The Dark Side of Low Carb Diets

For anyone who has to monitor food intake on a daily basis to maintain an ideal weight, will definitely understand the level of difficulty finding that exact diet that meets their individual needs.  This also is the greatest reason why each person must learn how their body reacts to certain foods, and factors in the exercise and intensity level of their daily routine.  For a person who is sedentary definitely would benefit from a low carb diet being that they require very little “immediate” energy needs.  Their lower resting metabolic rate would react far better to a diet higher in fat, and little to no carbohydrates from starches.  This will be covered more in detail in a later post, however, the purpose of this is to highlight how that style of diet while performing High Intensity Interval Training is a major detriment to ones training routine.

Nutrition and Athletic Performance, it is recommended that I consume approximately 6-10g of carbohydrates per kilogram of body weight. At 93 kilograms, that would equate to approximately 558 – 930 grams of carbohydrates, or 2200 to 3720 calories from carbohydrates. This approximation would put me well beyond the daily energy expenditure calculation of the Harris-Benedict equation. Having tracked my caloric intake for the last couple years, I have self-determined that 2200 calories is my set point, meaning that when I consume more, I gain weight, when I consume less I lose weight. In order to keep pace with the current recommendation of 65% of calories coming from carbohydrates, that would equal out to approximately 1430 calories coming from mostly complex carbohydrates (360 grams).

In a study by Kerksick (2008), research showed that ingesting high amounts of carbohydrates prior to a high intensity exercise session helped maintain glucose levels in comparison to subjects who were on low carbohydrate diets prior to the event, providing evidence that prolonged performance can be sustained for a greater time frame when ingesting more carbohydrates prior to the event. During exercise, maintaining blood glucose levels are critical for continued high output performance. In a similar study reported by Berksick, cyclist who ingested liquid carbohydrate at the onset, and during the event, maintained high blood glucose levels providing longer output to reach exhaustion. The key component to the study was glycogen levels at the onset of the activity. Those that had low glycogen levels prior to training were able to benefit from the ingestion of carbohydrates during activity. Subjects with high glycogen levels at the onset did not see much improvement from ingesting liquid carbohydrates during exercise. Relating these studies to my personal plan, ingesting of carbohydrates at least an hour prior to the session is important in maintaining proper glucose levels. I personally do not like to enter in to a fitness session with a full stomach, so I typically prefer to ingest fruit and nuts as a means to increase glycogen stores. I rarely find that during my style of workout, that I have little energy left to complete my session, so the idea of ingesting carbohydrates during my workout has not been a factor. I would plan to do so if the workouts became longer than 1 hour in duration with a similar intensity level. In regards to carbohydrate consumption, foods that rank low on the glycemic index are important to not raise insulin levels too quickly and aid the body in the production of fat. In the NSCA Performance Training Journal (Vol 2, #5), insulin helps promote fat production from the glucose in the liver and adipose tissue, and blocks the fat release from fat cells. So foods that are low on the glycemic index I would typically consume prior to a workout would be fresh fruits and vegetables, and some nuts and seeds to provide some additional protein and fat.
Low carbohydrate diets for an active individual would be counterproductive to their efforts of peak performance. Our body requires a constant energy supply, so depending on the intensity level and time frame of the activity would best determine the type and amount of carbohydrates to consume. It would be a basic explanation of Bioenergetics to understand how and why the muscles contract and for how long. The body requires ATP in order for a muscle to contract. This ATP is stored in limited amounts in the muscle and can typically sustain muscle contraction for approximately 6-10 seconds. Once that is depleted, the next available source to convert to ATP would be glycogen that is stored in the muscles and the liver. During moderate to high intensity exercise, carbohydrates (in the form of glycogen) supply more than 50% of the energy stores to the body (Cermack, 2013). Low carbohydrate diets would minimize the body’s ability to convert additional ATP and fatigue would typically set in with inadequate stores. With adequate amounts of glycogen, this glycolysis phase can help sustain muscle contraction for a couple minutes. After that, the body requires the presence of oxygen to help convert the pyruvic acid to the mitochondria to enter the Krebs cycle, which allows for a longer supply of ATP. Without adequate stores of glycogen in the muscle or liver, muscular fatigue will occur prior to the aerobic glycolysis phase which will mean a decrease in overall performance.
Kerksick, C., Harvey, T., Stout, J., Campbell, B., Wilborn, C., Kreider, R., & … Antonio, J. (2008). International Society of Sports Nutrition position stand: nutrient timing. Journal Of The International Society Of Sports Nutrition, 517. doi:10.1186/1550-2783-5-17
Cermak, N., & Loon, L. (2013). The Use of Carbohydrates During Exercise as an Ergogenic Aid. Sports Medicine, 43(11), 1139-1155
D’Assisi, Anthony, BPHC, CSCS, NSCA Performance Training Journal, Volume 2, Number 5, October 2003. The Reinvention of Nutrition Basics.
American College of Sports Medicine, Nutrition and Athletic Performance, 2009.

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