Overeating Fast Food Carbs Causes Signs of Liver Damage

Reading time: 4 – 6 minutes

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 [1].

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 [2]. A high concentration of ALT in the blood is also a marker of risk for type 2 diabetes [3].

fast-food-carbs.pngThe 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 [4]:

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 [1]:

… 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 [4]. 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 [4].

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.


  1. 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
    View abstract
  2. Clark et al. The prevalence and etiology of elevated aminotransferase levels in the United States. Am J Gastroenterol. 2003 May;98(5):960-7.
    View abstract
  3. 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.
    View abstract
  4. Fast-food binge harms liver, but boosts good cholesterol: study. Yahoo News. 2008 Feb 13.
About the Author

Walter Jessen is a senior writer for Highlight HEALTH Media.


  1. “a continuous long-term fast food diet may cause irreversible damage”

    This explains the increasing number of fatal first time heart attacks in people my age and younger. I am 40. Several classmates from my community have dropped dead from heart attacks and strokes over the past few years.

  2. Disturbing facts indeed, one of a growing number of reasons to avoid fast foot altogether. In The documentary “Supersize Me”, the excess fast food consumed caused similar effects on the liver.

  3. Wow, what an interesting article, Walter. Reading that, I was glad I only had an Iced Tea when I met a girlfriend at McDonald’s the other day. The study showing the effects on the liver should be a wake up call. We need to do something to make our foods healthier. I know so many families on the run to soccer practice, swing in there for a quick meal. They’d be better off to pack a dinner, just like lunch time on the go.

  4. Hi apdfranklin: You’re right. In fact, the lead researcher of the study said he copied “Supersize Me” to the best of his ability. Thanks for your comment.

    Hi Terry & Chrysalis: I don’t think the occasional fast food meal is going to greatly impact a person’s health. Like most things, moderation is key. However, based on the study results, frequent long-term fast food consumption should most definitely be avoided. Thanks for your thoughts.

  5. That is why the fast food is called junk food. And the most funny thing is after knowing all we like to take this junk food so much. ha..ha..ha.

  6. I think that this information is extremely important. In lower-income, urban areas in the US, like half of the City where I live, diabetes is a terrible problem and fast food is normal food. While there are certainly other causes of liver damage, and other risk factors for diabetes, diet itself seems relatively simple to control, in principal. Unfortunately, reality isn’t that simple and I see little evidence of moderation in diet. I also see lots of elderly people with the effects of long-term diabetes in my community, and it both tragic and at least partly avoidable. I don’t understand why more effort isn’t put into public health issues like this- diabetes has to be a big drain on the health care system as well as a human tragedy of epidemic proportions. I’m not saying that the issue is being ignored, just that it isn’t being dealt with effectively on a national scale in the US or elsewhere. Am I reading this correctly? Thanks for the great post!

  7. I think you’re reading it right Jim – the issue isn’t being ignored, it’s just not being dealt with effectively. Part of the problem is the fix requires work; many people won’t change their diet and start eating healthier. However, I think a larger part of the problem is the lack of health consumer education.

  8. Well what were you expecting?!?!??!!

  9. That is why the fast food is called junk food 🙂 .



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