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Blood sugar higher after fasting



I was recently diagnosed with type 2 diabetes. I am not taking medication for it. I have started testing my blood glucose levels at home, both fasting (first thing in the morning) and after dinner. My blood glucose level is consistently higher in the morning (160-175), compared to after eating (120-135). I also started a very low-carb diet (South Beach) at my doctor`s recommendation, and the less carbs I eat, the more my blood sugar has gone up. Is this normal in type 2 diabetes, or does it indicate something else?


There are quite a number of factors which affect blood glucose.  We think most commonly of the rise in blood glucose that results from carbohydrate intake.  However there are sources of glucose within the body which are intended to prevent the blood level from falling too low as well.  The liver releases glucose into the blood stream under the regulation of several hormones.  That is the major source of keeping the blood sugar from falling too low with either prolonged periods of fasting or when people exercise.  However, in people with diabetes, that source can release enough glucose to cause the blood level to go high.  The blood glucose can rise from a normal level to a high level as a result of this mechanism (referred to as the "dawn phenomenon").  Or, if for some reason the blood glucose goes too low, that can set off the release of the hormones intended to protect against low blood sugars [referred to as the Somogyi effect (most people pronounce this as soh-MOH-ji but the doctor who described this actually pronounced his name SOH-moh-ji).  These are called "counter-regulatory" hormones because they act to raise blood glucose opposite or counter to the action of insulin to lower blood glucose.  These include glucagon, epinephrine (also sometimes referred to as adrenaline), cortisol and growth hormone.  The release of these counter-regulatory hormones can cause an overshoot high blood glucose in response to a low blood glucose.  These counter-regulatory hormones can also be set off by stress or by exercise, so it would be helpful to assess the relationship of the rise in blood glucose to those factors.

There are several pieces of information that would help in sorting this out.  First, you would want to take into account whether you are eating late at night and what the composition is of what you are eating; that could be one source of a rise in blood sugar overnight.  Another issue would be to check the blood sugar in the middle of the night several times, perhaps at different times, and make sure that the blood sugar is not going low; this is more of an issue in people who are taking insulin or diabetes medicines that stimulate insulin release from the pancreas.  If a low is found, then the objective shifts towards preventing the low.  Assuming there is no low, there are some diabetes medicines which target reducing the liver's release of glucose.  These include metformin and a new hormone-like drug called exenatide.  However, the whole spectrum of diabetes medicines that don't just target meal-related rises in sugar may be considered to achieve the net effect of preventing an overnight high blood sugar.  This would include insulin, long-acting drugs which raise the production of insulin by the pancreas or drugs which improve target organ responses to insulin, the so-called glitazones. 

In summary, blood glucose can rise either from glucose that comes from outside the body (primarily food and sugar containing drinks) or from glucose that comes from inside the body, primarily from the liver.  The liver source glucose is primarily intended to protect against low blood sugars but it can cause the blood sugar to rise too high either spontaneously in the early morning hours (dawn phenomenon), after the sugars fall too low overnight (Somogyi effect), or in response to stress or exercise.  All of these are common problems in people with diabetes

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Response by:

Robert M Cohen, MD Robert M Cohen, MD
Professor of Clinical Medicine
College of Medicine
University of Cincinnati