Football is an intermittent multiple-sprint sport characterized by repeated bouts of short duration high-intensity sprints in an endurance context that also requires the maintenance of skills throughout the match [1]. In a 90-min match, the distance covered by a football player ranges from 8 to 13 km, depending on factors like players’ fitness level, field position, difficulty of the game, tactics of the team, and weather conditions [2–5]. The majority of the distance is covered by walking and low-intensity running, and it is mainly the high-intensity exercise periods that distinguish top-class players from the others. International top-class players perform 28% more high-intensity running (2.43 vs. 1.90 km) and 58% more sprinting (650 vs. 410 m) than professional players at a lower level [1]. Although players perform low-intensity activities for more than 70% of the game, heart rate and body temperature measurements suggest that average oxygen uptake for elite football players is around 70% of VO2Max with an estimated energy expenditure of 16 kcal/min [6, 7]. Since football players perform 150–250 brief, intense actions during a game [1], this indicates that the rate of anaerobic energy turnover is high during periods of a game. Even though this has not been studied directly, intense exercise during a game would lead to a high rate of creatine phosphate breakdown, which to a great extent is resynthesized in the following low-intensity exercise periods [7, 8]. The energy substrate utilized during a football match is mainly glycogen, as seen by the depletion of glycogen in some muscle fibers that could be related to fatigue toward the end of the game [9]. In high-intensity activities, such as sprints and jumps, glycogen contributes approximately 50% to ATP turnover, and the repeated sprint activity that characterizes a football match leads to a reduction in glycogen concentrations, which in turn may impair performance in the latter stages of a match [10]. In one study employing Loughborough Intermittent Shuttle Test (LIST), a protocol mimicking the demands of team sports like football, the authors found a significant reduction in muscle glycogen concentrations from before to after exercise, both in type I and type II muscle fibers [11]. A study employing the Copenhagen Soccer Test (CST) [10] found similar results: type I and type II muscle fibers exhibited significant glycogen depletion, with ~80% of fibers being completely or almost depleted (<200 mmol/kg d.w) of glycogen after 90 min of intermittent activity. These low concentrations have been shown to decrease the glycolytic rate [8]. Type II fibers seem to be the main responsible for decreases in performance when their glycogen content is low [12]. Furthermore, the depletion of muscle glycogen in the sarcoplasmic reticulum results in reductions in muscle calcium handling [13], compromising the contractile property of the muscle [14].

Fat oxidation appears to increase progressively during a game, partially compensating for the progressive lowering of muscle glycogen. Increased levels of triglycerides might occur in the second half due to elevated catecholamine concentrations. The decline in blood lactate concentration associated to an increase in plasma free fatty acids during the game confirms the change in substrate utilization during the game [8, 9].

Match-related fatigue is determined by a combination of central and peripheral factors. The decline in performance observed at the end of a match arises from a combination of several factors involving mechanisms from the central nervous system to the muscle cell itself and energy production [15]. Fatigue in football seems to occur at three different stages in the game: (1) after short-term intense periods in both halves, (2) in the initial phase of second half, and (3) toward the end of the game [16]. The first two stages are not directly related to nutrition issues, but fatigue at the end of the game is associated with low glycogen concentrations in a considerable number of muscle fibers.

Data from the 2014/15 Italian Serie A, English Premier League, and Spanish La Liga shows that the final 15 min of a match is the period when more goals occur and that top teams always have a better goal difference [17]. Then, it seems crucial to optimize nutritional strategies in order to reduce fatigue and maintain physical and technical performance throughout the match. In this context, it seems well established that high carbohydrate intake in order to maximize glycogen storage is a crucial strategy to enhance performance in a football match.

Carbohydrate and fat are the main fuels for training and competition, and its relative contribution to energy demands depends on several factors, such as pre-exercise carbohydrate storage, exercise frequency, intensity and duration, or even athletes’ training status [18]. Since carbohydrate availability to muscle and central nervous system can be compromised when the cost of the exercise exceeds endogenous carbohydrate storage, provision of additional carbohydrate may be crucial to enhance performance in high-intensity sports [19].

Carbohydrate daily intake necessary to recover from daily training sessions depends on its intensity and duration, and it must be carefully estimated. Louise Burke and colleagues defined, in 2011, general recommendations for carbohydrate intake for daily training recovery [20]. For a highly active athlete (e.g., moderate-to-high-intensity exercise of 1–3 h/day), a 6–10 g/kg/day carbohydrate intake must be achieved. The large interval provided covers many exercise durations and intensities, and these general recommendations should be fine-tuned with individual consideration of total energy expenditure, specific training needs, and feedback from training performance [20].

In a sport played outdoor like football, dehydration can have a negative impact on performance, especially when combined with heat stress. Although some individuals may be more or less sensitive to dehydration, the level generally accepted that is capable to induce performance degradations approximates >2% decrease in body mass [34]. In a football practice or match, dehydration values from 0.5% to 3.4% of body mass loss were reported [35], with higher losses being associated with temperatures from 27 °C [3] to 35 °C [36]. Data concerning dehydration and football performance is relatively scarce and inconclusive. Higher Ratings of Perceived Exertion (RPE) and slower sprint times at the end of LIST as well as a decrease of 5% on dribbling skills were observed with dehydration of 2.5% compared with 1.4% [37]. More recently after a LIST protocol, football skills and intermittent high-intensity exercise performance were similar with 2.5%, 1.1% and 0.3% of dehydration [38]. When another exercise protocol was used (Yo-Yo Intermittent Recovery Test), dehydration by 2.4% led to an increase in RPE and to a lower performance compared to 0.7% [39]. Interestingly, in this study, when players washed their mouths with plain water in a volume corresponding to 2 ml/kg body mass, without swallowing the fluid, mouth rinse resulted in 2.1% dehydration but also reduced the total distance run by the football players during the Yo-Yo Test.

Even with conflicting data, it is prudent to assess hydration status of players and try to avoid body mass losses above 2%, especially when it is known that football players start a practice or match play already in a dehydrated state, probably as a result of cumulative dehydration from previous training practices [36]. Moreover, the intake of sports beverages during a match can supply an additional source of carbohydrates, very useful in players that do not initiate the game with glycogen stores completely full.

Although the vast majority of studies regarding nutritional interventions have focused on physical performance, the possible impact of nutrition on technical performance (commonly known as skills) has become a matter of interest for the scientific community.

The results altogether are somewhat equivocal, but it seems evident that skill performance is affected by some factors which might threaten homeostasis, such as fatigue [40, 41], dehydration [42], and reductions in blood glucose concentrations [20]. The most important skills in a football match are passing and dribbling, due to its frequency, and shooting, due to its ability to decide the final result [43, 44]. The second half of a football match is usually associated with a decrease in technical skills, particularly in passing and shooting [45], with total possession and total ball distribution also suffering a reduction [41]. Proficiency in match-related skills might be even more important than high-intensity activity. A study with Premier League players found that overall technical and tactical effectiveness of the team rather than high levels of physical performance per se is a more important success determinant in football [46].

Based on studies assessing physiological demands of football players, specific nutritional recommendations have been developed. In order to evaluate the adequacy of nutrient and energy intake in these athletes, some studies tried to analyze it using food records (weighed or estimated), food frequency questionnaires, and other less detailed methods.