Fasting in Judo—Between Healthy Weight Control and Health Hazard: A Narrative Review

Abstract

Rapid weight loss strategies and weight cycling (losing and gaining weight repeatedly) are acknowledged problems in sports with weight categories, including judo. Extreme fasting, especially if combined with dehydration and intense physical exercise, may harm health and development, particularly those of children and teenagers engaging in judo competitions. However, there is substantial evidence for positive health effects of other forms of fasting. Here, we aim to provide an updated overview of the potential health risks associated with extreme dietary strategies in judo and contrast them with health-promoting fasting approaches. We conclude that the literature on the long-term health consequences of fasting in judo is scarce. This applies specifically to its potential association with eating disorders. Although many reports have highlighted the short-term risks of rapid weight loss, vulnerability and protection factors remain poorly understood. Rigorous scientific studies are needed to disentangle the factors that render fasting in judo healthy or unhealthy, considering both physical and mental health. We argue that a better understanding of weight management in judo is crucial to preventing health risks and designing healthy weight loss strategies, especially for young athletes.

1. Introduction

Kodokan judo, commonly known as judo, is a martial art originating from Japan and conceptualized and promoted by its founder Jigoro Kano. It is based on two primary principles, (i) the maximum efficient use of energy and (ii) mutual welfare and benefits [1]. Since World War II, judo has largely evolved towards becoming an Olympic combat sport and is now one of the most practiced combat sports worldwide [2]. Judo training often focuses on competitive purposes. However, an increasing number of practitioners value the diversity of judo training because of its health-promoting potential. This presented an important goal for Kano, who conceived of judo as a means to promote physical, coordinative, intellectual, and educational development [2]. Judo practice provides numerous emotional, psychological, and social benefits [2] but also promotes physical health by strengthening the skeletal system [3,4,5,6], appendicular muscle mass [3], and heart [7]. It also improves several aspects of metabolism, such as glucose and lipid metabolism [8]. Furthermore, increased gray matter tissue density in some brain areas, including regions in the frontal, parietal, and occipital lobes, compared to healthy controls in elite judo athletes has been reported [9]. Judo practitioners also had better postural and balance control compared not only to subjects not experienced in any sport involving equilibrium but also to dancers, even [10,11,12]. In addition, long-term judo training is thought to positively modulate neuroplasticity, based partly on its potential to modify lateral preferences [13]. Nevertheless, the vast majority of studies on judo have focused on it as a competitive sport. Research on the potential of judo to improve health and healthy aging remains scarce.

These potential health benefits contrast with the risks of competitive judo. A focus on competitive achievements and success may increase mental stress, promote specialization in competition-centered techniques and training modes, and increase the risk of injuries [2,14]. Furthermore, such focus may lead to unhealthy dietary habits, including rapid weight loss, because of the desire to stay in or change to reach a specific weight category. Whether and how these habits relate to the development of eating disorders and other lasting physical or mental health consequences remains poorly investigated. Also, the potential benefits resulting from periods of fasting and strict weight control in judo have rarely been explored. Nevertheless, awareness and knowledge of these aspects are crucial to identifying and avoiding unhealthy dietary habits. Such knowledge might also allow for reaping hitherto untapped health benefits from periodic fasting in judo, representing a form of “intermittent fasting”. In intermittent fasting—per definition—the timing of eating is restricted and interspersed with short-term fasts with the aim of improving health and specifically body composition and metabolism [15,16]. Different types of intermittent fasting are currently receiving great scientific interest, partly because they have been shown to reduce morbidity and mortality [17] and—in animal models—increase longevity [18]. In addition, intermittent fasting may be used to reduce body weight, theoretically, without marked reductions in performance and with potential long-term benefits related to body composition and power [19]. Thus, forms of intermittent fasting may represent healthy alternatives for weight control in judo. Certainly, these alternatives reduce weight more slowly than the approaches commonly applied to achieve rapid weight loss in judo. Regarding the prevention of detrimental outcomes of weight loss strategies in judo, the primary focus should be on the prevention of eating disorders. This is especially important in the context of youth development and the loss of promising junior athletes, which may be linked to pressure to adopt unhealthy lifestyles. Similar considerations apply to many sports other than judo, including many combat sports with weight categories, e.g., Brazilian jiu-jitsu [20], wrestling [21], taekwondo and karate [22], and a large number of other weight-sensitive sport disciplines (inter alia, because of direct weight requirements, esthetics, or advantages in terms of endurance). In such sports, an increased prevalence of eating disorders and disordered eating has been reported, especially for female athletes, but male athletes, for whom the consequences of unhealthy weight management strategies are even more poorly understood, may also be affected [23,24,25].

It is the purpose of this review to discuss the health-risks associated with fasting (rapid weight loss, weight cycling, and chronic weight control), specifically in competitive judo. Furthermore, we aim to highlight potential benefits related to the health-promoting effects of (intermittent) fasting. We intend to offer suggestions to judo athletes desiring to lose weight in a healthy way.

2. The Metabolic and Cardiovascular Benefits of Judo

Regular physical activity offers well-established health benefits, in particular related to metabolism and the cardiovascular system. It also partially protects against many chronic diseases [26]. Martial arts practice, in particular, exerts potential beneficial effects on balance, cognitive function, and psychological health [27]. Accordingly, regular judo practice appears to be associated with marked health benefits, including high physical fitness [28,29,30] and improved heart structure/function corresponding to high aerobic and anaerobic performance [31]. Moreover, it has been suggested to positively influence psychological and social development in children and teenagers [2]. Judo’s exceptional flexibility and modularity allow it to be practiced safely by all age classes, and it can be adjusted to individual/specific needs [2]. This is important when determining the appropriate levels of intensity and risks, especially when considering judo for recreational or health-promoting purposes.

Judo practice and competition require that athletes repeatedly and quickly overcome the body mass and resistance of their opponents, both statically and dynamically. The breaks between fighting phases and combat are relatively short, further increasing its metabolic and physical challenges. The high mean heart rates of around 85–90% of maximal heart rates measured during judo contests reflect the great energy expenditure associated with competitive judo [32,33]. Hence, judo is a sport with high demands on maximal and explosive strength, endurance, and metabolism in both the aerobic and anaerobic domains [31,34]. The anaerobic power and capacity of the upper body represent a determining factor for competitive success in judo [28,35]. Nevertheless, the oxidative system’s contribution to energy metabolism (about 70%) is high throughout judo matches when compared to the anaerobic glycolytic (8%) and ATP–Phosphocreatine (21%) systems’ contributions [34]. Still, one study that investigated the energy metabolism requirements of judo competitions found that lactate levels, a marker of anaerobic energy metabolism, rose to a mean of 12.3 ± 1.8 mmol/L in venous blood samples obtained from 16 national judo athletes post-contest [36]. In addition, their blood triglyceride, free fatty acid, and glycerol levels were significantly, but transiently, increased [36]. Their ammonia, hypoxanthine, xanthine, and urea levels showed similar increases [36]. These observations reflect a high reliance on protein and lipid metabolism during judo contests, which might be related to metabolic stress, training adaptation, and carbohydrate availability [36]. The consequences of pre-contest weight loss behaviors may contribute to these effects. Moreover, the specific biomechanical demands of judo have been suggested as important osteogenic stimuli, increasing bone metabolism and density [37]. An overview of its metabolic and physiological demands is provided in Figure 1.

In summary, high-level competitive judo athletes frequently have exceptional dynamic strength, muscular endurance, and both anaerobic and aerobic power and capacity [28,29]. These high metabolic and physiological demands may be linked to potentially favorable utilization of diverse nutrients for energy metabolism [38]. This could represent an additional, specific health benefit of judo, but this requires further elucidation.

3. Health Benefits of Fasting

Different types of fasting are used for various purposes. These include religious practices (Ramadan and other types of religious fasting), sociological or health reasons (e.g., desired weight reduction or a better body shape), and reasons related to competitive success in sports, such as being admitted into a desired lower weight category [15,39]. Fasting may be based on caloric restriction or intermittent patterns of food consumption.

Intermittent fasting is used as an umbrella term for a variety of methods of short-term energy deprivation, with phases of fasting that often last several hours (usually 12 h or more). During these phases, commonly, only liquids such as water or unsweetened tea are consumed. Such phases are alternated with periods in which food can be eaten with or without additional restrictions [15,40]. Well-designed forms of intermittent fasting have been shown to be beneficial in particular for cardiovascular and metabolic (e.g., lipid and glucose metabolism) health but in general have great, yet insufficiently explored, health potential [16,41,42,43]. Rapid weight loss strategies and pronounced dehydration are regularly applied by judo athletes and are frequently associated with compromised performance [44,45]. This may be mitigated or entirely prevented when using personalized intermittent fasting approaches [19] or when fasting periodically, such as during Ramadan, as long as the training load and energy levels are monitored [46,47]. Intermittent fasting, as opposed to continuous energy restriction, includes different sub-types, such as time-restricted eating (TRE), in which the daily window for caloric intake is typically about 6–12 h; short-term fasting; and alternate-day fasting. According to a recent network meta-analysis [39], among these approaches, alternate-day fasting is the most efficient approach for short-term (1–3 months) reductions in body weight, while TRE appears to be relatively more effective in reducing fasting glucose levels. Short-term fasting, with limitations in daily energy intake to about 25% for 2–3 consecutive or non-consecutive days of the week, led to the greatest short-term loss of lean body weight. These approaches are more effective when sustained over a longer period (>6 months) and less susceptible to the weight regain effects that commonly occur in response to continuous energy restriction approaches after approximately 4 months [39]. Huang and colleagues found that long-term TRE (7–12 months) was the most effective strategy among those investigated for achieving weight loss [39]. Therefore, it may be a valuable nutritional strategy for ultimately optimizing body composition and maintaining physical performance. These benefits may also apply to athletes aiming to reduce their weight with a limited loss of lean body mass and while maintaining their performance and training intensity [19,48]. A recent umbrella review by Sun et al. [16] concluded that intermittent fasting is a potent tool for reducing waist circumference, fat mass, fasting insulin, and systolic blood pressure while permitting increases in one’s fat-free mass and optimizing one’s lipid profile. In addition, intermittent fasting seems to benefit the gut microbiome by improving both the richness and diversity of the gut microbiota [49].

A few studies on judo athletes exist that looked into intermittent fasting in conjunction with Ramadan, while the literature on other religious fasting practices is scarce. During the month of Ramadan, athletes abstained from eating and drinking from sunrise to sunset according to the religious recommendations of Islam [47,50,51,52,53]. These athletes were largely able to maintain their normal training loads [47,50,51,52,53]. However, the results of these studies were inconsistent as far as performance is concerned [47,52,54]. In 15 elite junior judo athletes, intermittent fasting during Ramadan substantially changed their lipid profiles and hematological, inflammatory, and immunological outcomes, albeit these values generally remained within the normal reference ranges [50,51].

In conclusion, carefully executed types of intermittent fasting do not compromise performance, metabolism, and general health. Important factors for maintained performance during intermittent fasting include the avoidance of nutrient deficiencies and severe dehydration, as well as adequate coordination of fasting intervals with periods of vigorous exercise. Personalized fasting interventions can be efficient strategies for reducing body fat while maintaining fat-free body mass or muscle mass, thus improving body composition. Overall, such dietary approaches represent opportunities to optimize weight loss and performance in sports with weight categories, such as judo. Importantly, there are considerable health risks when combining fasting with dehydration and physical exertion in order to achieve rapid weight loss [19,55,56].

4. Judo, Unhealthy Dietary Strategies, and Eating Disorders

Official (International Judo Federation (IJF)) judo competitions for seniors (adults) are conducted with seven female and seven male weight categories. The lowest senior female weight category is −48 kg, and the lowest male weight category is −60 kg. Senior female athletes heavier than 78 kg and male athletes heavier than 100 kg compete in weight categories without an upper weight limit. Adapted weight categories exist for other age groups. Most competitively active judo athletes tend to reduce their body weight in just a few days immediately preceding competition. The purpose is to remain just under the upper limit of their weight category to obtain competitive advantages over lighter adversaries [22,57,58]. They use either long-term or rapid weight loss practices for this purpose [59]. A similar organization of weight categories also exists in many other combat sports [45]. In the following sections, we summarize the current state of the research on weight management strategies in judo, evaluating whether they may be associated with the development of eating disorders.

4.1. Methods

To provide an overview and analysis of the available literature on the risks and prevalence of eating disorders in conjunction with weight loss strategies in judo, we performed a literature search in PubMed, Google Scholar, Scopus, and CINAHL. We used the search terms “judo” AND “eating disorders” and considered all entries up to 9 October 2024. Original research and review articles were included in our analysis if eating disorders specifically in judo athletes were investigated or discussed. The majority of the results did not provide direct insights into eating disorders in judo players. These were excluded from further consideration for this paper unless important information on weight management in judo could be identified.

4.2. Rapid Weight Loss in Judo

It has been estimated that about 60–90% of combat sports athletes [45] use methods for weight loss, such as intensive exercise, reduced fluid intake, fasting (including reduced carbohydrate/fat intake and not eating at all the day before weigh-in), saunas, dedicated clothing, diuretics, laxatives, and purgative behaviors/vomiting [21,60,61,62,63]. Rapid weight loss refers to using such practices with the goal of losing weight (on average about 2–10% of one’s body weight) within approximately 1 week before a contest to compete in a lower weight class [60]. Judo athletes often start to use rapid weight loss strategies at an early age [45,64]. One study indicated that by the age of 13 years, 74% of judo athletes engage in rapid weight loss practices before competitions [65]. Most athletes use rapid weight loss methods to reduce their body weight by about 2–5%, but many also occasionally lose 5–10% and some more than 10%, with more severe weight loss being more common in elite athletes [45,64,66]. Usually, weight loss for a pre-competition weigh-in to compete in the lowest weight category possible is followed by post-competition weight regain. Then, one’s weight has to be decreased again for later competitions. Such patterns are called “weight cycling” [66,67]. While such practices may produce competitive advantages (by allowing athletes to compete in a lower weight category), they are also associated with health risks and, for extreme approaches, potentially even death, as reported in the 90s for three college wrestlers [68].

Nevertheless, the impact of rapid weight loss on performance is debated [69], and appropriate fasting strategies might even lead to metabolic and general health benefits, as discussed in Section 3. In addition, the association between weight loss and competitive success is difficult to establish due to the many confounding variables involved [59]. In terms of physiological or overall performance, Štangar and colleagues surveyed 138 elite-level female and male judo athletes and found 96% of them applied rapid weight loss methods, with 91% reporting negative effects of these methods on their energy levels, to the extent that 21% of them experienced a collapse period as a result of their weight loss practices [70]. In addition, Fortes et al. showed that rapid weight loss resulted in lower performance in a judo fitness test and concluded that rapid weight loss should not be used for performance optimization in judo [58].

In summary, rapid weight loss strategies are commonly applied in competitive judo, but how they affect performance remains poorly understood. In addition, severe forms of such approaches can pose threats to an athlete’s health.

4.3. Health Risks of Rapid Weight Loss in Judo

Weight loss in judo and other sport disciplines is often performed too rapidly [22], likely without sufficient adherence to nutritional guidelines. Such behaviors are associated with acute and chronic health risks [71]. In addition, in their meta-analysis, Chapa et al. [25] showed that athletes participating in sports with weight categories, such as judo, had higher levels of disordered eating.

An open question is whether weight loss habits in judo promote unhealthy dietary behavior and possible even facilitate the development of eating disorders. Eating disorders have been reported to be more prevalent in sports with weight categories than in the general population or other sports as a consequence of such athletes’ strong focus on weight [72,73,74]. Common eating disorders that are of relevance to athletes in weight-sensitive sports [23,25,75] include anorexia, bulimia, and binge-eating disorders. People with anorexia nervosa dramatically restrict their food intake and/or apply purgative behaviors. Bulimia nervosa describes behaviors of food restriction combined with compulsive binge-eating episodes and associated induced vomiting. Binge-eating disorders are characterized by regular episodes of ingesting greater amounts of food than normal and the perception of losing control over one’s own eating behaviors [76]. The surprisingly small body of relevant literature on the topic of disordered eating or eating disorders in judo athletes is summarized below in the context of the potentially adverse health consequences of rapid weight loss.

Rapid weight loss can cause diverse symptoms, including impairments in memory, concentration, and vigor but also feelings of confusion, rage, and depression, and it can lead to fatigue [45]. Furthermore, the perceptual motor skill performance [77], decision making [78], and mood [79] of judo athletes may be negatively affected by rapid weight loss strategies. The acute health risks of rapid weight loss are mostly related to hypohydration, which generally can impair cardiovascular, cognitive, and motor function [44]. Fluid restriction and “sauna suits” remain often used tools for rapid weight reduction [70]. Accordingly, a prevalence of hypohydration of 89% in judo athletes on the morning of the competition day was reported in one study [80]. Over 50% of these athletes were seriously hypohydrated at their morning weigh-in [80]. Repeated dehydration in rapid weight loss has been associated with increased markers for acute kidney injury in wrestlers and thus may represent risk factors for the development of kidney injuries [60], although this remains to be confirmed. Also, impaired erythropoiesis and hormonal imbalances were reported to be induced by rapid weight loss in athletes in different combat sports [81,82]. An increase in muscle damage markers was observed following a combination of dietary restriction and intense exercise training for weight reduction before competition [83,84]. This suggests impaired muscular function and increased susceptibility of muscle tissue to injury [83,84].

Beyond the acute risks, some studies report potential psychopathological effects in response to rapid weight loss in judo athletes. Among these risks are the development of eating disorders, which may be increased as a consequence of repeated unhealthy rapid weight loss practices, particularly in women [85]. Rouveix and colleagues [86] found an overall low prevalence of manifest eating disorders in judo athletes using the Eating Attitudes Test (EAT-26). However, 25% of the female judo athletes tested (3 out of 12) were “at risk” of eating disorders according to this test [86]. Furthermore, the corresponding EAT-26 scores of the female judo athletes were strongly correlated with body esteem [86]. These results were accompanied by a substantially higher occurrence of menstrual dysfunction in the female judo athletes (58.3%) as compared to female controls (7.1%) [86]. In another study, rapid weight loss did not acutely affect the menstrual cycle but had negative consequences on development, e.g., reduced body growth, in juvenile female judo athletes [87].

Also using the EAT-26, Filaire and colleagues [88] observed a higher prevalence of disordered eating attitudes among judo athletes (30% vs. 20% in controls) in a small questionnaire-based study in 20 judo athletes and 25 controls. These authors reported a significant positive correlation of disordered eating attitudes with body dissatisfaction and negative correlations with stress tolerance, emotional self-awareness, and mood. Importantly, the EAT-26 has later been doubted to adequately reflect eating disorders in sports [22]. Escobar-Molina and co-authors [89] observed eating disorders and symptoms of anxiety in an observational, descriptive study conducted in 144 Spanish judo athletes, especially in young women. Besides the menstrual dysfunction mentioned, risks related to bone health have also been suggested to be associated with rapid weight loss in female judo athletes [90]. However, clear relationships remain to be established. Furthermore, judo practice appears to be linked to improved bone metabolism and density, possibly counteracting the potentially detrimental effects of rapid weight loss on bone health [37].

The long-term effects of rapid weight loss practices in combat sports have rarely been studied [91]. Maksimovic and colleagues recently found a higher prevalence of metabolic syndrome, higher systolic and diastolic blood pressure, increased values of fasting blood glucose, and trends of higher triglyceride levels in former elite combat sports athletes who had employed rapid weight loss strategies during their competitive careers compared to former elite athletes from other sports who had not [92]. They concluded that this group of athletes is susceptible to negative metabolic alterations at the end of the competitive period [92]. The combat sports in this study included judo, jiu-jitsu (jūjutsu), karate, kickboxing, taekwondo, and boxing [92].

Taken together, rapid weight loss might compromise capacities that determine performance and increase the probability of injuries. However, the long-term outcomes of the dietary strategies associated with weight management in judo (including the potential modulation of eating disorder development) have rarely been investigated and remain largely unknown. A summary of the health risks and performance effects of rapid weight loss in judo athletes is provided in

Table 1. Summary table of health risks and performance effects due to rapid weight loss in judo athletes.

Outcome	Reference	Year	Study Characteristics	Sample	Sport(s)
↑ Eating disorders	Chapa et al. [25]	2022	meta-analysis	56 studies	judo and others
↑ Eating disorders	Filaire et al. [88]	2007	questionnaire-based cross-sectional study	N = 12	judo
↑ Eating disorders and menstrual dysfunction	Rouveix et al. [86]	2007	questionnaire-based study (EAT-26)	women and men, N = 24	judo
↑ Eating disorders	Tayeb et al. [85]	2022	questionnaire-based study (RWL-Q and assessment of eating disorders)	women, N = 31	judo
Weight cycling	Artioli et al. [64]	2010	review	N/A	judo
Weight cycling	Artioli et al. [66]	2016	review	N/A	judo
Weight cycling	Franchini et al. [45]	2012	review	N/A	judo
↑ Mood swings	Lakicevic et al. [79]	2024	systematic review	six studies	judo
↓ Decision making skills	Fortes et al. [78]	2017	randomized cross-sectional study	men, N = 42	judo
↓ Motor skills	Morales et al. [77]	2018	cross-sectional study	women and men, N = 38	judo
↑ Anxiety and menstrual dysfunction	Escobar-Molina et al. [89]	2015	observational, descriptive study	N = 44	judo
Hypohydration	Petterson et al. [80]	2014	cross-sectional study	N = 32	judo and others
↓ Body growth	Yoshida et al. [87]	2024	questionnaire-based, cross-sectional survey	women	judo
↓ Bone health	Uchizawa et al. [90]	2022	review	N/A	judo
↑ Skeletal muscle damage	Umeda et al. [83]	2004	cross-sectional study	men, N = 27	judo
↑ Skeletal muscle damage	Roklicer et al. [84]	2020	cross-over study	men, N = 18	judo
↓ Performance (judo fitness test)	Fortes et al. [58]	2017	randomized cross-sectional study	N = 20	judo
Energy collapse	Štangar et al. [70]	2022	questionnaire-based survey	N = 138	judo
Hormonal disturbances	Degoutte et al. [81]	2006	randomized cross-sectional study	men, N = 20	judo
Negative metabolic effects	Maksimovic et al. [92]	2024	retrospective case–control study	N = 75	combat sports, incl. judo
Metabolic syndrome, ↑ fasting glucose, ↑ triglycerides, ↑ blood pressure (SBP and DBP)	Lebron et al. [91]	2024	review	N/A	combat sports, incl. judo

Notes. SBP: systolic blood pressure; DBP: diastolic blood pressure; EAT-26: Eating Attitudes Test; RWL-Q: Rapid Weight Loss Questionnaire; N/A: not applicable.

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5. Discussion and Perspectives

Despite the well-recognized problem of unhealthy weight loss strategies in judo, the literature on this topic is surprisingly scarce. Practical applications of scientific recommendations on this topic are largely lacking. Judo practitioners still frequently engage in unhealthy weight reduction behaviors. Consequently, they may suffer from the somatic consequences of repeated rapid weight loss and weight cycling and from associated psychological pressure, similar to what has been reported for other weight-sensitive sports. Adverse outcomes may comprise injuries (e.g., kidney injuries due to dehydration), loss of talent because of the pressure to lose weight before competitions, and the development of eating disorders. In the spirit of judo’s primary principles (the maximum efficient use of energy and mutual welfare/benefits), these problems need to be addressed. Maximum efficient use of energy should be considered not just in the application of judo techniques but also in the context of maintaining a healthy body weight and responsible health management in general. In respect of the mutual welfare and benefit principle, it is essential that athletes are educated regarding healthy weight control and have access to the necessary support structure. In contrast, many health benefits have been attributed to intermittent fasting strategies, ranging from the prevention of chronic diseases to reduced mortality from many causes (see Section 3).

The health risks of unhealthy dietary practices related to weight category sports include the development of eating disorders and, in extreme cases, have already led to lethal outcomes, e.g., in wrestlers [68]. To control and remedy extreme weight loss practices in judo—and combat sports in general—suggestions have included banning weight cutting altogether, tightening regulations with regards to weight loss practices, and reducing the gaps between the different weight classes [93]. Evidence supporting the effectiveness of such approaches is generally lacking [93]. Artioli et al. [57] proposed an aggressive weight management program that would require competitive judo athletes to pass a hydration test after weigh-in and suggested imposing minimal permissible body fat limits for eligibility to compete. Such strict regulations are difficult to impose and enforce. So, at the very least, dietary consultations and early screening for eating disorder symptoms should be prioritized to prevent progression to severe eating disorders and other mental, physical, and physiological consequences [67]. Early screening for eating disorders appears to be most crucial in young female athletes. However, although male athletes appear to have healthier strategies for coping with stress linked to weight reduction, it has to be emphasized that this topic has been insufficiently explored. It should also be considered that children/teenagers who quit judo at a young age may have taken this decision partially because of social/institutional pressure to engage in weight loss practices. However, further research on how often this happens is necessary. The few available studies on inadequate weight loss practices indicate the important pedagogical necessity to improve knowledge and decision making in judo and other weight category sports with regard to athletes’ eating and fasting behaviors [57,87]. Such strategies include organizing and emphasizing the importance of food and nutrition education, especially for young judo practitioners and those with specific medical conditions, as recently suggested [94], and the early detection of nutrient deficits via food consumption analysis. Role model effects through educational programs involving successful active or retired elite athletes may be harnessed to increase awareness. Direct advice from those (former) athletes based on their own positive and negative experiences during their competitive careers could be used to communicate problematic dietary behaviors and point out successful and healthy strategies, especially for young competitive judo athletes. Events enabling such exchange between young athletes and their role models have been shown to be highly appreciated by the participants [95]. Similarly, the discussion of fasting in weight class sports should be an educational goal of dedicated influencers.

Rapid weight loss practices already occur among young judo practitioners, sometimes due to pressure from parents [96] or institutions (e.g., clubs, including peers and coaches). Educational measures starting at an early age (for children, parents, and coaches) are thus necessary to inform them of the health consequences of extreme and/or repeated weight loss practices and to provide guidance for healthy weight control and long-term metabolic health [71]. Establishing minimum standards of qualification and experience for athletes, coaches, and other staff members should be of high priority. Especially when considering young competitors, it is important to promote a long-lasting career and a healthy life rather than early competitive success—in agreement with judo’s primary principles. In this context, the reorientation of performance goals towards achievement goals is important for a health-focused judo practice [14].

Considering the pronounced health potential of well-designed fasting strategies (see Section 3), a challenge for future research will be the modification of potentially dangerous weight-class-related weight cycling into health-promoting fasting strategies. Especially, clear guidelines considering the health risks associated with severe hypohydration as a result of rapid weight loss are urgently needed. The exploration of the systematic use of potentially health- and performance-enhancing applications of (intermittent) fasting might lead to new avenues that harness healthy dietary strategies for weight loss in judo and in weight-sensitive sports in general. In addition, they might include new efficient strategies for targeting obesity. There is a wealth of implicit knowledge on professional weight control in judo and other combat sports. It would appear wasteful to disregard all this knowledge and the motivation associated with competition-related body weight manipulation when exploring novel applications to efficiently counteract the spreading “obesity pandemic” [97]. The combination of exercise (for example, judo) with optimized weight management elements seems to be a particularly promising approach to reducing overweight and obesity.

5.1. Conclusions

Previous research findings about protective strategies against unhealthy weight loss in judo have not yet found broad application. We concur that extreme weight loss approaches, in particular in young athletes, should be prohibited and sanctioned. However, considering the lack of implementation of such suggestions until now, educational measures may be more successful. Also, new, practical, and feasible strategies need to be developed and implemented in order to provide support to athletes, who may wish to achieve a slight to moderate loss of body weight in a healthy way and avoid the severe dehydration and mental stress that often accompanies extreme weight loss goals. In addition, it may be possible to develop some of the (healthy) aspects of weight loss strategies used by judo players to address overweight/obesity in non-athletes.

5.2. Future Directions

The association between unhealthy weight management in judo and other weight category sports and the development of eating disorders has rarely been investigated. The available studies are mostly based on inadequate research tools (e.g., the EAT-26), include too many confounding variables (e.g., competition-linked stress, general dietary habits, etc.), or suffer from a poor research design. Examples of poor research designs notably include low sample sizes and a lack of controlled, randomized, and especially long-term studies. Therefore, a rigorous investigation of the acute and long-term positive and negative outcomes of weight management strategies in judo and the identification of the individual protective or vulnerability factors involved are essential (Figure 2). Such individual factors may include coping strategies, personal eating habits, microbiome composition, medical conditions, etc. In addition, educational strategies should be proposed and implemented to raise awareness and enhance the competencies of the individuals involved in making health-promoting decisions. Dietary counseling of athletes and adequate formation of coaches and other stakeholders or role model/mentor/influencer approaches are among the promising approaches for this purpose. It is equally important to effectively reduce societal and institutional pressure to pursue unhealthy dietary strategies.

In addition, we think that the existing knowledge on the weight management that is intrinsically present in judo has been insufficiently considered. Extracting and using such knowledge in a systematic way and supplementing it with evidence-based knowledge from novel research on intermittent fasting could lead to improved guidelines for those aiming to lose weight for the purpose of competing in a specified weight category and for people wishing to lose weight for other reasons.

In conclusion, the health outcomes of rapid weight loss and weight cycling in judo still remain insufficiently understood to date, although the research is continuously aiming to raise awareness of potentially associated health problems. We believe that conceptualizing weight management strategies from competitive judo for health-promoting purposes might benefit both athletes and eventually maybe also non-athletes in terms of them achieving their weight loss goals in a healthier manner.