Blood Glucose

A simple one-time measurement of your blood glucose can give you great insight into your metabolic health, diet, and fueling practices. I have personally kept a glucose monitor handy to check my resting blood glucose, glucose during and after rides, and to check before and after meals. I am going to share why it is important to routinely check your blood glucose and the appropriate times to check.

First off, your fasted blood glucose first thing in the morning is probably one of the most important tests you can do, and if you were to only test every three months at one time, first thing in the morning would be the time to do so. Your fasted blood glucose can be a good reflection of your overall metabolic health. As athletes, we use a lot of carbohydrates which means we have to consume a lot of carbohydrates. A morning blood glucose test can indicate whether our bodies are tolerating this carbohydrate intake or not. A fasted blood glucose of less than 90mg/dL is considered healthy, between 90-100mg/dL is considered to be pre-diabetic, and above 100mg/dL is considered diabetic. If you are in the healthy range, great. If you are in the prediabetic range, seek help from a doctor and/or nutritionist to begin making dietary and lifestyle changes before things go too far. If in the diabetic range, definitely seek professional help.

The central nervous system (your brain and spinal cord) requires a blood glucose concentration of around 72mg/dL to function optimally. Throughout any given day, maintaining a stable blood glucose of around 70-100mg/dL will be best. Meals will spike glucose which is a normal physiological response to eating a meal high in carbohydrates, protein, and fat (the spike from macronutrients is greater in that order). Eating higher quality carbohydrates (whole grains, fruits, vegetables) vs processed carbohydrates and foods (candy, cereals, cakes), eating frequent moderate-sized meals throughout the day, and having balanced meals that contain all three macronutrients will lessen the height of the spike and lead to a more stable blood glucose level throughout the day.

Hypoglycemia is a common condition that athletes experience out on the road or trail. We are talking about bonking or hitting the wall here. This occurs when the muscle and liver glycogen stores are depleted, and the body begins to use up what is left of the blood glucose to fuel working muscles. This means that there will be a lower blood glucose level and when the brain senses this, it begins to shut you down by causing the bonk. The brain relies exclusively on blood glucose for fuel, and when the brain runs low on fuel, it will shut you down by making you feel tired, dizzy, confused, weak, hungry, and jittery. Hypoglycemia symptoms occur when blood glucose drops below 54mg/dL, and clinical hypoglycemia occurs below 45mg/dL. If blood glucose remains lower than this for long periods, unconsciousness or brain damage can occur.

Like I said before, the glucose spike is a completely normal response to consuming a balanced meal. The idea is to not make the spike higher than it needs to be. Carbohydrates (especially processed and refined ones) will spike glucose the most, followed by protein, then fats. It is best to consume a meal that contains all three macronutrients as well as fiber as these slower-digesting nutrients slow gastric emptying and lessen the glucose spike from that meal. So it is not a great idea to consume processed carb-heavy foods on their own outside of exercise. A blood glucose monitor can be used to check your response to a meal by checking 15 minutes after the meal, and two hours after a meal. After 15 minutes, the blood glucose level should be spiked, but by two hours, blood glucose should return to baseline.

Fueling training with carbohydrates in the form of sports drinks, gels, blocks, chews, and bars primarily serves the purpose of maintaining a normal/higher blood glucose level throughout the session, and providing additional fuel other than the stored glycogen for the working muscles. Working muscles are like a dry sponge and blood glucose is like a steady drip of water. When we are training, our muscles are burning carbohydrates at a pretty quick rate, especially when the intensity increases. Your liver can maintain adequate blood glucose levels for about an hour on its own given that you’ve had your pre-training meal and have your liver glycogen fully stocked before you start. Once your liver and muscles run out of glycogen after about two hours of continuous exercise, this is when you will experience the bonk. Steadily consuming carbohydrates at a rate of 30-90 grams per hour during training will provide the additional fuel to extend the duration you can exercise before bonking, and provide more fuel to go harder for longer. You do not need to worry about a glucose spike when taking in pure refined carbohydrates during exercise as your muscles will burn the excess before the spike gets too high (given that your intensity and fueling rate are appropriate!). Also, the sympathetic state of the nervous system (fight or flight) shuts down the insulin response to high blood glucose during exercise, so there is no worry about problematic insulin levels during exercise while fueling with carbohydrates.

To summarize, your fasting blood glucose is a good indicator of your current metabolic health and is largely related to your recent (3 month) dietary and lifestyle habits. A good fasting blood glucose is below 90md/dL. Your central nervous system requires around 72mg/dL to function optimally, so consuming consistent balanced meals throughout the day to keep levels around 70-100mg/dL will help you function at your best (except in the two hours after a meal where it is likely to be a little higher). A blood glucose level below 54mg/dL may bring rise to symptoms of hypoglycemia which include dizziness, nausea, hunger, and the jitters. If you are consistently hypoglycemic throughout the day, it may be a sign that you need to eat more consistently or more overall. The reverse is true if you are hypoglycemic shortly after meals (sugar crash).

Monitoring yourself is simple and relatively cheap, and the value of the data is a priceless insight into your long-term health. The Precisoin Neo glucose monitor is a great option for one-time testing that you can use anywhere to see how your blood glucose responds to various situations. If you are looking for more depth, a continuous glucose monitor such as the Freestyle Libre 3 Continuous Glucose Monitor is a great way to learn more about your blood glucose patterns across days and weeks.