The Effect of Varying Carbohydrate Intake on Training Performance in Professional Football Players

This study used a single-blind, placebo-controlled, randomized crossover design to examine the effects of different levels of daily carbohydrate availability during a pre-season training microcycle in professional male football players.

The study was conducted in an applied professional football environment during two consecutive pre-season training weeks. Each participant completed both dietary conditions. The order of the two conditions was randomized and counterbalanced. The training schedule and overall training content were matched between the two intervention weeks as part of the club's regular training program.

The two dietary conditions were designed to provide different daily carbohydrate intakes. In both conditions, participants followed a standardized food-based diet that provided 4 grams of carbohydrate per kilogram of body mass per day. In the higher-carbohydrate condition, participants also consumed three carbohydrate-containing study beverages per day, providing an additional 3 grams of carbohydrate per kilogram of body mass per day. This resulted in a total target intake of 7 grams of carbohydrate per kilogram of body mass per day. In the moderate-carbohydrate condition, participants consumed similar placebo beverages without added carbohydrate, resulting in a total target intake of 4 grams of carbohydrate per kilogram of body mass per day.

The study beverages were prepared from water and an artificially sweetened concentrate. In the higher-carbohydrate condition, maltodextrin was added to the beverage. In the moderate-carbohydrate condition, no maltodextrin was added. Beverages were provided in non-transparent bottles to support participant blinding. Participants were not informed of the carbohydrate content of the study beverages.

Dietary targets were individualized according to body mass. Breakfast and snacks were individualized according to participant preferences but standardized for carbohydrate content. Lunch was provided through the club's restaurant and adjusted to meet the carbohydrate target. Dinner targets were communicated using an image-based portion guide to support consistent carbohydrate intake outside the training facility. Participants were instructed to maintain their habitual protein and fat intake across both conditions.