Carb loading isn't complicated, but most runners still get it wrong. They wait too long, underestimate the numbers, or try to hit all those carbs through food alone. The right drink mix makes the math and practice manageable — high carbs, easy digestion, no surprises on race morning.
Carb loading works. The research is clear, the elite results back it up, and the strategy is straightforward — maximize glycogen stores in the 2–3 days before your race so you're not running on fumes by mile 18. The harder part is hitting the numbers you need to. For most runners, liquid carbs are the most practical way to get there.
Here's what to use, how much, and when.
Why marathon runners need carb loading drinks
Your body stores carbohydrates as glycogen, and glycogen is the primary fuel source for sustained high-intensity running. A marathon burns through it fast. Glycogen depletion is the main driver of fatigue in events lasting more than two hours — which means showing up under-loaded isn't a minor oversight; it's a performance limiter.
Show up topped off and you have more bandwidth to perform.
So, how do you carb load
Start 2–3 days out. If you're racing Sunday, that means Thursday, Friday, and Saturday. Sip throughout the day rather than trying to front-load at dinner — spreading intake across meals reduces GI discomfort and improves glycogen storage efficiency. The body can store roughly 500–600 g of glycogen when fully loaded, and getting there takes sustained high carbohydrate intake over at least 24–48 hours.
Don't wait until the night before. One big pasta dinner doesn't cut it.
The target is 8–12 g of carbohydrate per kilogram of body weight per day for 2–3 days pre-race. For an 80 kg (176 lb) runner, that's 640–960 g of carbs per day. Hitting that through solid food alone is uncomfortable and impractical. Liquid carbs help you get there without blowing up your stomach before the start line.
Top 5 carb loading drinks for marathon runners
1. The Feed High Carb Drink Mix
The Feed Lab High-Carb Drink Mix is built around a flexible, scalable formula with a 2:1 glucose-to-fructose ratio, optimized electrolytes, and easy digestibility across the full dosing range. Choose from 1-3 scoops, offering 30-90g of carbs.
2. Maurten Drink Mix 320
320 calories, 80 g carbohydrate, 200 mg sodium per serving. Maurten's hydrogel technology is designed to reduce GI distress at high carb concentrations — it's what Sabastian Sawe used in his London Marathon fueling plan, sipping it on the bus to the start and throughout the race. Higher price point, but elite-proven.
3. Maurten Drink Mix 160
The lighter version of the 320, the Drink Mix 160 offers 40 g carbohydrate. Same hydrogel technology — carbs encapsulate in your stomach for smooth delivery without cramping or sloshing — just half the concentration.
4. Skratch Labs Super High Carb
Powered by cluster dextrin, which breaks down gradually during digestion for a steadier energy release and lower GI distress risk. At a full 7-scoop 100g carbs serving, sodium comes in at 400 mg.
5. SiS Beta Fuel
80 g carbohydrate per serving through a 1:0.8 glucose-to-fructose ratio — maltodextrin and fructose hitting two separate absorption pathways simultaneously, which means higher carb utilization. Naturally flavored in Orange, Strawberry & Lime, and Red Berry. No artificial sweeteners. If you're the type who rotates flavors across a multi-day carb load to avoid taste fatigue, the three-option lineup makes that easy without changing anything about the fueling math.
What makes a good carb loading drink?
The basics: high carbohydrate content (40–100 g per serving), easy digestibility, minimal fiber, adequate electrolytes, and a flavor you'll actually keep drinking. In the 48 hours before a race, stick to low-fiber, low-fat carb sources to reduce GI transit time and lower the risk of race-day stomach issues.
Liquid carbs vs. solid food: why it matters
For nutrition to fuel your muscles, it has to leave the gut, enter the bloodstream, and reach the working tissue — in that order. Liquid carbohydrate sources empty from the stomach faster than solid food, particularly at isotonic or hypotonic concentrations. That's the practical case for drink mixes during carb loading: they're easier to digest, easier to consume in volume, and less likely to leave you feeling stuffed heading into race morning.
Can you mix carb loading products?
Yes, and it's often the right call. Use a high-carb base and layer in electrolyte powder if your sodium needs are higher. The Feed Lab High Carb plus a scoop of Skratch Hydration is a common combination for athletes who need more sodium without adding another full product. Mix and match based on your numbers, not habit.
What to avoid
High fiber, high fat, unfamiliar ingredients, overly concentrated formulas you haven't tested in training, and excessive caffeine if you're not used to it. The 48 hours before a race are not the time to experiment. Stick to what you've practiced and keep meals simple and fuel-focused.
How to know if carb loading is working
You should feel energized but not bloated. A small bodyweight increase of 1–2 kg is normal — each gram of glycogen is stored with roughly 3 g of water, so the scale going up slightly is a sign your muscles are loading, not a reason to panic. That's not a performance negative like athletes think, though. Carb loading allows you to enter the race literally loaded up for performance.
FAQ
How many days before a marathon should I start carb loading? 2–3 days out. A 3-day protocol consistently produces greater muscle glycogen concentrations than a single-day approach, with the biggest performance impact in events over 90 minutes.
Can I use regular sports drinks for carb loading? They help, but most contain only 14–20 g of carbs per serving and a lot of processed sugar, ingredients, and other fillers. You'll need dedicated high-carb drink mixes to realistically hit 8–12 g/kg/day targets.
What's the difference between carb loading and race-day fueling? Carb loading fills your tank. Race-day fueling keeps it from running dry. During the marathon, aim for 30–60 g of carbs per hour — gels and sports drinks are the most practical formats.
What if I have a sensitive stomach? Start with lower concentrations and work up. Simpler ingredient lists tend to tolerate better. When in doubt, work with a sports dietitian to build a protocol if you are in need.
How much water should I drink with carb loading drinks? Follow the product's mixing instructions and increase overall fluid intake — glycogen storage requires water, and under-hydrating during a carb load limits how much glycogen your body can actually store.
