Carb Loading Done Right: A Science-Based Guide

Carbohydrate loading — systematically increasing muscle glycogen stores before competition — is one of the oldest and most validated performance nutrition strategies. When done correctly, it can increase glycogen stores by 50-100% above normal levels and delay fatigue during prolonged exercise by 20-45 minutes.

When done incorrectly — which is most of the time — it produces bloating, GI distress, and no performance benefit.

Why Glycogen Matters

Muscle glycogen is the primary fuel source for exercise above approximately 65% VO2max. A well-fueled member stores roughly 400-500g of glycogen across liver and muscle. At competition intensity, that supply lasts approximately 90-120 minutes before depletion occurs.

For events lasting less than 90 minutes, normal glycogen stores are sufficient. Carb loading provides its greatest benefit for endurance events exceeding two hours: marathons, half-ironman and ironman triathlons, long-course cycling, cross-country skiing, and tournament-style sports with multiple games in a day.

The Modern Protocol

Early carb-loading protocols (Bergstrom et al., 1960s) involved a glycogen-depleting phase followed by a supercompensation phase. This approach worked but was impractical: the depletion phase left members feeling terrible, and the timing was difficult to manage.

The modern evidence-based protocol is simpler:

36-48 hours before the event: Increase carbohydrate intake to 10-12 g/kg/day
Reduce training volume to minimal during this period (taper)
No depletion phase needed — the taper combined with high carbohydrate intake achieves supercompensation without the misery

For a 70 kg runner, that means 700-840g of carbohydrate per day for one to two days. This is a lot of food, which is why most members underdo it.

Practical Execution

Eating 10-12 g/kg of carbohydrate in a day requires intention and planning. The common mistake is trying to “eat more pasta at dinner” — that is not enough. The carbohydrate needs to be distributed across every meal and snack.

Sample day for a 70 kg member (targeting 770g carbs):

Breakfast: Large bowl of oatmeal with honey and banana, 2 slices toast with jam, orange juice (150g carbs)
Mid-morning snack: Bagel with jam, sports drink (80g carbs)
Lunch: Large pasta portion with marinara, bread roll, fruit (160g carbs)
Afternoon snack: Rice cakes with honey, energy bar, juice (100g carbs)
Dinner: White rice with chicken (small portion), bread, sweetened iced tea (140g carbs)
Evening snack: Pretzels, dried fruit, sports drink (140g carbs)

Notice the pattern: low-fiber, low-fat, high-glycemic carbohydrate sources dominate. This is intentional — fiber and fat slow digestion and add unnecessary fullness when the goal is maximum carbohydrate absorption.

Common Mistakes

Not eating enough: Athletes underestimate 10 g/kg. They eat “a lot of carbs” but actually hit 5-6 g/kg. The protocol requires precision.
Too much fiber: Switching to whole grains and vegetables during the loading phase causes bloating and GI distress. Use refined carbohydrates.
Too much fat: Adding butter, cream sauces, and cheese increases calories but not carbohydrate content. Keep fat low during the loading window.
Trying new foods on race day: The loading period and competition day are not the time for dietary experiments. Use familiar, well-tolerated foods.
Loading for the wrong event: A 5K does not benefit from carb loading. The fuel demands are met by normal glycogen stores.

Race Morning

On competition day, a pre-event meal three to four hours before the start provides a final top-off:

1-4 g/kg of carbohydrate from familiar, low-fiber foods
Low fat and low protein to minimize GI risk
Adequate fluid with sodium

The combination of a proper loading protocol and a smart pre-event meal means the member starts with maximally fueled muscles and a topped-off liver.

For dietitians building competition-week nutrition plans, Calsanova’s day-type system allows you to set different macro targets for training, game, rest, and travel days — making periodized carb loading easy to prescribe and track.

Support the protocol: Scythene Electrolytes pair with your carb-loading fluids to maintain plasma volume and sodium balance through the loading window. Code MPS20 for 20% off. Shop Scythene →