“M. Apicius [Marcus Gavius Apicius, a first century AD Roman gourmet] made the discovery, that we may employ the same artificial method of increasing the size of the liver of the sow, as of that of the goose; it consists in cramming them with dried figs, and when they are fat enough, they are drenched with wine mixed with honey, and immediately killed.”

— Pliny the Elder, The Natural History, Book VIII, Chapter 77

For thousands of years, humans have created a tasty delicacy called foie gras from the livers of certain animals. Foie gras, which means “fatty liver” in French, is made by force-feeding animals, usually geese or ducks, a mash consisting of fat-soaked grain. Fatty livers are most easily induced in animals that regularly store extra fat for energy before migration. Humans also store energy easily, and modern lifestyles, including diets heavy in fat-soaked carbohydrates, have inadvertently created an epidemic of fatty livers in people. Some researchers estimate that the problem now affects one-third of the US population. 

Alcoholism was the main cause of fatty livers in the past

Doctors have long been familiar with fatty livers in alcoholics, in whom a combination of the toxicity of alcohol and dietary deficiencies converts liver cells into fat-laden bubbles. This condition is known as alcoholic steatosis and is the first step along a road that can lead to cirrhosis and liver failure. Alcoholic steatosis can be reversed if the patient stops drinking. If not, it can become progressively worse, leading to inflammation of the liver called alcoholic steatohepatitis. Ultimately this inflammatory degeneration can lead to a scarred and shrunken liver (cirrhosis) and to liver failure.

Non-alcoholic fatty liver becomes a new diagnosis

By 1980, the appearance of fatty livers and the kinds of problems that are associated with them in nondrinkers forced doctors to devise a new diagnosis—nonalcoholic fatty liver disease (NAFLD). As in alcohol fueled liver disease, NAFLD can also lead to inflammation, a condition called nonalcoholic steatohepatitis (NASH), and to cirrhosis and liver failure in some patients. Progression from NAFLD to NASH seems to require the additional effects of viral hepatitis or of toxic substances, like certain medications, both of which also play a role in some alcoholic liver disease progression. 
…..and becomes a serious problem

Since the 1980s, the prevalence of NAFLD has been climbing in parallel with the numbers of people affected by the metabolic problems of obesity, insulin resistance, and type 2 diabetes. Like these problems, NAFLD is now affecting younger people, even children. By 2006, NAFLD and NASH were the leading reasons patients were referred to liver specialists. They were also the leading cause behind diagnoses that led to 4 to 10 percent of liver transplants. While it is very difficult to make accurate estimates about the overall prevalence of NAFLD, by now it is clear that it is very common in people who have abdominal obesity, insulin resistance, and type 2 diabetes—perhaps affecting as many as 75 percent of such individuals.  
Why fat in the liver is bad for you

In a state of good health, the liver functions silently. Tucked up under the ribs on the right side of the abdomen, it is the size and shape of a deflated football and is the second largest organ in the body (the skin is the largest). The liver coordinates energy storage and regulation and makes proteins and cholesterol necessary to the health of all cells in the body. It also makes and secretes bile to absorb fats from the intestine and filters toxins from the blood to destroy them or ship them out with bile. The liver also stores vitamins and regulates the blood’s ability to clot in a fine-tuned range.  
 If necessary, the liver stores fat in its cells. Generally, this is a temporary state, and the fats are transported back to the body for use as an energy source or for storage in fat tissue. Obesity, insulin resistance, and diabetes, however, work together to keep fat in liver cells. Despite the stored fat the liver can continue to function well, producing no symptoms, unless other factors produce inflammation and scarring. NALFD is often discovered incidentally, because of abnormal liver function blood tests from inflammation, or a scan of the abdomen for other problems. 

Fat plus inflammation can trigger liver failure

When fat accumulation in the liver is accompanied by inflammation or occurs in someone who already has a scarred liver from other problems, like heavy alcohol use or hepatitis, liver failure and cirrhosis ( shrinkage from scarring) may follow. It is estimated that 20 percent of those with NAFLD have inflammatory changes in their livers, moving them from a diagnosis of NAFLD to a diagnosis of steatohepatitis, or NASH, which increases their risk of developing liver failure and cirrhosis. Unfortunately, there are no easy tests to determine the presence or absence of inflammation in the liver, and patients may have no symptoms. Liver function tests may remain normal, and although liver biopsy provides a definite diagnosis, it carries some risks and thus is not a suitable screening test for patients who have no symptoms or findings. 
Symptoms of liver disease

Symptoms of liver disease can be very vague until liver scarring and failure are well advanced. Fatigue, vague abdominal pain, and digestive complaints, as well as enlargement of the liver are early indicators. Jaundice (yellowing of the skin and eyes), fluid in the abdomen, poor clotting, and bleeding from the intestinal tract are late symptoms. Most people who have fatty livers will not go on to this degree of failure, just as most alcoholics do not, but there is no easy way to know who will and who won’t. 

What can be done?

In the presence of NAFLD it is important to avoid liver toxins such as alcohol and many drugs. With gradual weight loss, it is possible to reverse the accumulation of fat in the liver and to reduce liver inflammation, particularly if the weight loss program includes significant exercise to improve insulin sensitivity. Even in transplanted livers, NAFLD can recur as long as obesity, diabetes, and insulin resistance remain. Obesity surgery appears to reverse some of the liver problems in affected people and may yield new insights into the mechanism of insulin resistance. While researchers are striving to develop drugs that improve insulin resistance and alter fat transport and storage mechanisms, prevention, as always, is the best advice. This will require education, patience, self-discipline, and hard work, and it is particularly important for young people. While foie gras from a goose is tasty, its development in humans is undesirable.