New Research Finds How to Execute the Perfect Carb Load

Why It Matters

The results give coaches and athletes evidence‑based guidance for pre‑race nutrition, supporting ACSM’s high‑carb recommendations and potentially boosting endurance performance without added side effects.

Key Takeaways

• Two‑day carb loading at 10 g/kg boosts leg glycogen most
• No weight gain or GI distress observed at highest intake
• Study involved 11 trained endurance athletes over five‑day taper
• No ceiling effect up to 10 g/kg; higher may help
• Meals used low‑fiber carbs like sports drinks and jelly

Pulse Analysis

Carbohydrate loading has been a cornerstone of endurance training since the 1960s, but the optimal amount and timing remain debated. Early protocols required a week‑long depletion phase followed by high‑carb refeeding, a cumbersome approach for modern athletes. Contemporary guidelines from the American College of Sports Medicine recommend two to three days of 10‑12 g/kg, yet empirical data supporting these numbers have been limited. Understanding the physiological basis—glycogen supercompensation in both muscle and liver—helps explain why precise dosing matters for race‑day energy availability.

The Liverpool John Moores study provides a rare controlled comparison of 6, 8 and 10 g/kg intakes over a realistic two‑day taper. Using muscle biopsies, researchers documented a dose‑response relationship: each incremental increase yielded higher glycogen concentrations, and no plateau was observed at 10 g/kg. Importantly, participants did not experience weight gain, bloating, or gastrointestinal upset, challenges often cited as barriers to aggressive carb loading. These findings validate the higher end of ACSM’s range and suggest that athletes may safely push beyond traditional 8 g/kg targets without compromising comfort.

For practitioners, the takeaway is practical: plan two days of high‑carb meals (≈10 g/kg) focusing on low‑fiber, easily digestible sources such as sports drinks, gels, and refined carbohydrates. Pair the nutrition plan with a light training taper to preserve glycogen stores while avoiding excess fatigue. While the study stops at 10 g/kg, the absence of a ceiling effect hints that even higher intakes could be explored, albeit with careful monitoring of gastrointestinal tolerance. Incorporating a modest carb boost on race morning—through gels or a carbohydrate‑rich beverage—remains essential to replenish liver glycogen and sustain blood glucose during the early stages of competition.