The Liver's Role: How It Processes Fats and Carbs
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.
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.
Processing the body's fat is a key job for the liver. Once the liver is full of glycogen, it starts turning the glucose it absorbs from the blood into fatty acids, for long-term storage as body fat. The fatty acids and cholesterol are gathered as fatty packages and delivered around the body via the blood. Much of the fat ends up stored in fat tissues.
All of this extra fat produced and stored by the liver can sometimes lead the liver itself to get fat. In a condition known as nonalcoholic fatty liver disease, found in people who aren't heavy drinkers (who have their own liver problems), liver cells accumulate excess fat instead of sending it off to fat cells. This disease is common, affecting 20 percent of adults overall and the majority of people with obesity or diabetes, or both. Doctors may test your blood to determine whether you have an ailing liver. In some cases, they may use an imaging technique or a biopsy to detect disease.
For most people, fatty liver doesn't cause any symptoms. But when it does cause problems, the prognosis can be serious. Severe cases may end in cirrhosis, which is characterized by scarring and poor liver function. Cirrhosis can be fatal or may require a liver transplant.
Scientists are working hard to understand the connection between obesity, fatty liver, and diabetes, but little is certain. One theory blames fatty liver for the development of insulin resistance in the liver. An insulin-resistant liver ignores the hormone's signal to stop sending glucose to the blood. That raises blood glucose levels and increases the risk for type 2 diabetes. Some studies have found that slim people with type 2 tend to have fatty livers.
Diabetes also may be a cause of fatty liver and liver disease. People with diabetes are more likely to develop and die from liver disease than those without diabetes. There's a link between type 1 diabetes and liver disease, too, further supporting the idea that diabetes alone, without insulin resistance, is a factor in liver disease.
Save the Liver
Because of the links between diabetes and liver disease, people with diabetes and their health care providers have reason to focus on liver health and use tools such as a liver function test. Overweight people, particularly those who carry their extra weight around the middle, have the highest risk for liver problems and need to be extra diligent. There is no standard approach for the treatment of fatty liver, though there are medications in development. Typically, a doctor is likely to recommend losing weight, eating well, and exercising. These steps also help control blood glucose levels, of course, so what you do for your blood sugars is good for your liver, too.