If you saw the 2004 film "Super Size Me," then you will probably not be surprised that, according to a recent study, eating too much fast food can seriously damage your liver.

This is bad news, because you cannot live without a functioning liver. There is, however, good news — another study finds that many types of diet related liver damage can be reversed simply by eating healthier.

"There's strong evidence now that a fast-food type of diet — high in fat and sugar, the kind of diet many Americans subsist on — can cause significant damage to your liver and have extremely serious consequences for your health," says Brent Tetri, M.D., professor of internal medicine at the Saint Louis University Liver Center and a leading expert on non-alcoholic fatty liver disease.

"The good news is that most people can undo this damage if they change their diet and they keep physically active," Tetri says. "If they don't , however, they are asking for trouble."

According to Tetri, physicians are starting to see children and teenagers with cirrhosis, a serious liver disease once virtually restricted to adults with a history of alcohol abuse or hepatitis C. The prime suspect is the combination of eating far too much fast food or junk food and getting far too little exercise, which is an all too common feature of the lifestyles of young people today.

"The fact we're starting to see kids with liver disease should really be a wake-up call for anyone eating a diet high in fat and sugar and who's not physically active," Tetri says.

Tetri studied the effects on mice of a diet that mimicked a typical fast-food meal. The diet was 40 percent fat and high in high-fructose corn syrup, a sweetener used in soda and some fruit juices. The mice were also kept sedentary. As soon as four weeks, the mice had an increase in liver enzymes — a key indicator of liver damage — and the beginnings of glucose intolerance, a marker for type II diabetes.

Tetri is quick to emphasize that fast food per se doesn't causes liver damage. "The big issue here is caloric content," he says. "You can put away 2,000 calories in a single fast-food meal pretty easily. For most people, that's more calories than they need in an entire day."

For adults and children who eat a lot of fast food, Tetri urges four key steps to help reverse any damage they may have already done to their liver.
  1. Limit yourself to one fast-food meal a week. A visit to a fast-food restaurant should be considered a treat, not a regular event.
  2. When you do eat fast food, eat as healthfully as possible. If you are having a burger, hold the mayo, cheese, fries and sugary drinks. Or have a grilled chicken sandwich, a salad with a lower-fat dressing and bottled water.
  3. Be active. If you do not already exercise at least three times a week, start now. Regular exercise helps keep your weight down and helps your body better metabolize and process food.
  4. Ask your doctor to check your level of liver enzymes, a key measure of liver health. Many doctors now test this routinely when doing blood work on adults, but kids who eat a lot of fast food need to have their liver enzymes checked as well.
"Even for those people with the worst kind of diets, it's not too late to start exercising and eating right," Tetri says.