For years we have been told that we should be eating a low-fat/high-carbohydrate diet. The result has been an ever-growing obesity crisis and continued heart disease. Now, we see a shift toward a high-fat/low carbohydrate diet (e.g., the ketogenic diet). Of course, we are also taught that the body needs carbs for performance. So, which is it?
We teach in physiology and biochemistry that “fats burn in a carbohydrate flame” (more correctly, a “oxaloacetate flame”). Short of a full-on lecture on glycolysis, we know that in a state of fasting or starvation carbohydrate is depleted and oxaloacetate (the end-product of the tricarboxylic acid cycle or “Krebs cycle”) is not available to metabolize acetyl CoA from glycolysis and/or beta-oxidation (free fatty acid metabolism). Thus, acetyl CoA is converted in to ketones, which can be used for energy in the brain, heart, kidneys, and other tissues for energy. The result is less ATP being produced from fat—which can lead to increased fat loss. The question remains: does this result in decreased muscle performance. The quick and easy answer is, “yes and no”.
Claims are made that “studies show”, but these studies have almost all involved endurance exercise. It should be understood that there is an inverse relationship between carbohydrate and fat metabolism in relation to exercise time and intensity. (This is termed the “crossover concept”.) Fat will be the primary fuel for low-intensity/long-duration exercise, and carbohydrate will be the primary fuel for high-intensity/short-duration exercise. So, true, for most endurance exercise, there will be no detriment to performance on a low carbohydrate diet. (It would seem that all that talk about carbohydrate loading in the ‘70s and ‘80s was for naught.)
For weightlifting exercise and explosive muscle movements, the question is trickier. Clearly, explosive movements (e.g., sprinting, jumping, weightlifting, strength training, etc.) are fueled by stored adenosine phosphate (ATP) and/or stored muscle glycogen. For such activities, carbohydrates are necessary to maintain a high level of performance.
The argument can be made that muscle can be built on a high-fat/low-carbohydrate diet and that muscle glycogen can be replenished via gluconeogenesis of amino acids and glycerol (from the breakdown of fats—triglycerides) in the liver. This is likely the case if the emphasis in training is on hypertrophy rather than strength. The heavier the weight lifted (relative to maximum, i.e., the one-repetition maximum) the greater the dependence will be on the ATP-PC and glycolytic energy systems—and, thus, on carbohydrates.
The best approach to carbohydrates in the diet (i.e., in the macro balance) is to consider the training needs. On non-training days or endurance training day, a lower carbohydrate intake is probably warranted. On training days, carbohydrates should be relative to the training intensity/volume and be consumed near the training time (shortly before and/or after). Most of the carbohydrate intake on all days should come from vegetables. Fruits and “premium” carbs are best reserved for training days and selected with care.
Fats should not be consumed indiscriminately. Animal fat is often consumed to excess in some ketogenic diets. This is likely less than “healthy”. Fat selection should emphasize nuts, fish oils, olive oil, coconut oil, avocado, grass-fed butters, and the like.
Sensible recommendations for carbohydrates are: <0.5 g/lb of body weight on non-training days, 1.0 g/lb on most training days, and >1.0-2.0 g/lb on training days. Thus, total calories are determined by the caloric need (eucaloric for weight maintenance, hypocaloric for weight loss, and hypercaloric for weight gain). The ration of fat-to-carbohydrate will vary relative to training. Protein, in general, should be between 0.8-1.0 g/lb of body weight for most exercising adults.
Neither carbohydrates or fats are necessarily the enemy. Some are, of course, better than others, but healthy carbohydrates and fats are fine in the appropriate balance. That balance will depend on the individual. Adjust the macros according to the individual needs and response.
Be your best today; be better tomorrow.
Carpe momento!