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Blog / 2017 / March / Q&A - Carbohydrates, Performance & Weigh...
March 29, 2017

Q&A - Carbohydrates, Performance & Weight Loss: Is Low The Way To Go Or The Way To Bonk?

by Admin

ACSM and Wheat Foods Council recently hosted a webinar entitled Carbohydrates, Performance & Weight Loss: Is Low the Way to Go or the Way to Bonk? To watch a free recorded version of the webinar click here. The webinar is also available for two (2) CECs via ACSMceOnline.

Several questions were asked by attendees during the webinar. The answers to those questions are below, sorted by topical area.

Viewpoints presented in this blog reflect opinions of the author and Wheat Foods Council and do not necessarily reflect positions or policies of ACSM.

Carb Intake for Specific Sports/Training

Q: Can you give some examples of specific high carb foods that should be consumed before an endurance event lasting 1-2 hour (specifically soccer/hockey games where there are player substitutions)?

For soccer and hockey and other high-intensity intermittent sports, easily digestible carbohydrates (i.e. very little fiber) should be consumed 2-4 hours before games, with sports drinks consumed during the games. Examples of low-fiber easily digestible carbs could include rolls, tortillas, pasta, bread, rice, low-fiber breakfast cereals, crackers, white rice, potatoes or sweet potatoes without the skin, bananas or yogurt. Smaller portions of foods should be experimented with before training sessions to gauge tolerance.

Q: Do athletes in stop-and-go sports such as football need to load during the sport to replenish?

Athletes in HIIT sports with lots of downtime need to eat a high carbohydrate meal or snack (low fat, small amount of protein) 2-4 hours ahead of game time and then consume fluids w/carbohydrate as needed during the game. Special attention should be given to warm weather conditions when athletes are likely to lose considerable amounts of fluids and sodium through sweat. While most commercially available sports drinks will replenish some of the sodium losses, heavy sweaters may need to be assessed to make sure they are consuming enough sodium with their hydration fluids.

Q: Dr. Gaesser, based on these data, do you see a benefit of fat adaptation or the Train Low, Race High feeding method for athletes competing in high-intensity competitions lasting less than 1.5 hours, or those who complete, but do not "race" longer events (4-6 hour marathon).

There is no evidence to suggest that a "train low, race high" approach would benefit athletes competing in high-intensity competitions lasting less than 1.5 hours. For longer events, lasting 4-6 hours, there may be an advantage for persons wanting to "complete" the event without running out of glycogen, but there is no evidence to show that "racing" performance would be enhanced.

Q: In regard to a "post-workout snack," what are the benefits of consuming carbohydrates in addition to protein following a bout of exercise?

All forms of exercise, at all intensities, require the metabolism of glycogen (the storage form of carbohydrate) from the muscles and liver. Consuming carbohydrates after an exercise session replaces that glycogen.

Q: What are your thoughts on the glycemic index and performance?

Total carbohydrate intake is most important. The glycemic index is not that important. See the position statement from ACSM, Academy of Nutrition and Dietetics, and Dietitians of Canada (Medicine and Science in Sports and Exercise, 2016; 48(3): 543-68).

Q: What would be the recommendation for intermittent sports? You talked a bit about it, but what would be your thoughts?

For fueling intermittent sports (soccer, hockey, etc.), the best approach is to consume a high carbohydrate meal 2-4 hours prior to the event with plenty of fluids and sports drinks with electrolytes consumed during the event. Since a 75kg soccer player can burn approximately 1,500 calories in a game, consuming a carbohydrate/electrolyte solution is especially important. Although calorie needs can't be matched during a game, refueling with a high carbohydrate meal following the game will help recovery.

Q: When coaching someone RE: carbs and consuming enough to sustain high levels of physical activity, are we talking whole grain carbs (rice, pasta, breads, etc.) or fruits/vegetables?

Yes, all of the foods mentioned are carbohydrate sources. Dairy and legumes (beans) also provide carbohydrates. Grain sources of carbohydrates provide more calories by weight than vegetables or fruits (important for athletes) but also provide fiber, B vitamins, and folate (enriched grains only). Vegetables and fruits provide fewer calories but provide vitamins A and C, as well as plant polyphenols.

Q: With high-intensity intermittent training in obese subjects, what do you recommend: HCLF or LCHF, or balanced?

In terms of weight loss, the most important aspect for subjects is to reduce calories regardless of source. A low-fat diet ~(50% carb, 20-25% protein, 25-30% fat) has been shown in most studies to be the most beneficial for overall health.

Q: Would a fasted cardio workout fall under the category of having low carb availability?

Yes, that would be low carb availability.

Q: Would it be counterproductive to perform high-intensity exercise during a low-carb diet? The fact that your performance will be lower makes me think so.

It's unclear whether HIIT under low carb availability would be helpful or not, but certainly performance would be lower than while consuming a high-carb diet. Since most HIIT workouts are intended to be done at maximal intensity for short durations, if you can't reach maximal intensity, then the workout is compromised.

Definition of Low Carb, Normal & High Carb

Q: How are low-carb, "normal", and high-carb diets being defined? Many studies are being cited, but surely they all used different definitions for the quantities of the macros. Could 40(CHO)/30(PRO)/30(FAT) be considered high carb because there is still more carb than protein or fat?

There are no universally agreed upon definitions. High-carb diets generally are >60% of total energy from carbohydrates. Low-carb diets are generally <30% of total energy from carbs. Truly ketogenic diets are no more than about 10% of total energy from carbs.

Q: Could you please define the carbohydrate intake % of kcals at low-carb, normal, and high-carb diet?

There are no universally agreed upon definitions. High-carb diets generally are >60% of total energy from carbohydrates. Low-carb diets are generally <30% of total energy from carbs. Truly ketogenic diets are no more than about 10% of total energy from carbs.

Q: What should the ratio of primary source of CHO be in vegetables, fruits, and whole grains?
There are no specific guidelines. It would be difficult to consume enough fruits and vegetables to provide the necessary carbohydrate for athletes who train several hours per day. Grain sources would provide a denser form of carbs.

Body Weight & Carbs

Q: Can you go deeper on why glucose is not related to body weight?

Studies have shown that maximum rates of glucose absorption from the gut and oxidation in the body are unrelated to body weight. Therefore, recommendations for glucose consumption are in absolute terms, i.e., grams per hour (without regard to body weight).

Q: For fat loss, at the end of the day, does the whole amount of calories count in order to lose weight?

For the most part, calorie needs are determined by age, gender, height, and current weight. To lose approximately 1 pound per week, caloric intake must be lowered by 500 calories per day. Losing more than 1-2 pounds per week is not recommended since most people who do so are more likely to regain the lost weight.

Q: What is your take on lower carbohydrate based on somatotype? For example, an endomorph would benefit more from a lower carbohydrate diet than a lower fat diet, when it comes to fat loss.

I am unaware of any information on whether somatotype influences metabolic responses to diet. There is evidence that individuals who are insulin resistant may benefit more from a low-carb diet than from a low-fat diet, but there may be other dietary factors that influence this relationship (such as dietary fiber).

Acid/Base Balance, Gluten-Free, Paleo

Q: Do grains vary in acidity and/or alkalinity?

Yes, grains vary in terms of acidity/alkalinity. The effect on exercise performance, to my knowledge, has not been studied.

Q: In relation to high protein intake and acid-base balance, would you say that the increased blood acidity isn't directly due to the high protein, but rather the low carb/high fat that accompanies it? Increased acidity due to possible presence of ketone bodies or lactate?

The acid load associated with the high-protein diet is most likely due to the amino acids. Lactate during exercise while on a low-carb, high-protein diet is actually lower than while on a high-carb diet.

Q: With Paleo plans, it is claimed that "grains" are harmful to the small intestine and that's why they are not acceptable. What's your opinion on that?

Grains that contain gluten (wheat, barley, rye) are harmful to those with celiac disease and for some individuals with non-celiac gluten sensitivity. But these individuals are a small fraction of the population. Prevalence of celiac disease is thought to be about 1% of the population. Prevalence of non-celiac gluten sensitivity is not known, but best estimates are under 10%. For the vast majority of the population, grains are fine. In fact, whole grain consumption is consistently shown to be associated with good health and weight control.

Q: What are the advantages or benefits of getting carbohydrate consumption from whole grains as opposed to other plant sources?

Whole grains provide more fiber per serving than most fruits and vegetables except beans (kidney, black, chickpeas, lentils, etc.). Since many people do not or will not consume beans, the most effective way to increase fiber in the diet is through grains. The effects of fiber on colon health are well known, but the effects on cardiovascular health are even more beneficial. This may be due to the effects of fiber on beneficial bacteria in the gut.

Q: If you have gluten sensitivity or feel better by not consuming wheat, is there a way to have a high-carb diet?

If someone has gluten sensitivity, they should be tested for Celiac. To be effectively tested, the person must currently be consuming gluten or the test will come back as negative for Celiac. In the absence of Celiac, the only way to know if gluten-sensitivity is present is by an elimination diet where all FODMAPS (Fermentable, Oligo-, Di-, Mono-saccharides and Polyols) are removed and then carefully reintroduced to determine which oligosaccharides are causing the distress. To simply remove gluten without exploring other potential causes for the discomfort can lead to unintended nutritional consequences (reduced fiber, folate, iron intake). However, if gluten sensitivity or Celiac are confirmed, carbohydrates can be consumed from potatoes, dairy products, rice, corn, quinoa, oats, other gluten-free grains and legumes (beans), as well as fruits and vegetables.

Low Carb and Injuries

Q: Do we know if a relationship exists between low CHO diets and the incidence of overtraining syndrome in high endurance or elite athletes?

Overtraining syndrome or unexplained underperformance syndrome (UUPS) has many contributing factors, some of which may be due to low energy availability or under consuming key nutrients (e.g., protein or iron). While low-carbohydrate diets have not been linked directly to UUPS, they can certainly impact an athlete's level of perceived exertion. For more information about diet and overtraining syndrome, click here

High Carb Diets & Diabetes

Q: Has any research been done with active diabetics in relation to carbohydrate loads? Or at the very least, have hormonal levels also been tested as it relates to metabolism and, I guess, the pancreas?

I refer you to an excellent position statement on exercise and diabetes, published by the American Diabetes Association in 2016 (Diabetes Care, 2016; 39:2065-2078). It is available online here

Q: How about high-carb diet vs low-carb diet in diabetics?
I refer you to an excellent position statement on exercise and diabetes, published by the American Diabetes Association in 2016 (Diabetes Care, 2016; 39:2065-2078). It is available online here

Q: What about general health effects of high carb diets outside of performance? Many athletes (even elite) are being diagnosed with pre-diabetes and this becomes a concern.

This is a difficult question to answer without qualifying the characteristics of the high-carb diet. High-carb diets that are low in nutrient quality are not healthy. Dietary fiber, for example, is very important for health. High-carb diets that are high in fiber (from whole grains, fruits, vegetables, legumes) are healthier than an equally high-carb diet that is low in fiber. I'm not sure how many athletes, especially elite-level endurance athletes, are being diagnosed with diabetes or pre-diabetes. My hunch would be that this is not that frequent. Due to the tremendous individual variation observed in metabolic and performance responses to diet, individual results will vary and thus dietary strategies may need to be tailored to the specific needs of the athlete.

Keto Adaptation to Low Carb Diets

Q: In the Burke study the participants were only on the diet for 3 weeks. It is known that it takes at least 4 weeks to become keto adapted and until then, performance decrements may occur. Did any of the studies you referenced refuting low-carb diets allow for keto adaptation?

The exact amount of time needed to adapt to a ketogenic diet is not known. Three weeks is probably long enough. For up-to-date discussion on this, I refer you to the Burke study, which addresses this issue in detail (Burke et al., in the Journal of Physiology, published ahead of print on December 23, 2016).

Q: In the Bartlett study, or any of the studies that compare low-carb to hi-carb diets, are there studies in which, instead of high percentages of fat one were to include larger percentages of protein? Of course, some of that protein might be used for fuel but it would also, in theory, mitigate protein degradation resulting from exercise training.

Good question. Studies of effects of diet on performance are challenging because one has to consider carbs, fats and protein. Better protein balance may be maintained on a reduced-carb diet that is high in protein compared to fat. However, higher protein intakes may increase acid load and compromise tolerance for high-intensity exercise. This was shown in the study by Greenhaff et al. Diets with sufficient carbohydrate are important for competitive endurance performance, and it appears that going on a low-carb diet that is high in either fat or protein is not a good idea. But as Bartlett et al. suggest, a slightly higher protein intake (~20-25 grams) before, during, and/or right after a "train-low" session might be advisable.

Q: Could you explain what you mean by skeletal muscle adaptations with low carb?

These refer to enzymatic adaptations associated with increased capacity to oxidize fat as a fuel.

Q: So it is that our body knows we lack carbs and tries to store them and burn as little as it can?

Our bodies seem to have a high priority for replacing muscle glycogen. This is why fat is preferentially burned after exercise, especially after exercise that greatly reduces muscle glycogen. That is why carbohydrate intake is important during the recovery from intense exercise that depletes muscle glycogen.

Q: What about those that process fats and carbohydrates differently?

There is considerable individual variability in how we process macronutrients. Therefore, it can be expected that there will be considerable variability in how individuals perform under conditions of high or low carbohydrate availability. Still, there are no studies that have shown a low-carb diet will enhance exercise performance under competitive race intensities. And the study by Burke et al. indicates that a low-carb diet is likely to impair performance relative to a high-carb diet.

Q: With the Costill experiment, were participants in low-carb group adapted to a low-carb diet? Would someone who has followed a ketogenic diet fare better?

They were not adapted to a low-carb diet. The purpose of the study was to show that a low-carb diet prevents restoration of muscle glycogen levels within a 24-hour period, over three consecutive days of training. This study did not assess performance. It could be expected that athletes adapted to a ketogenic diet may have fared better during the three days of training because they would have used less muscle glycogen during the training sessions. Whether performance is improved on a ketogenic diet remains to be demonstrated. The study by Burke et al. (Journal of Physiology, published ahead of print on December 23, 2016) suggests that a ketogenic diet may impair performance.

Q: Are there studies comparing keto-adapted athletes to a traditional higher carb diet?
Yes, the study by Volek et al. (Metabolism, 2016; 65:100-110) compared keto-adapted endurance athletes with those who habitually consumed a high-carb diet. But this study did not include any actual performance measures. Keto-adapted athletes burned more fat during a submaximal exercise session, but this was well below competitive race pace.

Q: With this low-carb and higher fat diet, like with the Atkins Diet, is there an increased risk over time of heart attack because of the increase amount of fats in the diet? That is, cholesterol and LDL increase over time.

There are several short-term diet studies that show some improvements in cardiovascular and diabetes risk markers with a low-carb diet, but there are also several studies that show no improvements in health with carb-restricted diets. Moreover, there are several epidemiological studies that show health risks (including increased risk of premature death) associated with low-carb, high-protein (especially animal protein) dietary patterns.

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