Too much fast food and too little exercise can wreak havoc on the liver, according to results of a small Swedish study.

In the study, 18 trim, healthy adult volunteers who restricted their levels of physical activity to no more than 5,000 steps a day and ate at least two fast food meals every day for 4 weeks showed clear signs of liver damage. They also put on weight.

Another group of volunteers, who were matched to members of the first group by age and sex, maintained a normal diet and did not develop signs of liver damage or gain weight.

Dr. Fredrik H. Nystrom of University Hospital of Linkoping, Sweden and colleagues report their results in the medical journal Gut.

They designed their “fast food challenge” study to see what impact doubling the number of calories eaten daily and increasing body weight by 10 and 15 percent would have on liver health.

At the end of the 4 weeks, the fast food eaters had put on an average of 6.5 kilograms (14.3 pounds). Five increased their weight by 15 percent, and 1 person put on an extra 12 kilograms (26.4 pounds) in just 2 weeks.

Moreover, after just 1 week on the fast food diet, blood tests showed sharp increases in a liver enzyme called alanine aminotransferase (ALT). ALT levels more than quadrupled over the 4-week study period.

Doctors often use increases in ALT and other liver enzymes to diagnose liver disease before symptoms develop. In 11 fast food dieters, ALT rose to levels suggestive of liver damage.

The ALT increases were linked to weight gain and higher sugar and carbohydrate intake.

Too much fat in the liver is another sign of damage. Only one fast food eater developed “fatty liver,” but test results from the other participants showed a steep rise in fat content in their liver cells, which is associated with insulin resistance, a precursor to diabetes.

None of these changes were seen among the comparison group who maintained their normal diet.

SOURCE: Gut, February 2008.