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The feed zone - Nutrition Q&A with Monique Ryan - Exercise hypoglycemia

Published: Mar. 3, 2004

Dear Monique,
In a previous article you discussed hypoglycemia symptoms follow apre-exercise meal of carbohydrates. I have experienced this on random periods-usually after my morning coffee and bagel, and then setting out on a run.Generally this happens a mile out, and may last for the next two milesbefore passing. During the reaction period I slow down and just try tomaintain activity. What should one really do when this happens?
Thanks,
K.Dear Monique,
I train before work and get up, get dressed, and am immediately onthe bike, usually for 1-1.5 hours. So, should I slam down an orange juiceand banana before I go, or just go on an empty stomach and consume a sportsdrink while I am training?
Thanks,
S.T.Dear K. and S.T.,
Your questions are relevant as many triathletes and cyclists have totrain in the early morning and need to consume some food prior to training.With better weather ahead for many of us, longer early morning trainingis part of our future schedules. Also, often due to time constraints wemay need to eat something 30 to 60 minutes before training starts laterin the day. You may also need to eat an hour or so before training if therehas been a long time gap between the last meal and the start of a trainingsession, and hunger and limited fuel during training may become a significantissue. It may also be helpful to eat closer to longer training sessionsin which the added fuel provides a performance benefit.Of course when you wake up in the morning, your liver glycogen stores,which breakdown and maintain a steady supply blood glucose, are depletedfrom your overnight fast while sleeping. These liver glycogen stores maybe depleted as much as 80 percent from normal and will not be an amplefuel supply for early morning exercise.Despite these practical considerations, consuming carbohydrate in thehour prior to exercise has been a subject of some controversy over theyears, mainly because some athletes may experience lowering of blood glucoselevels during training when they consume carbohydrate this close to exercise(as described in the first question). But regardless, as described in thesecond question, when you train for 1-1.5 hours in the early morning onno food intake, you need to consider the best way to fuel your body.A number of studies have tested the effectiveness and possible hypoglycemiaconcerns in regards to consuming carbohydrate one hour before exercise. In these studies subjects consumed a variety of supplemental carbohydratesources such as fructose, glucose, sucrose, and amylopectin in supplementform (rather than from real food), anywhere from 30-60 minutes prior toexercise. Five of these studies found that the carbohydrate feeding didnot impair or hurt exercise, while four of these studies found the carbohydrateresulted in an actual performance improvement. So overall, eating 30-60min prior to exercise is very unlikely to impair performance, and may evenprovide a needed performance boost. But what was most interesting aboutthe various study results was the highly individual metabolic responsesamong subjects, with some subjects experiencing hypoglycemia with the pre-exercisecarbohydrate dose.Because some athletes experience more symptomatic transient hypoglycemiathan others do, researchers incorporated the glycemic index (GI) into theirstudy design. The glycemic index measures the blood glucose profile ofcarbohydrate foods. Lower glycemic index foods produce more stable bloodglucose and lower insulin responses than moderate or high GI foods. Itwas thought that consuming a lower glycemic index food would be well tolerated30-60 minutes prior to exercise and could improve performance. In otherwords, a bowl of home cooked oats may give you a more sustained boost thana big glob of high glycemic carbohydrate gel.When a high glycemic index food was compared to a low glycemic indexfood, results for nine studies were split down the middle. Utilizing alower GI food did appear to lessen marked increases in insulin and subseqentlowering of blood glucose levels. However, the performance implicationsof this manipulated metabolic response are less clear. Some studies foundan improvement in performance, while others did not. And it appears thatthe best designed studies found that lower glycemic index foods did notresult in a performance improvement, despite the blood glucose responsebeing favorably altered.So what does this mean? It really comes down to personal tolerance andpreferences. For athletes who are carbohydrate/insulin sensitive in the30-60 minutes before exercise, consuming a high enough amount of carbohydratemay simply offset any lowered blood glucose levels and hypoglycemic symptoms.Amounts of 70 grams or more seem to maintain blood glucose levels in individualssusceptible to exercise hypoglycemia. This 70 gm or more carbohydrate intakecan come from breads, cereals, juices, and fruits that you tolerate (froma gastrointestinal perspective). You can also utlize any easily digestedsports nutrition supplements. If consuming enough carbohydrate (greaterthan 70 gm) does not improve any symptoms, you can try foods with a lowerglycemic index. Most fruits have a lower glycemic index, as does real cookedoatmeal, and dairy milk and yogurt. There are some sports nutrition supplementsavailable that have a lower GI, with some carbohydrate sources being galactoseand honey. You can also make a smoothie as milk, yogurt, and fruit areall low glycemic index foods. Often it is a matter of convenience and tolerance.Insulin sensitive athletes can also consider another very practicalstrategy for maintaining blood glucose levels while exercising. One effectivetechnique is to simply consume adequate carbohydrate, about 30 to 60 gmper hour, during exercise. This may be more feasible during some trainingsessions than others, but will effectively diminishes any negative effectsof pre-exercise carbohydrate ingestion or hypoglycemic symptoms. For anearly morning training session on the bike, consuming a sports drink inample amounts will definitely make up for a quick and limited breakfast,and provide some needed hydration. During a running workout, a quick intakeof a gel may also help offset any hypoglycemic symptoms.
Thanks for your questions.
Monique


Monique Ryan, MS, RD is author of “CompleteGuide to Sports Nutrition,” and “SportsNutrition for Endurance Athletes,” from VeloPress. She is a regularcolumnist for Inside Triathlon and VeloNews magazines, and is founderof Personal Nutrition Designs, a nutrition consulting company based inthe Chicago area. Ryan regularly counsels athlete across North Americaon performance and health-related nutrition concerns and offers servicesthrough her website at www.moniqueryan.com.She is the nutritionist for the Performance Enhancement Teams for USA Triathlonand the T-Mobile Women’s Cycling Team. She also consulted with professionaltriathletes, the Saturn Cycling Team, and the Volvo-Cannondale MountainBike Team.We are interested in your nutrition questions. How are you currentlypreparing nutritionally for the upcoming race season? Do you have questionsabout pre-training eating, recovery, and weight loss/body composition?Ryan offers answers to a selected number of reader’s questions twice monthly.Readers are welcome to send their questionsdirectly to Ryan. The information provided in the “Feed Zone” doesnot constitute prescriptive nutritional advice. The information providedin this column is solely for general interest of the visitors to that siteand is intended for educational purposes only.