By James J. Kenney, PhD, FACN
The prevalence of nonalcoholic fatty liver disease (NAFLD) has been increasing in the USA and worldwide. NAFLD has increased dramatically in the USA and this increase has been closely associated with the increasing prevalence of obesity, the metabolic syndrome, and type 2 diabetes (1). It has been estimated that perhaps 20-30% of Americans now have NAFLD with the highest prevalence seen in Hispanic Americans (2). So while more and more people are developing NAFLD, most people with NAFLD are unaware they have this disease simply because in most people with NAFLD this disease produces no symptoms. This is similar to what we see with hypertension or high serum cholesterol levels, which in most people for many years produce no symptoms. However, in a significant minority of people with excessive fat deposits in their livers, this can lead to liver inflammation and eventually the death of liver cells and the development of liver cirrhosis. So NAFLD along with excessive alcohol intake and viral hepatitis has become a major cause of cirrhosis and liver failure.
NAFLD and Foie Gras
Fatty livers are not unique to humans. It has been known for many years that force-feeding ducks and geese for several months causes them to develop fatty livers. The fatty livers of these domesticated birds are called foie gras and are considered a delicacy by French chefs (3). Those who watched the documentary “Supersize Me” starring filmmaker Morgan Spurlock may recall Mr. Spurlock in effect foie gras-ed his own liver in just 30 days simply by eating 3 meals daily at McDonalds and always choosing to “supersize” his meal if asked by the counter person if he’d like that “supersized” (4). His physician became alarmed by the increase in the levels of aminotranferases in his blood. Elevated aminotransferase levels are often an early warning sign that NAFLD is progressing to a more dangerous stage in which there is a markedly increased risk of developing both liver cancer and/or a cirrhotic liver.
It seems clear that NAFLD is largely being driven by excessive calorie intake and is often closely associated with the development of insulin resistance. Bariatric surgery that leads to significant weight loss is known to reverse fat accumulation in the liver and insulin resistance. A healthier diet and exercise program can improve insulin sensitivity and lead to weight loss and almost certainly will reverse the accumulation of fat in the liver. Indeed, Morgan Spurlock’s liver function appeared to return to normal shortly after he returned to his previously healthy diet and lost much of the excess weight he gained while filming “Supersize Me”. Exactly what it is about typical fast food fare that promotes insulin resistance, weight gain, and in many people NAFLD is still being debated. Calorie-dense meals low in fiber and high in saturated fat, trans fat, and refined carbohydrates — especially when washed down with sugar-rich beverages — appear to be the most likely promoters of excessive calorie intake, insulin resistance, the metabolic syndrome, and NAFLD. A recent short-term study by Dr. Lustig in obese children fed them a diet where either 28% of the calories came from sugar or 10% of the calories came from sugar for 9 consecutive days. For 9 days, the majority of sugar calories were isocalorically replaced with more starch calories but other than that the experimental diet provided the same amounts of nutrients and the same total calorie levels as their usual baseline diet. Nevertheless, after just 9 days these 43 obese children saw a significant improvement in insulin sensitivity and reductions in serum trigylceride levels and more modest improvements in other parameters often associated with the development of type 2 DM, CVD, and NAFLD. The authors concude: “Isocaloric fructose restriction improved surrogate metabolic parameters in children with obesity and metabolic syndrome irrespective of weight change.” While this small study did not look at NAFLD, other research has suggested that an higher intake of refined sugars and especially fructose may well play an important role in promoting insulin resistance, perhaps in part by promoting excessive fat accumulation in liver cells (6).
Bottom Line: While more research is needed to clarify the relative risk of various components of a typical modern Western diet for promoting excessive calorie intake, insulin resistance, the metabolic syndrome, and NAFLD it is likely that replacing refined sugars high in fructose with whole grains and starchy vegetables and cutting back on foods high in saturated fat and trans fat and refined grains is likely to improve insulin sensitivity and curtail the accumulation of fat in the abdominal area and also in the liver.
- Younossi ZM, et. al. Changes in the prevalence of the most common causes of chronic liver diseases in the United States from 1988 to 2008. Clin Gastroenterol Hepatol. 2011;9:524-30.
- Ruhl CE, et. al. Fatty liver indices in the multiethnic United States National Health and Nutrition Examination Survey. Aliment Pharmacol Ther. 201541:65-76.
- Lustig RH, et. al.: doi:10.1002/oby.21371.
- Ouyang X, et. al. Fructose consumption as a risk factor for non-alcoholic fatty liver disease. J Hepatol. 2008;48:993-9.
Stephanie Ronco has been editing for Food and Health Communications since 2011. She graduated from Colorado College magna cum laude with distinction in Comparative Literature. She was elected a member of Phi Beta Kappa in 2008.