By Erika Gebel, PhD

February 2012

The liver is large and in charge. The dark reddish-brown organ sits in the upper right abdomen and, at about 3 pounds, is the largest one inside the body (the skin is the largest organ overall). The liver manages a dizzying array of tasks, including digesting fats, making and storing glucose, and serving as the body's detox center. A malfunctioning liver may lead to the development of type 2 diabetes or worsen high blood glucose levels for those who already have the disease.

Doctors know a lot about how the liver works, but not everything. The liver has myriad functions; some experts think there may be 500. By no means an exhaustive account of the liver's doings, this article focuses on how it processes fat and carbohydrate from what we eat.

Glucose Warehouse

The liver is an insulin-guided organ: Its behavior changes depending on the level of the hormone insulin in the body and how sensitive the liver is to that insulin. After eating, blood glucose levels rise, which in people without diabetes triggers the pancreas to release insulin into the blood. Insulin is the signal for the body to absorb glucose from the blood. Most cells just use the glucose to supply them with energy.

But the liver has a special job when it comes to glucose. When levels of glucose (and consequently insulin) are high in the blood, the liver responds to the insulin by absorbing glucose. It packages the sugar into bundles called glycogen. These glucose granules fill up liver cells, so the liver is like a warehouse for excess glucose.

When glucose levels drop, insulin production falls, too. The shortage of insulin in the blood is the signal that the liver needs to liquidate its assets, sending its glucose stores back into the blood to keep the body well fed between meals and overnight.

The liver doles out stored glucose and has the singular ability to make glucose from scratch. This is a critical function that keeps people alive when food is scarce. In people with diabetes, however, the liver doesn't process and produce glucose normally, adding to the challenge of blood glucose control.

The liver can't directly detect blood glucose levels; it knows only what insulin tells it. So, if there is a shortage of insulin or if the liver doesn't notice the insulin that's there, the liver assumes that the body needs more glucose, even if blood glucose levels are already elevated. That is why people with diabetes can have sky-high blood glucose even if they haven't eaten—for example, first thing in the morning. The liver is also responsible for the dangerously high blood glucose levels in people with diabetic ketoacidosis, a condition in which there is such a severe shortage of insulin that the body can't process glucose as energy. Instead, it uses fats. Ketones, waste products created when the liver breaks down fat, can be toxic in large quantities.