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Most triathletes love to eat, and many of us consider it another hobby when we aren’t swimming, biking, and running to a finish line. Destination races are often chosen based on their ability to be viewed as a “race-cation” because of the lively social gatherings, appetizing meals, delicious libations, and incredible sightseeing. While consuming calories is more complex than just providing energy for the body to function physiologically, many athletes either intentionally or unintentionally adjust calorie (energy) intake resulting in lower body weight or body composition. Do athletes participating in triathlons and other sports have these same fluctuations in energy expenditure and energy intake from pre-season through post-season? In a new study, Jesus et al. (2022) examined energy expenditure and energy intake in various non-weight and weight-sensitive sports during an athletic season during the preparatory phase and the main stage of competition to compare and contrast these values within season and between sport types.

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What is energy availability?

Energy availability (EA) is the difference between energy intake and energy expenditure to fat-free mass (FFM), as defined by Locks and Thuma in 2003. Through decades of research, it has been recognized that maintaining optimal EA is critical to the health and performance of active individuals. When EA is not supported, and energy intake does not match energy expenditure, low EA is associated with negative consequences, including implications for altered hormonal profiles, impaired reproductive function, and decreased bone mineral density. The difficulty lies in quantifying low EA, which in many studies is evaluated through the dietary logs of athletes. These logs are considered “self-report” and can easily be skewed toward over or underestimating energy intake. Along with the assessment of energy intake, body composition and activity energy expenditure must be assessed to accurately address the FFM portion of the equation and calculate EA. Measures of body composition and energy expenditure must use an appropriate methodology that is accurate but also reliable and specific to calculate EA.

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Comparing energy availability in triathlon to other sports

Original data from this research was collected by Silva et al. (2017). As part of a secondary analysis, Jesus et al. (2022) analyzed 88 athletes (27% female) for EA from basketball, handball, volleyball, swimming, and triathlon in the preparatory phase and 56 athletes (30.4% females) in the same sports for EA during the central portion of the competition phase of one athletic season. Inclusion criteria for participation included the following:

  1. Training for more than 10 hours per week,
  2. A negative test for performance-enhancing drugs,
  3. Athletes were not taking medications or dietary supplements.
  4. Female athletes were excluded if they were on oral contraceptives or were not having a regular (28 +/- 7 day) menstrual cycle.

Body composition (fat mass and FFM) was assessed through a four-compartment model including doubly-labelled water to assess total energy expenditure while resting energy expenditure was determined by indirect calorimetry. EA was based on energy intake minus estimated energy expenditure divided by FFM. Three levels of EA were defined, including 1. Clinically low EA (<30kcal/kg FFM), 2. Subclinical low EA (30-40 kcal/kg FFM for males or 30-45 kcal/kg FFM for females) and 3. Optimal EA (>40 kcal/kg FFM for males and >45 kcal/kg FFM for females).

Results suggested that in all sport types, participants increased their EA values from the preparatory portion of the season to the competitive phase, including 14% in basketball, 41.1% in handball, 16.3% in volleyball, 18.3% in swimming, and 29.3% in triathlon. A lower EA was observed at both measurement points for triathletes when compared to the other sports. Triathlon is considered a weight-sensitive sport due to the lower body weight during cycling and running producing an advantageous power to weight ratio. During the preparatory phase, 11 (12.5%) athletes across all sports were classified as clinically low EA, 25 (28.4%) as subclinical low EA, and 52 (59.1%) as optimal EA. However, by the competitive phase measurement, no athletes, regardless of sport, were classified as clinically low EA, 11 (19.6%) were classified as subclinical low EA, and 45 (80.4%) were considered to meet an optimal EA level.

One reason for EA improvement throughout the season may be related to what an athlete perceives as a negative outcome of increased body weight during the off-season. During the transition to the preparatory phase, athletes may manipulate body weight and composition by creating a more extreme calorie deficit. If an athlete is too rigid with these strategies, the unintended outcome could be low EA.

In contrast, during the competitive season, athletes may be more conscious of the importance of performance-fueling strategies that require additional energy at critical times (such as in the recovery from exercise) and an overall energy intake that results in better practices and training sessions. Of note is that handball players, who had the most considerable rise in EA from suboptimal to optimal over the athletic season, did not experience a significant change in fat mass but did experience a significant increase in bone mineral density. Lastly, the triathletes participating in the study did experience a significant metabolic adaptation or resting energy expenditure, which lowered metabolic activity for energy conservation purposes.

The bottom line

While it may be tempting after the off-season to lower your calorie intake and attempt to lose unwanted body weight quickly, a more pragmatic, practical approach for triathletes is to include a slight calorie deficit while keeping protein at 1.6-2.0g/kg of body weight is advisable for triathletes. In addition, knowing the negative acute and long-term physiological consequences of low EA should deter athletes from over-reaching and depriving their bodies of much-needed calories and nutrients, which could ultimately cause unwanted metabolic adaptations as the body attempts to conserve energy.

The goal of educational programs and health practitioners should be to increase awareness of the importance of adequate EA throughout the season to meet energy and micronutrient demands for healthy, happy triathletes.

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Kim Schwabenbauer, PhD, RD, CSSD, LDN, is a former professional triathlete turned registered dietitian, professor, consultant, speaker and triathlon coach with an emphasis in overall health, wellness and sports nutrition.