A study published in the journal Gut reports that too much fast food and too little exercise can harm the liver.

Swedish researchers selected 18 thin, healthy volunteers – 12 men and 6 women – to attempt a 5 to 15% body weight increase by eating at least two fast-food-based meals per day for four weeks. The participants in this intervention group also restricted their level of physical activity to no more than 5000 daily steps. A comparison group, matched for age and sex, ate a normal diet and maintained normal exercise levels.

The study authors desired to see if doubling calorific intake and increasing total body weight had any impact on participant’s liver health. Researchers checked liver enzyme and fat levels by analyzing blood samples both before the “fast-food challenge” began and at regular intervals throughout the four-week study period.

Changes in enzymes, such as alanine aminotransferase (ALT), and in hepatic triglyceride content (HTGC) were used to indicate liver damage. Abnormally high ALT levels are frequently seen in people who consume a lot of alcohol or who have been infected with the hepatitis C virus. HTGC measures fatty acid levels in the liver; too much fat in the liver leads to a condition called fatty liver disease.

At the end of the four weeks, the researchers reported:

  • Fast-food consumers had put on an average of 6.5 kg (14.3 lbs.) 
  • Five participants increased their weight by 15% 
  • One person gained 12 kg (26.4 lbs.) in two weeks
  • Sharp increases in ALT occurred after just one week on the fast food diet
    • The average ALT level increased four-fold from 22 U/l to of 97 U/l over the 4 weeks
  • ALT rose to liver damage levels in 11 participants
  • No changes were seen in levels in the comparison group

The increases in ALT levels were linked to weight gain and increased sugar and carbohydrate intake. One subject developed fatty liver disease, and there was a large rise in liver cell fat content in the other participants.

The authors note that an increase in the fat content of liver cells is associated with insulin resistance, which in turn is associated with the metabolic syndrome. Insulin resistance syndrome is a collection of biochemical abnormalities which are linked to an increased risk of diabetes and cardiovascular disease.

Fast-food-based hyper-alimentation can induce rapid and profound elevation of serum alanine aminotransferase in healthy subjects
Stergios Kechagias, Åsa Ernersson, Olof Dahlqvist, Peter Lundberg, Torbjörn Lindström, and Fredrik H Nystrom
Gut. (2008)
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Written by: Peter M Crosta