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Posted: January 5, 2006

Science of Sport: Are the Atkins, Zone, and South Beach Diets Slowing you Down??

By Kimberly Mueller-Brown, MS, RD

Many runners are jumping on the latest dietary crazes foregoing carbohydrate rich foods such as pasta, bagels, fruits, vegetables, and good ole Cheerios to slim down and enhance their health. Yet are these diets more destructive to their wellbeing? The truth about carbohydrate composition and its effects on running performance are revealed.

Here are the top ten reasons why high carbohydrate diets win the race.

Traditional guidelines posted by the American Dietetic Association recommend that 45-65% of total calories be consumed in the form of carbohydrates, with guidelines for endurance athletes focusing on the latter end of these recommendations during training and competition.1 The carbohydrate intake of elite distance runners in the United States2, Netherlands3, Australia4, and Southern Africa5 have been measured at 49%, 50%, 52%, and 50% respectively. Perhaps the most decorated distance runners in the world, however, are the Kalenjin (Kenyan) runners who reportedly won a staggering 40% of all major international middle- and long-distance competitions from 1987-1997.6 Interestingly, Kalenjin runners have a carbohydrate composition that tower over their competition with measurements reporting 75+% or 10.4 grams carbohydrate per kg of body mass, which may lead one to argue that running success and carbohydrate intake are directly related.7 In fact, there is a plethora of sound research showing the profound performance benefits associated with high carbohydrate intake, including optimal mental functioning, muscle glycogen saturation, enhanced fat burning, protection against protein/muscle breakdown, and improved immune function, just to name a few.8 Even so, such health authority as Dr. Atkins (Atkins Diet), Dr. Barry Sears (Zone Diet), and Dr. Agatston (South Beach Diet) question the efficacy of high carbohydrate diets for health and performance. This has lead to an explosion of low carbohydrate products in the marketplace and an adoption of new dietary habits by runners as means to shed body fat, enhance performance, and optimize health. This article will give you the low down on the effects of low carbohydrate dietary trends on running performance and ultimately shed light on the top ten reasons why a dietary focus on healthy carbohydrate sources (such as fruits, vegetables, legumes, and whole grains) will always aid in health and running performance.

#10: Low carbohydrate diets leave you mentally drained

Finding your motivation levels at an all time low? If you are following a low carbohydrate regimen, it is no wonder since the minimal amount of carbohydrate grams suggested for optimal mental functioning is listed at 130 grams or just over 500 calories. During the induction phase, Atkins followers are encouraged to keep carbohydrate intake to no more than 20 grams per day; if you are running enough, you can boost that up to 60-90 grams per day. You can see where this may be a problem. Approximately 75-100 grams (300-400 calories) of carbohydrate can be stored within the liver as glycogen. The energy stored within the liver helps maintain blood sugars and also fuels both the brain and working muscles. With blood sugars naturally rising and falling in 2-4 hour increments depending on metabolic efficiency, liver glycogen stores constantly need to be replenished with snacks consisting of some carbohydrate. When inadequate carbohydrates are consumed, liver glycogen levels fall quicker, causing blood sugars to drop; a lack of fuel being sent to the brain triggers dizziness, fatigue, headaches, and an overall feeling of sluggishness known as “bonking.”

#9 Low carbohydrate diets trigger premature muscle fatigue during exercise

Do you find yourself flashing jealous looks at your competition as they blaze by you at the end of that marathon while your muscles cramp and pace becomes slower than a turtle? Just like a race car storing its fuel in a tank, the human body stores carbohydrates as glycogen in the muscles and provides energy for muscle contraction and relaxation during activity. When following the high carbohydrate diet recommended by the American Dietetic Association, the average human body will store just over 2 grams (8-10 calories) of glycogen per pound of muscle tissue, with a potential for super-compensation with carbohydrate loading protocols similar to that seen with the Kenyan elite runners.9 This amount of muscle glycogen will supply the energy needed to train for ~2-2.5 hours at a moderate-to-high intensity. Athletes following lower carbohydrate regimens, however, have been shown to store approximately 45-75% less glycogen as compared to their “carbo-loading” training buddies. Therefore, athletes are more vulnerable to premature depletion of muscle glycogen, ultimately compromising muscle function and leading to debilitating cramps, slowed pace, reduced power output, and diminished endurance capacity, otherwise known as “hitting the wall.”10-12 This is not surprising considering Dr. Atkins suggests that athletes engaged in intense exercise for at least 45 minutes consume an increased, though still limited, amount of carbohydrates in phase 2 of his program.

#8 Low carbohydrate diets compromise immune function

Ahhhh Chooo! Sound familiar? Prolonged intense exercise reportedly decreases the plasma concentration of glutamine, an important fuel and precursor for DNA and RNA synthesis in cells of the immune system, and may consequently depress immune function making runners more vulnerable to infection in the 2 hours post workout.13 The immune suppression seen in runners may also be attributed to elevated levels of the stress hormone cortisol and a corresponding drop in lymphocyte production and T-cell activity seen after completion of hard training. Interestingly, low carbohydrate diets, specifically those yielding carbohydrate intakes less than 30 grams, seem to exacerbate this effect.14 Dr. David C. Nieman, exercise physiologist, has conducted much of the research looking at immune function in runners and has discovered that carbohydrate supplementation both during (~45 grams/hour) and immediately after (~45 grams) intense, prolonged exercise helps reduce cortisol levels and maintain lymphocyte production, thereby helping prevent infection.15

#7 Low carbohydrate diets affect mood

Yes, you may start to describe yourself as unpleasant to be around when following a low carbohydrate diet! Many who are testing low-carbohydrate approaches like Atkins and the South Beach Diet are reporting unusually elevated feelings of anger, tension and depression, enough so that a new term ‘Atkins attitude,’ has been adopted to describe it. Judith Wurtman, director of the Women’s Health Program at the Massachusetts Institute of Technology and the Adara Weight Loss Center, has conducted studies on rats showing a connection between low carbohydrate intake and low levels of serotonin – a neurotransmitter that promotes feelings of happiness and satisfaction. In her research, rats placed on a ketotic, or low-carbohydrate diet for three weeks were found to have lower levels of serotonin in their brains. Wurtman believes that same effect occurs in humans on low-carb diets, leading to pronounced feelings of depression and sadness, even rage.16

#6 Low carbohydrate diets are often deficient in essential nutrients

With a lack of grains, fruits, and vegetables being consumed in low carbohydrate diets, runners run the risk of developing dietary deficiencies of key nutrients including dietary fiber, which can affect digestive health; vitamin C, which can compromise immune function; folic acid, which may elevate risk for cardiovascular disease; and magnesium, which may elevate risk for cramping and also compromise bone health. A lack of fiber also increases your risk for cancers of the digestive track (because transit time is lengthened) and cardiovascular disease (because of fibers effect on fat and cholesterol). Low carbohydrate diets lack in the phytonutrients / antioxidants found in fruits, vegetables, legumes, and whole grains, all proven to aid in prevention of cancer and heart disease. 17,18

#5 Low carbohydrate diets slow muscle recovery

Having trouble walking down those stairs after last night’s killer track workout? Consumption of carbohydrate-rich foods post-exercise will help enhance recovery from workouts. Carbohydrate-rich foods cause a more rapid rise in blood glucose, which in turn triggers the release of insulin or the “master recovery hormone.” Insulin, the same hormone knocked by Dr. Atkins (Atkins Diet), Dr. Barry Sears (Zone Diet), and Dr. Agatston (South Beach Diet), actually facilitates the transport of carbohydrate, specifically glucose, from the blood into the muscle cell where it can be metabolized to produce energy that will prepare the muscle cell to do work again. Within 30-60 minutes post-exercise, consumption of a carbohydrate-rich snack plus a small amount of protein (e.g., banana mixed in low-fat yogurt) has been shown to triple the rate of muscle glycogen replenishment and muscle protein synthesis.19 Furthermore, as compared to a protein-only supplement taken post exercise, a carbohydrate-protein solution has been shown to enhance rate of glycogen storage by 5 times, thereby facilitating muscle recovery. 20

#4 Low carbohydrate diets increase risk for muscle injury during training

Do you find yourself constantly nursing little or big aches and pains? With a low carbohydrate intake during endurance training, this is inevitable since there is increased protein breakdown and consequent loss of lean body weight. Furthermore, the biomechanics of your running stride may be negatively affected due to cramping and muscle fatigue (also associated with depletion of muscle glycogen stores), aka “the wall”, thereby causing a variety of new aches and pains as well as muscle tightness. Finally, when insulin levels are chronically low, as they often are with a very low carbohydrate intake, catabolism (breakdown) of muscle protein increases, and protein synthesis is hindered.21

#3 Low carbohydrate diets increase risk for kidney stones

Ouch, it seems like something is stabbing me in the abdominal wall. I feel nauseous. Yes, these are just some of the symptoms associated with passing a stone. Sound like fun? When following a high protein, low carbohydrate meal plan, both uric acid and calcium oxalate stones are more likely to form. In fact, one study found that consumption of a low carbohydrate, high protein diet for 6 weeks delivers a marked acid load to the kidney, increasing the risk for stone formation.22 Combine this with dehydration during a race and you are a prime candidate for being stabbed by a “stone” – I guarantee that this won’t aid athletic performance. In 2003, former Ironman World Champion and pro triathlete Tim DeBoom unknowingly passed a stone during the race, which lead him to pass out and be whisked off to the medical tent, a medical DNF.

#2 Low carbohydrate diets can diminish bone health

Find yourself constantly dealing with stress fractures? Individuals consuming a higher ratio of protein to carbohydrates run the risk of developing brittle bones or osteoporosis. When the body digests protein, the kidneys work overtime to filter the toxic byproducts produced during breakdown of protein. Once filtered, protein is excreted in the urine; however, along with protein, there is increased urinary loss of calcium, which can ultimately compromise your bone health, thereby increasing your risk for bone fracture. In fact, consumption of a low carbohydrate, high protein diet over 6 weeks has been shown to significantly decrease estimated calcium balance and may increase the risk for bone loss and stress fracture.22 Injury of the bone will definitely inhibit maximum fitness performance.

#1 Low carbohydrate diets can trigger joint pain

Protein-rich sources such as meats, poultry, seafood, and eggs commonly consumed as part of a high protein regimen contain high levels of purines, which raise blood levels of a compound called uric acid. An excess of uric acid in the body causes gout, which is a form of arthritis. Elevated levels of uric acid in the blood may lead to needle-like uric acid crystals in joints, triggering pain. A new study published in the New England Journal of Medicine has confirmed the correlation between high protein intakes and gout. The researchers studied 47,150 men who had no history of gout at the beginning of the study. During the 12 years of the study, they documented 730 confirmed cases of gout. The relative risk of gout among men was highest among men with the highest intake of meat and seafood. They concluded that higher levels of meat and seafood consumption, like that seen in low carbohydrate meal plans, are associated with an increased risk of gout.23

Low carbohydrate diets are not fun and certainly won’t help aid running performance. So please resist from jumping on the latest “fad diet” bandwagon and continue your high carbohydrate ways, implementing such nutrient-rich foods as fruits, vegetables, whole grains, and legumes. Your muscles and body will thank you. There are countless ways to incorporate tasty, disease-preventing, sports-enhancing carbohydrate-rich foods into your diet without getting bored. Get a jump on the day and try the following quick, healthy, tasty, and balanced carbohydrate-rich breakfast: Blend ½ cup old fashioned oats, ¼ cup natural granola, 2 Tbsp slivered almonds, ¾ cup mixed berries, and 1 cup nonfat milk. Cook in microwave for 3-4 minutes. Healthy carbohydrate trails.


1. American College of Sports Medicine, American Dietetic Association, and Dietitians of Canada. Nutrition and athletic performance. Med. Sci. Sports Exerc. 32(12): 2130-2145, 2000.

2. Grandjean, A.C. Macronutrient intake of US athletes compared with the general population and recommendations made for athletes. Am. J. Clin. Nutr. 49: 1070-1076, 1989.

3. van Erb-Baart, A.M., Saris, W.H., Binkhorst, R.A, Vos, J.A. and J.W. Elvers. Nationwide survey on nutritional habits in elite athletes. Part I. Energy, carbohydrate, protein, and fat intake. Int. J. Sports. Med. 10(1 suppl): S3-S10, 1989.

4. Burke, L.M., Gollan, R.A., and R.S. Read. Dietary intakes and food use of groups of elite Australian male athletes. Int. J. Sport Nutr. 1(4): 378-394, 1991.

5. Peters, E.M., and J.M. Goetzsche. Dietary practices of South African ultradistance runners. Int. J. Sport Nutr. 7: 80-103, 1977.

6. Manners, J. Kenya’s running tribe. The Sports Historian. 17(2): 14-27, 1997.

7. Onywera, V.O., Kiplamai, F.K., Tuitoek, P.J., Boit, M.K., and Y.P. Pitsiladis. Food and macronutrient intake of elite Kenyan distance runners. Int. J. Sport. Nutr. Exerc. Metab. 14: 709-719, 2004.

8. American College of Sports Medicine, American Dietetic Association, and Dietitians of Canada; Joint Position Statement: Nutrition and Athletic Performance. Med. Sci. Sports Exerc. 32(12): 2130-2145, 2000.

9. Sherman, W.M, Costill, D.L., Fink, W.J., and J.M Miller. Effect of exercise-diet manipulation on muscle glycogen and its subsequent utilization during performance. Int. J. Sport Med. 2:114-118, 1981.

10. Kavouras, S.A., Troup, J.P., and J.R. Berning. The influence of low versus high carbohydrate diet on a 45-min strenuous cycling exercise. Int. J. Sport. Nutr. Exerc. Metab. 14: 62-72, 2004.

11. Widrick, J.J., Costill, D.L., Fink, W.J., Hickey, M.S., McConell, G.K., and H. Tanaka. Carbohydrate feedings and exercise performance: effect of initial muscle glycogen concentration. J. Appl. Physiol. 74: 2998-3005, 1993.

12. Williams, C., Brewer, J., and M. Walker. The effect of a high carbohydrate diet on running performance during a 30-km treadmill time trial. Eur. J. Appl. Physiol. 65: 18-24, 1992.

13. Parry-Billings, M., Budgett, R., Koutedakis, Y., Blomstrand, E., Brooks, S., Williams, C., Calder, P.C., Piling, S., Baigrie, R., and E.A. Newsholme. Plasma amion acid concentrations in the overtraining syndrome: Possible effects on the immune system. Med. Sci. Sports Exerc. 24: 1353-1358, 1992.

14. Gleeson, M., Blannin, A.K., Walsh, N.P., Bishop, N.C., and A.M. Clark. Effect of low- and high-carbohydrate diets on the plasma glutamine and circulating leukocyte response to exercise. Int J. Sport Nutr. 8: 49-59, 1998.

15. Nieman, D.C. Nutrition, exercise, and immune system function. Clinics in Sports Med. 18: 537-548, 1999.

16. Wurtman, R.J., and J.J. Wurtman. Carbohydrates and depression. Sci Am. 260(1): 68-75, 1989.

17. Bravata, D.M., Sanders, L., and J. Huang et al. Efficacy and safety of low-carbohydrate diets: a systematic review. JAMA. 289:1837-50 [review], 2003.

18. Brehm, B.J, Seeley, R.J., Daniels, S.R., and D.A. D'Alessio. A randomized trial comparing a very low carbohydrate diet and a calorie-restricted low fat diet on body weight and cardiovascular risk factors in healthy women. J Clin Endocrinol Metab. 88:1617-23, 2003.

19. Levenhagen D. L. et al. Post-exercise nutrient intake timing in humans is critical to recovery of leg glucose and protein homeostasis. Am J Phys, Endocrin Met. 280: E982-E993, 2001.

20. Zawadzki K.M., B.B. Yaspelkis, J.L. Ivy. Carbohydrate-protein complex increases the rate of muscle glycogen storage after exercise. J Appl Phys. 72, 1854-9, 1992.

21. Kimball, S.R, Vary, T.C, and L.S. Jefferson. Regulation of Protein Synthesis by Insulin. An. Rev. Phys. 56:321, 1994.

22. Reddy, S.T, Wang, C.Y., Sakhaee, K., Brinkley, L., and CYC. Pak. Effect of low-carbohydrate high-protein diets on acid-base balance, stone-forming propensity, and calcium metabolism. Am. J. Kidney Dis. 40(2):265-74, 2002.

23. Choi, H.K, Atkinson, K., Karlson, E.W., Willet, W., and G. Cuhan G. (2004). Purine-rich foods, dairy and protein intake and the risk of gout in men. N. Engl. J. Med. 350: 1093-1103, 2004.

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Kimberly J. Mueller, MS, RD, is a Registered Sports Dietitian and competitive endurance athlete who provides nutritional counseling and meal planning to athletes worldwide. You can contact her at . Information on her services can be found at

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