“Lessons from Continuous Glucose Monitoring In the years that I have used CGM, I have gleaned the following insights—some of which may seem obvious, but the power of confirmation cannot be ignored: Not all carbs are created equal. The more refined the carb (think dinner roll, potato chips), the faster and higher the glucose spike. Less processed carbohydrates and those with more fiber, on the other hand, blunt the glucose impact. I try to eat more than fifty grams of fiber per day. Rice and oatmeal are surprisingly glycemic (meaning they cause a sharp rise in glucose levels), despite not being particularly refined; more surprising is that brown rice is only slightly less glycemic than long-grain white rice. Fructose does not get measured by CGM, but because fructose is almost always consumed in combination with glucose, fructose-heavy foods will still likely cause blood-glucose spikes. Timing, duration, and intensity of exercise matter a lot. In general, aerobic exercise seems most efficacious at removing glucose from circulation, while high-intensity exercise and strength training tend to increase glucose transiently, because the liver is sending more glucose into the circulation to fuel the muscles. Don’t be alarmed by glucose spikes when you are exercising. A good versus bad night of sleep makes a world of difference in terms of glucose control. All things equal, it appears that sleeping just five to six hours (versus eight hours) accounts for about a 10 to 20 mg/dL (that’s a lot!) jump in peak glucose response, and about 5 to 10 mg/dL in overall levels. Stress, presumably, via cortisol and other stress hormones, has a surprising impact on blood glucose, even while one is fasting or restricting carbohydrates. It’s difficult to quantify, but the effect is most visible during sleep or periods long after meals. Nonstarchy veggies such as spinach or broccoli have virtually no impact on blood sugar. Have at them. Foods high in protein and fat (e.g., eggs, beef short ribs) have virtually no effect on blood sugar (assuming the short ribs are not coated in sweet sauce), but large amounts of lean protein (e.g., chicken breast) will elevate glucose slightly. Protein shakes, especially if low in fat, have a more pronounced effect (particularly if they contain sugar, obviously). Stacking the above insights—in both directions, positive or negative—is very powerful. So if you’re stressed out, sleeping poorly, and unable to make time to exercise, be as careful as possible with what you eat. Perhaps the most important insight of them all? Simply tracking my glucose has a positive impact on my eating behavior. I’ve come to appreciate the fact that CGM creates its own Hawthorne effect, a phenomenon where study subjects change their behavior because they are being observed. It makes me think twice when I see the bag of chocolate-covered raisins in the pantry, or anything else that might raise my blood glucose levels.”