Eating fast food every day and not exercising may be damaging to the liver, a small study finds.

The findings, published in the journal Gut, are based on 18 slim, healthy people (12 men and six women) who took a “fast food challenge” for four weeks, and a comparison group, matched for age and sex, who ate a normal diet.

The fast good group restricted their levels of physical activity to not more than 5,000 daily steps and ate at least two fast food meals every day.

Participants consumed a hamburger, fries and a soda at most fast food meals.

The aim was to double caloric intake and increase total body weight by between 10 percent and 15 percent to see if these had any impact on their liver health, it was reported.

Blood samples were taken before the challenge began and then at regular intervals throughout the study period, to check on their liver enzyme and fat levels.

Liver damage is often identified by symptomless increases in enzymes, of which alanine aminotransferase (ALT) is one, according to the background offered in the study.

Usually, higher than normal ALT levels are found in people who regularly drink large amounts of alcohol or who have been infected with the hepatitis C virus. But in a significant proportion of people, there is no obvious explanation.

Too much fat in the liver also indicates damage, and is known as “fatty liver.”

At the end of the four weeks, those in the fast food group had put on an average of 14 pounds. Five increased their weight by 15 percent and one person put on an extra 26 pounds in just two weeks.

Sharp increases in ALT occurred after just one week on the fast food diet. In 11 people ALT rose to levels indicative of liver damage. The increases were linked to weight gain and especially higher sugar and carbohydrate intake.

Only one participant 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.

No changes were seen in the group who continued to eat their normal diet.

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