Industry Presented Blog: Carbohydrate Conundrum Webinar Q&A
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Industry Presented Blog: Carbohydrate Conundrum Webinar Q&A

Potatoes USA | Feb 27, 2018

Viewpoints presented in this blog reflect opinions of the author and Potatoes USA and do not necessarily reflect positions or policies of ACSM.

Katherine A. Beals, PhD, RD, FACSM

Potatoes USA recently hosted an industry-presented webinar entitled: The carbohydrate conundrum: Are carbs essential or obsolete when it comes to health, fitness and athletic performance? Watch a free recorded version of the webinar. The webinar is also available for two (2) CECs via ACSM ceOnline.

Several questions were asked by attendees during the webinar and the answers are below.

Q- Are there studies that have examined the effects of a ketogenic diet on "high intensity" sports (e.g., power lifting, sprinting, etc).

The majority of studies have examined ketogenic diets in athletes participating in submaximal, endurance exercise (58-65% of Vo2 max) and most of these studies have measured alterations in substrate oxidation vs. actual performance, and with good reason. First, fat can only serve as a significant substrate under aerobic metabolic conditions (i.e., the aerobic energy system or oxidative phosphorylation). Anaerobic metabolism (such as would predominate in high intensity exercise such as sprinting) can only utilize glucose as a substrate, while the ATP-PCr energy system (which predominates in strength and power events, e.g., power lifting) utilizes ATP and phosphocreatine. So it would be very unlikely that a high fat diet would be beneficial for high intensity sports (since fat is not a viable fuel source for these sports). Second it is unlikely that endurance "performance" would be improved on a ketogenic, since to perform well in most endurance events (i.e., to "win") the athlete must complete a given distance in the shortest amount of time, which typically requires them to compete at an intensity leve higher than "submax". Indeed, an endurance athlete hoping to "win" his or her event while maintaining a submax intensity is going to be sorely disappointed. The only published study to date examining ketogenic diets in resistance-trained individuals is Wilson et al. (2017). (see abstract below).

Wilson et al. 2017 The Effects of Ketogenic Dieting on Body Composition, Strength, Power, and Hormonal Profiles in Resistance Training Males. J Strength Cond Res. 2017 Apr 7. [Epub ahead of print] Twenty-five college aged men were divided into a KD or traditional WD from weeks 1-10, with a reintroduction of carbohydrates from weeks 10-11, while participating in a resistance-training program. Body composition, strength, power, and blood lipid profiles were determined at week 0, 10 and 11. A comprehensive metabolic panel and testosterone levels were also measured at weeks 0 and 11.Lean body mass (LBM) increased in both KD and WD groups (2.4% and 4.4%, p<0.01) at week 10. However, only the KD group showed an increase in LBM between weeks 10-11 (4.8%, p<0.0001). Finally, fat mass decreased in both the KD group (-2.2 kg ± 1.2 kg) and WD groups (- 1.5 ± 1.6 kg). Strength and power increased to the same extent in the WD and KD conditions from weeks 1-11. No changes in any serum lipid measures occurred from weeks 1-10, however a rapid reintroduction of carbohydrate from weeks 10-11 raised plasma TG levels in the KD group. Total testosterone increased significantly from Weeks 0-11 in the KD diet (118 ng/dl) as compared to the WD (-36 ng/dl) from pre to post while insulin did not change.

Q- What about the effects of consuming exogenous ketones (e.g., as a supplement)? Has this been shown to improve performance?

Ketone supplements-(ketone salts and esters) have gained some limited popularity as a potential ergogenic aid among athletes, particularly endurance athletes. The goal is to increase ketone levels in the body quickly without having to follow a high fat, low carbohydrate diet (i.e., gain the hypothesized benefits of a ketogenic diet without having to actually follow it!). The limited available research does not show a performance benefit of supplementing with exogenous ketones. There was a very nice review paper on the topic published in the peer-reviewed journal, Sports Medicine, last year by Pinckaers and colleagues (Pinckaers PJ et al. 2017) (see abstract below).

Pinckaers PJ et al. Ketone Bodies and Exercise Performance: The Next Magic Bullet or Merely Hype? Sports Med. 2017; 47(3):383-391. Elite athletes and coaches are in a constant search for training methods and nutritional strategies to support training and recovery efforts that may ultimately maximize athletes' performance. Recently, there has been a re-emerging interest in the role of ketone bodies in exercise metabolism, with considerable media speculation about ketone body supplements being routinely used by professional cyclists. Ketone bodies can serve as an important energy substrate under certain conditions, such as starvation, and can modulate carbohydrate and lipid metabolism. Dietary strategies to increase endogenous ketone body availability (i.e., a ketogenic diet) require a diet high in lipids and low in carbohydrates for ~4 days to induce nutritional ketosis. However, a high fat, low carbohydrate ketogenic diet may impair exercise performance via reducing the capacity to utilize carbohydrate, which forms a key fuel source for skeletal muscle during intense endurance-type exercise. Recently, ketone body supplements (ketone salts and esters) have emerged and may be used to rapidly increase ketone body availability, without the need to first adapt to a ketogenic diet. However, the extent to which ketone bodies regulate skeletal muscle bioenergetics and substrate metabolism during prolonged endurance-type exercise of varying intensity and duration remains unknown. Therefore, at present there are no data available to suggest that ingestion of ketone bodies during exercise improves athletes' performance under conditions where evidence-based nutritional strategies are applied appropriately.

Q- If the goal is fat loss (or increased fat oxidation), and not high performance, what is the negative impact of a ketogenic diet? If the training protocol is primarily submaximal training and the focus is increasing fat oxidation, wouldn't a ketogenic diet benefit the "casual exerciser" seeking to lose body fat?

Research consistently shows that following a ketogenic diet will promote alterations in substrate oxidation during submaximal exercise, specifically a relative increase in fat oxidation and a relative decrease in carbohydrate oxidation. Thus, metabolically, it would seem to makes sense this type of diet could promote beneficial changes in body composition. But, as is true with many aspects of metabolism, it is not that simple and it is all "relative"! The keys lie in the terms "submax" and "relative". Most athletes routinely train at intensities higher than submax (they have to if they are going to improve performance and win races). The alterations in substrate oxidation on a ketogenic diet will likely not hold true for exercise above submax intensities (there is currently a lack of data in this area so we do not know for sure, but from a pure metabolic standpoint, high intensity exercise cannot be maintained without glucose as a fuel source). Ok, so what about recreational athletes and exercisers who spend a lot of time training in the "submax" zone? Here is where the term "relative" comes into play. Remember that weight loss (which includes fat loss) is a matter of energy balance (i.e., calories consumed and calories expended). A given exercise bout (let's use a 60 min run at 62% Vo2 max for an example) will expend a certain number of calories, let's say 500 calories. If we have two runners (same body weights), one following a ketogenic diet and one following an adequate carbohydrate diet, they will both expend 500 calories. The difference is that the runner on the ketogenic diet will oxidize relatively more fat vs CHO (let's say 60% fat and 40% CHO) compared to the runner on the adequate carbohydrate diet (who will oxidize 50% fat and 50% CHO). But, at the end of the day the calories they expended in the exercise bout will be similar; thus, assuming similar energy intake (and expenditure the rest of the day) fat loss will likely not be different. With the exception of the Wilson et al (2017) study (mentioned above), there have been no studies examining body composition changes in "athletes" following a ketogenic diet compared to those following an adequate carbohydrate diet. There are, however, several studies that have compared the Atkins diet (a well-known ketogenic diet) to lower-fat, more moderate carbohydrate diets in sedentary individuals. The results indicate that those on the Atkins diet often lose significantly more weight in the first few months; but, by the end of a year, weight loss is similar between the groups (and the initial, rapid weight loss is often attributed to the greater energy deficit-that is, a reduced calorie intake-- in the Atkins group).

Q- In the webinar you mentioned that ketogenic diets may actually be glycogen impairing vs glycogen sparing. Can you explain this?

Yes! In her review article covering the controversy of training high vs training low, Burke et al. (2010) emphasizes that the alterations in substrate oxidation (i.e., relative increase in fat oxidation and decrease in carbohydrate oxidation) may not be as metabolically beneficial to the athlete as they might seem. (see reference below) Specifically, fat adaptation enhances the metabolic pathways and upregulates enzymes involved in fat oxidation at the "expense" of pathways and enzymes involved in carbohydrate metabolism/utilization. Burke provides the example of pyruvate dehydrogenase (a rate-limiting enzyme in carbohydrate utilization), and indicates that some limited research shows that fat adaptation suppresses the activity of this key enzyme, thus, causing an impairment of the utilization of carbohydrate during exercise. She supports this metabolic effect with studies from her own lab as well as others that could find "no evidence of an expected improvement in exercise performance [on a high fat diet], but instead, a reduction in the ability to perform high intensity exercise". (Burke 2010).

Burke LM1. Fueling strategies to optimize performance: training high or training low? Scand J Med Sci Sports. 2010 Oct;20 Suppl 2:48-58.  Availability of carbohydrate as a substrate for the muscle and central nervous system is critical for the performance of both intermittent high-intensity work and prolonged aerobic exercise. Therefore, strategies that promote carbohydrate availability, such as ingesting carbohydrate before, during and after exercise, are critical for the performance of many sports and a key component of current sports nutrition guidelines. Guidelines for daily carbohydrate intakes have evolved from the "one size fits all" recommendation for a high-carbohydrate diets to an individualized approach to fuel needs based on the athlete's body size and exercise program. More recently, it has been suggested that athletes should train with low carbohydrate stores but restore fuel availability for competition ("train low, compete high"), based on observations that the intracellular signaling pathways underpinning adaptations to training are enhanced when exercise is undertaken with low glycogen stores. The present literature is limited to studies of "twice a day" training (low glycogen for the second session) or withholding carbohydrate intake during training sessions. Despite increasing the muscle adaptive response and reducing the reliance on carbohydrate utilization during exercise, there is no clear evidence that these strategies enhance exercise performance. Further studies on dietary periodization strategies, especially those mimicking real-life athletic practices, are needed.

Q- Is there a certain number of grams of CHO and or protein before exercise proven to improve power/performance?

The current recommendation is 20 grams of protein (containing at least 6 grams of essential amino acids) immediately before and/or within 2 hours after resistance training. For endurance exercise, the recommendation for carbohydrate before exercise is 1, 2, or 3 grams per kilogram of body weight 1, 2 or 3 hours before training (respectively). For post exercise recovery (endurance exercise). If there is less than 8 hours before the next training bout, the athlete should consume 1.0-1.2 grams per kilogram of body weight per hour for four hours. For protein, it is recommended the endurance athlete consume 20-30 grams of protein within 2 hours post exercise (including 6-10 grams of essential amino acids). This information can be found in the joint position statement from ACSM, AND and Dietitians of Canada.

Thomas DT, Erdman KA, Burke LM. Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. J Acad Nutr Diet. 2016; 116(3):501-528.


Katherine A. Beals, PhD, RD, FACSM is an Associate Professor (clinical) in the Department of Nutrition and Integrative Physiology at the University of Utah where she teaches graduate courses in macro and micronutrient metabolism, sports nutrition and research methods.

About Potatoes USA

Potatoes USA is the nation's potato marketing and research organization. Based in Denver, Colorado, Potatoes USA represents more than 2,500 potato growers and handlers across the country. Potatoes USA was established in 1971 by a group of potato growers to promote the benefits of eating potatoes. Today, as the largest vegetable commodity board, Potatoes USA is proud to be recognized as an innovator in the produce industry and dedicated to positioning potatoes as a nutrition powerhouse.