By Sheri Colberg, Ph.D.,FACSM
As a physically active person, you arelikely to be bombarded with claims about the superiority ofparticular diets and guarantees that specific nutritional supplementswill enhance your athletic performance. With the fierce competitionthat exists in sports nowadays, athletes look for any edge to improvetheir athletic ability. They will try almost any supplement ortechnique to get it—amino acid supplements, glycerol, sportsdrinks, creatine, carbohydrate loading, and ginseng, to name just afew. In reality, few of these advertised ergogenic aids (i.e.,anything that enhances performance) for athletes are scientificallyproved to enhance your physical prowess. Moreover, as an athlete withdiabetes, you may have special concerns about the effects of variousdiets and supplements on your diabetes control, as well as how andwhat to consume to maintain your blood sugars during exercise.
The first thing you should know is thatactive people can eat in more than one way and perform effectively insport and that the best way may be slightly different for everyone.The diets of diabetic athletes are as varied as the sports andactivities that they do. No one likes to have to stop exercisingbecause of low blood sugars, though, so preventing hypoglycemiaduring and after any activity is a high priority for everyone.Becoming low unexpectedly can be especially inconvenient if you’reout for a run or a long bike ride and are still a good distance fromyour destination. Prevention has a lot to do with your food intakeboth before and during the activity. In general, rapidly absorbedcarbohydrate is most effective to take during exercise, but proteinand fat can be helpful in preventing lows as well. The followingsections include some basic points to remember about the differentclasses of foods, along with a discussion of nutritional supplements.
Carbohydrate: Critical to Make It tothe Finish Line
Carbohydrate is the most importantenergy source for all types of exercise. Muscle glycogen (the mainstorage form of carbohydrate) is the primary source of energy for thelactic acid system, along with being the main fuel for moderate andintense aerobic exercise. Whenever you eat carbohydrate, it is brokendown by enzymes in your digestive tract, absorbed through the wall ofyour small intestine, and released as glucose into your blood, makingit the main simple sugar found there. Your muscles can take up anduse carbohydrate, but they generally use more of the glycogen alreadystored in them, as long as it’s available.
The more intensely you exercise, thegreater the rate of muscle glycogen depletion in the muscle fibersthat you’re using. Your liver also releases its more limitedglycogen stores as glucose into the bloodstream to try to maintainyour levels during exercise. Glycogen is critical to most activities,so if you deplete your muscle and liver stores during exercise, youwill become fatigued and either have to stop exercising or slow downconsiderably. You’ve heard of athletes "hitting the wall,"often around the 20-mile (32-kilometer) mark of a marathon; they’veusually just run out of glycogen at that point. Fat "burns"in a carbohydrate flame, so you can’t even use fat effectively asan alternative fuel after you’ve depleted your carbohydrate(glycogen and glucose) stores.
In general, most exercisers (even thosewithout diabetes) need to take in some carbohydrate before and duringprolonged exercise to help maintain their blood glucose levels,although consuming it usually doesn’t slow down the body’s use ofglycogen, which is primarily driven by the intensity of the workout.Any carbohydrate that you take in during exercise is rapidlymetabolized and begins to be available for your body to use withinabout five minutes. The type of carbohydrate that you need to consumedepends on factors such as how long you’ll be exercising, theintensity of your workout, and what your blood sugar and insulinlevels are before and during the activity.
Supplementing With CarbohydrateBefore, During, and After Exercise
Carbohydrate supplementation is aneffective performance enhancer whether or not you have diabetes. Ingeneral, taking in extra carbohydrate is not usually necessary forevents lasting an hour or less, if you start with normal muscle andliver glycogen stores and moderately low levels of insulin. But youmay need to take in carbohydrate for exercise lasting less than anhour, depending on how much insulin is in your system and whetheryour blood glucose is likely to drop during the event. If you’rerunning low on glycogen for any reason or your insulin levels are toohigh, your muscles will use more of your blood glucose than normal,and you’ll likely have to supplement then as well.
If you train on a regular basis, youwill need to take in enough carbohydrate every day to restore yourmuscle and liver glycogen levels between workouts. The time when yourbody restores glycogen most rapidly is during the first 30 to 120minutes after exercise. If you want to minimize your risk oflater-onset lows, take in some carbohydrate and keep your bloodsugars under control during this time to optimize its repletion. Whenyou have diabetes, you have to be especially careful to keep yourblood sugars in control before and after exercise so that yourglycogen repletion takes place normally. Your body needs adequateinsulin levels, especially more than an hour after exercise whenglucose uptake into your cells becomes more dependent on insulin.Taking in some carbohydrate immediately after you finish a workout orrace will speed up your initial glycogen replacement and help loweryour risk of developing low blood sugars later, all with minimal needfor insulin during that period.
Carbohydrate intake also helps ensurethat your glycogen stores are maximally loaded by the time your nextworkout rolls around. Keep in mind, though, that glycogen repletioncan take 24 to 48 hours, and you need to control your blood sugarswell during that time for maximal carbohydrate replacement. If youeat a low-carbohydrate diet, full restoration of glycogen will takelonger; you may want to consider taking in more carbohydrate of anyGI than your normal during that time (at least 100 grams per day) andtaking enough insulin (if you use it) to facilitate the storage ofcarbohydrate as glycogen in your muscles and liver.
Particularly during longer workouts ora long sports event, carbohydrate supplementation benefits allathletes. During marathons or triathlons, extra carbohydrate helpsmaintain your blood sugar levels, enabling you to keep going at afaster pace for longer without fatiguing. Supplementing even worksfor intermittent, prolonged, high-intensity sports like soccer, fieldhockey, and tennis. Always take in adequate carbohydrate, along withsufficient (albeit likely reduced) insulin before, during, and afterprolonged moderate- or high-intensity workouts to maintain andrestore your muscle and liver glycogen and blood glucose, especiallyduring that window of opportunity for glycogen repletion right afteryou finish exercising. If your blood sugars are normal or slightlylow before exercise, you may also want to take in 10 to 15 grams ofmoderate- or high-GI carbohydrate without any insulin coverage rightwhen you start, especially if your blood glucose levels typicallystart to drop during the first 30 minutes of an activity.
This column is excerpted from DiabeticAthlete’s Handbook (released November 2008 from HumanKinetics), which contains essential exercise-related information andexamples for Type 1, Type 1.5, and Type 2 diabetic exercisers. Moreinformation is available at www.shericolberg.com.