Sunday, November 6, 2011

The Nutrition Debate #30: Is Fructose a Liver Toxin? Is it Really Poison?

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 many baked goods, For a fuller exposé, take a look at the last column, #29, “Fructose: Formerly Known as Fruit Sugar,” also archived on my blog at www://

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 recent 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 or beet sugar. HFCS and sucrose are basically the same, and both are equally bad for you.

The problem is not with the glucose component of sucrose. Once absorbed through the wall of the small intestine, glucose goes to virtually all the cells of the body and is used for energy or it is stored mostly in the muscles and liver as glycogen, a ready form of quick energy. Either way – used quickly or stored and used later – it is metabolized (broken down and “burned”). Glucose is the preferred and most commonly 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 stored there. Scientists, noting that the liver’s function is to filter out toxins, think that fructose is toxic. Remember, before modern agriculture, fruits were available seasonally and were far less sweet because they had not been hybridized. In addition, refined processed sugars were nonexistent. When we eat large doses of sugar the liver becomes overloaded with fructose. Is fructose toxic to the liver? Not in the sense of an acute toxin. It is, these scientists claim, a “chronic hepatotoxin.” In the words of Robert H. Lustig, MD, presenter of UCSF’s YouTube video, “Sugar: The Bitter Truth” in their Mini Med School for the Public series, fructose is “alcohol without the buzz.” No wonder that excess fructose consumption over a long period of time is frequently thought to be a cause, and is certainly associated with, non-alcoholic fatty liver disease (NAFLD), also on the rise.

Lustig adds: “Fructose increases de novo lipogenesis (fat formation), triglycerides and free fatty acids in most adults.” Fructose is a carbohydrate, but “it is metabolized like fat,” he says; therefore, “a high sugar diet is a high fat diet”.

In addition to Dr Lustig’s work, a 2005 a scientific paper titled “Fructose, insulin resistance and metabolic dyslipidemia,” from the Clinical Biochemistry Division, Department of Laboratory Medicine and Pathobiology, Hospital for Sick Children, University of Toronto, 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, perturbs glucose metabolism and glucose uptake pathways, and 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...”

Dr. Lustig’s video presentation 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 may have some influence in Washington as well.

© Dan Brown 11/6/11

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