Understanding Insulin Resistance

Insulin is a peptide hormone best known for its action in causing the storage of blood glucose in cells. Because insulin is the messenger that triggers the storage of energy, it causes the accumulation of body fat in people whose body cells become insulin resistant.

Insulin resistance is when the body’s cells don’t respond to insulin as effectively, requiring more insulin to store glucose. This often results in excess energy storage, producing weight gain. However, this is only part of what insulin does in the body, and in truth, insulin is vital to life in several ways.

Elevating Insulin Levels (Hyperinsulinemia): The Beginnings of Insulin Resistance

Insulin receptors on the surface of cells respond to insulin. In situations where insulin exists at a much higher concentration than normal, those receptors lose sensitivity, a process called insulin resistance. When this happens, the pancreas will then have to produce additional insulin, raising the concentration, to accomplish the storage of glucose.

Insulin levels don’t exist at a completely stable level in a healthy person, though, because levels do rise after consuming carbohydrates that are absorbed as glucose. The insulin level then goes back to normal after its work is done.

About 4 out of 10 people in the United States have some degree of insulin resistance. This drives not just an elevated number of type 2 diabetes cases but also many other health issues such as benign prostatic hyperplasia (BPH), erectile dysfunction (ED), polycystic ovarian syndrome (PCOS), nearsightedness, hair loss, skin tags, and of course, gout and atherosclerotic heart disease.

Even vestibular disorders can be caused by insulin resistance, and it is now thought that it plays a central role in the promotion of Alzheimer’s disease and other neurodegenerative conditions.

Despite these well-documented associations between disease states and insulin resistance, researchers have mostly focused on type 2 diabetes. The only major exception is brain health, where researchers have extensively documented the benefits of ketogenic diets in improving brain health.

Insulin resistance causes insulin levels to rise long before blood glucose levels do. The list of conditions that are associated with, or even caused by, high insulin can happen without someone being diabetic.

Most people may never realize that insulin resistance is the disease's puppet master because it is not something that is routinely evaluated with lab work. This is unfortunate because the elevated glucose that results from insulin resistance is due to poor insulin sensitivity. Chronically elevated insulin levels cause desensitization of insulin receptors over time, and the cycle continues.

The Many Effects of Insulin

The most obvious effect of insulin is to lower our blood glucose levels after we’ve consumed food that has resulted in elevated blood glucose. Any extra glucose that isn’t stored as glycogen in the liver or muscles (which together can store a total of only about 500g) is converted to triglycerides.

Triglycerides then get transported to fat cells, where they are stored as fat. These steps demonstrate that one of insulin’s primary roles is to cause the storage of fuel for future use. Excess fat accumulation and inflammation cause cells to resist insulin’s storage instructions, which is how we become insulin resistant.

Overall, insulin’s energy storage effects result in glucose being stored as glycogen in the liver or muscles, glucose is converted to triglycerides to be stored as body fat, or amino acids being converted into proteins. All of this storage is caused by insulin.

Insulin opens doorways into the cell known as glucose transporters, or GLUT. These doorways then allow the cell to absorb glucose and store it for later use. Much of this happens in muscle tissue, which plays a big role in glucose storage and utilization. This is thought to be why some athletes can consume tremendous amounts of carbohydrates and yet seemingly have a low rate of insulin resistance.

Insulin doesn’t just regulate blood sugar, though. It is also responsible for reducing or stopping lipolysis, which is the breaking down of fat to use as fuel. Functionally, it’s logical that the hormone that causes energy storage would prevent the release of stored energy.

Insulin also promotes amino acid and ion transport in the body, so that ingested protein can be used to build new proteins in other parts of the body. Because of this factor, insulin is required for muscle growth. This is evident from the fact that an untreated type 1 diabetic will also be very thin and sarcopenic. This isn’t seen often in the modern world due to increased awareness and treatment availability for type 1 diabetes.

There are other effects of insulin, such as the regulation of DNA. Insulin is involved in mRNA transcription and the formation of new proteins, as well as DNA synthesis.

Obesity and Insulin Resistance

Obesity is not a prerequisite for insulin resistance, as the condition does not occur equally in different individuals. The storage capacity of fat cells is an individualized trait.

Additional storage can come from fat cells enlarging or from growing new fat cells to provide additional storage. When a person can grow new fat cells, they can keep gaining weight without developing IR.

This can result in an obese individual whose insulin sensitivity is relatively normal, a situation known as “metabolically healthy obese”. It is estimated to occur in up to 10% of obese people.

On the other hand, some people cannot store much fat and can become insulin resistant if they eat excess carbohydrates without gaining much weight. This body type is known as TOFI, or “thin outside, fat inside,” sometimes also known as “skinny fat.”

Overall, we can see that the action of insulin is consistently shifting the body from withdrawing and burning energy to storing energy.