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“It’s logical for people to point the finger for high fasting blood sugar numbers at what they eat between dinner and bed, but surprisingly food isn’t the lead villain,” says Robert Chilton, M.D., a cardiologist and professor of medicine at the University of Texas Health Science Center at San Antonio. The true reason for why blood sugar goes up when fasting is related to compromised hormonal control of blood glucose levels.
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Essential hormones for blood glucose control
During the years (up to a decade) that type 2 diabetes develops, the hormonal control of blood glucose breaks down. Four hormones are involved in glucose control:
How the essential hormones work in the body
When diabetes is not present, the body handles the changing supply of and demand for glucose (the energy from food) 24 hours a day. This system involves the four hormones—what we’ll call the messengers—and a continuous feedback loop that moves messages between the brain, gut, pancreas and liver. Here is how the system works in someone without diabetes:
When fasting
As blood glucose falls after peaking from the last food eaten, the pancreas puts out less insulin hormone. At the same time, two other hormones wane: amylin and glucagon-like peptide 1 (GLP-1), which help store and use glucose. A fourth hormone, glucagon, kicks into gear to offer a constant flow of glucose. Glucagon sends messages to the liver and muscles to make glucose from stored energy.
After eating
Food raises blood glucose and sends a message to the intestines to release GLP-1, which primes the insulin and amylin spigots. These hormones help cells use the glucose from food to fuel the body. The glucagon spigot turns off because there’s little need for glucose from the liver or muscles when food is available. The impact of food on blood glucose, even for a large, high-fat meal, lasts less than six hours.
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Here are two other situations that may cause high fasting blood glucose levels:
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