Carbohydrate loading and mental focus -
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When a new season approaches, many of us enjoy pursuing the local farmers market to see what seasonal fresh produce is available. Fall lends itself to more starchy vegetables - potatoes, cauliflower, broccoli, cabbage, which is especially nice as the weather gets cooler.
Over the years, as the diet culture in our society has grown, carbohydrates, including starches, have been viewed as "bad. Carbohydrates break down into glucose which is the preferred energy source for the brain, and in turn, glucose supports the brain's overall functioning.
Carbs are a necessary source of fuel for the brain. All carbohydrates grains, beans, dairy, fruits, starchy vegetables, and sugar break down into glucose. Glucose is fuel for our cells. Specifically, glucose is the preferred source of fuel for the brain.
That being said, low glucose levels leave the brain without fuel, leaving it susceptible to mood changes. Additionally, there are two types of carbohydrates - simple carbs think sweets or sugary drinks and complex carbs including starches and fiber.
While both simple and complex carbs break down into glucose, they do so at different rates. Simple carbs are a shorter molecular strand and break down in the body faster, which gives the body energy but for shorter amounts of time.
Complex carbs, a longer molecular strand, take more time to break down and give the body more sustainable, long lasting energy.
Fiber, a complex carbohydrate, also supports a healthy gut. Fiber is the food source for the "good bacteria" in our gut. The good news is that, for most of us, our bodies do a really great job of regulating glucose levels. However, there are still a few things we can do to provide the brain with the fuel it needs to stabilize our moods as best we can.
Complex carbohydrates are carbohydrates that are naturally paired with fiber. Examples include whole grains, beans, starchy vegetables and fruits. The fiber within these carbohydrates holds onto glucose within the digestive system, making it more difficult for the body to absorb glucose.
Complex carbohydrates provide the brain with the glucose it needs, but in small amounts over time. Just like fiber makes glucose in complex carbohydrates more difficult for the body to absorb, so does fat and protein. A greater understanding of whether different types of carbohydrate affect the storage localization within muscle is also warranted.
While muscle glycogen depletion is more commonly associated with prolonged strenuous endurance exercise, even short but intense exercise bouts can result in significant reduction of muscle glycogen content [ 30 , 34 , 35 ]. Thus, one could assume that because of this, glycogen loading would be warranted.
However, the evidence is not as conclusive, as glycogen loading before shorter duration events does not always translate into performance improvements [ 30 , 36 ]. For instance, Sherman and colleagues showed that for runners undertaking a half-marathon, glycogen loading was of no benefit to performance [ 36 ].
Based on this, it is not currently recommended to perform glycogen loading for events shorter than 90 min [ 32 ]. This is especially pertinent for sports where increased BM could significantly hinder performance by reducing sustainable relative exercise intensity e.
However, it is important to discern between functional BM i. Whether liver glycogen stores can also be super compensated remains to be established, as currently there is no clear evidence that this is possible [ 20 ]. Varying carbohydrate intake does indeed change fasting liver glycogen concentrations [ 41 ], and this shows that sufficient carbohydrate intake is required to start an exercise session with normal liver glycogen stores.
However, whether glycogen stores could be increased to higher-than-normal levels remains to be established. It is often overlooked that if competition is to be performed in the morning after an overnight fast or any period of prolonged fasting , liver glycogen stores may be compromised.
Namely, in the postabsorptive phase e. On the contrary, muscle glycogen stores are typically not affected by an overnight fasting period [ 42 ]. As numerous competitions start in the morning, it is pertinent that the meals after overnight fast are designed so that there is a focus on liver glycogen repletion.
While this has not been directly assessed, it could be speculated that providing athletes with a mix of different types of monosaccharides would be beneficial.
This suggestion is based on previous observations that combining glucose-based carbohydrates with either fructose or galactose offer benefits on liver glycogen synthesis over glucose-based carbohydrates only [ 43 , 44 , 45 ]. Indeed, a recent study found improved exercise capacity with a breakfast consisting of fructose-glucose-based carbohydrates as compared to glucose-based carbohydrates only [ 46 ].
This would advance practical advice not only from the perspective of optimization of liver glycogen levels, but also from the perspective of preventing consequences of rebound hypoglycemia, which can occur in some athletes when exercise bouts are initiated close to a meal [ 47 ].
Current nutritional guidelines for athletes advise to consume carbohydrates during exercise at different rates and in relation to the duration of exercise bouts, as will be discussed later [ 1 , 2 ]. There are currently two proposed mechanisms of carbohydrate ergogenicity. Firstly, carbohydrates can be sensed in the oral cavity, causing an activation of certain brain regions, leading to stimulation of the central nervous system, as shown by improved performance by carbohydrate mouth rinsing [ 49 , 50 , 51 ].
Secondly, and most importantly, carbohydrates provide an additional fuel source for ATP formation during exercise. Carbohydrate ingestion during exercise maintains stable blood glucose levels over long exercise sessions [ 52 ] and maintains carbohydrate oxidation rates despite declining muscle glycogen stores so that ingested carbohydrates substitute endogenous carbohydrate stores [ 53 , 54 ].
In addition to this, exogenous carbohydrates can spare or even completely suppress liver glycogen breakdown [ 55 , 56 ]. While some studies have found sparing of muscle glycogen with carbohydrate supplementation during exercise [ 57 , 58 ], most of the studies assessing whole muscle glycogen utilization did not see this effect [ 28 ] and a recently published study that evaluated different carbohydrate ingestion rates during cycling exercise did not observe sparing of muscle glycogen in a muscle fiber type-specific manner either [ 59 ].
However, more recent evidence indicating the importance of compartmentalized glycogen metabolism to muscle function opens new avenues for investigating the mechanistic basis of carbohydrate feeding during exercise [ 29 ]. Galactose has typically not been recommended to be ingested during exercise due to a belief that it is not as readily oxidized [ 61 , 62 ].
However, recent evidence demonstrates that at moderate dosages i. It remains to be demonstrated directly, but these data indicate that oxidation of galactose during exercise is not limited when provided as lactose at moderate ingestion rates. Thus, lactose as a source of galactose and glucose can be ingested as an alternative carbohydrate source during exercise, at least in lactose-tolerant individuals.
It is believed that at this ingestion rate, the sodium-glucose linked transporters SGLT1 in the small intestine become saturated [ 25 ]. This notion is based on the observations that when fructose, whose absorption from the small intestine utilizes a different transporter i.
As a result of this, athletes are recommended to ingest mixtures of glucose- and fructose-based carbohydrates when training or competition is longer than 2. Most studies investigating combined ingestion of glucose-based carbohydrates and fructose utilized a glucose:fructose ratio, and this has since become a standard recommendation [ 60 ].
However, a closer examination of the literature reveals that a ratio closer to unity i. Thus, it could be recommended that composite glucose- and fructose-based carbohydrates in a ratio close to unity are ingested irrespective of exercise duration. The suggestion that glucose-fructose mixtures be recommended over single transportable carbohydrates even when exercise duration lies within 1—2.
Most studies to date investigating exogenous carbohydrate oxidation rates have been performed on moderately to highly trained athletes, but not in elite athletes whose absolute energy demands can be vastly higher. However, endogenous carbohydrate oxidation was not further spared by the higher carbohydrate dose, and thus whether there would be an additional performance benefit requires clarification.
Current evidence indicates that glucose delivery to the active tissue i. Bypassing intestinal absorption by infusing glucose and maintaining glycaemia did not result in higher exogenous glucose oxidation rates [ 74 ], whereas infusing glucose to maintain hyperglycemia i.
This occurred without a reduction in muscle glycogen use, but rather with suppression of fat oxidation rates. As oral ingestion of very large amounts of glucose i.
Yet, evidence for recommending such high ingestion rates i. It could be that athletes whose energy turnover rates during exercise are very high and thus have a high glucose flux to muscle due to increased blood flow proportional to absolute exercise intensity [ 83 ] could benefit from carbohydrate ingestion rates that are higher than currently recommended, but this requires further evaluation.
Additionally, it remains to be established what occurs at intensities in heavy and severe exercise intensity domains, as some evidence indicates that despite higher carbohydrate demands, exogenous carbohydrate oxidation rates do not further increase [ 84 ].
Nonetheless, at present, it cannot be recommended to alter the currently recommended maximal carbohydrate ingestion dose during endurance exercise i. There have been many attempts to increase exogenous carbohydrate oxidation rates by co-ingestion of carbohydrates with other nutrients or nutritional supplements, a topic recently reviewed by Baur and Saunders [ 85 ].
There was no effect from co-ingestion with protein [ 86 ], calcium [ 87 ] or sucralose [ 88 ], use of different glucose polymers [ 89 ] or use of drinks with different osmolality [ 90 ], whereas effects of caffeine co-ingestion yielded mixed results [ 91 , 92 ].
More recently, use of hydrogel-forming carbohydrate drinks and gels has been popularized, and while the majority of studies found this strategy not to affect exogenous carbohydrate oxidation rates [ 95 , 96 ], a recent study found that there could be a positive effect when using solely monosaccharide-based carbohydrate solutions i.
More research is required to better understand a potential utility of the hydrogel. While a vast majority of the studies discussed in the present article are based on interventions conducted in thermoneutral conditions, athletes are commonly required to exercise in extreme environments e.
In recent years, advances have been made in understanding how these environmental stressors affect carbohydrate metabolism during exercise [ 98 ] and more work is expected to be undertaken in the upcoming years. When comparing exercise at the same relative exercise intensity between hypoxia and normoxia, there appear to be no differences in substrate oxidation rates [ ], whereas if the absolute intensity is matched, there is an increase in carbohydrate oxidation rates [ ].
This is met with a reduced ability to oxidize exogenous carbohydrates during exercise at both the same absolute [ ] and relative intensity [ ] It was hypothesized that this is largely explained by reduced peripheral insulin sensitivity because of increased oxidative stress in hypoxia [ ].
Interestingly, altitude acclimation i. Thus, it appears that sufficient pre-exercise carbohydrate intake plays a crucial role in sustaining intense exercise in hypoxia [ ]. Exercise in the heat at the same absolute intensity is accompanied with increased rates of glycogenolysis and thus glycogen utilization in non-heat acclimatized individuals [ , , ].
This effect is somewhat alleviated with heat acclimation [ ], making another argument towards the importance of undertaking heat acclimation before competing in the heat [ ]. Similarly, as with hypoxia, exogenous carbohydrate oxidation rates in non-heat acclimated athletes are reduced under heat stress [ ].
The underlying mechanisms are not yet completely understood. The latter could in turn result in accumulation of glucose within the cell and a reduced glucose gradient between muscle cells and blood [ , ]. Of note is also the fact that under heat stress, athletes are exercising at a higher relative exercise intensity, which drives increased carbohydrate oxidation rates [ 99 , ].
It remains to be explored whether heat acclimation somehow alleviates reductions in exogenous carbohydrate oxidation rates in the heat.
From the applied perspective, currently, the most important solution to circumvent this is combining glucose- and fructose-based carbohydrates so higher exogenous carbohydrate oxidation rates can be achieved than those seen with glucose alone [ ]. The main aim of carbohydrate nutrition in the post-competition period is recovery of liver and muscle glycogen stores.
This does not necessarily imply that carbohydrate intake needs to be such that repletion of glycogen stores always needs to be rapid given that the next exercise session might not require full glycogen stores e.
It is believed that for a full repletion of muscle glycogen stores, 24—36 h [ 21 ] are required, whereas for the complete repletion of liver glycogen, 11—25 h are needed [ ].
Current nutritional guidelines recommend athletes ingest moderate to high glycemic index carbohydrates as soon as possible at the rate of 1. However, a close examination of the literature reveals that these guidelines are perhaps too simplistic, especially for elite athletes. Scrutiny of the evidence for the optimal dosage of carbohydrates to be ingested in the early hours of post-exercise recovery reveals that there is only one study available comparing 1.
While it is difficult to compare results between different studies given that different methodological approaches have been used, it appears that there is a good relationship between the dosage and the amount of muscle glycogen resynthesis spanning at least from 0 to 1.
Thus, given that there is also a relationship between training status and the capacity to store muscle glycogen [ 28 ], it could be hypothesized that, absorption permitting, higher ingestion rates would be favorable to elite athletes whose relative proportion of muscle mass is higher.
More research is required to elucidate if this is the case. In addition to this, an emerging topic within the post-exercise recovery period, with an aim to improve functional capabilities of athletes, is the type of carbohydrates ingested in recovery.
Namely, advances have been made on the type of carbohydrates i. While there appears to be no benefit of ingesting multiple types of carbohydrates i. Advancing these data are studies showing that recovery of cycling exercise capacity is greater after ingestion of a combination of glucose-based carbohydrates and fructose as compared to glucose-based carbohydrates only [ , ], likely because of higher carbohydrate availability within both liver and muscle glycogen pools.
It has been hypothesized but not established that combining glucose with both galactose and fructose would result in more rapid replenishment of both glycogen pools [ ]. Interestingly, this strategy did not translate into improved cycling performance [ ].
The results of the latter study are thus surprising. However, a close examination of the results offers a potential explanation and opens new research questions. Namely, two studies [ , ] quantified utilization of in-recovery ingested carbohydrates in the subsequent exercise bout and found an increase in its use, indicating an increased carbohydrate availability.
However, the increase of carbohydrate oxidation rates in the study assessing subsequent cycling performance was such that by the time the cycling time trial was initiated, glycogen stores within the body were likely the same in both conditions.
Thus, more work is required to define the precise scenarios when a functional benefit can be expected; however, there appears to be a uniform observation that in terms of metabolism, ingestion of composite carbohydrates is beneficial.
A summary of current knowledge on the effectiveness of different monosaccharide types on repletion of different glycogen depots i.
Based on the current evidence, it could be recommended that athletes seeking to recover glycogen stores as quickly as possible consider ingesting carbohydrates from a combination of glucose-based carbohydrates and fructose to optimally stimulate both liver and muscle glycogen resynthesis.
The same recommendation cannot currently yet be given for galactose as whilst combined galactose-glucose favorably affects liver glycogen synthesis it is currently unknown how effective it is in the replenishment of muscle glycogen stores. Short-term recovery of muscle and liver glycogen stores after exhaustive exercise using different combinations of monosaccharides.
Fructose-glucose carbohydrate mixtures have been demonstrated to be very effective in replenishment of both muscle and liver glycogen stores. On the other hand, while glucose-based carbohydrates cause robust rates of muscle glycogen replenishment, liver glycogen synthesis rates are inferior as compared to a combination of fructose-glucose- and galactose-glucose-based carbohydrates.
No data are currently available for muscle glycogen synthesis rates after ingesting a galactose-glucose mixture. It is hypothesized but not established that combining fructose-galactose-glucose-based carbohydrates would be optimal for post-exercise repletion of both glycogen pools.
CHO carbohydrate. Training can be described as undertaking structured workouts with an aim to improve or maintain performance over time by manipulating the structure, intensity, duration and frequency of training sessions [ , , ]. As total energy requirements and, consequently, carbohydrate demands are high in endurance-based sports, it is fair to assume that optimization of carbohydrate intake in these sport disciplines plays an important role.
Early sports nutrition guidelines [ ] advised athletes to both train and compete with high carbohydrate availability, and this approach dominated until , when Hansen and colleagues observed that a reduction in carbohydrate availability before certain training sessions in untrained individuals could potentially enhance training adaptations [ ].
In this study, leg kicking exercise training was performed in a week-long training study. Each leg was subjected to a different treatment. Muscle biopsy analysis also showed more positive metabolic adaptations hydroxy acyl-CoA dehydrogenase [HAD] and citrate synthase [CS] activity in the leg training with reduced muscle glycogen stores.
While very attractive, the strategy was found to be effective in untrained individuals, and more work was required to see if similar findings could be observed in already trained individuals.
As a result, this study was a landmark study paving the way for further investigations into whether different approaches to nutrient availability in trained athletes are beneficial based on different goals: training adaptation or competition performance.
In addition to carbohydrate availability manipulations to influence training adaptations, the concept of training the gut also needs to be considered to become a part of the training process to potentially improve tolerance to high carbohydrate ingestion rates during exercise especially [ , ], as the prevalence of gastrointestinal issues during exercise is large [ , ].
While the concept of training with high carbohydrate intakes to improve tolerance to ingested carbohydrates seems warranted, it remains to be established whether such practice leads to improved absorption of ingested carbohydrates and by what mechanisms or leads to just improved tolerance.
Recent evidence from rats indicates that a combination of a high carbohydrate diet and exercise does not result in an increased number of glucose transporters in the intestines [ ], and it could be thus speculated that improved tolerance can occur independently of improved absorption capacity.
Building from the study by Hansen and colleagues, research started to focus on ways to optimize training adaptations and not necessarily optimize performance within these training sessions in trained individuals.
Indeed, studies investigating molecular signaling responses after acute bouts of training with low muscle and liver glycogen stores in trained individuals provided promising results [ 10 , ]. The concept is well described elsewhere [ , ].
Using this approach, some studies demonstrated metabolic benefits, such as reduced reliance on carbohydrates during moderate-intensity exercise [ , ]. However, a recent meta-analysis of nine studies investigating long-term benefits of carbohydrate periodization on performance outcomes suggests that this approach does not always enhance performance in the long term over training with high carbohydrate availability [ ].
Perhaps important to understand when interpreting these data is that large training volumes are accompanied by substantial energy turnover. Even if a training session is initiated with adequate muscle glycogen stores, they will be markedly reduced by the end of it [ 28 ], creating a suitable environment for activation of crucial molecular signaling pathways thought to be responsible for positive adaptations [ ].
One of the fundamental principles of endurance training is achieving sufficient training volume [ , ]. For instance, elite cyclists are reported to cover more than 30, km on the bike in a single year [ ].
Large training volumes are reported in other endurance sports as well [ ]. This provides support for the notion that accumulation of sufficient training volume is of paramount importance among elite endurance athletes. Training with high carbohydrate availability i. Thus, training with low carbohydrate availability should likely be at best viewed as a more time efficient way to train [ , ] rather than the optimal way.
Thus, manipulating carbohydrate availability before and during training sessions could affect molecular responses after exercise bouts. However, focusing solely on activation of pathways such as AMPK could be too reductionist, as it does not account for the recovery that is required after such a session, as, for instance, it is well known that protein breakdown is increased during such sessions [ , ].
In addition to this, recent evidence indicates that the time between two exercise sessions rather than carbohydrate availability is the important modulator of the training responses after the second exercise bout [ , ].
To circumvent this, attempts have been made to rescue the reduction in training capacity by utilization of ingestion of ergogenic aids. In line with this, carbohydrate and caffeine mouth rinsing have been shown to improve high-intensity exercise performance when conducted under a carbohydrate-restricted state [ ].
Whether training adaptation can be enhanced with this approach has not been studied. More recently, building on previous work [ ], the effects of delayed carbohydrate feeding in a glycogen depleted state i.
While performance outcomes were unclear, delayed carbohydrate feeding enabled maintenance of stable blood glucose concentrations without suppressing fat oxidation rates and thus created a favorable metabolic response.
Again, whether such an approach leads to longer-term enhancement in training adaptation remains to be seen. More broadly there is a need to further explore the potential benefits of commencing exercise with low carbohydrate availability to maximize both the metabolic and mechanical i.
Another popular reason for undertaking training with low carbohydrate availability is the notion that such an approach would lead to increases in fat oxidation rates during competition and spare endogenous carbohydrate stores with a limited storage capacity and by doing so improve performance [ 18 , ].
A recent study indicated that the capacity to utilize fat during exercise in an overnight fasted state is best correlated with CS activity [ ], a marker of mitochondrial content [ ] that is itself well correlated with training volume [ ].
More research is required to better understand if training and diet can be structured so that substrate oxidation rates would be altered in favor of fat oxidation without being part of general improvements seen with training per se, and whether this could lead to improvements in endurance performance.
Unfortunately, the prevalence of relative energy deficiency in sport RED-S remains high [ ]. Building on the previous evidence that sufficient carbohydrate intake can ameliorate symptoms of overtraining [ , ], it has recently been proposed that there might be a link between relative RED-S and overtraining and that a common confounding factor is carbohydrate [ 11 ].
Recent data support an important role for dietary carbohydrate, as low carbohydrate, but not low energy availability, affects bone health markers [ ], and deliberately inducing low carbohydrate availability to promote training adaptations and remaining in energy balance by increasing fat intake does not offer any benefits over a combination of energy and carbohydrate deficit—even more, it can impair glycemic regulation [ ].
Whether carbohydrate availability is the crucial part in the development of RED-S remains to be properly elucidated. Collectively, periodizing carbohydrate intake based on the demands of training and especially an upcoming training session currently appears to be the most sensible approach as it 1 allows the execution of the prescribed training program, 2 minimizes the risk of high carbohydrate availability impeding training adaptations and 3 helps minimize the risk for occurrence of RED-S.
A framework for carbohydrate periodization using this concept is depicted in Fig. Framework for carbohydrate periodization based on the demands of the upcoming exercise session.
Exercise intensity domain selection refers to the highest intensity attained during the exercise session. The exact carbohydrate requirements are to be personalized based on the expected energy demands of each exercise session. CHO carbohydrates, CP critical power, LT1 lactate threshold 1, LT2 lactate threshold 2, MLSS maximal lactate steady state.
While provision of exact recommendations for carbohydrate intake before and during exercise forms part of sports nutrition recommendations provided elsewhere [ 1 , 2 ], we believe that interindividual differences in energy and thus carbohydrate requirements are such that optimization of carbohydrate intake should be personalized based on the demands and the goals of the exercise session one is preparing feeding for.
For instance, aggressive provision of carbohydrate intake during exercise deemed beneficial among one population [ 73 ] in another population could lead to unwanted increase in muscle glycogen utilization [ 81 ].
In addition to this, even within sports commonly characterized as featuring extreme energy turnover rates, day-to-day differences are such that provision of exact carbohydrate guidelines would be too inaccurate [ 22 , ].
Thus, personalization of carbohydrate intake during exercise is warranted, as described in the next section. A certain level of personalization of energy and carbohydrate intake has been a standard part of nutritional guidelines for athletes for years [ 1 , 2 , ].
Practitioners and athletes have a wide array of tools available that can help them personalize energy and carbohydrate intake.
For instance, energy turnover for past training sessions and even energy requirements of the upcoming training sessions can relatively easily be predicted in sports where wearables exist to accurately quantify external work performed i.
Assuming fixed exercise efficiency one can then relatively accurately determine energy turnover during exercise. Knowing the relative exercise intensity of a given training session can further advance the understanding of the carbohydrate demands during exercise, as depicted in Fig.
As described in Sect. Thus, it is possible for athletes to predict energy turnover rates during exercise and adjust the carbohydrate intake accordingly. In addition to this, the literature describing the physiological demands of a given sporting discipline can also be very insightful.
For instance, energy turnover using gold-standard techniques has been assessed in many sporting contexts, including football [ ], cycling [ 22 ] and tennis [ ]. By knowing the energy demands, structure and goals of an upcoming training session, one can devise a suitable carbohydrate feeding strategy.
Besides making predictions on total energy turnover during exercise, it is useful to establish the rate of glycogen breakdown, as very high-intensity efforts can substantially reduce muscle glycogen content without very high energy turnover rates [ 34 , ], especially as low glycogen availability can negatively affect performance [ 30 ].
Attempts have been made to find ways to non-invasively and cost-effectively measure muscle glycogen concentrations e. These data can be useful for practitioners to determine the relative i.
However, whilst knowledge of exercise demands can help with tailoring, an implicit assumption is that all athletes will respond in a similar manner to an intervention, which may not be the case.
In this respect, despite the present limitations in the practical assessment of muscle glycogen in field settings, gaining more readily accessible information on individual athlete physiological responses could still be of value to achieve higher degrees of personalization than those that current guidelines allow.
Recently, use of continuous glucose monitoring CGM devices has been popularized among endurance athletes, with an aim of personalizing carbohydrate intake around exercise for optimal performance.
Certainly, knowledge of blood glucose profiles has the advantage that specific physiological data are generated from the individual athlete.
These devices have a rich history in the field of diabetes treatment, and their utility has clearly been demonstrated [ ]. For a device to be deemed of use and its use recommended to a wider audience, both of the following criteria must be met: 1 the parameter that the device is measuring should have contextual relevance i.
While there is no doubt that CGM devices are useful in non-exercise contexts, their utility during exercise per se remains to be clearly established. Indeed, CGM devices appear to have limited validity during exercise [ , ], and this may be due to the complex nature of blood glucose regulation during varying types and intensities of exercise.
Blood glucose concentrations are a result of glucose uptake by the tissue and glucose appearance i. While it has been known for a long time that hypoglycemia can associate with task failure [ ], its occurrence does not always precede it [ ].
Therefore, further investigative work is required to establish whether differential blood glucose profiles using validated technology during exercise can be identified and be used to individualize carbohydrate intake during exercise. In addition to tracking glycaemia during exercise, tracking it throughout the day could also be proven useful.
A recent study utilizing CGM devices compared daily blood glucose profiles in elite trained athletes with those in a sedentary population and discovered large discrepancies in blood glucose concentrations throughout the day between both groups [ ].
Elite athletes spent more time in hyper- and hypoglycemia as compared to sedentary controls, giving an appearance that glycemic control might be impaired.
While periods of hyperglycemia are expected due to post-exercise high carbohydrate intakes, observations of hypoglycemia occurring especially at night during sleep were somewhat surprising.
This knowledge can then be used to potentially individualize strategies to counter these episodes of impaired glycemic control in real time. While utilization of CGM devices during exercise to guide carbohydrate intake during exercise cannot be presently advised, athletes could individualize carbohydrate ingestion rates during exercise by establishing their highest exogenous carbohydrate oxidation rates [ 25 ].
To do this, one requires the ability to know carbon isotope enrichments of the ingested carbohydrates and in expired carbon dioxide. For example, advances have been made in methodology to easier quantify stable carbon isotope abundance in expired air [ ], a methodology currently used for quantification of exogenous carbohydrate oxidation rates [ 25 ].
Thus, this approach could be spun off from research and be used in practice as well to identify carbohydrate intake rate and carbohydrate compositions that optimize exogenous carbohydrate oxidation in individual athletes.
Finally, most research to date has investigated carbohydrate intake in a healthy male population, and thus current carbohydrate guidelines are founded on this evidence.
Despite decades of intense carbohydrate research within the field of sports nutrition, new knowledge continues to be generated with the potential to inform practice.
In this article, we have highlighted recent observations that provide a more contemporary understanding of the role of carbohydrate nutrition for athletes.
For example, our article suggests a stronger emphasis be placed on scaling carbohydrate intake before competition to the demands of that subsequent activity, with particular attention paid to the effects of concomitant exercise during the preparatory period.
At high ingestion rates during exercise i. Furthermore, short-term recovery may be optimized by combining glucose-fructose to target both liver and muscle glycogen synthesis simultaneously. Finally, there has been substantial investigation into the role of commencing selected exercise sessions with reduced carbohydrate availability to provide a beneficial stimulus for training adaptation.
The abovementioned suggestions are designed to build on the wealth of knowledge and recommendations already established for athletes.
Nonetheless, what this review has also revealed is that gaps in our current understanding of carbohydrate nutrition and metabolism in relation to exercise performance remain.
Some remaining research questions arising from the present article are presented in Table 1. Answering these research questions could allow continued advancement and refinement of carbohydrate intake guidelines and, by doing that, further increase the possibility of positively impacting athletic performance.
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Endurance athletes have Carbohydraet touted the benefits of carbo-loading Boost mood naturally which, for Carbohydrate loading and mental focus, simply involved ingesting loadiing Carbohydrate loading and mental focus pasta and bread the night before a race and calling it good. A smart carb-cramming plan, however, is ficus more strategic. Research suggests, Carbohydratte example, that starting to ramp up carb intake a few days before an event can provide the best results. It also shows that by carbing up properly, an athlete can maximize endurance, maintain focus and improve strength. And those who exercise hard enough to deplete their muscles of glycogen a process that generally takes 60 to 90 minutes of strenuous exercise, so think runners, cyclists and cross-country skiers — not low-key walkers or joggers will need more than their usual dose of carbs to keep them going. Carnohydrate dietitians set the record straight. What Is Carb Loading? Who Should Try Carb Loading? How Carb Loading Can Enhance Your Performance Arrow. Types of Carbo Loading Arrow.
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