The 4Rs Framework of Sports Nutrition: An Update with Recommendations to Evaluate Allostatic Load in Athletes

ition were proposed in recent years as an evidence-based framework to optimize post-exercise recovery within the context of allostasis. Under this paradigm, it is important to consider that each R represents a factor with a tremendous in- fluence on the allostatic response and improves individual components of the allostatic load (AL), which will positively impact the exercise-induced adaptations and the athlete’s recov- ery. The 4Rs correspond to the following. (i) Rehydration—This is necessary to guarantee the post-exercise consumption of at least 150% of the body mass lost during the exercise accompanied by sodium (if faster replacement is required). (ii) Refuel—Carbohydrate intake (~1.2 g/kg body mass per hour for up to 4 h post-exercise) is essential not only in restoring glycogen reserves but also in supporting the energy needs of the immune system and facilitating tissue repair. Despite changes in substrate utilization, a ketogenic diet generally has neutral or negative effects on athletic performance compared to carbohydrate- rich diets. (iii) Repair—The ingestion of high-quality protein stimulates post-exercise net muscle protein anabolism and might contribute to faster tissue growth and repair. The use of certain supplements, such as creatine monohydrate, might help to enhance recovery, while tart cherry, omega-3 fatty acids, and dietary nitrate (e.g.,Beta vulgaris,Amaranthus L.), as well as other herbal extracts containing flavonoid-rich polyphenols, deserve further clinical research. (iv) Recuperate—Pre-sleep nutrition (casein- or protein-rich meal with slow digestion rate) has a restorative effect, facilitating the recovery of the musculoskeletal, endocrine, immune, and nervous systems. In this article, we update the 4Rs framework, Life2025,15, 867 https://doi.org/10.3390/life15060867

(e.g.,Beta vulgaris,Amaranthus L.), as well as other herbal extracts containing flavonoid-rich polyphenols, deserve further clinical research. (iv) Recuperate—Pre-sleep nutrition (casein- or protein-rich meal with slow digestion rate) has a restorative effect, facilitating the recovery of the musculoskeletal, endocrine, immune, and nervous systems. In this article, we update the 4Rs framework, Life2025,15, 867 https://doi.org/10.3390/life15060867

Life2025,15, 867 2 of 31 delve deeper into the allostasis paradigm, and offer theoretical foundations and practi- cal recommendations (the 4Rs app) for the assessment of AL in athletes. We cautiously propose an AL index (AL index) for physique competitors and elite athletes to evaluate the cumulative physiological stress induced by exercise and, thereby, to adjust exercise and nutrition interventions. Keywords:allostasis; sports nutritional sciences; physiological adaptation; biomarkers; cacostasis 1. Introduction to the 4Rs Framework of Sports Nutrition To better understand the nutritional strategies that influence post-exercise recovery, the 4Rs—Rehydrate, Refuel, Repair, and Rest—was proposed as an operational framework for sports nutrition by Bonilla et al. (2020) [1]. These four Rs do not attempt to replace existing techniques or construct a new, rigid paradigm in this regard, but rather seek to introduce the strategic application of nutritional strategies that should be considered during the recovery process in athletes (Figure). In practice, “Recuperate” might be considered a broader term that includes not only passive recovery (e.g., sleep) but also active strategies to address fatigue accumulation, injury recovery, or mental relaxation in order to restore functionality [2]. Overall, the Rest/Recuperate component highlights the importance of downtime to repair tissue and restore energy, including passive and active strategies depending on the athlete’s situation. Figure 1.The 4Rs framework of sports nutrition. Source: designed by the authors (D.A.B.).

Life2025,15, 867 3 of 31 This approach divides the nutrition intervention into four interrelated scenarios that follow the post-exercise time course to optimize the exercise-induced adaptations and recovery. Available clinical evidence and recommendations by professional organizations support the structure of the 4Rs framework, as shown in Table. Table 1.Clinical evidence and recommendations by professional organizations on the 4Rs. 4Rs Practical Recommendation Clinical Evidence * Professional Organization Rehydration Fluid replacement is a fundamental nutritional strategy that depends on the athlete’s needs, the environment, and the specific sports event. Adequate rehydration involves ~1.5 L per kg of body mass lost post-exercise, with electrolytes (mainly sodium) and carbohydrates (<6%w/v) to promote faster recovery. •López-Torres et al. (2023) [3] •Pérez-Castillo et al. (2023) [4] •Rowlands et al. (2022) [5] •Zubac et al. (2019) [6] •Holland et al. (2017) [7] •IOC (2023) [8] •GSSI (2023) [9] •UEFA (2021) [10] •DGE (2020) [11] •SDA (2020) [12] •ISSN (2018) [13] •NATA (2017) [14] •ACSM (2007) [15] Refuel Carbohydrate intake (~1.2 g/kg body mass per hour for up to 4 h post-exercise) is essential not only in restoring glycogen reserves but also in supporting the energy needs of the immune system and facilitating tissue repair. Specifically, 20 g of creatine (5 g dose on four occasions beginning on the same day of fatiguing exercise) may promote muscle glycogen resynthesis in the first 24 h post-exercise. Despite changes in substrate utilization, a ketogenic diet generally has neutral or negative effects on athletic performance compared to carbohydrate-rich diets. •Cheng et al. (2025) [16] •Lehman et al. (2024) [17] •Ramos-Campo et al. (2024) [18] •Díaz-Lara et al. (2024) [19] •Koerich et al. (2023) [20] •Craven et al. (2021) [21] •Margolis et al. (2021) [22] •Nielsen et al. (2020) [23] •McCartney et al. (2018) [24] •Roberts et al. (2016) [25] •ISSN (2024) [26] •UEFA (2021) [10] •DGE (2020) [27] •DGE (2020) [28] •ISSN (2018) [13] •AND, DC, and ACSM (2016) [29] Repair Post-exercise ingestion of high-quality protein (0.3—0.5 g/kg body mass) and creatine monohydrate (0.1 g/kg body mass) supports tissue growth and repair. The potential of tart cherry, omega-3 fatty acids, dietary

al. (2018) [24] •Roberts et al. (2016) [25] •ISSN (2024) [26] •UEFA (2021) [10] •DGE (2020) [27] •DGE (2020) [28] •ISSN (2018) [13] •AND, DC, and ACSM (2016) [29] Repair Post-exercise ingestion of high-quality protein (0.3—0.5 g/kg body mass) and creatine monohydrate (0.1 g/kg body mass) supports tissue growth and repair. The potential of tart cherry, omega-3 fatty acids, dietary nitrate (e.g.,Beta vulgaris,AmaranthusL.), and other herbal extracts containing flavonoid-rich polyphenols deserves further clinical research. •Pearson et al. (2023) [30] •Doma et al. (2022) [31] •Jones et al. (2022) [32] •Hill et al. (2021) [33] •Jiaming and Hossein (2021) [34] •Carey et al. (2021) [35] •Gao and Chilibeck (2020) [36] •Morton et al. (2018) [37] •ISSN (2025) [38] •DGE (2020) [39] •ISSN (2017) [40] •ISSN (2017) [41] •AND, DC, and ACSM (2016) [29]

Life2025,15, 867 4 of 31 Table 1.Cont. 4Rs Practical Recommendation Clinical Evidence * Professional Organization Rest/ Recuperate Optimal sleeping time and quality are necessary to benefit the allostatic response after exercise. Alcohol should be avoided due to its inhibitory influence on several aspects of recovery. Ideally, caffeine should not be consumed for up to 4 h before bed. Pre-sleep nutrition has a restorative effect, facilitating the recovery of the musculoskeletal, endocrine, immune, and nervous systems. Pre-sleep nutritional strategies include whey, casein, or protein-rich meals; >150 mg of aqueous ashwagandha root extract; cherries; kiwi fruit; fish oils (omega-3 PUFAs); and valerian. •Gardiner et al. (2024a) [42] •Gardiner et al. (2024b) [43] •Gong et al. (2024) [44] •Fatima et al. (2024) [45] •Trommelen et al. (2023) [46] •Reis et al. (2021) [47] •Dela Cruz and Kahan (2021) [48] •Cheah et al. (2021) [49] •Gratwicke et al. (2021) [50] •Walsh et al. (2021) [51] •Snijders et al. (2019) [52] •Barnes (2014) [53] •AASM (2021) [54] •ISSN (2017) [55] * Preference was given to meta-analytic evidence when available. ACSM: American College of Sports Medicine; AND: Academy of Nutrition and Dietetics; DC: Dietitians of Canada; DGE: Deutschen Gesellschaft für Ernährung—GermanNutrition Society; GSSI: Gatorade Sports Science Institute; IOC: International Olympic Committee; NATA: National Athletic Trainers’ Association; PUFAs: polyunsaturated fatty acids; SDA: Sports Dietitians Australia; UEFA: Union of European Football Associations. When the strategies outlined in the 4Rs framework are effectively implemented through consistent nutritional adherence and compliance, exercise-induced adaptations may be optimized. In fact, several research groups have recommended or used this ap- proach for the metabolomic and proteomic profiling of athletes [56], as a holistic view of nutrition and healing in injured athletes [57,58], as a working model that should be prioritized to understand physiological requirements and nutritional recommendations for equestrian riders [59], and during the promotion of health-related lifestyles among university students [60]. In this article, we delve into the allostasis paradigm as the foundation of the 4Rs framework and explore recommendations for the evaluation of allostatic load. We suggest an allostatic load index (AL index) for physique competitors and elite athletes to assess

requirements and nutritional recommendations for equestrian riders [59], and during the promotion of health-related lifestyles among university students [60]. In this article, we delve into the allostasis paradigm as the foundation of the 4Rs framework and explore recommendations for the evaluation of allostatic load. We suggest an allostatic load index (AL index) for physique competitors and elite athletes to assess the cumulative physiological stress induced by exercise. 2. Materials and Methods This review incorporated elements of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Extension for Scoping Reviews (PRISMA-ScR) [61]. It encom- passes the identification, selection, evaluation, and synthesis of available evidence in a narrative format. 2.1. Information Sources The primary sources for the articles included the following online databases: PubMed/MEDLINE, Web of Science, and Google Scholar. The comprehensive molec- ular biomarker database MarkerDB v2.0 (available at, accessed on 3 March 2025) was searched for experimentally verified biological markers in humans [62].

Life2025,15, 867 5 of 31 2.2. Search Strategy The search string included free terms such as “sports nutrition”, “allostasis”, “body composition”, “allostatic load”, “allostatic overload”, and “physiological adaptation”. Each term was combined with keywords such as long-term, chronic, acute, nutrition, exercise, recovery, athletes, and biomarkers. The reference lists of the selected articles were also manually searched for additional literature (snowballing). 2.3. Findings Presentation The authors collaborated remotely and contributed to the development of this arti- cle considering their standing and individual expertise in the field. Discrepancies were identified and resolved through discussion between authors where necessary. All com- munications and coordination throughout the process were completed electronically and were led by the first author. This article is organized into sections including (i) allostasis and adaptation; (ii) current approaches to biomarker monitoring in athletic populations; (iii) how to measure the allostatic load in athletes; and (iv) applied practice. Finally, future directions are presented to guide upcoming research in the field. 2.4. The 4Rs App To ensure effective translation into practice, the “4Rs app” was developed within the free software environment for statistical computing and graphics R v4.4.0 [63] and the Shiny package v1.10.0 [64]. The development of the app had four phases: (i) con- ceptual design, where the educational goals of the 4Rs in sports nutrition were defined (including the allostatic load index and a scorecard for dietary supplements); (ii) UI/UX prototyping, where a responsive interface using HTML, CSS, and Shiny widgets was built; (iii) back-end integration, to connect interactive logic with nutrition algorithms via R scripts and reactive modules; and (iv) testing and deployment, where we tested the output, applied thematic styles (The 4Rs Framework branding), and deployed it via https://www.shinyapps.io/ (DOI: 10.5281/zenodo.15377939). 3. Allostasis and Adaptation Stress is understood as the response to internal or external stimuli, referred to as stressors, which induce disruptions that exceed the usual physiological thresholds [65]. In simple terms, stress can be associated with a degree of perturbation within a biological system after exposure to a given stressor—this results in different stress types according to the type of perturbation, such as metabolic stress, psychological

as the response to internal or external stimuli, referred to as stressors, which induce disruptions that exceed the usual physiological thresholds [65]. In simple terms, stress can be associated with a degree of perturbation within a biological system after exposure to a given stressor—this results in different stress types according to the type of perturbation, such as metabolic stress, psychological stress, mechanical stress, etc. Complementarily, allostasis refers to a biological system’s ability to adapt to daily challenges through predictive adjustments to maintain viability [66,67]. It is worth noting that allostasis and homeostasis are complementary components of integrative physiological regulation [68,69]. Allostasis is an extension of homeostatic parameters from single stable states to variational and relationally stable states—to clarify any doubts regarding the current conceptualization of homeostasis and allostasis, readers may refer to the article “Conceptual Foundations of Physiological Regulation Incorporating the Free Energy Principle and Self-Organized Criticality” by Bettinger and Friston (2023) [70]. Within the allostasis–interoception framework [71–73], and considering sports nutri- tion as a working example, chronic stimuli such as energy restriction, exercise-induced stress, or sleep disruption associated with pre-competition anxiety (external and inter- nal stressors) can trigger systemic adaptations that recalibrate regulatory parameters to prioritize resource allocation towards activities that are critical for immediate survival (e.g., changes in substrate utilization, alterations in gene expression, exerkine regulations,

Life2025,15, 867 6 of 31 changes in mood and focus, etc.). These factors—individually or, more likely, collectively— influence athletic performance by contributing to maladaptation. As with any biological system, the human adaptation process needs two critical fac- tors: energy and time. The energy factor has recently been defined as “allostasis and stress-induced energy expenditure” by Bobba-Alves et al. (2022) [74]. In athletes, this con- sequently influences the total daily energy expenditure, as has been discussed for injured athletes [58,75]. This approach may also provide insights into individual responses during nutrition and exercise interventions, potentially explaining phenomena at different organi- zation levels, such as leptin pathway alterations, reductions in resting energy expenditure, menstrual cycle irregularities, and increased susceptibility to lean mass loss—all hallmarks of energy restriction-induced stress [76,77]. The time factor is connected to the restorative period required to repair tissue and to correct interoceptive prediction mistakes, as well as the many mechanisms that keep internal conditions within the new setpoint of adaptation. For example, this includes recovery periods between exercise sessions and adequate sleep for psycho- and physiological recuperation [1] (Figure). As a result, both energy and time factors influence each individual/population’s allostatic load, which can be described as the cost that a biological system must pay in order to reset its physiological parameters during the adaptation process [78]. Figure 2.The time course of exercise-induced adaptation. Transient changes in metabolite sensing and signaling during/after exercise drive the gene transcription of early genes; myogenic regula- tors; genes of carbohydrate metabolism, lipid mobilization, transport and oxidation, mitochondrial metabolism, and oxidative phosphorylation; and transcriptional regulators of gene expression and mitochondrial biogenesis. Source: designed by the authors (D.A.B.). Refer to Bonilla et al. (2020) [1] for further information. It is worth noting that Chrousos (2009) introduced the term cacostatis (“bad state”, from Ancient Greekκακóς[kakós], which means “bad”) to refer to this state of disharmony and the cacostatic load as the cumulative pathophysiological burden of the organism [79]. Following this etymological conceptualization, the beneficial adaptation that leads to the

(2009) introduced the term cacostatis (“bad state”, from Ancient Greekκακóς[kakós], which means “bad”) to refer to this state of disharmony and the cacostatic load as the cumulative pathophysiological burden of the organism [79]. Following this etymological conceptualization, the beneficial adaptation that leads to the

This article updates the 4Rs framework and offers recommendations for assessing allostatic load in athletes.