NUTRITION
SHOULD ATHLETES MONITOR THEIR BLOOD GLUCOSE LEVELS? LIKE A CAR’S FUEL GAUGE, NEW DEVICES CAN EASILY MONITOR YOUR BLOOD GLUCOSE LEVELS. SHOULD ATHLETES BE USING THESE? BY JAMIE SHEAHAN, M.S, R.D.
A
thletes have a tendency to become a bit obsessed with data. Determined to be the healthiest and fittest versions of ourselves, we track metrics like miles logged, daily step count, sleep, heart rate, and the like. Knowledge is power after all and thanks to advancements in technology we increasingly have access to all sorts of information about our health and fitness. Just glancing at my smart watch I could tell you how many hours of restful sleep I got last night (not nearly enough apparently), my respiration rate (no idea how my watch has that figured out), my training status (patting myself on the back for being “productive” today), my resting heart rate (all indications point to the fact that I am still alive), total steps for the day (sitting at my desk all morning hasn’t done me any favors), and that’s just to name a few. For many athletes these stats can be a tool to not only optimize their health, but also performance. As if all those metrics weren’t enough, athletes are just starting to tap into a new tool; continuous glucose monitoring (CGM). To be clear, CGM devices aren’t new. Individuals with diabetes have relied on them for years as a way to manage their blood sugar instead of taking regular readings from finger pricks. While diabetics use CGM devices to avoid the health complications from blood sugar getting too high (hyperglycemia) or too low (hypoglycemia), a few startup companies are looking to offer these devices for individuals who don’t have an actual medical need. These companies claim CGM devices can also be used to increase energy, reduce inflammation, promote recovery, and enhance athletic performance. Sounds good in theory, but can CGM devices really live up to the hype?
WHAT CGM DEVICES DO CGM devices measure an individual’s glucose, more commonly referred to as sugar. As a health indicator, monitoring one’s blood glucose can be very eye opening. Anytime you consume a source of carbohydrates, those carbohydrates are digested then absorbed into the blood stream as glucose, causing a rise in blood glucose levels.
for those already motivated to adopt a healthier diet and lifestyle.
HOW ATHLETES ARE USING CGM
Athletes are finding new uses for continuous glucose monitoring devices, long used by diabetics. Adobe
The body likes to maintain rather tight control on blood glucose levels, so a big spike in blood glucose from a large pasta dinner or candy bar elicits a response from the body to rein this in, primarily through the activity of insulin. Insulin functions almost like a key by binding to cells and allowing them to take glucose in, thereby lowering how much is circulating in the blood. In an ideal world when blood glucose levels become elevated the pancreas pumps insulin into the bloodstream and glucose falls back into a normal range pretty quickly. However, the average American diet is far from ideal. Refined grains and added sugars, which comprise much of the standard American diet, cause a more significant rise in blood glucose than our bodies were designed to handle. That’s bad news for our health because prolonged elevations in blood glucose and large post-meal spikes increase the risk for type 2 diabetes, cardiovascular disease, stroke, obesity, and cancer. That’s where CGM devices supposedly come in. By inserting a tiny sensor in the upper arm or abdomen, CGM devices transmit continuous glucose readings to a device or app on the user’s phone without the need for constant finger pricks throughout the
day. The sensor is covered by a patch and is typically replaced every 7 to 14 days. As opposed to finger pricks, CGM devices don’t actually measure blood glucose, but instead measure glucose levels in the interstitial fluid. Fortunately, the levels of glucose in blood and interstitial fluid are very close so the numbers can still be interpreted the same. Regardless, the question is what’s the benefit from knowing your glucose levels if you do not have type 1 or type 2 diabetes? It really comes down to the individual. Imagine you just polished off a large creemee and got a reading from your CGM device that your glucose levels are off the chart. Would that really deter you from indulging in such a summertime staple in the future? That’s where we come back to the adage that knowledge is power. Knowledge is only powerful if we use it. Perhaps realizing how certain foods effect glucose levels would prompt some individuals to consume a healthier diet. However, to date there are no published studies showing CGM is correlated with any dietary changes or positive health outcomes for those without diabetes. The jury is still out, but it seems for now using CGM to improve one’s health is no magic bullet and only beneficial
Even if CGM isn’t necessarily the ticket to optimal health, there is increasing interest among athletes in using the device to help optimize performance. Any athlete who has “bonked” before can understand the serious toll low blood glucose can have. That feeling of legs turning into cement blocks and the inability to form a coherent sentence comes down to a lack of fuel going to the muscles and nervous system. Just like a car when it runs out of gas, when your body runs low on glucose no amount of grit or determination will allow you to continue on. This is because during high intensity exercise our muscles rely heavily on glycogen as a fuel source. Glycogen, the storage form of carbohydrate in the body, is broken down into glucose to provide a quick and accessible fuel source to power muscles. Unfortunately, the amount of glycogen our bodies can store is limited to enough to power roughly 90 to 120 minutes of exercise. Hence the recommendation to consume exogenous forms of carbohydrates in the form of gels, sports drinks, gummies, and the like during prolonged activity. In theory this is where CGM could help. By essentially acting as the body’s fuel gauge, athletes could use CGM to determine when and how many carbohydrates to consume in order to avoid a dip in glucose that could hinder performance. However, there is a big discrepancy between the theoretical and realworld application. The effect glucose levels have on athletic performance is complicated. Although glycogen serves as the predominant fuel during highintensity exercise it is not the only fuel being used. Fat is also a fuel source for working muscles. The degree to which fat versus glycogen is used is determined by a number of factors, the most significant of which is exercise intensity. Go for a leisurely walk and glycogen hardly factors in as fat provides nearly all the necessary energy to put one foot in front of the other. Take that walk up a notch to an easy trot and the body starts to rely a bit more on glycogen, but only
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