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One of the bugaboos of modern nutrition is the excessive consumption of fructose. Once a relatively hard-to-get sweetener actually prescribed by doctors for diabetics, fructose has become the bane of modern dieters due to wildly excessive use in the form of high-fructose corn syrup.
Fructose in small amounts is actually a health food. It is only when fructose is consumed in excessive amounts that it is detrimental to health. Small amounts of fructose, generally up to about 25 grams (100 calories) per day, not only aren't toxic, they can enhance health. Here are the facts about fructose and its safe inclusion in modern diets.
Our taste buds are pre-programmed to respond to the taste of fructose.
Fructose is the predominant sugar in fruit. Pound for pound, gram for gram, fructose is sweeter than other common sugars such as sucrose (cane sugar) or glucose(the predominant sugar in grains and syrups, including unrefined corn syrup). Our tongues sense sweetness from fructose more quickly than from other kinds of sugar, and the taste response induced by fructose is more intense that that generated by most other common kinds of sugars.
In the modern world, fruit is not the only (or even primary) source of fructose.
The main source of fructose for most people in North America is high-fructose corn syrup, which is actually a mixture of the super-sweet sugar fructose, concentrated by a refining process, and the so-so sweet sugar glucose. High-fructose corn syrup is found in soft drinks and baked goods and even in many other foods labeled as "naturally sweetened."
Chemically, table sugar, or sucrose, consists of a molecule of fructose chemically bound to a molecule of glucose. The digestive process releases fructose from table sugar, too, and specialized transporter proteins carry it from the gut to the liver.
Only the liver can use fructose as fuel.
Glucose can be used as fuel by cells all over the body, but fructose can only be "burned" by the liver. The liver has to produce enzymes to transform fructose into two chemicals called dihydroxyacetone phosphate and glyceraldehyde.
If the liver isn't up to the task, however, the fructose becomes fat (more precisely, triglycerides) in the liver itself. When fructose is consumed in excess, the liver gets sicker and sicker.