Although fructose exists naturally, as an added sugar in processed foods it may be a culprit in the rise of fatty liver disease and associated with the growth in obesity and diabetes rates. In 2011, Americans are consuming more fructose-containing foods than ever before, and some populations are getting up to one-third of their calories from fructose foods and beverages. However, your body metabolizes fructose differently from other sugars. That difference may set the stage for the development of fatty liver disease--a spectrum of conditions involving a buildup of fat on one end and liver failure on the other.
Fructose Facts
Fructose is a monosaccharide, or simple sugar, found in honey and fruit---and in added dietary sugars. It is one part of the formulation of high-fructose corn syrup, or HFCS, the ubiquitous sweetener found in everything from soft drinks and sweet snacks to bread and cereal. HFCS is one of the primary ways Americans get fructose. Consumption of fructose has grown substantially in the United States, and since the introduction of HFCS, it has skyrocketed. In the April 2004 "American Journal of Clinical Nutrition," biomedical researchers reported that consumption of HFCS jumped more than 1,000 percent in just two decades and dominates as the added sweetener of choice by food processors and beverage makers. Researchers publishing in the December 2010 "Journal of the American Society of Nephrology" say that increase is a contributor to the obesity epidemic. They say that on average, Americans consume about 74g of fructose each day, and African-Americans and Hispanics are consuming as much as 30 percent of their diet from added sugar sources like HFCS.
Fructose Metabolism and the Liver
Fructose makes a distinct metabolic journey through your body. A special transporter in the intestine absorbs fructose initially, and then up to 70 percent is taken up by a transporter in the liver. The remaining fructose travels through your kidneys, fat tissue and other organs. In the liver, an enzyme converts fructose to another form. During this metabolism in the liver, a step is skipped that other sugars like glucose normally undergo. Thus, say two German nutritional researchers, fructose's metabolism allows it to "continuously and uncontrollably" enter into the pathway where your liver generates blood sugar. This is where trouble can start if you consume too much fructose.
Fructose and a Buildup of Liver Fat
Fructose-containing food can predispose you to a buildup of fat in your liver, according to a group of University of Chicago investigators. They say that when fructose hits the liver it promotes lipogenesis, a process in which sugar is converted to fatty acids and ultimately forms triglycerides and cholesterol. In fact, this process may stimulate excessive production of triglycerides and be related to insulin resistance.
Dietary Fructose Can Worsen Fatty Liver Disease
Though it starts as a simple buildup of fat in your liver cells, fatty liver disease can progress to a disease state in which your liver is impaired by inflammation, then scarring and then cirrhosis if unchecked. The progression can build silently for years in some, and in others, reverse on its own. Scientists don't know what makes fatty liver advance, but they suspect fructose consumption may be involved. Researchers from the Nonalcoholic Steatohepatitis Clinical Research Network publishing in the journal "Hepatology" examined the link between consuming fructose and the severity of fatty liver disease. They monitored the fructose consumption of 427 people and noted the condition of their livers. Increased fructose consumption was linked with high triglycerides, bad cholesterol, overeating, high uric acid levels and worsening of fatty liver to the stage at which it begins to scar. They concluded that fructose is an environmental risk factor that you could easily take out of your diet to prevent the progression of fatty liver disease.
References
- "The American Journal of Clinical Nutrition"; Consumption of High-Fructose Corn Syrup in Beverages May Play a Role in the Epidemic of Obesity; George A. Bray, et al.; April 2004
- "Journal of the American Society of Nephrology"; The Effect of Fructose on Renal Biology and Disease; Richard J. Johnson et al.; December 2010
- "Journal of Nutritional Biochemistry"; Dietary Fructose and Intestinal Barrier: Potential Risk Factor in the Pathogenesis of Nonalcoholic Fatty Liver Disease; Astrid Spruss and Ina Bergheim; September 2009
- "Journal of Hepatology"; Fructose Consumption as a Risk Factor for Non-alcoholic Fatty Liver Disease; Xiaosen Ouyang et al.; June 2008
- "Digestive Diseases and Sciences"; Nonalcoholic Fatty Liver Disease: A Review and Update; Jeffrey R. Lewis and Smruti R. Mohanty; March 2010
- "Hepatology"; Increased Fructose Consumption is Associated with Fibrosis Severity in Patients with Nonalcoholic Fatty Liver Disease; Manal F. Abdelmalek et al.; June 2010
