Glucose is the primary source of sugar found in our blood, and its levels are tightly controlled. Following a meal when blood glucose levels are elevated, the pancreas releases insulin, which signals for the removal of glucose from our blood so it can be stored as glycogen in our muscle, liver, and fat cells for later use. Between meals glycogen is broken down to provide energy, to keep our hearts pumping and our muscles moving.

Type 2 diabetes is an extreme example of this careful control going awry when our bodies are either unable to produce insulin or no longer respond to insulin (aka insulin resistance). When blood sugar levels become severely high, the kidneys, which normally filters waste from our blood into urine, start excreting glucose into our urine as a last-ditch effort to lower blood sugar levels. Extremely high blood sugar levels can also damage the kidneys, resulting in some of the other symptoms associated with diabetes such as weight-gain because our bodies retain more water and salts.