What better topic is there to discuss after the gluttony most of us experience over the Thanksgiving and other fall/winter holidays than carbohydrate loading? (Actually, it probably should be excess calorie consumption in general, but you get the idea.) The following is excerpted from The Athlete’s Guide to Diabetes (2019) and gives you a better understanding of the topic from an exercise physiology (and diabetes) point of view.
Most athletes can benefit from taking in enough carbohydrate before long-distance events to start exercising with fully restored or even supercompensated glycogen stores. Traditionally, this loading technique consisted of 3 to 7 days of a high-carbohydrate diet combined with 1 or 2 days of rest or a reduction in exercise volume, a method known as tapering. For endurance athletes, loading is recommended to consist of taking in 8 to 10 grams of carbohydrate per kilogram of body weight (e.g., 560 to 700 grams for someone who weighs 70 kg, or 154 pounds)—but that is admittedly a lot of carbohydrate to handle if you have to match it with insulin or are very resistant, and it is not necessary.
Even a single day with enough carbohydrate and food intake and rest or tapering can effectively maximize your carbohydrate stores, so you do not need to spend a week, or even 3 days, overconsuming it. Maximal glycogen storage is dictated by how much muscle mass you have, but it is typically around 300 to 400 grams total in all your skeletal muscle, along with 75 to 100 grams of liver glycogen, for the average person. As long as you consume enough calories and taper or rest for a day, taking in up to 40 percent of your calories as carbohydrates is more than adequate to fully reload your glycogen. For someone consuming 2,000 calories and resting on a pre-event day, that amounts to around 200 grams of carbohydrate—more than enough if you are not starting out fully depleted. It’s also likely that you can fully restore your glycogen on far less carbohydrate, especially if you have been following a low-carbohydrate diet and are fully fat-adapted.
Training Tip: To maximize your glycogen stores, all you really need is 1 day and a combination of rest, enough calories in your diet, and good blood glucose levels for that day. You do not need to do traditional carbohydrate loading to make this happen.
The key for carbohydrate loading to be effective for exercisers with diabetes is to ensure that your muscles can take up any available glucose, which only happens if you have sufficient levels of insulin and enough sensitivity to it to prevent hyperglycemia and promote glucose uptake. Consuming higher-fiber carbohydrate sources and those with a lower glycemic effect will help prevent an excessive rise in your blood glucose and be effective for loading. In fact, a study showed that participants actually end up with higher glycogen stores when they maintain more normal blood glucose levels while loading with less carbohydrate (50 percent of calories from carbohydrate instead of 59 percent in that study). To optimize your liver glycogen replacement, keeping your blood glucose as close to normal as possible is also most effective.
From Colberg, Sheri R., Chapter 4, “Eating Right and Supplementing for Activity” in The Athlete’s Guide to Diabetes: Expert Advice for 165 Sports and Activities. Champaign, IL: Human Kinetics, 2019.