Retrospective #30: Is Fructose a Liver Toxin?

Fructose is ubiquitous in the food supply. It is 67% of the natural sugar found in an apple as well as 50% of table sugar (sucrose), 55% of high fructose corn syrup (HFCS) in sweetened soft drinks, and 42% of the HFCS used in bread and other baked goods. For a fuller exposé, scroll down to Retrospective #29, “Fructose: Formerly Known as Fruit Sugar,” also archived on my blog at www.thenutritiondebate.com.

The amount of all sugars is increasing each year in the American diet. Since 2000, however, the amount of fructose has leveled off and even declined slightly, precipitating the Corn Refiners’ Association 2011 TV ad campaign to repair the image of HFCS. In it, a pretty young woman says, “I learned, whether it’s corn sugar or cane sugar, your body can’t tell the difference. Sugar is sugar.” I agree. HFCS is essentially not much worse than table sugar made from sugar cane. HFCS and cane sugar (sucrose) are basically the same, and both are equally bad for you.

Part of the problem is the unique way fructose is metabolized. Glucose, once it has been absorbed through the wall of the small intestine, is distributed throughout the body for energy. It is also stored as glycogen, mostly in the liver and muscles, to be ready for quick energy. Either way – used quickly or stored and used later – it is metabolized (broken down, “burned” or stored). Glucose is thus the most commonly available and readily used form of energy.

Fructose is different. It cannot be metabolized by the body for quick energy. Once it enters the bloodstream it goes directly through the portal vein to the liver and is processed there. Scientists, noting that the liver’s function is to filter out toxins, think that fructose is toxic. In this context, remember, before modern times, fruits were only seasonal and were far less sweet because they had not been hybridized. In addition, refined sugar didn’t exist.

When we eat large doses of sugar, the liver becomes overloaded with fructose. In the words of Robert H. Lustig, MD, presenter of UCSF’s YouTube video, “Sugar: The Bitter Truth,” fructose is “alcohol without the buzz.” Fructose is a “chronic hepatotoxin.” Excess fructose consumption over a long period of time is thus now thought to be the cause, and is certainly closely associated with, non-alcoholic fatty liver disease (NAFLD), also on a very steep rise.

In addition to Dr Lustig’s work, a 2005 a scientific paper titled “Fructose, insulin resistance and metabolic dyslipidemia,” from Department of Laboratory Medicine and Pathobiology, Hospital for Sick Children, University of Toronto, Canada, concludes: “An important but not well-appreciated dietary change has been the substantial increase in the amount of dietary fructose consumption from high intake of sucrose and high fructose corn syrup...” A high flux of fructose to the liver, the main organ capable of metabolizing this simple carbohydrate…leads to a significantly enhanced rate of de novo lipogenesis and triglyceride (TG) synthesis...” Fructose-induced insulin resistant states are commonly characterized by a profound metabolic dyslipidemia... Thus, emerging evidence from recent epidemiological and biochemical studies clearly suggests that the high dietary intake of fructose has rapidly become an important causative factor in the development of the metabolic syndrome. There is an urgent need for increased public awareness of the risks associated with high fructose consumption...”

Simply put, Lustig says: “Fructose increases de novo lipogenesis (fat formation), triglycerides and free fatty acids.”  Fructose is a carbohydrate, but “it is metabolized like fat,” So, when the liver detoxifies fructose by making glucose, and has all the glycogen it can hold from a big slug of fructose, the liver makes fat (triglycerides) from fructose. Fat!

Dr. Lustig’s video includes a slide entitled “Fructose is Not Glucose,” with five bullets, summarized here:

1.      Fructose is 7 times more likely than glucose to form Advanced Glycation End Products (AGE’s).

2.      Fructose does not suppress Ghrelin, the hunger hormone.

3.      Acute fructose does not stimulate Insulin (or Leptin: The brain doesn’t see that you ate, so you eat more).

4.      Hepatic fructose metabolism is different. (rather than forming glycogen, de novo lipogenesis occurs).

5.      Chronic fructose exposure promotes the Metabolic Syndrome.  

But Dr. Lustig says that because fructose is a chronic toxin, not an acute toxin, the USDA/FDA “won’t touch it.” That may be, but personally I think Cargill and Archer Daniels Midland have some influence in Washington as well.