But pretty soon we also discover that logic has limitations. We go to bed at night with good numbers and wake with high numbers. But we didn't eat in our sleep. Or we make the mistake of thinking 'food = spike, fasting = no spike' and find that after eating nothing for six hours we might be normal or even high when we expected to be low.
It doesn't seem to make sense, does it? "I Ate Nothing! Why Are My BGs high?".
I am no expert on this, but I am pretty good at looking things up and then testing the things I read against my own results. My body, my science experiment. So I checked this out a long time back when I first came across the term "liver dump". Here is my rough version, based on the best explanation I've seen (or that I could understand at my level:-) . This is the medical-speak version:
"Stores of readily available glucose to supply the tissues with an oxidizable energy source are found principally in the liver, as glycogen. Glycogen is a polymer of glucose residues linked by a-(1,4)- and a-(1,6)-glycosidic bonds. A second major source of stored glucose is the glycogen of skeletal muscle. However, muscle glycogen is not generally available to other tissues, because muscle lacks the enzyme glucose-6-phosphatase.
The major site of daily glucose consumption (75%) is the brain via aerobic pathways. Most of the remainder of is utilized by erythrocytes, skeletal muscle, and heart muscle. The body obtains glucose either directly from the diet or from amino acids and lactate via gluconeogenesis. Glucose obtained from these two primary sources either remains soluble in the body fluids or is stored in a polymeric form, glycogen. Glycogen is considered the principal storage form of glucose and is found mainly in liver and muscle, with kidney and intestines adding minor storage sites. With up to 10% of its weight as glycogen, the liver has the highest specific content of any body tissue. Muscle has a much lower amount of glycogen per unit mass of tissue, but since the total mass of muscle is so much greater than that of liver, total glycogen stored in muscle is about twice that of liver. Stores of glycogen in the liver are considered the main buffer of blood glucose levels."
For the really detailed version click on the links.
Below I put that in words that I understand. I am no biochemist, so if any experts are reading this please correct any errors I make or omissions from over-simplification.
We need glucose for energy. When we eat a meal it is usually a mix of carbohydrates, protein and fats. Carbohydrates are an easily converted source which quickly appear as glucose in our blood. We also, more slowly, obtain glucose by gluconeogenesis from protein or even fats and also from the stored energy in our liver and other organs.
When we create more glucose than our immediate needs some is stored. Some is stored as fat, especially if we have excess insulin floating around, and some is converted to glycogen. Glycogen is stored mainly in the liver and the muscles. The muscles are selfish because the glycogen stored in the muscles can usually only be used for the muscles, but the glycogen stored in the liver is our supply for any glucose needed by the rest of the body. When the body needs it the right amount is automatically released to the right places. As a result there is always a steady flow of energy to meet a person's needs, regulated to demand, regardless of when or what they eat.
At least, that is how it works in non-diabetics. It is the body's version of a fuel tank. Unfortunately, for type 2s, the system can be flawed. Type 2s on the internet use the term "liver dump" for the release of excessive glycogen fr0m the liver to become blood glucose at times when it wasn't really needed or wanted.
For example, one cause of the Dawn Phenomenon is thought to be the body sensing our need for energy when we are about to wake, leading to excessive glycogen release until we eat and send the signal to stop the release. That's why a breakfast soon after we wake is an essential meal for many of us. Similarly, fasting, exercise or heavy physical activity can lead to a liver dump if the body senses the reduction in blood glucose levels and over-compensates with excessive glycogen release.
Preventing liver dumps is complex and I know no general solution. For dawn phenomenon the most common treatment is to eat a late night snack; but the reports of successful snacks vary widely so it's best to perform your own experiments until, hopefully, you find the one that works for you. A minority never does, and others find that the only solution for them is basal insulin.
For those who experience liver dumps after fasting the solution is easy. Don't fast for long periods. Eat something every few hours, even if it is only a small snack.
For those who get them during or after exercise, I have seen reports of success from people who spread small carby snacks across the period of exercise, including a snack before starting.
Sorry I can't be more specific with answers on this one, just suggestions. Once again it's your body, your science experiment
Cheers, Alan, T2, Australia.
Everything in Moderation - Except Laughter
Postscript: Another good comment on the "Dawn Phenomenon can be found in the Misc.Health.Diabetes FAQs. Click on the link and scroll down to "Why is my morning bg high? What are dawn phenomenon, rebound, and Somogyi effect?".