Your body uses glucose as energy. Glucose is a single sugar molecule that comes from a variety of foods including starches and fruit. When you eat sugar and starches the glucose is released into the bloodstream. If there is a lot of glucose in the blood it becomes thick and heavy, like syrup, which makes it difficult for the blood to circulate so your body sends a signal to your pancreas to release the hormone insulin. Insulin works like a key unlocking cells to escort glucose inside of them and out of the blood.
Refined sugar and starches are quick to digest and so release a lot of glucose all at once into the blood. The pancreas in turn releases a large amount of insulin to take care of it. Imagine I have a bunch of beads. If I were to take twenty of those beads and throw them on the floor it wouldn't take very long for one person to pick them up. If I threw a thousand beads all over the floor though it would take a long time for one person to pick those up so it would be more efficient to have twenty people helping. So the pancreas releases a lot of insulin all at once to quickly put away the high amounts of glucose.
The body requires some glucose to remain within the bloodstream because it is the only source of energy for the red blood cells. So imagine that I told those twenty people to pick up all but 10 beads. Imagine the mass confusion that would ensue! So basically when a lot of insulin is released too much glucose is removed from the blood resulting in fatigue, lack of energy, moodiness, and all sorts of effects.
In order to balance the blood sugar again the liver releases another hormone called glucagon which tells the cells to release glucose back into the blood.
In hypoglycemia (low blood sugar) often the individual is eating too many refined carbohydrates and sugars causing an excessive amount of insulin to be released. These people may also have an issue where the liver is not working properly or is so congested that it is having difficulty producing the glucagon hormone to re-balance the blood sugar. When hypoglycemia goes on for too long the cells may actually become "gummed" up and so they become resistant to allowing insulin to dock. This is what happens in Type II diabetes which used to be called Adult onset diabetes until children started getting it. This is not surprising considering the amount of refined carbohydrates and sugar the average American kid gets in their diet.
Type I diabetes involves a dysfunction of the pancreas so that it is not producing enough insulin. In my experience, diet plays a very important role in Type I diabetes as well.
In order to resolve glucose regulation issues I recommend a very low refined carbohydrate diet. I also highly recommend eating more fat and protein with each meal as either will slow down the glucose release avoiding the roller coaster of insulin and glucagon response.
Many of my clients with blood sugar issues keep a jar of coconut oil mixed with honey and a little nut butter to taste with them at all times. When they feel low in blood sugar they take a spoonful of this mixture. The honey gives a quick glucose boost while the coconut oil is used by the body for a slow release of energy to keep the red blood cells fed. Some people will also need to address their overall liver and pancreas health for long term resolution.