Maximizing fat-free mass is desirable for athletes involved in activities

Keywords:

1. Introduction

In sports nutrition, management of the body composition of athletes is a common practice. Loss of body weight [BW] in athletes is generally motivated by the desire to optimize performance by increasing the strength-to-body weight ratio [e.g., powerlifting or weightlifting] or to compete in a discipline limited by BW category [e.g., boxing], or for aesthetic reasons in sports that require it [e.g., bodybuilding] [,,,]. However, a hypocaloric diet could result in a significant loss of fat-free mass [FFM], which could affect the athlete’s performance [,,]. Therefore, nutritional strategies during a weight loss phase in athletes, in addition to reducing fat mass [FM], should aim to maintain FFM [,,].

Current recommendations regarding BW loss in athletes favor more moderate approaches with the intention of minimizing the negative effects associated with rapid BW loss. It has been observed that a loss of BW of 0.5–1.0 %/week, accompanied by a high protein intake and resistance exercises, could favor the retention of FFM during fat loss phases [,,,,,,,,,,,]. Nevertheless, the scientific literature on this topic in resistance-trained athletes is very limited. The latest research focuses on bodybuilders, being necessary scientific literature on dietary–nutritional and supplementation recommendations for fat loss in these athletes [,,].

Unlike in other sports where strength exercise is used to complement to the athlete’s specific training, in disciplines such as powerlifting, weightlifting and bodybuilding, resistance training forms the basis of the training []. While in weightlifting and powerlifting, a reduction in FM could improve performance through an increase in the strength-to-body weight ratio [,,], in preparation for a bodybuilding competition, a drastic reduction in FM is required to achieve optimal muscle definition [,,,,].

The aim of this review is to provide a comprehensive overview of dietary–nutritional strategies for the loss of FM and the maintenance of FFM in resistance-trained athletes from a theoretical and contextual point of view, to enable focused future systematic reviews in some subtopics. This review can be an evidence-based guide for implementing the limited and relevant available data to resistance-trained athletes during periods of calorie restriction.

2. Materials and Methods

The work comprised a descriptive study, involving a narrative review, to answer the research question, “What are the dietary–nutritional recommendations for optimal fat loss in resistance-trained athletes?”. A structured search was carried out in the PubMed, Epitesmonikos and Scopus databases, using descriptors as the Medical Subjects Headings [MeSH], entry terms and natural vocabulary related to the aim of the study []. In addition, reference lists were used for further search of the selected papers for related references.

3. Energy Intake

To achieve weight loss, the implementation of an energy deficit is required, by reduction of the energy intake [EI] and/or an increase in caloric expenditure. The exercise activity thermogenesis [EAT] is one of the components of energy expenditure associated with physical activity-related energy expenditure [,]. The magnitude and duration of this energy deficit will determine the amount of weight loss []. The performance of resistance exercise prevents the loss of FFM during periods of caloric restriction [CR] []; however, resistance-trained athletes represent a population that already performs this type of training. Traditionally, the 3500 kcal [,] rule has been used, which postulates that after accumulating a weekly caloric deficit of 3500 kcal, 1 lb of BW [0.45 kg] is lost. However, this static mathematical model of weight loss has been repeatedly questioned since, among other issues, it does not necessarily account for the metabolic adaptations caused by the energy deficit itself [,,], nor the non-lipid fraction of the adipose tissue [,]. Hall et al. [] recently proposed the “rule of 55 kcal/day per pound of BW”. Hall et al. [] explain that a person who maintains a deficit of 500 kcal per day could reduce their weight by 9 lb [4 kg] in total over a year [500 kcal/day divided by 55 kcal/day/lb], reaching a plateau at 12 months. With this 55 kcal/day rule, Hall et al. indicate a dynamic relationship between diet calories and weight loss and presents a more realistic view of the challenges experienced by patients with obesity []. However, after an objective analysis, it can be seen that the caloric intake of these people increased in an unconscious manner over time [], due in part to the increased appetite experienced after the application of an energy deficit []. This fact, added to the physiological adaptations that reduce daily energy expenditure [], facilitates the appearance of the so-called plateau in weight loss. Some of these adaptations are highlighted in the review of Trexler et al. [], who concluded that after the implementation of a caloric deficit in order to lose fat, the body activates different mechanisms to minimize this weight loss. These include a reduction in daily energy expenditure [mainly due to the loss of body mass itself and the decrease in energy expenditure associated with physical activities other than exercise, the so-called non-exercise activity thermogenesis or NEAT], greater mitochondrial efficiency in the use of energy and changes in circulating hormone levels. Therefore, these factors should be considered, since, as the fat loss phase progresses, a lower caloric intake will be required to compensate for these adaptations. In aesthetic athletes, these adaptations are reduced, in part because these athletes are characterized by strict adherence to their diets [], and by increased daily energy expenditure through cardiovascular exercise throughout contest preparation [,,,,,,].

An important aspect to consider when determining the magnitude of the caloric deficit is the potential for more aggressive energy restriction to result in greater loss of FFM [], as indicated by the results of several case studies which showed greater retention of FFM with weekly weight losses of 0.5% [] than with losses of 0.7% [] or 1% of BW per week []. In the case of the latter study, the loss of FFM amounted to 42.8% of the total weight. These data are in line with the last two revisions of the nutritional recommendations for athletes during their preparation for a natural bodybuilding competition [,], for which slow weight losses were recommended in order to preserve the maximum amount of FFM, especially in the final stage of preparation, since, as the competitor reduces his or her FM, the risk of FFM loss increases when he or she is subjected to a caloric deficit [].