Position of the Working Group Sports Nutrition of the German Nutrition Society (DGE): Energy Needs in Sports

Athletes expend greater amounts of energy as a result of their training. However, these amounts vary during the competition year and are influenced by such factors as the training period and intensity.

Measuring energy expenditure is a complex process that is often achieved through indirect calorimetry. A calculation is possible when certain limitations are taken into consideration.

Energy expenditure corresponds to energy requirements. Energy requirements should be covered by energy intake adapted to individual needs. Low energy intake can lead to reduced energy availability. Low energy availability not only has a negative impact on the bone metabolism and menstrual cycle – there may also be consequences of a hematological, metabolic, psychological, gastrointestinal and immunological nature. This has adverse effects on the performance capacity, training adjustment, concentration and coordination, and can lead to an increased risk of injury.

Matching energy intake to energy expenditure is an important cornerstone in the diet of athletes and a significant prerequisite for maintaining their health and performance.

KEY WORDS: Athletes, Calorimetry, Energy Availability, Resting Energy Expenditure, Metabolic Equivalent

Sportler haben bedingt durch das Training einen gesteigerten Energieverbrauch. Dieser ist jedoch im Verlaufe eines Wettkampfjahres variabel und wird unter anderem von der Trainingsdauer und -intensität beeinflusst.

Die Messung des Energieverbrauchs ist komplex und erfolgt häufig über eine indirekte Kalorimetrie. Eine Berechnung ist unter Berücksichtigung bestimmter Einschränkungen möglich.

Der Energieverbrauch entspricht dem Energiebedarf. Der Energiebedarf sollte durch eine angepasste Energiezufuhr gedeckt werden. Eine geringe Energiezufuhr kann zu einer reduzierten Energieverfügbarkeit führen. Eine niedrige Energieverfügbarkeit hat nicht nur negative Auswirkungen auf den Knochenstoffwechsel und den Menstruationszyklus, sondern es ist auch mit hämatologischen, metabolischen, psychologischen, gastrointestinalen und immunologischen Konsequenzen zu rechnen. Daraus resultieren negative Einflüsse auf die Leistungsfähigkeit, Trainingsanpassung, Konzentration, Koordination und ein erhöhtes Verletzungsrisiko.

Eine dem Energieverbrauch angepasste Energiezufuhr ist ein wichtiger Eckpfeiler in der Ernährung des Sportlers und eine wesentliche Voraussetzung für Gesundheit und Leistungsfähigkeit.

SCHLÜSSELWÖRTER: Athleten, Kalorimetrie, Energieverfügbarkeit, Ruheenergieumsatz, metabolisches Äquivalent

Athletes have special dietary needs. In a consensus statement on sports nutrition, the International Olympic Committee (IOC) stated that diet influences performance capacity and advised athletes to apply dietary strategies adapted to individual needs during and after training and competitions to maximize their physical and mental performance (19). It should be kept in mind that athletes are not a homogeneous group; there are in fact numerous factors that influence energy and nutrient needs (e.g. body weight, size, body composition, training program, duration, intensity). It must also be considered that, depending on the training and competition phase within the annual cycle and even within any given week, athletes plan the intensity and duration of their training sessions in very different
ways (17, 36, 37).

A young high-performance athlete also has an increased, growth-related need for energy and nutrients (11, 39). Furthermore, the body weight and body composition of athletes in competitive sports and especially in youth competitive sports can also vary widely within the same type of sport (34, 41). This becomes particularly clear in track and field, in which athletes in endurance sports weigh 50-60 kg and throwers can weigh up to 130 kg (33).

While energy intake of humans is limited to their meals and possibly drinks, energy expenditure is a continuous process designed to maintain numerous activities and functions in our bodies. Daily energy requirements correspond to the energy expenditure over a 24-hour period (10). Accordingly, appropriate energy intake is a key factor in the human diet. Ideally, the energy intake matches the energy requirements. This is the amount of nutritional energy that guarantees a stable body weight and promotes health and fitness (10). However, energy requirement is not a fixed quantity and is influenced by numerous factors. These include e.g. body weight, body composition, physical activity, growth, pregnancy and nursing period. Physical activity is the most variable component in energy
requirements (10, 44).

Adult endurance athletes report training programs ranging from 500 to 1,000 hours per year (17) or a running distance of >150 km per week (17, 36). In extreme situations such as the Tour de France or Race Across America, energy expenditure may be five times as much as when the athletes are at rest (18, 43). For individual long-distance races, this can result in an energy expenditure of >10,000 kcal per day (14). In contrast, there are also phases with low physical activity during a training year, in which daily energy requirements are at a lower level, owing to a potential training period of less than two hours per week. This makes it comparable to that of a person who exercises recreationally (17, 36, 37).

Based on the factors that influence the energy expenditure outlined above, the energy needed by most athletes lies between 1,500 kcal and 6,000 kcal per day and during the sports season can be estimated at 2,000 kcal to 5,000 kcal per day for a person weighing 70 kg, for example (37).
This variation in individual energy requirements must be considered during nutrition counseling. As a result, nutrition counseling professionals must address the type of sport/discipline and conditional training and competition exertions in order to get an accurate estimate of (current) energy requirements.

Energy expenditure can be determined through various methods (e.g. direct calorimetry, indirect calorimetry, heart rate) (10). Indirect calorimetry is often used under lab conditions. In this process, the oxygen intake (V˙O2) and carbon dioxide output (V˙CO2) are measured via spirometry in liters per minute and calculated according to the
Weir formula (42).

Weir Formula

Energy (kcal/min) = 3.9 x V˙O2 (L/min) + 1.1 x V˙CO2 (L/min)

Indirect calorimetry makes it possible to determine the resting energy expenditure, the basal metabolic rate and the total energy expenditure. Additionally, V˙O2 and V˙CO2 can be recorded with mobile devices during selected physical activities in the field. By using portable spirometry for a soccer training game, it was possible to show an average energy consumption of 1,340 kcal for a period of 90 minutes, but there were great differences in the energy consumed by the studied players (1,050-1,750 kcal) (13). When measuring energy expenditure with spirometry, it should also be noted that the additional CO2 formed by the bicarbonate buffer system with increased training intensity limits the accuracy of the values determined through indirect calorimetry for energy expenditure and substrate utilization. This applies particularly to physical exercise above a respiratory quotient (RQ) of 1.0.

Despite these limitations, it is possible to capture energy expenditure during physical activities through spirometric data for guidance. The results from numerous studies to determine the oxygen intake (V˙O2) during selected physical activities were summarized in the Compendium of Physical Activities (2, 3, 4) and are updated regularly on the Compendium website (5). The Compendium has established itself as a widely used and accepted source to estimate energy consumption in recent decades (4, 39). The information in the Compendium is provided as a so-called “metabolic equivalent of task (MET)” (Box).

One MET corresponds to resting energy expenditure and is defined as 1 kcal per kg of body weight per hour (kcal/kg body weight/hour). The MET values accordingly stand for a multiplication factor of resting energy expenditure (see examples 1 and 2). This is comparable with information about the Physical Activity Level (PAL). This is defined as the ratio of total energy expenditure to resting energy expenditure, but in contrast to MET, the applicable period is 24 hours. The PAL value thus refers to the additional daily energy consumption used during physical activities relative to the resting energy
expenditure (10, 20).

The MET values describe specific activities, for which activity-related data are then available (Table 1). The MET values of the Compendium are in a range of 0.95 (sleeping) and 23 (running at 22.4 km/h) (4).

Based on the knowledge of resting energy expenditure (see formula for the calculation below), it is possible to calculate energy expenditure for different activities (Figure 1 with example 1 and 2).

This approach has established itself for estimating the energy expenditure during physical activity, but it comes with a few limitations that must be considered (4, 39). For example, the METs only apply for people without a mental or physical disability aged 18-65 years. It should also be considered that persons who are more physically fit reach a higher metabolic rate per unit of time with the same relative intensity of training (32). The intensity information (e.g. casual, general, strenuous) for the METs may be particularly misleading. Subjectively, a sports activity (e.g. soccer) can be perceived as very strenuous (e.g. owing to poor fitness). However, it is quite possible that a trained player has objectively run more and thus also shows greater energy expenditure while perceiving the activity “only” as moderately
strenuous.

Additionally, a key factor in estimating energy expenditure is knowledge of resting energy expenditure. This can be determined with an indirect calorimetry, as described above. This is a complicated process, however, and is only rarely applied as a matter of routine. In general, the resting energy expenditure is thus calculated with available formulas.

Harris and Benedict (1918) (16)

Men: REE [kcal/day] = 66.5 + 13.8 x weight [kg] + 5.0 x size [cm] – 6.8 x age [years]

Women: REE [kcal/day] = 655 + 9.6 x weight [kg] + 1.8 x size [cm] – 4.7 x age [years]

Cunningham (1980) (8)

REE [kcal/day] = 500 + 22 x LBM (Lean Body Mass)

Müller (2004) (10)

REE [MJ/day]* = 0.047 x weight (kg) + 1.009 x gender (women = 0, men =1) – 0.01452 x age (years) + 3.21

*Conversion of MJ into kcal by multiplying by 239

However, studies have shown that the calculated values do not always correspond to the measured values (7, 15). Although the mean values may generally coincide, there may still be a considerable discrepancy between measured and calculated resting energy expenditure in individual cases (7, 15). Since the fat-free body mass significantly influences the resting energy expenditure and is generally higher in athletes than non-athletes, it makes sense to use a corresponding calculation formula that takes fat-free body mass into account. The Cunningham formula (1980) is often applied in this respect. However, studies that compare the Cunningham formula with measured resting energy expenditure data show inconsistent results (7, 40).

Additionally, resting energy expenditure varies and may not be considered a fixed quantity. In some types of sports (e.g. weight-class sports, ski jumping, endurance sports), there are attempts to reduce body mass during selected periods in a season or to keep it low by means of a chronically low energy intake. This can lower resting energy expenditure during the season. However, this effect seems to be cancelled out at the end of the season with correspondingly higher energy intake (28).

In some types of sports or disciplines (e.g. ski jumping, high jump, marathon running), low body weight can provide an advantage in the performance or the regulations may necessitate a certain body weight on the day of the competition. To attain low body weight, athletes tend towards chronically low energy intake or, if possible, an increase in energy expenditure during training (24, 30). This is often referred to as a negative energy balance as well as low energy availability (EA).

Energy Availability is Defined as:

Energy availability = energy intake – energy expenditure during training

The EA is referred to in kcal per kg of fat-free mass (FFM) (Figure 2 with example 3 and 4).

The concept of energy availability is prevalent especially in sports nutrition and refers less to the traditional energy balance; instead it mainly considers the supplied amount of energy minus the energy used during sports. This results in the amount of energy available to the organism to maintain its basic functions (25, 39).

Studies involving female athletes show that low energy availability (<30 kcal per kg FFM) leads to a higher risk of signs of fatigue and overtraining, immunodeficiency, menstrual disorders and stress fractures (25, 26). Low energy availability is also seen as closely related to the development of the Female Athlete Triad. This is a symptom complex related to menstrual cycle disorders, impaired eating behavior and lower bone density in female athletes (12, 31).

This phenomenon has not yet been systematically studied in men, but comparable results may be assumed (9, 21, 22). Since low energy availability can occur in both genders, it was suggested that the term Female Athlete Triad be replaced with the term Relative Energy Deficiency in Sports (RED-S) (29). This is also intended to take into account that low energy availability does not limit itself to bone metabolism and menstrual cycle disorders, but can also have hematological, metabolic, psychological, gastrointestinal, and immunological consequences. This is associated with negative influences on performance capacity, training adjustment, concentration, coordination, and an increased risk of injury (39). More in-depth information on this topic can be found in the freely accessible review by Nattiv et al. (2007) (31), De Souza et al. (2014) (12), Mountjoy et al. (2014) (29), Mountjoy et al. (2018) (30) and in a special issue of the International Journal of Sport Nutrition and Exercise Metabolism (Volume 28, Issue 4, July 2018).

Risk groups for low energy availability include athletes who deliberately ensure they have low body weight (e.g. weight reduction phase, permanently low body weight) or are pressured to maintain low body weight. Low energy availability may also affect athletes who e.g. do not eat enough for lack of time and/or underestimate their own energy requirements. It may also be attributable to the fact that hunger is suppressed for sports-related reasons, leading to insufficient energy intake (26). In phases of weight loss, it is important to ensure that energy availability of 30-45 kcal per kg FFM is guaranteed despite reduced energy intake (26).

When applying the concept of energy availability in a consulting practice, it must be kept in mind that information is needed on energy intake, energy expenditure during training as well as data regarding fat-free mass.

The limitations relating to determining energy expenditure are described above. General challenges in determining energy intake through the various nutrition survey systems are not part of this position paper but described in detail elsewhere (6, 27, 38).

Additionally, in nutrition surveys with athletes, it must be kept in mind that a one-time documentation of diets (e.g. once per year) will lead to a flawed evaluation of the nutritional situation, since energy intake can vary greatly owing to the different levels of exertion in training and competitions. The phenomena of underreporting, underrecording or underestimation and overestimation also occur in this group (6, 23, 27, 38). The significant causes named here include changes in eating behavior during the protocol phase, erroneous statements due to social desirability, and documentation errors in terms of the amount and description of the consumed foods (27). In nutrition surveys, athletes seem to “forget” to record such things as snacks or drinks, which can result in an erroneous evaluation of their energy intake (23, 27). Overall, this can lead to a misinterpretation of energy intake in the range of 10-45% (27) and in individual cases to a caloric deficit of >1,500 kcal per day (7).

Additionally, the body composition must be measured to obtain information on fat-free mass. Different results may be obtained depending on the measuring method (1), however, which, in turn, influences the calculation of energy availability.

Despite the limitations described above, it is recommended that more attention be paid to the topic of energy requirements in sports so that warning signals for low energy availability and the associated negative consequences on health and performance can be detected at an early stage.

Depending on the training and competition phase within the yearly cycle, there can be enormous differences in energy requirements of athletes. Determining energy expenditure precisely is not easy, but can nevertheless be approximated. Energy intake that is adapted to individual needs is a key cornerstone in sports nutrition. In general, it is thus important to ensure adequate energy intake appropriate for the situation in order to meet the training and potentially growth-related needs. Inadequate energy intake can lead to low energy availability with the previously described consequences for health and performance.

The authors wish to thank Dr. Angela Bechthold and Birte Peterson-Sperlich from the Science Department at the DGE.

Conflict of Interest
The authors have no conflict of interest.