The big picture: Insulin is a hormone that regulates energy flux throughout the body and helps control your blood sugar. When tissues stop responding normally to insulin, you’re at increased risk for metabolic diseases such as type 2 diabetes.

Insulin is produced by the pancreas and enables the absorption of glucose by cells in the muscles, fat, and liver for energy.

Insulin is created by the beta cells of the pancreas and allows the cells in the muscles, fat and liver to absorb glucose that is in the blood, giving them the needed energy to function.
Unneeded glucose is converted into fat for storage.
As a result, insulin also affects other metabolic processes, such as the breakdown of fat and protein.

Increasing levels of insulin indicates progression towards insulin resistance, and eventually diabetes.

Impaired insulin regulation signifies a reduced ability of insulin-sensitive tissues (muscle, fat, and liver) to respond to insulin signaling thus impairing their glucose uptake. This is called insulin resistance.
At first, the pancreas can compensate by making more insulin so individuals with this condition won't experience any symptoms.
Over time, however, insulin resistance can progress, requiring higher levels of insulin in order to keep glucose levels normal eventually, exhausting the pancreatic ability to produce this hormone.
Eventually, the pancreas can no longer produce enough insulin to overcome the cells' resistance, resulting in higher blood glucose levels.

Insulin resistance is considered the hallmark for metabolic abnormalities, as it results in hyperinsulinemia (high insulin levels) and hyperglycemia (high glucose levels), producing a systemic inflammation associated with the development of several chronic diseases: type 2 diabetes, cardiovascular disease, and cancer.

Decreasing levels of insulin may indicate progression towards type 1 diabetes.

Type 1 diabetes, a less common condition, is an autoimmune disease where the beta cells that produce insulin in the pancreas are destroyed.
Without insulin, the cells of the body cannot absorb insulin from the bloodstream and, thus, become starved of energy.
Additionally, rising blood sugar produces oxidative stress, which can lead to complications such as nerve damage or heart and kidney disease.