Elevated fasting glucose while on low carb/ketogenic diet?

Low carbohydrate diet and ketogenic diet are rapidly becoming the “new” most recommended diets for diabetes, weight loss and metabolic syndrome patients.  These diets work very well for most people and lower their blood sugar levels, and body weight.  In fact, I recommend low carb/ketogenic diet (with varying degree of strictness for different diseases. For patients with diabetes, cancer and autoimmune diseases, I usually recommend more strict ketogenic diet along with limits on foods with high plant toxins such as lectins, phytoalexins and oxalates etc.

However a small percentage of people may see a rise in their fasting blood sugar after a prolonged period of very low carb or ketogenic diet. Why is this and is this something to be concerned of?

There are several possible reasons why your fasting glucose may rise even if you are on a low carb or ketogenic diet.

  1. Dawn Phenomenon. This refers to the rise of glucose in early mornings due to diurnal changes of our hormones, esp. cortisol. Normally cortisol levels rise in the morning, preparing us for a day’s work ahead.  Cortisol increases our alertness, mobilizes energy for our body’s use by raising blood sugar levels.  This is normal and happens to everyone. People who are on low carb or ketogenic diet, tend to have more marked Dawn Phenomenon.  Usually there is no need for concern of dawn phenomenon.  However, we do need to be aware of overreacting adrenal glands which may secret higher than normal amounts of cortisol when under high stressed (early phase of adrenal fatigue or adrenal insufficiency).  When this happens, you need to seek out a trained doctor (usually a functional medicine doctor) for help.
  1. Adaptive Glucose Sparing, this is also called physiological insulin resistance. This may happen to those who have been on very low carb or ketogenic diet for quite a while and their body is used to burning fat as fuel (so called keto adapted or fat adapted), with much reduced need for glucose. Under these circumstances, glucose is reserved for tissues that need glucose for energy mostly or even absolutely. Fats can only be metabolized as fuel through a biochemical process called TCA cycle in the mitochondria the little powerhouse in our cells. But a few types of cells don’t have mitochondria such as red blood cells and the cells in some part of our eyes. Some of our immune cells also adapted to use mostly glucose as fuel in a process called aerobic glycolysis (in layman’s term: fermentation without oxygen, since these cells are charged with a duty to enter infected sites where oxygen is scarce).  Most other types of cells including our brain cells can burn fat as fuel. After being on low carb/ketogenic diet for a prolonged period, our body has adapted to burning fat as fuel and reserving glucose for those cell types that require glucose for energy.  So most of our body cells (especially our muscles) learned to “reject” glucose as fuel, sparing glucose for those tissues that have a higher need for glucose. This is called physiological insulin resistance, different from pathological insulin resistance. This is also part of the reason why fasting glucose may rise for those who have been on prolonged low carb/ketogenic diet.  No need to worry.
  2. Measurements of our glucose metabolism: Fasting Blood Glucose, HbA1c, HOMA-IR. Fasting blood glucose in only one measurement at a particular time. HbA1c measures the average glucose level over the past 3 months or so, hence, it’s a better measurement of your recent past glucose levels. But fasting glucose and HbA1c only tells part of the story.  A better assessment is to take into account both blood glucose and insulin levels.  HOMA-IR stands for homeostatic model assessment of insulin resistance.

HOMA-IR = (Blood glucose (mMol/L) * Insulin) / 22.5 or

HOMA-IR = (Blood glucose (mg/dL) * Insulin) / 405

HOMA-IR results:

  1. Excellent Insulin Sensitivity: < 1
  2. Early Insulin Sensitivity: > 1.9
  3. Severe Insulin Resistant: > 2.9

Take 2 different scenarios:

Patient A, fasting glucose of 96, fasting insulin 4 uIU/mL, HOMA-IR: (96 x 4) / 405 = 0.94

Patient B, fasting glucose 84, fasting insulin 14 uIU/mL, HOMA-IR: (84 x 14) / 405 = 2.9

Patient A’s fasting glucose is higher than Patient B’s. However, when both fasting glucose and insulin are counted, Patient B is at greater risk for diabetes and metabolic complications in the future.








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