The ability of ketogenic low‐carbohydrate (CHO) high‐fat (K‐LCHF) diets to enhance muscle fat oxidation has led to claims that it is the ‘future of elite endurance sport’. There is robust evidence ...that substantial increases in fat oxidation occur, even in elite athletes, within 3–4 weeks and possibly 5–10 days of adherence to a K‐LCHF diet. Retooling of the muscle can double exercise fat use to ∼1.5 g min−1, with the intensity of maximal rates of oxidation shifting from ∼45% to ∼70% of maximal aerobic capacity. Reciprocal reductions in CHO oxidation during exercise are clear, but current evidence to support the hypothesis of the normalization of muscle glycogen content with longer‐term adaptation is weak. Importantly, keto‐adaptation may impair the muscle's ability to use glycogen for oxidative fates, compromising the use of a more economical energy source when the oxygen supply becomes limiting and, thus, the performance of higher‐intensity exercise (>80% maximal aerobic capacity). Even with moderate intensity exercise, individual responsiveness to K‐LCHF is varied, with extremes at both ends of the performance spectrum. Periodisation of K‐LCHF with high CHO availability might offer opportunities to restore capacity for higher‐intensity exercise, but investigations of various models have failed to find a benefit over dietary approaches based on current sports nutrition guidelines. Endurance athletes who are contemplating the use of K‐LCHF should undertake an audit of event characteristics and personal experiences to balance the risk of impaired performance of higher‐intensity exercise with the likelihood of an unavoidable depletion of carbohydrate stores.
figure legend CHO ox: rate of carbohydrate oxidation; CPT: carnitine palmitoyltransferase; Fat ox: rate of fat oxidation; FAT/CD36: Fatty Acid Translocase; GNG = gluconeogenesis; Glycogen: concentration of muscle glycogen; HSL: hormone sensitive lipase; IMTG: concentration of intramuscular triglyceride; Max: maximal; O2:oxygen; PDHa: active form of Pyruvate Dehydrogenase; ↔: remains the same; ↔: remains the same but with a variable response; ↑: is increased; ↓: is decreased.
During the period 1985–2005, studies examined the proposal that adaptation to a low-carbohydrate (<25 % energy), high-fat (>60 % energy) diet (LCHF) to increase muscle fat utilization during exercise ...could enhance performance in trained individuals by reducing reliance on muscle glycogen. As little as 5 days of training with LCHF retools the muscle to enhance fat-burning capacity with robust changes that persist despite acute strategies to restore carbohydrate availability (e.g., glycogen supercompensation, carbohydrate intake during exercise). Furthermore, a 2- to 3-week exposure to minimal carbohydrate (<20 g/day) intake achieves adaptation to high blood ketone concentrations. However, the failure to detect clear performance benefits during endurance/ultra-endurance protocols, combined with evidence of impaired performance of high-intensity exercise via a down-regulation of carbohydrate metabolism led this author to dismiss the use of such fat-adaptation strategies by competitive athletes in conventional sports. Recent re-emergence of interest in LCHF diets, coupled with anecdotes of improved performance by sportspeople who follow them, has created a need to re-examine the potential benefits of this eating style. Unfortunately, the absence of new data prevents a different conclusion from being made. Notwithstanding the outcomes of future research, there is a need for better recognition of current sports nutrition guidelines that promote an individualized and periodized approach to fuel availability during training, allowing the athlete to prepare for competition performance with metabolic flexibility and optimal utilization of all muscle substrates. Nevertheless, there may be a few scenarios where LCHF diets are of benefit, or at least are not detrimental, for sports performance.
Abstract It is the position of the Academy of Nutrition and Dietetics (Academy), Dietitians of Canada (DC), and the American College of Sports Medicine (ACSM) that the performance of, and recovery ...from, sporting activities are enhanced by well-chosen nutrition strategies. These organizations provide guidelines for the appropriate type, amount, and timing of intake of food, fluids, and supplements to promote optimal health and performance across different scenarios of training and competitive sport. This position paper was prepared for members of the Academy, DC, and ACSM, other professional associations, government agencies, industry, and the public. It outlines the Academy’s, DC’s, and ACSM’s stance on nutrition factors that have been determined to influence athletic performance and emerging trends in the field of sports nutrition. Athletes should be referred to a registered dietitian nutritionist for a personalized nutrition plan. In the United States and in Canada, the Certified Specialist in Sports Dietetics is a registered dietitian nutritionist and a credentialed sports nutrition expert.
Current sports nutrition guidelines recommend that athletes only take supplements following an evidence-based analysis of their value in supporting training outcomes or competition performance in ...their specific event. While there is sound evidence to support the use of a few performance supplements under specific scenarios (creatine, beta-alanine, bicarbonate, caffeine, nitrate/beetroot juice and, perhaps, phosphate), there is a lack of information around several issues needed to guide the practical use of these products in competitive sport. First, there is limited knowledge around the strategy of combining the intake of several products in events in which performance benefits are seen with each product in isolation. The range in findings from studies involving combined use of different combinations of two supplements makes it difficult to derive a general conclusion, with both the limitations of individual studies and the type of sporting event to which the supplements are applied influencing the potential for additive, neutral or counteractive outcomes. The repeated use of the same supplement in sports involving two or more events within a 24-h period is of additional interest, but has received even less attention. Finally, the potential for individual athletes to respond differently, in direction and magnitude, to the use of a supplement seems real, but is hard to distinguish from normal day to day variability in performance. Strategies that can be used in research or practice to identify whether individual differences are robust include repeat trials, and the collection of data on physiological or genetic mechanisms underpinning outcomes.
Throughout the sport-science and sports-medicine literature, the term "elite" subjects might be one of the most overused and ill-defined terms. Currently, there is no common perspective or ...terminology to characterize the caliber and training status of an individual or cohort. This paper presents a 6-tiered Participant Classification Framework whereby all individuals across a spectrum of exercise backgrounds and athletic abilities can be classified. The Participant Classification Framework uses training volume and performance metrics to classify a participant to one of the following: Tier 0: Sedentary; Tier 1: Recreationally Active; Tier 2: Trained/Developmental; Tier 3: Highly Trained/National Level; Tier 4: Elite/International Level; or Tier 5: World Class. We suggest the Participant Classification Framework can be used to classify participants both prospectively (as part of study participant recruitment) and retrospectively (during systematic reviews and/or meta-analyses). Discussion around how the Participant Classification Framework can be tailored toward different sports, athletes, and/or events has occurred, and sport-specific examples provided. Additional nuances such as depth of sport participation, nationality differences, and gender parity within a sport are all discussed. Finally, chronological age with reference to the junior and masters athlete, as well as the Paralympic athlete, and their inclusion within the Participant Classification Framework has also been considered. It is our intention that this framework be widely implemented to systematically classify participants in research featuring exercise, sport, performance, health, and/or fitness outcomes going forward, providing the much-needed uniformity to classification practices.
New Findings
What is the topic of this review?
The nutritional strategies that athletes use during competition events to optimize performance and the reasons they use them.
What advances does it ...highlight?
A range of nutritional strategies can be used by competitive athletes, alone or in combination, to address various event‐specific factors that constrain event performance. Evidence for such practices is constantly evolving but must be combined with understanding of the complexities of real‐life sport for optimal implementation.
High‐performance athletes share a common goal despite the unique nature of their sport: to pace or manage their performance to achieve the highest sustainable outputs over the duration of the event. Periodic or sustained decline in the optimal performance of event tasks, involves an interplay between central and peripheral phenomena that can often be reduced or delayed in onset by nutritional strategies. Contemporary nutrition practices undertaken before, during or between events include strategies to ensure the availability of limited muscle fuel stores. This includes creatine supplementation to increase muscle phosphocreatine content and consideration of the type, amount and timing of dietary carbohydrate intake to optimize muscle and liver glycogen stores or to provide additional exogenous substrate. Although there is interest in ketogenic low‐carbohydrate high‐fat diets and exogenous ketone supplements to provide alternative fuels to spare muscle carbohydrate use, present evidence suggests a limited utility of these strategies. Mouth sensing of a range of food tastants (e.g., carbohydrate, quinine, menthol, caffeine, fluid, acetic acid) may provide a central nervous system derived boost to sports performance. Finally, despite decades of research on hypohydration and exercise capacity, there is still contention around their effect on sports performance and the best guidance around hydration for sporting events. A unifying model proposes that some scenarios require personalized fluid plans while others might be managed by an ad hoc approach (ad libitum or thirst‐driven drinking) to fluid intake.
Caffeine and sports performance Burke, Louise M
Applied physiology, nutrition, and metabolism,
12/2008, Letnik:
33, Številka:
6
Journal Article
Recenzirano
Athletes are among the groups of people who are interested in the effects of caffeine on endurance and exercise capacity. Although many studies have investigated the effect of caffeine ingestion on ...exercise, not all are suited to draw conclusions regarding caffeine and sports performance. Characteristics of studies that can better explore the issues of athletes include the use of well-trained subjects, conditions that reflect actual practices in sport, and exercise protocols that simulate real-life events. There is a scarcity of field-based studies and investigations involving elite performers. Researchers are encouraged to use statistical analyses that consider the magnitude of changes, and to establish whether these are meaningful to the outcome of sport. The available literature that follows such guidelines suggests that performance benefits can be seen with moderate amounts (~3 mg·kg
-1
body mass) of caffeine. Furthermore, these benefits are likely to occur across a range of sports, including endurance events, stop-and-go events (e.g., team and racquet sports), and sports involving sustained high-intensity activity lasting from 1-60 min (e.g., swimming, rowing, and middle and distance running races). The direct effects on single events involving strength and power, such as lifts, throws, and sprints, are unclear. Further studies are needed to better elucidate the range of protocols (timing and amount of doses) that produce benefits and the range of sports to which these may apply. Individual responses, the politics of sport, and the effects of caffeine on other goals, such as sleep, hydration, and refuelling, also need to be considered.
Celotno besedilo
Dostopno za:
DOBA, FSPLJ, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Key points
Three weeks of intensified training and mild energy deficit in elite race walkers increases peak aerobic capacity independent of dietary support.
Adaptation to a ketogenic low ...carbohydrate, high fat (LCHF) diet markedly increases rates of whole‐body fat oxidation during exercise in race walkers over a range of exercise intensities.
The increased rates of fat oxidation result in reduced economy (increased oxygen demand for a given speed) at velocities that translate to real‐life race performance in elite race walkers.
In contrast to training with diets providing chronic or periodised high carbohydrate availability, adaptation to an LCHF diet impairs performance in elite endurance athletes despite a significant improvement in peak aerobic capacity.
We investigated the effects of adaptation to a ketogenic low carbohydrate (CHO), high fat diet (LCHF) during 3 weeks of intensified training on metabolism and performance of world‐class endurance athletes. We controlled three isoenergetic diets in elite race walkers: high CHO availability (g kg−1 day−1: 8.6 CHO, 2.1 protein, 1.2 fat) consumed before, during and after training (HCHO, n = 9); identical macronutrient intake, periodised within or between days to alternate between low and high CHO availability (PCHO, n = 10); LCHF (< 50 g day−1 CHO; 78% energy as fat; 2.1 g kg−1 day−1 protein; LCHF, n = 10). Post‐intervention, V̇O2 peak during race walking increased in all groups (P < 0.001, 90% CI: 2.55, 5.20%). LCHF was associated with markedly increased rates of whole‐body fat oxidation, attaining peak rates of 1.57 ± 0.32 g min−1 during 2 h of walking at ∼80% V̇O2 peak . However, LCHF also increased the oxygen (O2) cost of race walking at velocities relevant to real‐life race performance: O2 uptake (expressed as a percentage of new V̇O2 peak ) at a speed approximating 20 km race pace was reduced in HCHO and PCHO (90% CI: −7.047, −2.55 and −5.18, −0.86, respectively), but was maintained at pre‐intervention levels in LCHF. HCHO and PCHO groups improved times for 10 km race walk: 6.6% (90% CI: 4.1, 9.1%) and 5.3% (3.4, 7.2%), with no improvement (−1.6% (−8.5, 5.3%)) for the LCHF group. In contrast to training with diets providing chronic or periodised high‐CHO availability, and despite a significant improvement in V̇O2 peak , adaptation to the topical LCHF diet negated performance benefits in elite endurance athletes, in part due to reduced exercise economy.
Key points
Three weeks of intensified training and mild energy deficit in elite race walkers increases peak aerobic capacity independent of dietary support.
Adaptation to a ketogenic low carbohydrate, high fat (LCHF) diet markedly increases rates of whole‐body fat oxidation during exercise in race walkers over a range of exercise intensities.
The increased rates of fat oxidation result in reduced economy (increased oxygen demand for a given speed) at velocities that translate to real‐life race performance in elite race walkers.
In contrast to training with diets providing chronic or periodised high carbohydrate availability, adaptation to an LCHF diet impairs performance in elite endurance athletes despite a significant improvement in peak aerobic capacity.
Postexercise muscle glycogen resynthesis in humans Burke, Louise M; van Loon, Luc J C; Hawley, John A
Journal of applied physiology (1985),
2017-May-01, 2017-05-01, 20170501, Letnik:
122, Številka:
5
Journal Article
Recenzirano
Odprti dostop
Since the pioneering studies conducted in the 1960s in which glycogen status was investigated using the muscle biopsy technique, sports scientists have developed a sophisticated appreciation of the ...role of glycogen in cellular adaptation and exercise performance, as well as sites of storage of this important metabolic fuel. While sports nutrition guidelines have evolved during the past decade to incorporate sport-specific and periodized manipulation of carbohydrate (CHO) availability, athletes attempt to maximize muscle glycogen synthesis between important workouts or competitive events so that fuel stores closely match the demands of the prescribed exercise. Therefore, it is important to understand the factors that enhance or impair this biphasic process. In the early postexercise period (0-4 h), glycogen depletion provides a strong drive for its own resynthesis, with the provision of CHO (~1 g/kg body mass) optimizing this process. During the later phase of recovery (4-24 h), CHO intake should meet the anticipated fuel needs of the training/competition, with the type, form, and pattern of intake being less important than total intake. Dietary strategies that can enhance glycogen synthesis from suboptimal amounts of CHO or energy intake are of practical interest to many athletes; in this scenario, the coingestion of protein with CHO can assist glycogen storage. Future research should identify other factors that enhance the rate of synthesis of glycogen storage in a limited time frame, improve glycogen storage from a limited CHO intake, or increase muscle glycogen supercompensation.
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