By Sam Walls CK, CSCS, Exercise Physiologist (CEP), Sports Nutritionist (CISSN)

Within the exercise science community, one of the most fiercely debated topics is the appropriate recommendation with respect to carbohydrate intake for high level performance. Most of us have seen the guy trying to lose weight by eating bacon bits for dinner with a side of pork rinds, or the athlete wolfing down on a tub of ice cream, while maintaining such a lean physique that you can literally see the internal architecture of his muscles. In this article, I will discuss the factors that influence the optimal approach when it comes to carbohydrate consumption.


If we look at the wide range of studies, we can clearly see that both low and high carbohydrate meal plans have demonstrated very promising results. On one end, we see the lower carbohydrate ketogenic-style diets demonstrating the ability to foster weight loss, while maintaining muscle mass. At the other end of the spectrum, we witness athletes improving exercise time to exhaustion via diets higher in carbs. The strategy used depends on the goal of the athlete; with activities characterised by higher intensities possessing a greater need for muscle glycogen.

When choosing your level of carbohydrate intake, it’s important to consider three things:

   1. Is weight loss a priority?

   2. Is exercise intensity crucial for success?

   3. How many training sessions are performed during the week?

It is important to realize that we have a limited supply of muscle energy stored in our body, which amounts to approximately 300-400 grams of glycogen in the muscle, and a few grams in the liver. This storage form of energy is only able to sustain moderate activity for about two to three hours; unless you are burying the needle, at which point then the energy is burned at a much quicker rate. This fuel is of extreme importance for extensive events like a marathon, triathlon, or a gut-wrenching battle during an MMA fight. Even during brisk continuous activity we might burn a gram of carbohydrates per minute; which has led many sport scientists to recommend higher carbohydrate diets and the use of nutrients during a training bout to prevent drops offs in training intensity. Such diets rich in carbohydrates (60-70%) have been shown to increase training capacity and replenish energy stores that have been depleted.

    As you can see in the chart above, increasing daily carbohydrate intake is

correlated to greater muscle glycogen stores. Just by jacking up the carbohydrate intake, muscle glycogen stores can almost double, which is a common strategy used

to maximise performance. Note: Data in chart obtained from Essentials of Sport Nutrition and Supplements


For the seasonal competitor, it becomes especially important to maintain energy stores during extremely high training frequencies or volumes. High level athletes have been known to weight train at extremely high volumes, which could easily lead to overtraining and critical drops in performance.3 All it takes is a few hard sets and our glycogen stores can dwindle down by 30-50% (4, 5). When training on empty, lean tissue can burn away like kindling on a camp fire, as our hard earned muscle becomes the new currency to pay the piper. The beautiful thing is that we can correct this issue by providing our bodies with adequate amounts of fuel before exercise, or at least 30 minutes before we go belly up in a training session6. With all these possible shortcomings, why would we ever choose to go to the “low carb” side of the equation?  The answer to the riddle lies in the above considerations. The ketogenic approach

may be appropriate when used as a method to drop serious fat stores, or during

a light training phase when general fitness and weight loss take precedence over high

training intensity. For the raw athlete who loves lifting heavy weight while staying lean,

the optimal approach would be to maintain a low body fat percent with topped up glycogen stores.


Let’s now look at a sample training cycle for an individual trying to cut up, while preparing for high level performance. As you can see in the chart above, carbohydrates are restricted during the off-season when the training intensity and volumes are low to promote accelerated fat loss during a time when fats can act as the primary fuel source for performance. When fat loss goals have been achieved and we approach the competitive season or an intensive training phase, we can gradually increase carbohydrates up to 45% of the athlete’s daily intake. Research has shown this percentage can produce similar results in performance to diets much higher in carbohydrates (7). Nutrient timing also becomes a major focus during this phase, as the use of macronutrients and supplements can enhance muscle building and nutrient delivery when carbohydrate intake is low.


For more information on this topic, please refer to International Society of Sports Nutrition’s text book, “Essentials of Sports Nutrition and Supplements” or the open access Journal of the International Society of Sport Nutrition (


1. Essentials of Sports Nutrition and Supplements. Eds. Jose Antonio, Ph.D., Douglas Kalman, M.S., RD, Jeff Stout,

    Ph.D., Mike Greenwood, Ph.D., Darryn Willoughby, Ph.D. Humana Press, 2008: 626

2. ISSN exercise & sport nutrition review: research & recommendations Kreider et al. Journal of the International

    Society of Sports Nutrition 2010, 7:7

3. A.N. Vorobyev, The scientific basis of weightlifting training and technique. Soviet Sports Review March 1979, Vol

    14(1): 2

4. Principles and Practice of Resistance Training.  Michael H. Stone, Meg Stone, William A. Sands. Human


5. Lambert, C.P and M.G. Flynn, J.B.Boone el al. 1991. Effects of carbohydrate feeding on multiple-bout

    resistance exercise. Journal of Applied Sport Science Research 5(4):192-197.

6. Essentials of Sports Nutrition and Supplements. Eds. Jose Antonio, Ph.D., Douglas Kalman, M.S., RD, Jeff Stout,

    Ph.D., Mike Greenwood, Ph.D., Darryn Willoughby, Ph.D. Humana Press, 2008: 297,331

7. Essentials of Sports Nutrition and Supplements. Eds. Jose Antonio, Ph.D., Douglas Kalman, M.S., RD, Jeff Stout,

    Ph.D., Mike Greenwood, Ph.D., Darryn Willoughby, Ph.D. Humana Press, 2008: 297

8. Coggan AR, Coyle EF. Reversal of fatigue during prolonged exercise by carbohydrate infusion or ingestion.

    Journal of Applied Physiology 63: 2388-2395, 1987

9. Nutrition for Health, Fitness, & Sport 8th ed, Melvin H Williams, McGraw-Hill Science, 2007

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