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A recent study evaluating the effects of fast-food-based overeating on liver enzymes and liver triglyceride content has been making the news this week. However, most media sources have been incorrectly interpreting the results. The Swedish study, published in the British Medical Association journal Gut, suggests that eating too much fast food can cause liver damage .
The goal of the study was to examine the potential link between changes in serum alanine aminotransferase (gene symbol ALT) to the amount of fatty infiltration in the liver of healthy non-obese subjects. ALT is an enzyme that, when present at high levels in the blood, is a diagnostic indicator of nonalcoholic fatty liver disease . A high concentration of ALT in the blood is also a marker of risk for type 2 diabetes .
The Swedish investigation assessed the effects of four weeks of fast-food-based hyper-alimentation (meaning overeating) on the levels of serum ALT in 18 young, lean individuals (12 men, 6 women). The participants increased their caloric intake by eating two fast-food-based meals a day while minimizing their physical activity. Over the course of the study, seventeen of the 18 participants increased their body weight by 5 –15%. At the end of four weeks, 13 of the 18 subjects had developed pathological serum ALT concentrations (meaning ALT levels observed in diseased liver). Surprisingly, pathological levels of ALT were observed in most patients as early as one week after the study began, and were more than four times normal on average by the end of the study. Only two of the 18 individuals developed liver steatosis or fatty liver, a benign, non-progressive condition, whereby fat accumulates in liver cells.
The authors of the study conclude that chronically or intermittently elevated ALT can be caused by food alone. Lead researcher Fredrik Nystrom, M.D., Ph.D., at the University Hospital of Linkoping, said a key finding of the study was that signs of liver damage were linked to carbohydrates :
It was not the fat in the hamburgers, it was rather the sugar in the coke.
Indeed, the researchers specifically indicate in the study’s discussion section that :
… when examining the relationship of the increase in ALT to intake of different nutrients, fat intake was unrelated increase in ALT while sugar and carbohydrate intake at week 3 clearly related to the ALT increase. This is in accordance with earlier findings by Solga et al who demonstrated that higher carbohydrate intake was significantly associated with an increased risk of biopsy-proven hepatic inflammation in morbidly obese patients undergoing bariatric surgery.
Most media sources, however, are focusing on the fat in fast food, not the carbohydrates. This is in sharp contrast to the study results, which paradoxically found a health benefit, apparently from fat. HDL cholesterol levels (the good cholesterol) increased over the four-week period, correlating with the increase in saturated fat . Although the cholesterol findings have yet to be published, Dr. Nystrom indicated they were consistent with the French Paradox, the observation that the French, despite intake of a high-fat diet, suffer low incidence of coronary heart disease .
The data from this study indicates that, although the liver can regenerate itself, a continuous long-term fast food diet may cause irreversible damage. We’ve talked previously about the effects of healthy fast food on endothelial function. This latest study demonstrates yet another negative consequence of fast food on our health.
Kechagias et al. Fast food based hyper-alimentation can induce rapid and profound elevation of serum alanine aminotransferase in healthy subjects. Gut. 2008 Feb 14 [Epub ahead of print]. DOI: 10.1136/gut.2007.131797
Clark et al. The prevalence and etiology of elevated aminotransferase levels in the United States. Am J Gastroenterol. 2003 May;98(5):960-7.
Vozarova et al. High alanine aminotransferase is associated with decreased hepatic insulin sensitivity and predicts the development of type 2 diabetes. Diabetes. 2002 Jun;51(6):1889-95.
- Fast-food binge harms liver, but boosts good cholesterol: study. Yahoo News. 2008 Feb 13.