Fasting blood sugar level
In his work with patients, Denis Slinkin does not use a single marker to determine if someone has a blood sugar problem.
He performs a complete blood test which includes lean glucose, A1c, fructozamine, uric acid and triglycerides (along with other lipids) and makes them do post-tests at home for 3 days with a variety of foods. If they have a few post-acceptance spikes and all other markers or are normal, I don't care. If they have high levels of BG, A1c and fructozamine on an empty stomach and they have spikes, I am concerned and will do further research.
On a similar note, Denis wrote that A1c is not a reliable marker for people because of the context: there are many conditions unrelated to blood sugar that can make A1c look high or low. So if someone is normal on all the other blood sugar markers, but they have high A1c, that usually doesn't bother me. With all that in mind, let's look at some research. According to continuous glucose monitoring studies in healthy people, normal blood sugar levels at fasting are 83 mg/dL or less. Many normal people have normal blood sugar levels at fasting in the middle and early 70s.
Although most doctors will tell you that anything below 100 mg/dL is normal, it may not be so. In this study, people with FBS above 95 were more than 3 times more likely to develop diabetes in the future than people with FBH below 90. This study showed a gradual increase in the risk of heart disease in men with FBS above 85 mg/dL, compared to men with FBS 81 mg/dL and below. Even more important for understanding FBG is that it is the least sensitive marker for predicting diabetes and heart disease in the future. Several studies show that "normal" FBG levels in the mid 90s predict diabetes diagnosed ten years later.
Much more important than a single measurement of blood glucose on an empty stomach, the number of hours per day we spend in the blood FBSexceeds the level known to cause complications, and is approximately 140 mg/dL (7.7 mmol/l). One of the warnings here is that very low-carbohydrate diets will produce elevated blood glucose levels on an empty stomach. Why is that? Because low-carbohydrate diets cause insulin resistance. Carbohydrate restriction leads to a natural reduction in insulin levels, which in turn activates hormone-sensitive lipase. The fatty tissue then breaks down and un-esterified fatty acids ("free fatty acids" or NEFA) are released into the bloodstream. These NEFAs are captured by the muscles that use them as fuel. And since the muscle's fuel needs are met, insulin sensitivity is reduced.