Carbohydrate Strategies For Climbing Performance

This article outlines dietary carbohydrate feeding strategies for climbers, with specific recommendations for training and recovery periods, competition and project preparation, with research references that informed these guidelines.

I also recommend listening to ClimbSci - Episode 02 - Carbohydrate where Brian and I discuss the science behind fuelling with carbohydrates.

Facebook: comments and discussion.

Page updated: 17/10/2017

Contents

Fuel for the Work Required

Quantitatively, it has been estimated that the rate of ATP generation based on the carbohydrate oxidation is in the range of 0.51 to 0.68 mmol per second per kg body mass. In comparison, the rate of ATP generation based on triacylglycerol fueling is approximately two- to threefold lower (0.24 mmol per second per kg body mass).1

I believe the better strategy for optimising training output, climbing performance, and improving body-composition, is not taking a linear approach to carbohydrate (CHO) intake, but rather a day-to-day, meal-to-meal periodised approach.

We do not train, perform, or recover in the same way every day (week, month), and yet we often take a linear or lifestyle approach to our diets, be it "high-carb", "primal/paleo", LCHF (low-carbohydrate high-fat), or "ketogenic" to support our goals.

Limiting carbohydrate makes sense in the context of health, limiting carbohydrate at the expense of training output and performance does not. Though there is data on the potential for "train low" or "sleep low" strategies to augment the training effect, there is no data on sustained low-carbohydrate diets improving maximal performance outside of confounding factors like lower body-weight. In contrast, we have years of data showing carbohydrate augments both endurance and high-intensity exercise performance.

Just because one strategy is efficacious in one context at one time, does not mean that the same strategy is efficacious in all contexts at all times. If you are continuing to force square pegs into round holes in the event they might eventually fit, you are falling behind the person putting round pegs into round holes day after day, and getting better and better at it.

The ketogenic diet has received considerable attention in the popular press and many claims have been made recently. However, it is important to realize that, to date, not a single study has demonstrated performance benefit of a ketogenic diet, including the early study that is often referred to (Phinney, 1983). Thus, at present, there are no data on ketogenic diets in athletes on which to base performance claims.2

Programmed periodisation of carbohydrate intake rather than chronic linear consumption allows for greater training volume, recovery, adaptation, and favourable body-composition changes, these will ultimately lead to better overall climbing performance.

Using a "fuel for the work required"3 approach allows us to maintain metabolic flexibility: the ability to metabolise fat at higher aerobic intensities without compromising carbohydrate (glucose/glycogen) metabolism when maximum power output is required.

You do not have to choose sides between fuelling with fat or carbohydrate, rather you should choose the strategy that does the most at the right time and in the right context.

Why Carbohydrate?

Let me first ask you a question…

Why wouldn't you want to consume carbohydrate?

Over the last number of years, there has been much research and discussion on the contribution of the "Western Diet" to obesity and lifestyle related diseases. The diet can be summed up as being high in energy (kcal) and low in nutritional quality, generally consisting of refined food products typically high in refined carbohydrates, particularly sugars, and high in added fats such as vegetable oils.

We know that the obesity epidemic is predominantly driven by a steady increase in food supply and daily energy intake over the years.4 Additional refined carbohydrates have been added to existing our diets, replacing more protein, and without a subsequent lowering of fat intake. But the health implications did not arise due to an isolated macronutrient (e.g. sucrose) or even just excessive energy intake, but rather the combination of both.

If you consume any macronutrient (carbohydrate, fat, protein) in excess—which by definition means higher than your relative need for it in a specific window of time—your body has to handle the excess. The macronutrient illicits an effect relative to the body's needs, and the body's relative capacity to handle the excess. The dose makes the poison.

Two scenarios:

  1. You have just woken after 8 hours of sleep. The night before you did a full-body training session followed by a chicken and avocado salad for dinner. You have a large fried breakfast, danish pastry, two glasses of orange juice, and a cappuccino with sugar.
  2. It's Friday evening, you have just got back from the work. You have a large takeaway pizza, two beers, ice-cream, and 30 minutes later you are a watching a movie with a bowl of popcorn and bag of jelly beans.

In both cases you are consuming an excessive amount of energy (kcal), carbohydrate, fat, and protein in a single feeding window. The difference is though, in the first scenario you were at "higher relative state of need".

That is, you are coming out of an overnight fast, you body is recovering from a training session, you had a small low-carbohydrate meal before bed, and you are about to start your working day. Therefore your muscles and liver have lower levels of glycogen (stored carbohydrate), you were metabolising both glycogen and fat for energy overnight, and your protein needs are higher (negative nitrogen balance).

In the second scenario, the typical working day with little physical activity and two meals with snacks in-between, places you in a "lower relative state of need". That is before you even order the pizza, your energy and macronutrient needs are fairly low. Now couple the Friday night feasting with almost no physical activity until the following day, and you can imagine what the body has to go through to deal with the excess.

Chronically repeat various graded versions of the second scenario, and you have the metabolic health epidemic you see today.

My point is that a meal and it's ingredients have an effect positive or negative relative to the body's "state of need" for it, and though there are indeed vastly more complexities to nutrition, very simply speaking the problems seen with any dietary choice comes down to an excess and/or deficiency relative to the need in a window of time, be it acutely or over the long-term.

There are plausible mechanisms and research evidence that support the suggestion that consumption of excess sugar promotes the development of cardiovascular disease (CVD) and type 2 diabetes (T2DM) both directly and indirectly.5

The present experiments provide clear evidence that the amount of carbohydrate in a diet determines whether a high-fat diet will induce obesity, or not.6

…when fructose supplements diets with excess calories compared with the same diets alone without the excess calories, it leads to weight gain and all of its downstream cardiometabolic disturbances, including an increase in fasting glucose, whole-body and hepatic insulin resistance, apolipoprotein B, fasting and postprandial triglycerides, uric acid, and markers of nonalcoholic fatty liver disease.7

Apart from improvements in HbA1c over the short term, there is no superiority of low-carbohydrate diets in terms of glycemic control, weight, or LDL cholesterol.8

In pooling the totality of the highest-quality evidence from randomized controlled trials, they confirm that fructose in substitution for glucose or sucrose over a wide dose range has the ability to reduce postprandial glycemic responses and improve longer-term glycemic control without incurring any adverse effects.7

Clinical diet intervention studies in healthy men and women that definitively demonstrate that sugar consumption at commonly-consumed levels can increase risk factors for metabolic disease in the absence of body weight and fat gain are missing.5

Indirect estimates of metabolic health, such as insulin sensitivity and glycemic control, revealed no consistent effect of dietary carbohydrates on these variables, irrespective of the occurrence of body mass change. However, certain markers of cardiovascular disease risk (ie, blood triglycerides and HDL cholesterol) do appear to respond positively and relatively rapidly to a reduction in dietary carbohydrate intake across a range of absolute ingestion rates, although this effect was not consistent across all studies.9

Therefore, it is not helpful to assume because in certain contexts carbohydrate is unhealthy, that carbohydrate is wholly unhealthy and should be avoided entirely.

Energy Provision

All energy requiring processes in the body are served by the transfer of energy from an unstable molecule called adenosine triphosphate (ATP). Energy is released from ATP when the terminal phosphate is cleaved off the molecule by water (hydrolysis) resulting in: Energy + P + Adenosine Diphosphate (ADP).

The relationship between substrate energy contribution and power output. Carbohydrates (glucose) is the primary contributing substrate used during the first 6-60 seconds of exercise.

Fundamentally all sources of energy: exogenous "dietary" (e.g. carbohydrate, fat, protein, alcohol), and endogenous (e.g. blood glucose, glycogen, fat, protein), are metabolised in varying length multi-step processes to resynthesise ATP.

These metabolic processes require ATP, and yield ATP at varying rates and volume. Since energy cannot be created or destroyed only transferred, we can talk about energy metabolism as "ATP turnover".

Exercise power output is predicated on ATP availability and the rate of ATP turnover. Initial resting levels are high, and short-step metabolic pathways can resynthesise ATP rapidly, but as the duration of exercise increases these initial pathways have to be superseded by longer-step pathways which though generate more overall ATP, do so far slower. The limitation being in part the location, transport and deliver of molecules and co-factors.

Quantitatively, it has been estimated that the rate of ATP generation based on the carbohydrate oxidation is in the range of 0.51 to 0.68 mmol per second per kg body mass. In comparison, the rate of ATP generation based on triacylglycerol fueling is approximately two- to threefold lower (0.24 mmol per second per kg body mass).1

Substrate Contribution in Climbing

I am not aware of (yet) any direct studies on substrate contribution in climbing, but we do have data on resistance and endurance exercise.

Resistance exercise is typically characterised by short bursts of nearly maximal muscular contraction, and in comparison to endurance exercise (e.g. >1 hour running or cycling), resistance exercise would better mimic the exercise modality of climbing.

Phosphocreatine (PCr/CP) and glucose derived from the breakdown of glycogen (glycogenolysis) are the major substrates of the energy delivery pathways for resistance exercise.

Phosphocreatine (PCr)

Small stores of PCr in muscle tissue can transfer phosphate (P) directly to ADP via an enzyme (creatine kinase) resulting in creatine (Cr) and ATP. The phosphagen system is the primary source of ATP resynthesis during the first 10-15 seconds of work, the dominant pathway during low-oxygen availability (anaerobic) maximal power output and interval exercise (short rest/exercise periods).

PCr itself is only resynthesised during aerobic conditions (rest/recovery periods) via ATP produced through oxidative phosphorylation (OXPHOS) in the mitochondria. The same enzyme (creatine kinase) facilities the transfer of phosphate (P) from ATP back to creatine (Cr) producing ADP + PCr. The rate of PCr resynthesis is then dependent on the muscles oxidative capacity, and training modalities that improve mitochondrial biogenesis would increase OXPHOS capacity.10

You have experienced the effect of resting between boulder attempts. The "power recovery" you feel is the recovery of muscle PCr from the ATP generated at rest. This is also why optimising muscle creatine stores through daily supplementation with creatine monohydrate has demonstrated both power and work volume improvements across multiple sports.

While it is likely that observed increase in power output is due to the ability of creatine to rapidly re-phosphorylate ATP for rapid energy generation, recent evidence indicates that this response may also be a result of decreased muscle glycogen utilization and muscle protein degradation.11

Glycogen (glucose)

Glycogen is long branched chains of hydrated glucose molecules (3g water to 1g glucose), and is made and stored in the cells of the liver (~100g) and muscles (~350-700g depending on diet, training status, muscle fibre type composition, sex and bodyweight) and can be reduced by fasting, low intake of dietary carbohydrate, and/or by exercise.12 It is because of the water content of glycogen, that you can gain or lose kilograms of body-weight over a weekend, and why low-carbohydrate diets appear to be so effective in the short-term.

During exercise glucose is liberated from glycogen, each glucose molecule metabolised yields 2 ATP and 2 molecules pyruvate. After the phosphagen (PCr) system this is the shortest-step anaerobic process which contributes ATP during the first 6-60 seconds of work.

If oxygen is present, pyruvate is used in aerobic energy metabolism with 1 glucose molecule ultimately yielding 32 ATP molecules. If no oxygen is present, pyruvate is metabolised to lactate, where lactate is converted to glucose in the liver or back to pyruvate. During high-intensity exercise lactate accumulates due to the lack of oxygen, but the "burn" you feel in your muscles and often resulting fatigue, has nothing to do with lactate acid (conjugate acid of lactate), but rather the accumulation of other metabolites such as hydrogen ions (H+) and phosphate (P).13 20-90% of lactate formed during exercise is resynthesised back to glycogen in the muscle, but glycogen synthesis from lactate is not favourable in the presence of elevated blood glucose or insulin.14

Substrate Use Data

Studies have shown that 6 sets of leg extensions performed at 35% 1-RM (35% of the maximum weight you could lift once "1 rep") decreased muscle glycogen by 38%, and 3 sets of biceps curls to failure reduced muscle glycogen to 25%.15

A study involving 8 bodybuilders arm-curl training (80% 1-RM) showed PCr decreased 62% and glycogen 12% after 1 set, and 50% and 24% after 3 sets. The 62% decline in PCr following 1 set of resistance exercise (~37 sec of work), is similar to the 64% decline shown following 30 sec maximal sprint.16

PCr is restored acutely after 1 min recovery, and almost fully after 3 minutes. However lactate and H+ would not be fully cleared, and thus fatigue is likely caused by decreased PCr, and increased H+ as exercise continues.16

In a 2016 study, CrossFit athletes' consuming a mean carbohydrate (CHO) intake of 6g/kg/d versus 3g/kg/d completed 154.4 (± 29.0) versus 139.2 (± 28.0) repetitions during their 12 minute workout (+15.22; +10.9% improvement), and the high-CHO group's VO2 increased from 38.2 (± 4.9) to 40.0 (± 3.9).17

Repetitions completed (mean ± SD) during the pre-CHO intervention (mean of baseline performance tests; Pt1 + Pt2) and the post-CHO intervention (Pt3) by the CHO and control group. (n=18). *Post CHO was significantly different from Pre CHO in both groups (p = 0.002).

Running on Carbohydrate or Fat?

Quoting my Instagram post: Running on Carbohydrate or Fat? to provide further context on how carbohydrate (glycogen) metabolism allows greater sustained power output.

Fat metabolism requires oxygen, and to generate the same rate of ATP turnover as glycogen metabolism, you literally have to breath harder. Though this may not be directly evident in climbing, but the fact remains, carbohydrate metabolism provides more power ouput at a lower oxygen consumption. Take that as you will.

The energy cost of running for the average person is around 1.0 kcal/kg/km

If you were burning fat, you would get around 4.71 kcal per liter of oxygen you consume. If you were burning carbohydrate, you would get around 5.06 kcal/l of oxygen consumed.

The slide provides an example 55 kg elite (0.9 kcal/kg/km) runner who would expend roughly 2089 kcal over a 24 km marathon.

Greater glycogen availabilty allows greater power production with less oxygen consumption.

If they wanted to run the marathon in 2 hours, and derived the majority of their energy from fat, they would be required to consume 3.70 liters of oxygen per minute (l/min) to maintain their speed. If they had a maximum VO2Max of 80 ml/kg/min, they would have to run at 84% of their VO2Max to finish in time.

If the same runner derived the majority of their energy from carbohydrate, they would only have to consume 3.48 l/min of oxygen, and run at 79% of their VO2Max to finish in time.

So, put yourself in their shoes. Which would you prefer to run, which would feel more comfortable? Running at 84% or 79% of VO2Max?

More so, if you can run at 84% of VO2Max using fat, why not run at 84% of VO2Max using carbohydrate, run faster, and thus finish under 2 hours.

Fuel use during sport is always a mix of carbohydrate and fat. This post is not about a high-carbohydrate diet versus low-carbohydrate diet, but the point is, that the person with the greater available carbohydrate stores (muscle glycogen) will have the greater available power production at both lower and higher intensities then the person with less available glycogen stores.

Greater glycogen availabilty allows greater power production with less oxygen consumption.

Nutritional Considerations for Bouldering (2017)

Around the time I was preparing the original show notes for ClimbSci - Episode 02 - Carbohydrate, and what has now become this article; Smith, E, et al released their excellent 2017 review paper titled: Nutritional Considerations for Bouldering (PDF).

Quoting their carbohydrate recommendations:

The recently updated position paper on Nutrition and Athletic Performance, recommends carbohydrate intakes for athletes ranging from 3 to 12 g/kg/day (Thomas et al., 2016). However, a carbohydrate intake of ~5 g/kg body weight/day is sufficient to maintain glycogen stores during other sports featuring similar elements of repetitive high-intensity bouts of exercise and resistance training (Tipton et al., 2007). It is important to tailor carbohydrate intake in line with training periodisation and daily energy goals. Carbohydrate consumed 1-4 hours before training enhances skeletal muscle carbohydrate oxidation and glycogen resynthesis, particularly important in the morning after an overnight fast (Thomas et al., 2016). In sports such as bouldering, where carbohydrate depletion is not a primary concern, the pre-training meal need not be carbohydrate focussed and an intake of 1 g/kg of body weight prior to exercise should be sufficient (Maughan & Burke, 2012). The use of carbohydrate loading is not necessary for high-intensity, short duration events such as bouldering and may have an adverse effect on performance due to the associated weight gain.18

It should be encouraging to you that different researchers have come to similar conclusions, and that both of us highlight…

It is important to tailor carbohydrate intake in line with training periodisation and daily energy goals.18

Carbohydrate (CHO) Intake Recommendations

The above long preamble was to provide the background before I list my recommendations, and importantly the references that informed my recommendations. Certainly take the time to read data and make your own decisions on the subject.

What follows is what I feel are practical applications of carbohydrate feeding strategies for climbing, derived from the currently available data in other sports and research. I may be wrong, and welcome feedback so I can continue to update these recommendations for everyone's best possible use.

Facebook: comments and discussion.

Daily Strategies

  • Muscle glycogen stores are roughly ~400g, liver glycogen stores ~100g, and depending on the intensity and duration of the climbing/training session, upper/lower-body glycogen could be reduced by ~20-40%.
  • CHO intake (daily total) of 5-7g/kg (body mass) would suffice for moderate- to high-intensity climbing/training days. I.e. ~350g-500 CHO per day for a 70kg climber.
  • CHO intake (daily total) of 3-5g/kg would suffice for low-intensity or skill-based training days like fingerboard, mobility, yoga, etc. I.e. ~200-350g CHO per day for a 70kg climber.
  • CHO intake (daily total) of 3g/kg would suffice for recovery or rest days. I.e. ~200 CHO per day for a 70kg climber.
  • CHO intake (post-session) of 3g/kg post- climbing/training leading to bed would suffice to restore glycogen levels. I.e. ~200g CHO consumed in the hours after climbing/training leading to bed for a 70kg climber.
  • CHO intake (peri-session) of ~30-60g with ~500ml of liquid every hour of moderate- to high-intensity climbing/training is likely to improve performance, maintain high workloads and focus, and positively influence liver and muscle glycogen recovery rates. The addition of caffeine has been shown to improve performance in most individuals and may augment glycogen recovery. I.e. 500ml sports drink (or sugary snacks) plus a cup of coffee.
  • Rinsing the mouth with a CHO drink (or sucking a candy) but not ingesting it (CHOR), has been shown to improve performance, attributed to the activation of regions of the brain associated with reward and motor control. CHOR may be beneficial if no further CHO is wanting to be ingested due to worries about gastrointestinal distress, or to aid the management of energy balance during caloric restriction. Interestingly the CHO does not have to taste sweet. I.e. Maltodextrose (Amendments)

Specific Periodised Strategies

  • CHO intake of 5-7g/kg/day leading up to and within the climbing/training session, but with no consumption of CHO after the session "train high, sleep low", may augment endurance training and improve body-composition.
  • CHO intake of ≥7g/kg/day during high-intensity overreaching training periods (1-2 weeks) may attenuate the negative effects of intensified training on symptoms of overreaching, performance reduction is less profound, tolerance to training volume increased, and better recovery.

Preparation for Project or Competition

  • Glycogen stores can be optimised by 24-36 hours of rest (avoiding muscle damaging climbing/training) with CHO intakes of 7g/kg/day. I.e. ~500g CHO for a 70kg climber.
  • 3-days of CHO-loading (≥7/kg/d) may be beneficial before events, but climbers should experiment first due to water gain, possible bloating and subjective feelings of heaviness. Since CHO can be carried, CHO-loading probably unnecessary.
  • CHO-loading is not recommended for climbers with clinical issues such diabetes I or II, endocrine disorders, or are sensitive to weight gain. Moderate CHO intake (5-7g/kg/day) would suffice. Please consult a medical specialist if unsure.

Day of Project or Competition

  • Climbers must experiment with CHO types, amounts, timing, meal combinations (CHO, protein, fat), and supplements (sports drinks, gels, etc), well before events. The decision, testing, and practice of event feeding strategies is essential to mitigate performance impairment.
  • Consume 3-4g/kg CHO 3-4 hours away from event, and 1-2g/kg CHO ~1 hour before event. I.e. 200-300g, and 70-100 CHO for a 70kg climber.
  • Low-glycemic CHO are able to sustain blood-glucose during events, but be wary of consuming high-fiber CHO due to possible gastrointestinal issues.
  • ~30-60g of CHO with ~500mls of liquid every hour of event is likely to improve performance, maintain high workload and focus, and positively influence liver and muscle glycogen recovery rates. The addition of caffeine has been shown to improve performance in most individuals and may augment glycogen recovery. I.e. 500ml sports drink (or sugary snacks) plus a cup of coffee. This strategy along with post-session CHO consumption (3g/kg) is essential if there are multiple events spread across the day.
  • Rinsing the mouth with a CHO drink (or sucking candy) but not ingesting it (CHOR), has been shown to improve performance, attributed to the activation of the brains regions associated with reward and motor control. CHOR may be beneficial if no further CHO is wanted to be ingested due to worries about gastrointestinal distress. (Amendments)
  • Worth repeating: Experiment and test your event feeding strategy well before an event.

Considerations During Menstrual Cycle

  • During low-hormone menstrual phases (first and last week), women are physiologically similar to men in CHO metabolism and glycogen recovery. During the first two weeks of the follicular phase, oestrogen increases before dropping with progesterone rising in the following two weeks of the luteal phase. The follicular phase allows for greater CHO use, and would lend itself to the upper range of CHO intake and higher intensity training or projects. During the luteal phase there is lower CHO but higher fat usage, lending to the lower range of CHO intake and moderate to low training intensities or projects. Power endurance performance may be affected negatively during the (high progesterone) peak of the luteal phase, but much longer >90 endurance training (i.e. running, cycling) may be benefited due to greater reliance on fat and the glycogen sparing effect of this phase.
  • Program your hard training sessions with higher CHO intake during your low-hormone phases.

Considerations for Diabetic Individuals

Important: I am not a dietitian, so please consult a medical sports nutrition specialist if you have concerns of about nutrition strategies for individuals with diabetes or other metabolic syndromes.

The mid-postprandial period offers a window of opportunity to diabetes patients to exercise and blunt the glucose surge without fear of hypoglycemia (low blood glucose). The early and late postprandial periods are “grey” segments, constantly vulnerable to intrusion by hepatic glucose.19

  • Postprandial: Early- (0-30 min), mid- (30-90 min), late- (>90 min)
  • Pre-meal exercise uses endogenous glucose and muscle glycogen
  • Exercise during mid-postprandial period uses exogenous glucose, glucose being abundant in the blood 30-90 minutes post-meal
  • Start and finish the daily exercise session within the bounds of the mid-postprandial (30-90 min of exercise) period, and you are assured of plentiful supplies of blood glucose.

Notable References Informing Guidelines

The above were my recommendations, what follows are bulleted research references which should aid you in understanding whether or not my guidelines are sensible.

As I come across pertinent new research I will update these lists.

Training and Performance on a High-Carbohydrate Diet

  • Consuming CHO during training and performance and increasing exogenous CHO-OX results in improved endurance performance.20
  • Consuming 10g/kg/d CHO versus 5g/kg/d CHO (both with 2g/kg/d protein) has been shown to promote greater muscle glycogen (+65%), and power output (+10.7%) over 4 weeks of intense twice-daily rowing training.21
  • CrossFit athletes' consuming a mean CHO intake of 6g/kg/d versus 3g/kg/d completed 154.4 (± 29.0) versus 139.2 (± 28.0) repetitions during their 12 minute workout (+15.22; +10.9% improvement), and the high-CHO group's VO2 increased from 38.2 (± 4.9) to 40.0 (± 3.9).17
  • High-CHO (and high energy) intake can attenuate the negative effects of intensified training (1-2 week training camp) on symptoms of overreaching, performance reduction is less profound, tolerance to training volume increased, and better recovery.22
  • CHO-electrolyte (6.4% solution) consumed every 15 min during 90 minutes of high-intensity exercise reduced glycogen utilisation by 22% compared to placebo, and improved endurance capacity likely due to higher plasma glucose for muscle metabolism and the central nervous system.23
  • CHO consumption (without electrolytes) during high-intensity cycling has been shown to stablise plasma sodium (Na+) levels.24
  • CHO consumption during exercise can attenuate the increase in cortisol during exercise, and spare muscle glycogen contributing to faster restoration of serum IL-6 (pro-/anti-inflammatory cytokine) during recovery which may inhibit the effects of pro-inflammatory cytokines such as TNFα25
  • CHO consumption during and after exercise affects immune cell function, serum cytokine and myokine expression, promoting anti-inflammatory and immunostimulating effects.25
  • High-CHO diet increases the number and activity of sodium glucose co-transporter transporters in the intestines, allowing greater CHO absorption and oxidation during execercise.2
  • CHO consumption can prevent the deterioration of the electrical properties of muscle fibre membranes, and protect membrane excitability by increasing Na+/K+ pump activity26
  • CHO ingestion rates of 15–30 g/h with ~500 mL of fluid will likely lead to the greatest overall performance compared to supplementing only amino acids during acute strength and conditioning training sessions.27
  • A glucose+fructose mix (i.e. sucrose) is absorbed at a faster rate in the gut and is burned more effectively as fuel sources compared to just glucose.28
  • Caffiene has been shown to improve glycogen synthesis, and has a glucoe partitioning effect.29

Restricting Carbohydrate Post-Training

  • Consuming CHO immediately after training results in the highest rates of glycogen synthesis30
  • Restricting CHO immediately after training results in deprived glycogen levels, impacting performance within the next 4-8 hours, and has not been shown to influence metabolic gene expression. However after 24 hours glycogen is recovered to pre-exercise levels as long as sufficient CHO and energy is consumed.31
  • Resistance training (set of leg extensions to fatigue) depleted muscle glycogen by 30%, and without post-training CHO, levels increased by only ~5% after 6 hours.14
  • Training with high-glycogen and high-CHO availability, but not consuming CHO post training "train high, sleep low" has shown to improve endurance performance and body-composition.32
  • Superimposing 4 weeks of CHO restriction (only ~80g CHO post-training) with regular endurance training had no superior effects on performance and muscle adaptations in elite endurance athletes.33
  • Consuming low-CHO high-fat after training has not been shown to increase regulatory genes associated with mitochondrial biogenesis, but may impair muscle protein synthesis and muscle remodelling processes thereby potentially causing maladaptive responses for training adaptation if performed long-term.34
  • Protein consumption before, during and after exercise does not attenuate AMPK signalling in human skeletal muscle when exercising in a glycogen-depleted state.35
  • CHO supplementation is the most effective means for minimizing immune disturbances during exercise recovery.36

Training and Performance on a Low-Carbohydrate Diet

  • Although low-CHO high-Fat diet will increase fat oxidation, perhaps by increasing fat metabolism enzyme activity, it can reduce CHO metabolism enzyme activity.37 Therefore FAT-OX is increased, partly because of inability for CHO-OX. Since CHO-OX is important for high-intensity exercise such adaptations are unwanted.
  • Consuming a low-CHO diet may impact the intestines capacity to absorb CHO leading to reduced CHO oxidation.2
  • Short-term high-intensity exercise mostly utilises energy from phosphocreatine (PCr) and glycolysis, therefore elevated FAT-OX rate after adaption to a LCHF diet is unlikely to increase performance.38
  • CHO mouth rinsing (CHOR) without ingestion has been associated with increased performance, benefits which have been attributed to activation of the brains regions associated with reward and motor control. Anaerobic performance may be optimised with CHOR to minimise gastrointestinal distress in comparison to ingesting CHO.39 (Amendments)
  • CHO mouth rinse compared to PLA or CON does not provide a significant or practically meaningful improvement or detriment in upper-body muscular strength and endurance. Athletes and coaches should not employ a CHO mouth rinse to enhance upper-body maximal muscular strength or endurance.40 (Amendments)
  • High-intensity exercise was not improved after 3 weeks of intensified training in a ketogenic diet group (-1.6%), but did improve in athletes consuming high-CHO (6.6%) and mixed (5.5%).41
  • A ketogenic diet in CrossFit athletes improved body-composition without negatively impacting lean body mass, strength, or power performance.42 Changes in performance, likely confounded by changes in body weight.
  • It appears that so-called "keto adaptations" (e.g. FAT-OX, mitchondrial factors) are in place within a month, thus 2 years of ketogenic dieting, has the same degree of "fat adaptation" as 3 weeks.43
  • In view of the detrimental effects of low carbohydrate availability on the immune system, chronic carbohydrate restriction should be avoided during intense periods of training.36

The ketogenic diet has received considerable attention in the popular press and many claims have been made recently. However, it is important to realize that, to date, not a single study has demonstrated performance benefit of a ketogenic diet, including the early study that is often referred to (Phinney, 1983). Thus, at present, there are no data on ketogenic diets in athletes on which to base performance claims.2

Menstrual Cycle Impact on Carbohydrate Use

  • Differences in estrogen concentration between men and women during longer-endurance exercise result in improved performance in women after men have depleted their glycogen stores. Women in the luteal phase compared to follicular phase have less reliance on CHO during endurance exercise. It is possible that estrogen may not be the primary mediator of the decrease in glycogen utilization observed during the luteal phase.44
  • A reduction in maximal endurance performance during mid-luteal phase, but effect was not observed for jumping and sprint performance.45

Carbohydrate Overfeeding and De Novo Lipogenesis

  • Intake of physiologically normal carbohydrate levels has no impact on adipose tissue levels via de novo lipogenesis, suggesting that the human body can accommodate intake of relatively large amounts of carbohydrates without a need to store carbohydrates as fat.46
  • Previous studies have reported that in response to a hypercaloric challenge, shifts in substrate oxidation are dominated by the need to maintain carbohydrate balance, due to its limited storage capacity. Increases in carbohydrate intake are therefore buffered by almost equal increases in carbohydrate oxidation, even at carbohydrate excesses of up to roughly 30-50% of daily energy expenditure, before net de novo lipogenesis becomes physiologically important. Whereas carbohydrate intake stimulates its own oxidation, several studies have shown that fat intake does not stimulate its own oxidation—at least not in the short term in lean healthy adults. For instance, two studies found that 50% carbohydrate overfeeding increased carbohydrate oxidation about two-fold to match carbohydrate intake, and this change was accompanied by an increase in energy expenditure, whereas 50% fat overfeeding increased fat oxidation rates by only ~20% with no change in energy expenditure.47
  • Glycogen storage capacity in man is approximately 15 g/kg body weight and can accommodate a gain of approximately 500g before net lipid synthesis contributes to increasing body fat mass. When the glycogen stores are saturated, massive intakes of carbohydrate are disposed of by high carbohydrate-oxidation rates and substantial de novo lipid synthesis (150 g lipid/d using approximately 475 g CHO/d) without postabsorptive hyperglycemia.48

2017 Review: Dietary carbohydrates, components of energy balance, and associated health outcomes

The role of dietary carbohydrates in the development of obesity and associated metabolic dysfunction has recently been questioned. Within the last decade, the Scientific Advisory Committee on Nutrition carried out a comprehensive evaluation of the role of dietary carbohydrates in human health. The current review aims to complement and extend this report by providing specific consideration of the effects of the component parts of energy balance, their interactions, and their culmination on energy storage and health.9

  • There is no universally accepted threshold for what constitutes a "high-" or "low-" carbohydrate diet, and understandably so because individual requirements can vary hugely. Nonetheless, the habitual carbohydrate intake in most studies in this review is typically 200 g/day or more, whereas the magnitude of carbohydrate restriction varies greatly among studies, with the more severe regimens limiting carbohydrate intake to 100 g/day.
  • The minimal changes in body mass with carbohydrate restriction alone render it unlikely that this is a major factor driving net changes in energy balance.
  • Complete restriction of carbohydrates during the morning via extended fasting has resulted in less energy being voluntarily expended through low-intensity physical activities, concomitant with lower average blood glucose values.
  • Overall, the data available in relation to dietary carbohydrates and adiposity are inconsistent, but most evidence indicates greater adiposity in response to higher carbohydrate diets.
  • The majority of trials suggest there is no systematic change in markers of insulin sensitivity or glycemic control even in response to relatively extreme manipulation of dietary carbohydrate content that impacts energy intake and body mass/composition.
  • What can be concluded, however, is that manipulating dietary carbohydrate content in favor of lower carbohydrate intake can positively impact some markers of cardiovascular disease; most commonly an increase in HDL cholesterol and rapid reduction in blood triglycerides is seen.

Bullet points are verbatim quotes from the 2017 review. Do read the whole paper to fully understand context.

Amendments

If I ever change my mind, need to correct, or remove anything in this article, I will list it below and strike the original content.

  • 19/09/2017: CHO mouth rinsing (CHOR) [Removed]
    • CHO mouth rinse compared to PLA or CON does not provide a significant or practically meaningful improvement or detriment in upper-body muscular strength and endurance. Athletes and coaches should not employ a CHO mouth rinse to enhance upper-body maximal muscular strength or endurance.40

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