Should Protein Be Included in CHO-Based Sports Supplements?

PREVAILING VIEW There is presently no convincing scientific support for the contention that protein be included in CHO-based sports supplements. Before any such strategy can be truly advocated, published evidence should first reveal consistently positive effects on practically meaningful outcomes (i.e., performance) across multiple independent laboratories, ideally also isolating plausible mechanisms of action. With due consideration of the precise context and nature of these effects, I propose that a "worthwhile" nutritional supplement must fulfill at least one of the following interrelated criteria: true "supplementation" of the diet (i.e., either compensating for deficiencies or meeting increased requirements); supplement formulation facilitates digestion, absorption, and/or metabolism to more effectively deliver active ingredients than possible via whole foods; and/or optimal timing for supplement ingestion renders it impractical to acquire active ingredients via whole foods as a meal (e.g., effects are either short-lived or situation dependent). A relevant example to illustrate these contextual issues is CHO-based sports supplements per se (i.e., without added protein), the use of which is supported in a recent joint position statement (25) both because of the increased CHO requirements of many athletes beyond the typical diet and the efficacy of specially formulated CHO supplements, which are easily incorporated into athletes' preexercise, midexercise, or postexercise regimen (p. 719-21). In contrast, that same position statement attests that even the slightly elevated protein requirements of athletes are almost always met by diet alone and that "…protein or amino acid supplementation has not been shown to positively impact athletic performance…" (p. 715). The perspective set out below will therefore defend the prevailing view that CHO without protein should be included in sports supplements; initially by presenting the balance of published data that have yet to reveal any ergogenic or mechanistic benefit of added protein or amino acids during exercise, before questioning whether the positive effects evident in recovery can legitimately be interpreted as supporting any practical value of these supplements when considered in a real-world context (e.g., in the fed state and/or when following existing guidelines for CHO intake). Combined CHO-Protein Ingestion during Exercise Although some studies have shown ergogenic benefits when combined CHO-protein supplements are ingested during exercise (11,13,28-30), one of these actually reflects an alternative but ultimately no more effective choice of pacing strategy (30), and the majority of evidence on this topic conforms to the prevailing view that there is no benefit (4,9,19,22,26,35-37). Could it then be argued that positive findings emerging from even only a minority of studies nonetheless demonstrate that added protein can enhance performance, albeit if that effect may be specific to the experimental setup in certain laboratories? On the contrary, even those researchers observing performance benefits (13,28,29) have also reported negative outcomes when conducting similar studies (9,19,26,30,36). In fact, the only discernible methodological factor to explain why certain studies have observed a benefit of added protein is that all these studies have compared CHO-protein supplements relative to control supplements providing CHO alone at a lower energy content and/or below the recommended intake for the exercise tests used (11,13,28,29). Whereas these findings are undoubtedly of mechanistic interest, the only logical interpretation from a practical viewpoint is that protein is an unnecessary addition to an otherwise adequate CHO supplementation regimen. In summary, the case against including protein in CHO supplements to be ingested during exercise is fundamentally grounded in the numerical balance of just four published studies demonstrating any benefit of added protein (11,13,28,29) opposed to nine showing no effects on physical performance (4,9,19,22,26,30,35-37), with the few extant reports of benefit explained by the insufficient quantities of CHO ingested in these studies. Lastly, another major problem facing the challenging view is the absence of any empirically supported mechanism to explain why ingesting protein during exercise would be expected to impart performance gains, with the most plausible proposed mechanisms (e.g., altered skeletal muscle metabolism) having recently been comprehensively examined and largely discounted (6). Combined CHO-Protein Ingestion in Recovery Whereas combined CHO and protein simply lacks efficacy when ingested during exercise, this does not negate any possibility that added protein may be of practical value in other situations (e.g., between exercise bouts). The question under debate, however, is not whether ingesting protein can be efficacious under certain circumstances but whether protein should be included in CHO-based sports supplements. These are conceptually very different questions, with valid justification for the inclusion of protein dependent not only on demonstrable efficacy but also on whether benefits persist even when evaluated within the context of the habitual diet. This point has greater relevance to recovery than during exercise, as meals are usually a more viable option in recovery. For this reason, consideration of the criteria identified earlier leads inexorably to the conclusion that protein is an unnecessary addition to supplements in a real-world setting. The first of these criteria is easiest to address. Athletes may have a slightly increased daily protein requirement (34), so dietary protein supplementation might at first seem appropriate for this population. However, the vast majority of athletes in westernized societies exceed their recommended protein intake even without supplementation such that long-term protein requirements are almost always met by diet alone (20) and even the potential short-term benefit of added protein for muscle glycogen synthesis after exercise does not apply to conditions where the existing diet is already adequate (3). Ingestion of added protein therefore does not supplement the habitual diet in the true sense because there is no chronic protein deficiency to be rectified and also no acute acceleration in the delivery of coingested CHO, provided that sufficient is ingested. The only remaining issues to consider are whether protein itself might be more effectively delivered to relevant tissues if ingested in the form of a supplement, particularly at time points so proximal to exercise that meals become an impractical option. Indeed, recent studies on this topic indicate that the temporal proximity and precise types of protein or amino acids ingested can mediate both acute protein synthetic rates and chronic accrual of lean tissue (23). However, these studies do not necessarily imply that feeding must occur immediately after exercise, just not delayed by as long as 2 h (8,24), and neither do they rule out the informed selection of certain whole foods such as milk. Informed dietary choices could still therefore be based on emerging knowledge of the more effective constituent proteins (e.g., whey) (23) and such foods could easily be consumed as part of a meal within the first hour after exercise. Ultimately, until combined CHO-protein supplements are shown to be clearly superior to carefully considered mixed meals, it remains an (in)convenient truth (perspective dependent) that whole foods can achieve the desired protein-mediated effects while simultaneously being more likely to provide a variety of other important nutrients (also reducing the risk of contamination with harmful or illegal substances) (10). REPLY TO THE CHALLENGING VIEW It is highly conducive to an informative debate that both Dr. Stevenson and myself independently chose to present our initial perspectives with separate consideration of CHO-protein ingestion during exercise and then in postexercise recovery. Moreover, it is intriguing that these purposely contrasting perspectives cite essentially the same body of evidence and even concur that neither during nor after exercise are CHO-protein mixtures any more effective than simply ingesting adequate quantities of CHO without protein. Where our interpretations differ is in Dr. Stevenson's risk-benefit analysis whereby, in the absence of any likely detriment to performance, added protein can be justified based on the slightest probability of either performance enhancement in certain situations or some "other" benefit. Before responding to the latter possibility of these "other" benefits, this approach can firstly be evaluated in more general terms. Aside from the fact that at least one study has shown a detrimental effect of combined CHO-protein ingestion on performance (35), I feel this risk-benefit analysis does not give due recognition to the majority of studies reporting no ergogenic effects of added protein (i.e., just one example of potential benefit takes precedence over any number of well-controlled studies to the contrary). It also seems unlikely that the enhanced performance apparent in the minority of studies has simply been undetected by all others (i.e., type 2 errors), given that the latter seem to have been conducted with at least equal scientific rigor to those that have detected effects. To reverse this argument, given the existing balance of published evidence and likely publication bias on this topic, perhaps the few examples of benefits may reflect false-positive results within the commonly accepted type 1 error rate (i.e., 5%). Ultimately, rather than adding protein or anything else to sports supplements "just in case," the approach informing my prevailing view was evidence based, with plausible explanations to reconcile any apparently conflicting findings. In this case, the few documented benefits of added protein for either performance during exercise or recovery thereafter are easily accounted for by the low amounts of CHO ingested in those studies. It therefore remains questionable why anyone would even consider including protein in a sports supplement when the likelihood of attaining a slight performance enhancement is entirely dependent on that supplement already being deficient in another nutrient with far better-established ergogenic properties (i.e., CHO). Returning to the possibility of the "other" benefits associated with including protein in CHO-based sports supplements, Dr. Stevenson rightly identifies the established roles of supplementary protein for recovery in a broader sense and/or over multiple days of sustained training. Indeed, coingestion of CHO and protein in the immediate postexercise period clearly facilitates processes contributing to both short-term recovery and long-term adaptations (e.g., muscle glycogen and protein synthesis, respectively), with consequent translation into functional/whole-body end points (e.g., improved restoration of performance and training responses) (3,17). However, to reiterate the view expressed in my initial perspective, there is no reason why these same outcomes cannot be achieved using nutritionally balanced whole foods as part of a more holistic approach. In fact, studies cited in the challenging view as evidence of improved rehydration with combined CHO-protein ingestion is a prime example of this reasoning (32,39). This is because the superior supplement in these studies was actually milk, with the greater fluid retention primarily attributed not to the presence of protein but to milk's naturally elevated electrolyte content (32). Finally, without intending to individually critique particular studies, I feel this reply must address the issue of attenuated exercise-induced muscle damage with protein ingestion given that this forms a recurrent theme in the challenging view. Impaired muscle function is the most practically meaningful and arguably most valid quantitative measure of exercise-induced muscle damage, yet my own measurements of this variable in recovery are consistent with almost every other extant study in showing no practical benefit whatsoever of added protein for the recovery of strength (2). The only consistent finding on which to base the view that protein ingestion can protect against muscle damage is therefore the reduced systemic activity of creatine kinase commonly observed with CHO-protein supplements-but what does this actually mean? The response of systemic creatine kinase to exercise can often be dissociated from most other indices of muscle damage (e.g., soreness and strength impairment), partly due to variability in the rate at which the enzyme is cleared from the circulation (12). Therefore, it is entirely possible that protein ingestion may similarly affect the kinetics of the creatine kinase response without reflecting differences in the state of muscle damage/repair. Even accepting that combined CHO-protein ingestion may reduce creatine kinase efflux from muscle or that the previously discussed improvement in fluid balance by only ∼300 mL may partly be attributable to protein rather than electrolytes, we are still left without any evidence that these factors translate into practically worthwhile outcomes (i.e., improved physical performance) (39). CONCLUDING STATEMENT Athletes, coaches, and supplement manufacturers understandably strive to gain competitive advantage by adopting nutritional strategies in anticipation of future empirical support. However, the scientific data currently available indicate that protein is not an effective addition to CHO-based sports supplements when ingested during exercise, whereas the potential advantages of added protein during recovery can be most comprehensively achieved via whole foods as part of a balanced diet. James A. Betts, FACSM Human Physiology Research Group Department for Health University of Bath United Kingdom CHALLENGING VIEW Dietary CHO intake is fundamental to an athlete's nutritional program to provide fuel to the working muscle and to facilitate muscle glycogen synthesis between exercise sessions. As a consequence of this, a wide range of CHO-based sports supplements are commercially available. During the last 20 yr, evidence has been emerging that the addition of protein to CHO-based supplements may be beneficial; however, this remains a controversial This challenging view will present the evidence that the of protein with The majority of studies in this have on CHO-protein intake either during exercise or in recovery from exercise, but of nutritional strategies during recovery also become nutritional strategies in many CHO-Protein During Exercise studies have the effect of protein with CHO compared with CHO only during exercise. reported a improvement in time to after h of when ingested a of CHO and protein compared with a of others have reported in time to when including protein in a CHO supplement during exercise The studies that have shown no performance improvement after a of CHO and protein over CHO only are those that have provided sufficient CHO to requirements during exercise or when the addition of protein does not the energy content of the supplement this, a recent study by reported that adding a of protein to a provided during exercise at least exercise relative to a CHO supplement as CHO and over more Although the evidence for an improvement in performance from adding protein to a CHO supplement during exercise seems to be it is unlikely that protein with CHO during exercise will have a detrimental effect on Indeed, there are other effects that may be of benefit to the of protein with CHO during exercise has been shown to protein balance by synthesis and in a positive protein balance during exercise and during recovery The inclusion of protein in a CHO supplement consumed during exercise has been shown to reduce indices of postexercise muscle compared with CHO supplements for CHO content or during have reported attenuated of soreness and creatine kinase h after exercise when protein was added to a CHO supplement provided during and immediately after exercise compared with CHO It is therefore the benefits of a CHO-protein during exercise on immediate performance are still this nutritional strategy can have a positive effect on the recovery and therefore may exercise performance on CHO-Protein during Recovery from Exercise during recovery from exercise on CHO intake to muscle glycogen the effects of adding protein to CHO have very on muscle glycogen during short-term recovery the postexercise some contrasting the general is similar to that for during if CHO is provided in adequate quantities then the addition of protein no benefit. However, reducing the CHO content of a supplement and adding an appropriate of protein does not seem to have any detrimental effects on muscle glycogen or Indeed, the addition of protein to a CHO supplement has many other potential benefits, and in many reducing the CHO content and the protein content of a supplement will in a superior recovery strategy than CHO The majority of studies the performance benefits of adding protein to a CHO recovery supplement have only considered the effect of supplementation on a exercise a few Although some athletes will a many more will or on days and therefore a supplement that will to a of performance over multiple The addition of amino acids to a CHO consumed during a period has been shown to reduce muscle damage by a in and exercise performance after days of exercise compared with when CHO only was consumed in athletes reported increased time to no in and muscle damage after days of exercise after CHO-protein compared with CHO with a CHO-protein immediately after training for in lower and muscle soreness in compared with when CHO only was consumed after training no differences in performance after the training and there in performance in Therefore, for those athletes to performance over days of training or adding protein to a CHO supplement would be CHO alone in the recovery period after a exercise seems to have no effect on of exercise-induced muscle damage In fact, reported and increased when consumed a CHO after exercise. On the contrary, a recovery CHO and protein attenuated and for h after exercise and attenuated in and of the The addition of protein to a CHO may advantages in of rehydration during recovery from exercise. There is evidence that protein after exercise-induced fluid retention over with no added protein A very recent study from James has reported that a protein is than an and electrolyte CHO consumed after exercise in the In both ingested a to of body however, the of of CHO for of protein reduced over the by mL by the end of the data that supplementation with a of CHO and protein after exercise content and in both and in and and are therefore an important part of the training It has been reported that have an attenuated postexercise in due to an insufficient protein intake for the effect of providing a CHO-protein supplement after exercise during an training program on and and to exercise in with the and adaptations to training all increased after the CHO-protein Although is in this this evidence that CHO alone during the postexercise period may not be the most appropriate nutritional to facilitate all of recovery. In summary, there are benefits of adding protein to a CHO supplement to be consumed both during and after exercise. The of CHO-protein mixtures in many a more effective nutritional strategy than CHO particularly over the REPLY TO THE PREVAILING VIEW The point in my challenging perspective is that the addition of protein to a CHO-based sports supplement should be considered in view of the available evidence on all of exercise training and performance as as adaptations to training. Although the of sports is to exercise performance, we should not on the effects of a supplement on acute exercise performance but consider the practical of the supplement and the potential of I that the prevailing perspective on the performance results of acute studies, at still provide conflicting Combined CHO-Protein Ingestion during Exercise The provided by Dr. for not including protein in a CHO supplement to be ingested during exercise is based on studies that have the effects of CHO a CHO-protein during an acute of exercise on consideration has been given to the other reported benefits of protein with CHO during exercise (i.e., the effects on protein balance and indices of postexercise muscle and these factors are likely to affect exercise In supplements will be on a daily by and it is important to consider the broader practical of the supplement and the potential benefits to the As in the contrasting perspective, findings in to acute exercise performance, there seems to be no detrimental effect of reducing the CHO content of a supplement to a of protein. Indeed, the potential benefits of some protein may be more to performance over days of training and A very recent study by this reported that a CHO-protein supplement during exercise during of in a body enhanced and improved competitive exercise performance in compared to when CHO only was This is one of the first studies to the effects of a CHO-protein on exercise performance and recovery in a Although it is that we out studies, we should be and on nutritional strategies based on the results of these studies, particularly if they only during a exercise Combined CHO-Protein Ingestion during Recovery to the prevailing view of Dr. Betts, the addition of protein to a CHO supplement to be consumed during recovery from exercise is unnecessary for protein intake during recovery is achieved carefully meals consumed as part of the habitual diet and providing that sufficient CHO is the addition of protein does not provide any benefit to CHO delivery and muscle glycogen In response to the first I that meals can be a viable option during recovery from exercise but practical issues often it very in some for an to a considered mixed within the first hour after exercise. other training and of foods and and a reduced postexercise are the in a athletes are unlikely to adequate protein their habitual diet within the hour after exercise to the recovery Therefore, on the optimal timing and of an athlete's postexercise intake is not a reason to protein from CHO-based recovery supplements. The point to address is the issue that protein does not provide any benefit in of CHO delivery and muscle glycogen provided that sufficient CHO is ingested. However, as in the contrasting perspective, there seem to be no detrimental effects of reducing the of CHO provided in a supplement and this with a of protein or amino a practical perspective, it is not always for an to during recovery from exercise. athletes are or training that such of CHO may not be particularly as studies have reported after the ingestion of such amounts of CHO Therefore, the coingestion of protein with a of CHO would be a more practical approach to postexercise feeding because similar rates of muscle glycogen can be and as documented in the contrasting there are other benefits of protein in the postexercise CONCLUDING STATEMENT The of a sports supplement to be based on scientific evidence and on practical and I that the addition of protein to CHO-based supplements results in a more nutritional for muscle glycogen can be achieved without the for and CHO during skeletal muscle and is and rehydration may also be These factors are important to both the and strength in the adaptations to training and not just the short-term performance effects. In the scientific evidence on performance is still the addition of protein to a CHO-based supplement a more practical approach to the training and recovery of particularly those or in multiple on the same or Stevenson and Research of University United Kingdom