What is fructose? Fruit sugar, right? Well, yes and no. It is found in copious amounts in fruit, of course, but so are other sugars. Free fructose, the monosaccharide, is 57% of the total sugar found in an average apple, but free glucose, another monosaccharide, is 23%. Sucrose, a disaccharide sugar, composed of equal parts fructose and glucose, is the remaining 20%. So, combining the free fructose with the fructose bound up in sucrose, the total fructose in an apple is 67% of the sugars. (Trust me on the math here.) The remaining one-third is glucose.
Apples and pears are on the high end of the fructose scale. Apricots, at 39%, are at the low end. The sugar in bananas is 50% fructose, grapes 53%, and peaches 46%. Honey is 50.5% fructose (free and combined). Besides tree and vine fruits (berries), fructose is also found in other foods found in nature, for example, sweet corn and sweet red peppers and most root vegetables (e.g., red beets, carrots, onions and sweet potatoes). Generally, most of the fructose is bound up in sucrose, which as we said is equal parts fructose and glucose. Sucrose in its processed form is table sugar, which is made from refining sugar cane or sugar beets. Table sugar is therefore 50% fructose.
According to Wikipedia, “Commercially, fructose is usually derived from sugar cane, sugar beets and corn, and there are 3 commercially important forms:” 1) processed crystalline fructose, 2) high-fructose corn syrup (HFCS), and 3) sucrose. HFCS is also used in baked goods to “improve browning, for palatability and taste enhancement.”
Starting in the early 70’s, as sugar consumption peaked in the U.S., HFCS began to erode the sucrose market. By 2000 they were consumed in the U.S. in equal amounts. HFCS is commonly found in food and drink in two forms: The 55% fructose/41% glucose form is in use in the U.S. in non-dietary soft drinks. The 42% fructose/53% glucose formulation is used primarily in processed foods and baked goods. The balances in both forms are “other sugars.”
“The primary reasons fructose is used commercially in foods and beverages is its low cost and its high relative sweetness. It is the sweetest of all naturally occurring carbohydrates; at room temperature it is 1.73 times as sweet as sucrose,” but when heated it loses this advantage, according to Wikipedia. The sweetness of fructose is “perceived earlier,” has a “higher peak,” and “exhibits a synergy effect when used in combination with other sweeteners.” It has “greater solubility,” “increases starch viscosity more rapidly, and achieves a higher final viscosity than sucrose.” It also “retains moisture for a long period of time even at low relative humidity,” and therefore “can contribute to improved quality, better texture, and longer shelf life to the food products in which it is used,” according to Wikipedia. Now you know why a Twinkie or a Devil Dog stays soft forever. It’s the HFCS!
If you haven’t noticed how ubiquitous HFCS has become in the processed food supply, let me give you a snapshot. In the bread aisle at my local supermarket I found it in most of the “soft” goods and long shelf life items: Devil Dogs and Twinkies, of course, and fruit pies and muffins; also, in hot dog and hamburger rolls and, naturally, in Wonder Bread. I also found it listed as 4th ingredient in Weight Watchers 100% Whole Wheat bread, just before molasses!
Fundamentally, however, regardless of whether the formulation of fructose you consume is 55%, 42%, or 50% fructose, as in table sugar (sucrose), we all consume ever increasing amounts of fructose each year, whether we know it or not. We eat much more fructose than we think, and much more than the amount that is found in fresh fruit. Remember, sugar -- ordinary table sugar, made from sugar cane -- is half (50%) fructose.
So, why does it matter? Because fructose, in the words of Robert H. Lustig, MD, is “poison.” Dr. Lustig is professor of Clinical Pediatrics in the Division of Endocrinology at the University of California San Francisco. His research focuses on childhood obesity. He contends that, in the amounts we are eating it, fructose is toxic to the liver.Want to know why? You can watch his 90-minute 2009 video, “Sugar: The Bitter Truth,” from UCSF’s “Mini Med School for the Public” on YouTube. It’s had over 8 million views. Or stay tuned. In the next Retrospective I will summarize Lustig’s answer to the question, “Is Fructose a Liver Toxin.” My original post in 2011 had over 1,000 hits. And the next, “Carbohydrates and Sugars,” about 10,000.