Last year an article in the New York Times caught my eye. The article was about fructose, the main kind of sugar in fruit.  This article was not discussing the fructose in fruit however but, rather, high-fructose corn syrup (HFCS), a cheaper-than-sugar sweetener used extensively in all kinds of processed foods, including ketchup and barbecue sauces, breakfast cereals, snacks, breads, and manufactured drinks of all kinds.  One single tablespoon of ketchup or barbecue sauce contains a teaspoon of HFCS. Some brands of low fat, fruit-flavored yogurt contain up to ten teaspoons of HFCS. 

That’s why I recommend buying plain, whole milk yogurt and adding your own fruit, nuts, seeds, vanilla extract, cinnamon, or cocoa powder.   

The article in the NY Times, which reviewed a small study from the Journal of Nutrition, discussed how different the metabolism of fructose is from the metabolism of glucose, which is the main sugar into which foods are broken down.  The article reported that the body converts fructose into stored body fat by a much more direct route than it converts glucose. 

When glucose is absorbed into the bloodstream, the liver determines whether the glucose needs to be used immediately for energy, or whether it can be stored for future use.  When fructose is absorbed, however, it is quickly converted to a type of fat called triglyceride.  High levels of triglycerides are strongly associated with impaired sugar metabolism, insulin resistance, and diabetes. 

The study found that when a person ate fructose at breakfast, the body was more likely to store not only the calories eaten at breakfast, but those eaten at lunch as well.  The diversion of fructose calories to fat storage was evident not only in the meal at which the fructose was consumed, but in subsequent meals as well. 

This article was extremely popular.  Readers had posted more than 150 comments after only a few days.  I noticed that many were confused about whether the warnings about consuming high-fructose corn syrup extended to fruit as well.  They did not.  But why not?  Why is it all right to eat fructose from fruit but not from corn syrup?  The difference between high-fructose corn syrup and fructose-containing fruit can be summed up in a single word -- fiber. 

It seems to me that the faster we absorb a food, the more difficulty we have metabolizing it.  We evolved to eat foods that are absorbed slowly.  Which foods are these?  Protein, fat (natural only) and complex carbohydrates.  Fruits, vegetables, whole grains and beans are the sources of fiber, or complex carbohydrate.  Simple carbohydrates, namely sugar and starch, are the substances that are absorbed rapidly.  Foods that are absorbed slowly also slow the digestion of other foods eaten at the same time.  These are the foods that, in general, constitute a more healthful diet. 

So it should not surprise you to learn that almost all the simple carbohydrates are manufactured, man-made products.  They are not found in nature.  Sugar is not found in nature as crystals; industry makes it that way.  The primary industrial sources of sugar -- beets, dates and sugar cane -- are all rich in fiber. The manufacturing process separates the fiber from the sugar. 

In contrast to what you learned in school, however, sugar is not the only simple carbohydrate.  Starch, a simple chain of glucose molecules, is so easily separated into its individual component glucose molecules that eating a slice of white bread (made from flour that has been stripped of its fiber and wheat germ) raises blood sugar levels just as fast and high as the same number of calories of table sugar.  The processed food industry uses enormous amounts of simple carbohydrate.  They are all absorbed rapidly, and they are called by names such as maltodextrin, dextrose, food starch, maltitol, glycerol, white flour, glycerin, cane syrup, modified food starch, wheat starch, sorbitol, and, of course, high-fructose corn syrup.

A molecule of fructose is and always will be a molecule of fructose, no matter what its source.  But its rate of absorption will be affected dramatically by the presence of other foodstuffs, like fiber, that are ingested along with it.  The fiber in fruit is essential to slowing the digestion of the fructose present in the food.

So I recommend to my patients that they avoid not only HFCS, but that they skip the glass of juice and eat the whole fruit instead.  Why? If juice is, as you may know, a good way to increase one’s blood sugar rapidly, then you can assume it contains little or no fiber. 

So eat that apple, kiwi, strawberry, melon or peach, and let the fiber do its job, slowing the absorption of fructose, or fruit sugar, in those delicious pieces of fruit.  And eat plenty of vegetables, beans, whole grains, dairy and meats in their natural, unprocessed forms.  None of these will ever contain any high-fructose corn syrup.