Acknowledgement:
I am routinely indebted to Dr. Mercola's work--in this case, to his clear explanation of the kinds of sugars that are present in the American diet. His pages, along with Dr. Lustig's exceptional lecture, are the primary sources for the information in this article.

Fructose is Dangerous

As Dr. Mercola writes, "too much fructose creates a metabolic disaster in your body". In his YouTube lecture, Dr. Lustig goes one further: "Fructose is a poison". Unbound fructose goes straight to the liver, which has to process it. And since unbound fructose is contained in virtually every soft drink and processed food we consume, we get a lot of it.

Here's why it's dangerous.

• Fructose feeds the bacteria that cause gastric distress.
  So you've having a problem with indigestion, you'll want to eliminate sources of concentrated fructose from your diet.
  
  
• Fructose is converted to fat and cholesterol.
  Glucose is good. Every cell runs on glucose. Dr. Lustig calls it "the energy of life." Glucose in sugars becomes blood glucose. 80% of it is burned directly by the cells. Only 20% of glucose gets to the liver. Of that amount, 98% is stored as glycogen--a safe, storage-form of sugar that is burned when needed. (The liver can store an unlimited amount of glycogen.) About 2% of the 20% that got to the liver (.4%, in all) is converted to VLDL (very low density lipoprotein), the bad cholesterol.
  
  But 100% of fructose gets to the liver, because only the liver is capable of dealing with it:
  • A lot of it is converted to uric acid--breaking down ATP to do it. That's a double whammy, because the ATP can no longer be burned for energy (reducing liver function), and because uric acid has harmful consequences of it's own.
  • That process also leads to inflammation.
  • Some gets converted to ATP (energy).
  • 30% is converted to VLDL. That's the dangerous lipoprotein that becomes arterial plaque (other forms of LDL don't). What doesn't become plaque is stored as fat.
  • Some of the fructose escapes as free fatty acids, which causes insulin resistance in muscle tissue.
  • Some remains in the liver as harmful fatty acid deposits.
    
    
• In fact, 30% of fructose is converted to fat.
  With glucose, on the other hand, virtually none is stored as fat.
  
  
• Unlike glucose, fructose does not stimulate insulin or leptin
  Insulin from the pancreas suppresses ghrelin, the appetite hormone secreted by the stomach, so you're less hungry. Leptin generated by fat cells tells your brain that you've taken in all you can handle. If the meal has sufficient fiber, the PYY hormone released by the ileum (intestine) tells your brain that you're full. Together, grhelin, leptin, and PYY regulate how much you eat, and how much you weigh. Highly concentrated fructose knocks out two of the three. If you're getting in a food without much fiber (think soda and fast foods), then you have no governor at all on your appetite.
  
  
• Worse, fructose tells your brain that you're starving, and increases your appetite.
  Fructose induces leptin resistance--so even when fat cells are saying "We're full", the brain isn't hearing it. So kids given a can of soda before a meal actually eat more, rather than less, because the soda is loaded with high fructose syrup. (Video: Sugar, the Bitter Truth)
  
  And according to a Wikipedia article on Leptin:

  A published study suggests that the consumption of high amounts of fructose causes leptin resistance and elevated triglycerides.... (The subjects) ate more and gained more weight than controls fed a high fat, high calorie diet.^[64][65][66]

The harmful consequences are many:

• Fructose elevates uric acid, which raises blood pressure, damages your kidneys, and leads to chronic, low-level inflammation.
  
  
• Fructose produces rapid weight gain and abdominal obesity (“beer belly”)
  As Dr. Lustig points out, a can of soda is virtually equivalent to a can of beer. It has the same number of calories, and is metabolized in the liver in the same way. So kids get "soda belly".
  
  
• Fructose elevates triglycerides, blood sugar, and blood pressure.
  
  
• Because of the high volume of fats created in the liver, fructose can produce NAFLD (non-alcoholic fatty liver disease).

Note:
There is exactly one time when fructose is helpful. After extreme exercise (like a marathon), when glycogen is completely depleted, fructose causes glycogen stores to be rebuilt more rapidly. So fruit and even sugar makes sense after severe, extreme exercise.

Fructose Antidotes

Dr. Lustig points to two natural "antidotes" for fructose:

• Exercise
  Exercise speeds up the metaboliosm, which causes more of the fructose to get converted to energy, rather than being converted to VLDL cholesterol and free fatty acids. It also lowers stress, which reduces appetite.
  
  
• Fiber
  Fiber slows the digestive process, so fructose arrives at the liver little by little, instead of all at once. The slower arrival rate also means that more of it is converted to energy.

Sugars and Starches

• Raw honey is 53% fructose, but it contains enzymes, minerals, and as many anti-oxidants as spinach.
  
  
• Fruit has high levels of fructose, but it's combined with fiber, plus enzymes, vitamins, and minerals.
  Fiber slows digestion and fills you up. So you eat less in the first place, and the fructose is delivered slowly enough that it can be converted to ATP (energy), with less excess to become fat. So the danger is contained, as long as you eat the whole fruit, with all of the fiber. (Juices, on the other hand, are just another variety of high-fructose syrup, or HFS.)
  
  
• Sucrose (table sugar) is 50% fructose and 50% glucose.
  They're bound together, one-for-one, in the sucrose molecule. That molecule is readily split during digestion, but with the glucose stimulating the production of both insulin and leptin, there is at least some kind of limit on how much you're hungry for.
  
  
• Maple sugar is 50% fructose.
  Basically the same as table sugar--while not 100% healthy, it's a combination your body can handle, and something we've had for thousands of years.
  
  
• Starch breaks down to glucose--not fructose.
  So potatoes and pasta may be "high-carbohydrate foods", but they have none of the adverse effects of fructose. (Since the liver can store an unlimited amount of glycogen, the worst that happens is that you have an enlarged liver and a lot of energy for endurance activities.)
  
  
• Stevia and Lo Han contain no fructose.
  No glucose, either. Somehow, they manage to taste sweet without having any sugar at all (and therefore, virtually no calories). Quite a trick. Stevia has an aftertaste though. Need to try Lo Han.

Clearly, the real danger lies in highly concentrated doses of fructose.

Sources of Highly Concentrated Fructose

When you start reading labels, you'll find these substances in virtually every package in a typical American grocery store. (And as soon as enough people learn to avoid them, American corporations will find some other way to entice you.)

High Fructose Corn Syrup

This is the one we knew about. Like artificial sweeteners, it's one that the public is slowly coming to avoid, as its dangers become more widely known. (See What's Wrong with High Fructose Corn Syrup?)

But think we're in the clear? Think again. The industry has been hard at work finding new better ways to produce poisons for profit. The two newest are Crystalline Fructose and Agave Syrup.

Crystalline Fructose

Dr. Mercola's pages say it best:

• There is over 35 years of hard empirical evidence showing that refined man-made fructose like HFCS metabolizes to triglycerides and adipose tissue, not blood glucose. (See this scientific study.)
  
  
• Despite the evidence against fructose, the industry has created a new high-octane version of HFCS that’s 99 percent fructose, called “crystalline fructose”.... (It) may also contain arsenic, lead, chloride and heavy metals."

Agave Syrup

Dr. Merola writes, "Agave syrup, falsely advertised as 'natural', is typically HIGHLY processed and is usually 80 percent fructose. The end product does not even remotely resemble the original agave plant."

There's more on his Agave page (requires registering):

• Agave is heavily promoted as a low glycemic food, enticing diabetics.
• Fully chemically processed sap from the agave plant is known as hydrolyzed high fructose inulin syrup.
  (In other words, it's high fructose agave syrup!)
• Agave syrup is not a live food. The natural enzymes are removed to prevent  agave syrup from fermenting.
• Agave is, for all intents and purposes, highly concentrated sugar.
• Sugar and sweeteners wreak havoc on your health and are highly addictive.
• The alleged benefit of agave for diabetics is purely speculative. Very few agave studies have been documented.
• Agave syrup can be anywhere from 55 percent to 90 percent fructose.
• Since most  agave syrup has such a high percentage of fructose, your blood sugar will likely spike just as it would if you were consuming regular sugar or HFCS.

Given the high percentage of fructose, Agave syrup is simply a high-fructose syrup (HFS) made from agave, instead of from corn (HFAS, instead of HFCS). And it's being sold as a healthy alternative.

Can the FDA or USDA Do Anything?

Reading from the FDA charter, Dr. Lustig points out that the FDA has a mandate to regulate acute poisons (those that cause immediate harm), but not chronic poisons (those that cause long term harm), even when the FDA knows for a fact that the substances do in fact, produce chronic obesity and disease.

In other words, according to the FDA charter--a charter that is determined by our legislators, who are pretty much at the whim of corporate lobbyists--the FDA can do nothing at all.

The USDA, meanwhile, does nothing, because declaring our foods bad would make it impossible to export American "food" products.

Conclusion

There is no doubt whatever that American coporations play fast and loose with the facts. Despite years of documented studies on the effects of fructose, and despite the industrial high-heat processes that are used to make Agave syrup, it is marketed as a "natural", "healthy" alternative to sugar.

In short, anyone who has devoted themselves to avoiding HFCS and other egregious substances in American foods has been gulled into ingesting the exact same substance under another name.

So here I am, writing yet another article on something in the American food supply that you need to avoid to stay healthy. Nothing makes me madder than a nutritional poison that purports to be healthy. But American corporations will do anything and everything they can get away with, for the sake of profit. According to the insidious mantra of "personal responsibility", it's up to you to avoid the crap they're selling.

Well, take responsibility. Write your representatives to legislate against the ingredients those companies use. Tell them to impose punitive taxation on people who sell poisons for profit. Make the taxes retroactive, to pay for the harm they have already caused. Tax the past earnings of the executives who made the decisions, by way of civil suit if in no other way. And then put the criminals out of business.

Resources

Lectures

• Sugar: The Bitter Truth (If you care about your health, you must view this video.)
  Dr. Robert Lustig's lecture (University of California, San Francisco), clearly describes the exact metabolic pathways by which fructose produces insulin resistance, generates uric acid, and turns into cholesterol and fat.
  http://www.youtube.com/watch?v=dBnniua6-oM

Articles
Register to read the articles at the Mercola site. You'll be glad you did.

• This Addictive, Commonly Used Food Feeds Cancer Cells, Triggers Weight Gain, and Promotes Premature Aging
  http://articles.mercola.com/sites/articles/archive/2010/04/20/sugar-dangers.aspx
  
  
• Fructose Truly is Much Worse Than Glucose (register to read it)
  http://articles.mercola.com/sites/articles/archive/2009/05/16/Dont-Believe-the-Hype-Fructose-Truly-is-Much-Worse-Than-Glucose.aspx
  
  
• Wikipedia article on Leptin
  http://en.wikipedia.org/wiki/Leptin
    
• Agave: A Triumph of Marketing over Truth
  http://articles.mercola.com/sites/articles/archive/2009/07/02/Agave-A-Triumph-of-Marketing-over-Truth.aspx
  
  
• What's Wrong with High Fructose Corn Syrup?
  http://treelight.com/health/nutrition/HFCS.html
  
  
• What's Wrong with American Foods?
  http://treelight.com/health/nutrition/AmericanFoods.html
  
  
• What's Wrong with American Corporations?
  http://treelight.com/health/society/Corporations.html
  
  
• Eliminate Indigestion -- Naturally
  http://treelight.com/health/healing/Indigestion.html