Chicago Marathon 2026: Build Your Race-Day Nutrition Plan in 5 Steps

The Chicago Marathon is one of the fastest courses in the world. Flat, fast, and packed with 50,000 runners snaking through 29 neighbourhoods along the lakefront. But that flat profile is deceptive — it lulls runners into starting too fast and fueling too late.

Every year, thousands of well-trained athletes hit the wall between miles 18 and 22. Not because their legs gave out, but because their nutrition plan did. Or worse — they never had one.

If your race is in October, you have roughly four weeks to lock in a nutrition strategy that matches your body, your pace, and the conditions you'll face on race day. Here's how to build one from scratch.

Step 1: Calculate your sweat rate from your training data

Everything starts with knowing how much fluid you lose per hour. Not an average from a website — your actual sweat rate, measured in conditions as close to race day as possible.

Here's the simple method:

1. Weigh yourself without clothes before a 60-minute run.
2. Run at your target marathon pace.
3. Don't drink during the run (or measure exactly how much you drink).
4. Weigh yourself again immediately after, without clothes.
5. Every kilogram lost equals roughly one litre of sweat.

If you lost 0.8 kg in an hour, your sweat rate is approximately 800 mL/hr.

The catch: your sweat rate changes with temperature, humidity, and fitness. A sweat test done in July heat won't match what you'll lose on a 12°C October morning in Chicago. If you trained through summer, your sweat rate has likely increased by 15–30% due to heat acclimatisation. In cooler race conditions, expect it to drop.

Run your sweat test again this month. Ideally, do it at a pace and temperature that's close to what you expect on race day. Chicago in October averages 10–15°C at the start, warming to 15–20°C by mid-race — but it can spike higher. In 2023, race-day temperatures hit 24°C.

If you're using a Garmin or Apple Watch, you already have heart rate and pace data from every training run. Sweatr pulls this data automatically and estimates your sweat rate across different conditions — so you don't have to guess what happens when race day is warmer or cooler than your test run.

Step 2: Set your carbohydrate target per hour

The science is clear: runners performing for longer than 90 minutes benefit from 60–90 grams of carbohydrate per hour. That's the range. Where you fall in it depends on three things:

1. Your body weight. A 55 kg runner needs less total fuel than an 85 kg runner.
2. Your finishing time. A 3:15 marathoner burns through glycogen faster per minute than a 4:30 marathoner — but the slower runner is out there longer and needs more total fuel.
3. Your gut tolerance. If you haven't trained your gut to absorb 90 g/hr, starting there on race day is a recipe for nausea.

For most marathoners, here's a practical starting point:

• Sub-3:30 finishers: Target 70–90 g/hr. You're burning carbs at a high rate and have less time to consume them.
• 3:30–4:30 finishers: Target 60–80 g/hr. You have more time per aid station but need to stay consistent.
• 4:30+ finishers: Target 50–70 g/hr. Lower intensity means a higher percentage of fat oxidation, but you still need carbs to finish strong.

These aren't numbers you should arrive at on race morning. Test them in your September long runs. If you feel bloated or nauseous at 80 g/hr, drop to 60 and build up. If you feel strong, hold steady.

Your Garmin or Apple Watch tracks your training load, heart rate zones, and pace — all inputs that affect how many carbs you burn per hour. Sweatr uses this data to calculate a personalised carb target that adjusts as your training changes.

Step 3: Build your gel and hydration schedule around the course

Chicago has 20 aid stations, roughly every mile from mile 1 through to the finish. Water is available at every station; Gatorade Endurance at most. Knowing this lets you build a practical fueling schedule rather than guessing when to take a gel.

Here's a sample schedule for a 4:00 marathoner targeting 70 g carbs/hr:

| Mile | Time | Action | |------|------|--------| | 3 | ~0:27 | First gel (25g carbs) + 150–200 mL water | | 6 | ~0:55 | Second gel + water | | 9 | ~1:22 | Gel + electrolyte drink or salt cap | | 12 | ~1:49 | Gel + water | | 15 | ~2:16 | Gel + electrolyte top-up | | 18 | ~2:43 | Gel + water — the critical window | | 21 | ~3:10 | Final gel if tolerated, sip water to finish |

Two critical rules:

Start early. Take your first gel by mile 3, not mile 6. Your glycogen stores are full at the start, but the carbs you consume now take 15–20 minutes to hit your bloodstream. Waiting until you feel depleted means you're already behind.

Take gels with water, never with sports drink. Doubling up on carbohydrate concentration slows gastric emptying and increases the risk of stomach distress. If you're drinking Gatorade at an aid station, skip the gel at that stop.

If you're using Maurten or another hydrogel-based product, the water rule is less critical — but still don't double up with a carb-heavy sports drink.

Step 4: Plan for Chicago's specific conditions

Chicago's course has three things that make fueling different from a generic plan:

The lakefront wind. Miles 8–10 and 22–24 run along the lake. A headwind increases effort without increasing pace — meaning your heart rate climbs and you burn through glycogen faster while feeling like you're working harder. Don't cut back on fuel because your pace feels easy in sheltered miles. Stick to the schedule.

The temperature swing. The race starts at 7:30 AM, often in cool conditions (10–13°C). By the time mid-pack runners reach mile 18, it's usually 5–8 degrees warmer. Your sweat rate in the second half will be higher than the first. If you calculated your hydration based on the cool start, you'll be under-drinking by mile 15.

Plan to increase fluid intake slightly in the second half. If you're drinking 150 mL per aid station in the first half, bump it to 200 mL from mile 13 onward — especially if the sun is out.

The crowd energy trap. Chicago has some of the best crowd support in marathon racing. The roar through Wrigleyville and Pilsen can push you to run faster than your plan. Faster pace means higher carb burn. If you go out 15–20 seconds per mile faster than planned in the first 10k, your fueling schedule is already wrong. Discipline in pacing protects your nutrition plan.

Step 5: Test everything in your next two long runs

You have two to three long runs left before taper. Use every one of them as a dress rehearsal for race-day nutrition.

Long run 1 (this weekend or next): Run the full gel schedule at marathon pace. Note what feels good, what causes discomfort, and when energy drops. Weigh yourself before and after to validate your sweat rate.

Long run 2 (two weeks before race): Refine based on what you learned. Adjust gel timing, swap products that didn't sit well, and finalise your hydration volume. This is your last chance to experiment.

Taper long run (10 days before race): Run a shorter version (12–15 miles) with the exact products and timing you plan to use on race day. No changes after this run. Lock it in.

What to track during each test run:

• Did you feel bloated or nauseous at any point? If yes, when?
• Did your energy drop before the next gel? If yes, tighten the interval.
• How much fluid did you consume vs how much you lost?
• Did the products you chose taste good at effort? Some gels that taste fine at rest are unbearable at 80% effort.

If you're wearing an Apple Watch or Garmin, review your heart rate data from each long run. A heart rate that drifts upward in the final third — even as pace holds steady — is a sign of dehydration or glycogen depletion. It's one of the clearest signals your watch gives you that your fueling plan needs adjustment.

Sweatr tracks this automatically. It pulls your heart rate, pace, and training load data from your watch and cross-references it with your fueling log to flag exactly where your plan broke down — and how to fix it for the next run.

Race morning: the 4-hour countdown

Your race-day nutrition doesn't start at mile 1. It starts the moment you wake up.

4 hours before the gun: Eat a familiar breakfast — 100–150g of easily digestible carbs. Oatmeal with banana, white toast with jam, a bagel with honey. Nothing new, nothing high in fibre or fat.

2 hours before: Sip 400–500 mL of water or dilute electrolyte drink. Stop drinking large volumes after this point to avoid needing the toilet at the start.

30 minutes before: One final gel or a few swigs of sports drink. This tops off blood glucose without overloading your stomach.

At the start line: Take a deep breath. You've tested your plan, you know your numbers, and you have a schedule written on your arm or programmed into your watch. The work is done.

The fueling plan isn't the plan — the data behind it is

Generic advice says "take a gel every 45 minutes." But your body isn't generic. A runner who weighs 60 kg, sweats 600 mL/hr, and finishes in 4:30 needs a completely different plan from a runner who weighs 85 kg, sweats 1.2 L/hr, and finishes in 3:15.

The difference between a good race and a bad one often comes down to whether your fueling matched your physiology — not whether you followed someone else's template.

Sweatr calculates your personalised race-day nutrition plan from the data your Apple Watch, Garmin, or Strava already collects. It accounts for your body weight, your sweat rate across different conditions, your training load, and the specific demands of your race — including course elevation, expected weather, and your goal pace. No spreadsheets, no guessing, no generic advice.

Your Chicago Marathon fueling plan should be as personal as your training plan. Build it from your data, test it in your long runs, and show up on race morning knowing exactly what to do.