reduced mileage means your muscles are repairing and restocking. But they can only restock if you give them the raw material — and that starts on Thursday.

Thursday: 72 Hours Out — Begin the Carb Ramp

Thursday is the quiet start. You are not stuffing yourself. You are gently increasing your carbohydrate intake from your normal training diet to about 7 to 10 grams of carbohydrate per kilogram of body weight per day.

For a 70 kg runner, that means roughly 490 to 700 grams of carbohydrate spread across the day. That sounds like a lot, but spread over meals and snacks it is manageable.

What to eat: Oatmeal with honey and banana for breakfast. A large bagel with jam as a mid-morning snack. Rice or pasta with a light sauce at lunch. Pretzels or rice cakes in the afternoon. Another pasta or rice-based dinner. The key is high-carb, low-fibre, low-fat foods that are easy to digest.

What to drink: Start sodium loading today. Add 1,000 to 1,500 mg of extra sodium across the day through electrolyte drinks, salted foods, or salt tabs. This pre-loads your plasma volume and prevents the dehydration that catches runners who only drink water. Aim for at least 2.5 to 3 litres of total fluid.

What to avoid: High-fibre foods like raw vegetables, beans, and bran cereals. These sit in your gut and can cause bloating and GI distress on race day. Also avoid anything new — this is not the week to try a new restaurant or an unfamiliar food.

Check your watch: Weigh yourself first thing in the morning and note it. You will use this as your baseline. Check your HRV and resting heart rate — both should be stable or improving as taper continues.

Friday: 48 Hours Out — Peak Carb Loading

Friday is your highest carbohydrate day. Your muscles are actively storing glycogen, and today is when you top them off.

Keep targeting 7 to 10 g/kg of carbohydrate. If anything, lean toward the higher end today. Your meals should feel carbohydrate-heavy without being uncomfortably large.

What to eat: Toast with honey and a banana for breakfast. A smoothie with fruit and juice mid-morning. A large bowl of white rice with chicken at lunch. Rice cakes with jam in the afternoon. Pasta with a simple tomato sauce for dinner. Sip a sports drink between meals.

What to drink: Continue sodium loading — another 1,000 to 1,500 mg of extra sodium. Your urine should be pale yellow, not clear. Clear urine means you are over-diluting and flushing out the sodium you just took in. If your urine is completely clear, ease off the plain water and add more electrolytes.

What to avoid: Alcohol — even one glass of wine disrupts sleep quality and glycogen storage. Spicy food — your gut does not need any additional irritation right now. Large amounts of protein or fat — they slow carbohydrate absorption and can leave you feeling heavy.

Check your watch: Weigh yourself again in the morning. You should be 1 to 2 kg heavier than Thursday. This is not fat — it is glycogen and water. Every gram of glycogen stored pulls roughly 3 grams of water with it. This weight gain is a good sign. Your body is loading fuel. If your weight has not budged, increase carbohydrate intake today.

Saturday: 24 Hours Out — Maintenance and Calm

Saturday is the hardest day because your instinct is to eat everything in sight. Resist that. Your glycogen stores are nearly full from Thursday and Friday. Today is about maintenance, not maximisation.

Drop back to about 5 to 7 g/kg of carbohydrate. Eat smaller, more frequent meals. Think of today as keeping the tank full without overfilling it.

What to eat: Your usual pre-run breakfast — whatever you ate before your long runs during training. A familiar lunch with carbs and a small amount of protein. Snack on pretzels, rice cakes, or crackers through the afternoon. Your Saturday dinner should be moderate in size, familiar, and carb-focused. White rice, plain pasta with a light sauce, or a simple sandwich all work well.

What to drink: Normal hydration — 2 to 2.5 litres of fluid with electrolytes. You can ease off the aggressive sodium loading, but do not switch to plain water only. Keep some electrolyte content in your drinks. Stop drinking large volumes by 8 PM to avoid too many overnight bathroom trips.

What to avoid: Anything you have not eaten during training. Saturday dinner at the race expo buffet is tempting, but unfamiliar food from a catering line is a common source of pre-race GI disaster. Cook your own dinner or eat somewhere you trust. Avoid heavy cream sauces, red meat, and anything deep-fried.

Timing matters: Eat your dinner by 6 to 7 PM. You want a solid 12 to 14 hours between your last big meal and race start. This gives your stomach time to fully empty and reduces the risk of nausea in the early miles.

Check your watch: Look at your sleep data from the night before. If your HRV is normal or elevated and your resting heart rate is low, you are in good shape. If your resting heart rate is elevated, check whether you are dehydrated or stressed — sometimes an extra glass of electrolyte water and some calming music before bed is all you need.

Sunday: Race Morning — The Final 4 Hours

This is the meal you have practised in training. Do not change anything. Whatever you ate before your long runs — eat that.

3 to 4 hours before the gun: Eat 1 to 2 g/kg of carbohydrate. For a 70 kg runner, that is 70 to 140 grams. A bagel with honey and a banana is roughly 100 grams of carbs. Oatmeal with maple syrup and a sports drink works too. Keep protein and fat minimal.

2 hours before: Sip 500 ml of an electrolyte drink. Not plain water — you want sodium to hold that fluid in your bloodstream rather than sending it straight through your kidneys.

1 hour before: Stop eating solid food. You can sip a sports drink or have a small gel if you feel you need it, but your stomach should be empty by now.

30 minutes before: One final sip of electrolyte drink — about 200 ml. Visit the porta-potty one last time.

At the start line: Your glycogen stores are full. Your hydration is dialled. Your stomach is empty. You have done this before on your long runs. The only difference is the bib pinned to your chest.

How Your Watch Data Tells You It Worked

One of the most underused aspects of pre-race preparation is the data your watch already collects. Here is what to look for across the 72-hour countdown.

Body weight trend: A 1 to 2 kg increase from Thursday to Saturday morning confirms glycogen loading is working. If you see no change or a decrease, you are under-eating carbs.

HRV: A stable or rising HRV through Thursday to Saturday suggests your body is absorbing the taper and your nervous system is ready. A sharp drop on Saturday might signal stress, poor sleep, or dehydration — all fixable if you catch them early.

Resting heart rate: Should be at or below your 30-day average by Saturday. If it is elevated, check hydration and stress levels.

Sleep quality: Race-week insomnia is common and usually harmless — it is Friday night's sleep that matters most. If you slept poorly on Saturday night, your glycogen stores are still full. One bad night does not wreck your race.

The athletes who perform best on race day are not the ones who carb-load the hardest. They are the ones who track, adjust, and arrive at the start line knowing their body is ready — not guessing.

Sweatr builds this entire 72-hour countdown automatically from your training data, body weight, and wearable metrics. It calculates your personal carbohydrate targets, sets your sodium loading protocol, and tracks your watch data to confirm you are on track. No spreadsheet, no guesswork — just a plan calibrated to your body.

The Short Version

Thursday: Start carb loading (7-10 g/kg carbs). Begin sodium loading (1,000-1,500 mg extra). Weigh yourself. Avoid fibre.

Friday: Peak carb day. Continue sodium loading. Expect 1-2 kg weight gain. Avoid alcohol. Watch your urine colour.

Saturday: Ease to maintenance carbs (5-7 g/kg). Eat familiar foods only. Dinner by 7 PM. Check HRV and resting HR.

Sunday morning: Eat your practised pre-race meal 3-4 hours out. Sip electrolytes. Stop solids 1 hour before. Trust your preparation.

Your marathon was not decided in the last 10 kilometres of training. It was decided in the 72 hours before you pinned on your bib. Nail this window and you remove one of the biggest variables standing between you and a strong finish.

Sweatr takes your Apple Watch or Garmin data and builds a personalised 72-hour countdown plan — carb targets by body weight, sodium loading matched to your sweat rate, and race-morning timing based on your start time. Download Sweatr and take the guesswork out of race week.