Hungry, shaky, sleepy, anxious, dizzy, confused, nervous, sweaty, irritable, or "hangry". Ever experience any of these symptoms right after starting a workout? These are symptoms of hypoglycemia, or low blood sugar. This is a condition that can occur in under certain circumstances shortly after starting to exercise.
In response to eating carbohydrates our body releases insulin, a hormone that’s main goal is to drive glucose into cells for storage or use. This normal process is what returns our blood sugar to normal following a meal. During exercise, a separate process, independent of insulin, pulls glucose from the blood stream and into muscle, also lowering blood sugar.
Now, imagine for a moment what could happen if both of these processes were to occur at their full capacity at the same time. This is what is known as reactive, or rebound hypoglycemia, meaning your blood sugar gets too low. If you’ve ever had this happen, you know how tough it is to keep working out.
Historically, it was recommended to avoid carbohydrates before exercise altogether to prevent this phenomenon from happening; however, our viewpoint on this has changed.
In those that have experienced reactive hypoglycemia or are prone to it, the timing and type of carbohydrates before exercise is important. Since both blood glucose and insulin concentrations peak 20-40 minutes after eating a meal/snack, eating carbohydrates within the 10 minutes before starting to exercise or during the warm up is one strategy.
Also, choosing low glycemic index (GI) carbohydrates, such as a slightly under-ripe banana, may also help. This will result in a gradual (versus rapid) rise in blood glucose and therefore insulin.
If neither of these strategies work for someone who is prone to reactive hypoglycemia, avoiding all carbohydrates within 90 minutes of exercising might be worth a try.
Outside of exercise, paying close attention to the timing and composition of meals and snacks can help manage reactive hypoglycemia.
Eating small meals and snacks no more than 3-4 hours apart throughout the day can help keep blood sugar stable. Also, regularly including high-fiber foods (whole grains, fruit, and vegetables), lean proteins (animal and non-animal sources), and healthy fats (nuts, seeds, avocado, fish, and liquid oils) as part of a well-rounded diet can help. Limit or avoid simple high GI carbohydrate foods (soda, candy, etc.), particularly on an empty stomach. And if you choose to consume alcohol, avoid sugary mixers and be sure to have some food on board when you do drink.
Everyone is different in how their body tolerates carbohydrates. If you do suffer from reactive hypoglycemia, experiment with the type and timing of meals prior to working out. Hypoglycemia isn’t a medical condition as many think. Rather, it’s a symptom of dietary imbalance that can be corrected with strict attention to what a person eats, and when.
Lauren Larson is a Registered Dietitian Nutritionist (RDN) with a comprehensive private nutrition practice focused on sports nutrition-related diet and lifestyle modifications for active and athletic people. She is a passionate endurance athlete, avid trail runner, cyclist, and triathlete. For nutrition counseling contact Lauren at LaurenLarsonMSRDN@gmail.com .
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