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Scientific Evidence Continues to Suggest that Fructose is a Cause of Obesity


  • Table sugar (Sucrose)
  • High fructose corn syrup (HFCS)
  • Fruit juice
  • Honey
  • Agave syrup
Written by Mark J. Holland MD
January 3, 2013

The Journal of the American Medical Association yesterday published results from a small (20 people) study performed by medical researchers at Yale University recently. The study used magnetic resonance imaging (MRI) and other techniques to assess the ability of two different kinds of sugar (glucose vs fructose)  to suppress hunger in people. The results are consistent with a growing collection of evidence suggesting that fructose is a "special case" amongst sugars and that it alone, unlike all other studied sugars, lacks that ability to suppress hunger in response to its ingestion. In other words, glucose (blood sugar) fills you up, fructose does not.

I'll have more to say on this later but I wanted to post this preliminary comment today.

Fructose (Fruit Sugar): Fructose is found in its pure form in fruits. Unlike glucose, fructose is not normally found in human blood. Fructose can only be processed by the human liver and there is growing (but not-yet conclusive) scientific evidence that large doses of fructose may harm human health and worsen obesity.

  • Fructose is also often called "fruit sugar" because much of the sweet taste of some fruits comes from fructose.
  • Most fruits contain other sugars besides fructose.
  • ·All fruits (except watermelon) contain huge amounts of fiber that "dilute" fructose so much that they are absolutely safe to eat in whole-fruit form. Fruit juices may NOT be so safe or healthy.
  • Fructose is currently a controversial sugar. Some (but not all) scientific studies in animals and people suggest that excess fructose consumption may be harmful to human health and may specifically increase risk for obesity, metabolic syndrome and type-2 diabetes. 
  • High fructose corn syrup (HFCS) is a VERY controversial sweetener today. As the name suggests, HFCS contains a lot of fructose (relative to old-fashioned Karo corn syrup-which is essentially pure glucose).
  • There are several popular HFCS mixtures:
  • HCFS 42: Used in baked goods., This contains 42% fructose, 53% glucose and 5% "other" sugars, mostly maltodextrins
  • HFCS 55: Used in soft-drinks: 55% Fructose
  • HCFS 90: 90% fructose
  • HCFS is used in so many foods because it is sweeter and cheaper than sucrose (table sugar).
  • HFCS was "invented"--actually the process to make it was invented-- in the 1970's and the operation became commercially viable in the mid-1980s
  • There is an eerie correlation between the introduction of HFCS-55 in soft-drinks in the USA in the mid-1980's and the obesity epidemic in the USA, especially the epidemic of obesity in children.
  • The corn industry---basically Archer Daniels Midland Corporation, Cargill and a few other conglomerates--- is spending a lot of money to convince the American public that HFCS is "Corn Sugar" and is a "Natural" product. The problem is that the manufacture of HFCS is about as industrial and non-natural as any in the food industry.
  • Regardless of the possible problems that may be caused by fructose, HFCS may be contaminated with heavy metals because the product is often stored for long periods of time in railroad tanker cars whose stainless-steel welds contain dangerous heavy metals like cadmium that may leech into the HFCS stored within.
  • I personally think that it is wise to avoid HFCS
  • Pure crystalline fructose is a "low-glycemic" sugar, but it is important to understand why: "Glycemic Index" is a measure of how fast blood-glucose levels rise after consumption of a food. Fructose and glucose are different molecules. If one were to imagine a "frycemic index" that measure the effect of foods upon blood-fructose levels, then fructose would be very high on the "frycemic index".
  • "Agave Syrup" is a low-glycemic sweetener (and is advertised as such) but it is nearly pure fructose and therefore carries all the potential harm that has thus far been discussed in relation to fructose.
  • Fructose is absorbed poorly by the human gut unless it is mixed with glucose. Certain proteins that move fructose from the gut to the blood stream require glucose to function.
  • Fructose "malabsorbtion"---the inability of some people (perhaps most of us) to absorb pure fructose MAY (or may not) be a cause of irritable bowel syndrome (IBS) and other digestive disorders
  • Sucrose (table sugar) is 50% fructose and therefore ultimately barely-less a source of potentially harmful fructose than HFCS-55.
  • Some studies strongly suggest that fructose promotes obesity in mice, rats and people because it causes resistance to a naturally produced, normal hormone called Leptin.
  • Leptin is found in mice, rats, people and probably all mammals and leptin is produced by fat cells and leptin suppresses appetite.
  • Given the fact that statement (1) above is true, leptin resistance should and does cause weight gain. Therefore, if fructose causes leptin resistance (and I think that it does), then fructose should cause obesity (and I think that it does).
  • THEREFORE it is probably wise to limit fructose consumption. Small amounts from whole fruits are cleary fine (and even good for you), but fruit juices, sodas and sugary foods are NOT.