Highlight HEALTH

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].

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 [4]:

It was not the fat in the hamburgers, it was rather the sugar in the coke.

Indeed, the authors 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.

References

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
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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.
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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.
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4. Fast-food binge harms liver, but boosts good cholesterol: study. Yahoo News. 2008 Feb 13.

Have you ever wondered if those healthy fast food meals are really any better for you? McDonald’s has the Fruit ‘n Yogurt Parfait, Wendy’s offers Garden Sensations salads and at Burger King you can even get a veggie burger.

Yogurt, salad, veggie burger … these are all healthy foods.

However, new research suggests that healthy fast food meals have the same effect on your cardiovascular system as a burger, fries and a soda.

The endothelium is a thin layer of cells that line the interior surface of blood vessels. Endothelial cells line the entire circulatory system, from small capillaries to veins and arteries to the heart. These cells are responsible for regulating blood flow and blood pressure through vasoconstriction and vasodilation.

High-fat meals have a negative effect on endothelial function, causing endothelial dysfunction, meaning there is less elasticity of blood vessels and reduced blood flow. Endothelial dysfunction is a marker for cardiovascular disease and can lead to atherosclerosis or high blood pressure, increasing the risk of heart disease and stroke.

Ten years ago, a study linked diet and endothelial dysfunction [1]. Twenty healthy men and women with normal levels of total and low-density lipoprotein cholesterol were fed four randomly administered breakfasts: a high-fat meal consisting of Egg and Sausage McMuffins with fried hash browns, a low-fat meal, a high-fat meal after taking the antioxidants vitamin C and vitamin E, and a low-fat meal with the same vitamin pretreatment. Ultrasound was then used to measure changes in blood vessel tone and blood flow in the brachial artery. The researchers found that decreased vasodilation occurred for up to 4 hours following the high-fat meal, while no significant changes were observed in blood vessel tone and brachial blood flow after the low-fat meal, the high-fat meal with vitamins or the low-fat meal with vitamin pretreatment. The study demonstrated the benefits of vitamins C and E, and the authors concluded that antioxidants help maintain normal endothelial function. Today, vitamin-rich side orders are prevalent throughout the fast food industry.

Researchers now have found that these presumably healthier alternatives to a burger and fries does not significantly differ with respect to their acute impairment of endothelial function [2]. Endothelial function, measured again using ultrasound, and cardiovascular disease risk markers were measured in 24 healthy volunteers who randomly received one of three fast food meals on three study days separated by 1 week:

• Big Mac with regular side orders (french fries, ketchup and Sprite)
• Vegetarian burger with regular side orders (french fries, ketchup and Sprite)
• Vegetarian burger with vitamin-rich side orders (salad, balsamic dressing, yogurt with fruit and Minute Maid orange juice)

Unexpectedly, all three meals resulted in decreased endothelial function. In contrast to the study ten years ago, even consumption of the vegetarian burger with vitamin-rich side orders resulted in decreased vasodilation. The researchers suggest that the reduced endothelial function may be attributable, at least in part, to the increase in baseline arterial diameter following a meal.

Why the conflicting results? The vitamin pretreatment given in the study 10 years ago was extremely high - over 10 times (1000 mg) the recommended daily intake of vitamin C and over 50 times (800 IU) the recommended daily intake of vitamin E [3]. While a salad, yogurt and orange juice are good, healthy foods, they contain substantially lower levels of antioxidants.

These results come in the wake of another study finding that fast food branding makes children prefer happy meals [4]. NewScientist reported that:

… children in the study were twice as likely to prefer the McDonalds-branded carrots as the plain-packaged ones. This suggests that marketing savvy could perhaps convince youngsters to make healthful choices. Some companies have already begun experimenting with this tactic by using Mickey Mouse cartoons to sell sliced fruit and placing Curious George stickers on bananas.
Last month McDonalds announced it would shift its advertising targeted to children under the age of 13 to focus on the 375-calorie Happy Meal, which it says meets current dietary standards outlined by the government.

What does all this mean? It means that eating a side salad with your burger or adding carrots in your child’s happy meal can’t prevent the harmful affects of fast food on the vascular system. Eating healthy doesn’t mean an apple here and a carrot there, it means a complete change in the types of meals we eat.

References

1. Plotnick et al. Effect of antioxidant vitamins on the transient impairment of endothelium-dependent brachial artery vasoactivity following a single high-fat meal. JAMA. 1997 Nov 26;278(20):1682-6.
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2. Rudolph et al. Acute effects of various fast-food meals on vascular function and cardiovascular disease risk markers: the Hamburg Burger Trial. Am J Clin Nutr. 2007 Aug;86(2):334-340.
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3. Dietary Reference Intakes: Vitamins. U.S. Department of Agriculture National Agriculture Library.
4. Robinson et al. Effects of fast food branding on young children’s taste preferences. Arch Pediatr Adolesc Med. 2007 Aug;161(8):792-7.
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