They’re less than 100 mg/dL after not eating (fasting) for at least 8 hours. And they’re less than 140 mg/dL 2 hours after eating.
During the day, levels tend to be at their lowest just before meals. For most people without diabetes, blood sugar levels before meals hover around 70 to 80 mg/dL. For some people, 60 is normal; for others, 90.
What’s a low sugar level? It varies widely, too. Many people’s glucose won’t ever fall below 60, even with prolonged fasting. When you diet or fast, the liver keeps your levels normal by turning fat and muscle into sugar. A few people’s levels may fall somewhat lower.