In the world of exercise and training there is a long standing interest in how much carbohydrate an individual should consume. The short answer: it depends. A while ago, I realized that no one nutritional regimen provides a fit all for all. This sounds simple but it was actually a profound realization for someone who has spent the last 20 years study fat cells, muscle cells, physiology and metabolism. How much carbohydrate you consume and which nutritional philosophy you adhere to completely depends on at least 3 criteria: 1) your current metabolic health, 2) your training program, and 3) your life-style. To better address these criteria let’s quickly review how your body responds to food. When you eat a meal your blood sugar rises. The beta-cells of your pancreas sense this increase in blood sugar and respond by releasing insulin. Insulin is a profoundly anabolic hormone. It signals to your skeletal muscle to take up the sugar circulating in your blood stream; any remaining energy is then diverted for storage in your fat cells. Importantly, insulin also signals to your liver telling it to stop making and releasing sugar into the bloodstream. “Wait? My liver makes sugar?!” Yes, it does. When you are in a fasted state your liver actually produces sugar (glucose via gluconeogenesis) and releases it into your circulation in order to maintain a fasting blood sugar to keep your brain running. Once you have food on board and insulin is released, it shuts down the release of this sugar or glucose by the liver. In this metabolic system when nutrients are consumed, skeletal muscle is the primary organ responsible for removing sugar from the blood stream. Interestingly, exercise independent of insulin action also stimulate glucose uptake into skeletal muscle-but that discussion is for another post. Carbohydrates are forms of sugar and when ingested stimulate insulin production and release into circulation. Refined carbohydrates, which are carbohydrates that have been processed to remove the whole grain such as in white bread, are potent stimulators of insulin secretion and thus energy uptake and storage.
Let’s now talk about the 3 criteria I listed above that should be considered regarding carbohydrate consumption. 1) Current metabolic health: an individual who has metabolic health concerns such as impaired insulin sensitivity (e.g. elevated fasting blood glucose level) would be well suited to reduce their overall consumption of carbohydrate. By doing so, they may reduce high levels of circulating insulin and potentially improve their insulin sensitivity and blood glucose levels. 2) Training program: there is a wide array of variability regarding nutrient and carbohydrate intake depending on the athlete and their training goals but some carbohydrate intake, particularly around the training window, is considered beneficial. For example, I am a nearly 40 year old Cross Fitter who trains on average 4 days a week. Outside of my training window and on recovery days I limit my carbohydrate intake primarily consuming carbohydrates through vegetables and fruit. However, immediately following a training session I consume ~60 grams of carbohydrate (glucose drink) along with 25 grams of whey protein based on the following metabolic system. Immediately following a training session, the enzymes in your skeletal muscle are preferentially primed for taking up and metabolizing sugar for the production of glycogen; a process termed glycogen super-compensation. If you store more glycogen in your skeletal muscle you will be able to perform more work (i.e. muscle contraction) as this is a readily available energy source. Athletes that train at incredibly high levels actually consume lots of carbohydrates during defined windows around their training (check out Annie Thorisdottir, Rich Froning, and Kari Pearce for example). Finally, criteria number 3) your life-style: as I mentioned earlier no single nutritional program is the end all be all for metabolic health and performance for every single individual. Many people are limited by finances, time, motivation, and commitment but that does not mean you shouldn’t get after it and start trying things. If you don’t see or feel results? Try something different. Self-experiment until you find a way of eating and training that works for you and that makes you happy! No words ring truer than those of Greg Glassman, “Eat meat and vegetables, nuts and seeds, some fruit, little starch, and no sugar. Keep intake to levels that will support exercise but not body fat.”