Should You Be Monitoring Your Blood Sugar?
Blood glucose monitoring for performance is becoming more common. Here's what you need to know.
Get full access to Outside Learn, our online education hub featuring in-depth fitness, nutrition, and adventure courses and more than 2,000 instructional videos when you sign up for Outside+.
Bob Troia, 46, a Brooklyn-based technology entrepreneur who runs the personal-optimization blog Quantified Bob, started tracking his blood sugar in 2014. A 23andMe DNA test indicated that he had an above-average risk of developing type 2 diabetes, though Troia wasn’t a typical type 2 candidate. He ate a balanced diet, got enough sleep, and exercised five days a week, including weight training, running, and competitive soccer. But he still discovered some surprising spikes in his daily blood-sugar numbers.
“I wondered, why aren’t people proactively monitoring this stuff?” Troia says. “You look at the proliferation of diabetes and realize this doesn’t happen overnight. It happens over decades, and it’s largely preventable.”
Troia’s concern is understandable. According to the Centers for Disease Control and Prevention, 30 million Americans are diabetic, about 28.5 million of whom are type 2, and another 84 million have prediabetes. Normal blood glucose in adults is defined as a fasting value below 100 milligrams per deciliter; prediabetes is defined as a fasting reading between 100 and 125.
Troia didn’t just want to ward off chronic disease, however. He wanted to optimize his health. To better understand how his blood sugar behaved, he turned to a continuous glucose monitor. The devices were first approved for physician use by the FDA in 1999. CGMs, like Dexcom’s G6 and Abbott’s FreeStyle Libre, utilize sensors that adhere to your skin, along with a portable scanner that collects readings. Less painful and more convenient than traditional finger-prick glucometers, CGMs provide a comprehensive picture of blood-sugar levels throughout the day.
Health professionals aren’t concerned only about chronically elevated blood glucose; they also worry about about big swings in blood sugar, sometimes referred to as glycemic variability, which can be brought on by certain foods, stress, and other lifestyle factors. When blood sugar rises in healthy adults, the pancreas secretes insulin, which helps the body absorb the extra glucose. But frequent, sustained spikes over time are associated with type 2 diabetes and the insulin resistance that is a symptom of the disease. While it’s still unclear to what degree blood-sugar spikes lead to specific health risks, there does appear to be a connection.
The more data Troia gathered—not just on blood sugar but also on sleep quality, physical activity (with a Fitbit and an Oura ring), and food intake (tracked in an app he developed)—the better he understood how his weekly habits affected his health. These insights helped him to better control glucose with dietary modifications. Blood sugar fluctuates naturally throughout the day, especially after meals, but blood glucose can respond differently from person to person, even when they eat the same foods. In a large but controversial study published in 2015 by the Weizmann Institute of Science in Israel, researchers monitored blood glucose in 800 people, who consumed a combined 47,000 meals over the course of a week. In one case, a participant saw their glucose jump after eating cookies but not bananas, even though the total calories were similar. Another person in the study had the opposite result.
When Troia analyzed his own glucose readings, he noticed that cooked white rice spiked his blood sugar to near diabetic levels. But if he added a little coconut oil, the impact was notably lower. (The fat slowed digestion.) Following a long cross-country flight, he also discovered that his glucose levels were higher than normal for several days, likely from travel-related stress. On mornings after his twice-a-week soccer games, his blood sugar was much lower than on other days, probably due to the high-intensity exercise.
In a study published in 2018, researchers at Stanford University used CGMs to study blood sugar in 57 adults, some with diabetes and some without, for two to four weeks. The results revealed that severe glucose variability appeared in 25 percent of the nondiabetic participants. The paper suggests that monitoring glycemic variability—already shown to help predict problems like cardiovascular disease down the road—can be more informative than your annual fasting-glucose values or other biomarkers.
“Do I think healthy people should be monitoring their glucose levels? Absolutely,” says Michael Snyder, chair of the genetics department at Stanford and the study’s senior author. “If you have really good glucose control, you may not need it. But there are a surprising number of people who don’t have good glucose control, and they have no idea.”
Ben Greenfield, a biohacker and the bestselling author of Beyond Training, believes that blood glucose may be the most important health metric you can continuously track. That’s because glucose levels serve as a proxy for metabolic health and risk for certain chronic diseases. A triathlete and obstacle racer, Greenfield has been monitoring his own glucose levels since 2014, even though he isn’t diabetic. He believes that understanding individual glucose variability can help healthy athletes in several ways: by stabilizing energy levels, improving fueling for training and competition, and bolstering cellular health (insulin resistance has been linked to impaired mitochondrial function and density).
Regular exercise helps maintain healthy blood sugar, but athletes are hardly immune. A study published in 2016 in the Journal of Diabetes Science and Technology caused moderate alarm because it showed that despite regular exercise, some endurance athletes have prediabetic levels of blood glucose—possibly due to high-carbohydrate diets.
Typically individuals with a risk of diabetes might have their fasting-glucose levels checked once a year, at a routine physical. That may be enough to flag a problem, but the point of nondiabetics using CGMs, which is off-label though not illegal, is to help prevent issues before they crop up. You currently need a prescription to purchase CGMs (see “Take a Stab,” right), but some units are available online or can be bought over the counter in Europe. The technology may soon be available in other wearable devices, too. In 2016, Apple filed a patent that suggested it is developing technology that uses light sensors to track glucose molecules. And early last year, Fitbit invested $6 million in Sano, a San Francisco–based startup working on a minimally invasive glucose monitor.
“Ninety percent of people who are prediabetic have no idea they are prediabetic, and up to 70 percent will go on to develop type 2,” says Stanford’s Snyder, a type 2 diabetic himself. “If you can see what’s happening before you lose glucose control, you can figure out ways to manage it before it’s too late.”