Too much fast food and too little exercise can harm the liver, reveals a small study published ahead of print in the journal Gut.
The findings 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 5000 daily steps and ate at least two fast food meals, preferably in well known outlets, every day.
The aim was to double calorific intake and increase total body weight by between 10% and 15% to see if these had any impact on their liver health.
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.
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 6.5 kg. Five increased their weight by 15%, and one person put on an extra 12 kg in just two weeks.
Sharp increases in ALT occurred after just one week on the fast food diet, and more than quadrupled from an average of 22 U/l to of 97 U/l over the entire period.
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.
Insulin resistance is associated with the metabolic syndrome, a collection of biochemical abnormalities which are linked to an increased risk of diabetes and cardiovascular disease.
No such changes were seen among those who continued to eat their normal diet.
(Source: Gut: British Medical Journal : February 2008)