Lactose is the sugar found in milk and essentially nowhere else in the world. (There are a few reports of traces being found in various plants, but it's not clear whether those can be confirmed.) There are about 12 grams of lactose in a cup, eight ounces, of milk. That's one reason why nutritionists favor milk over sodas. An equivalently-sized glass of Coke has 27 grams of sugar.
But what kind of sugar is sugar? In the United States the word "sugar" on an ingredients list means sucrose, the sugar that is found in sugar cane or sugar beets. Any other sweetener must be individually named.
What's in these sweeteners? The new January-February 2010 issue of the Nutrition Action Healthletter (so new that the website hasn't been updated to mention it yet: what's wrong with people who can't get their websites up to date?) has an interesting sidebar to its cover article on "Sugar Overload." It tells you what's in sugars. It may not be what you expect.
Lactose is a disaccharide, meaning it is made up of two simple sugars, glucose and galactose. Sugar is an example of a carbohydrate and all carbohydrates eventually break down in the body to form glucose, which is the body's energy source. Glucose is already there. Galactose breaks down in about 45 minutes. Complex carbohydrates, like the starches, are usually just long chains of glucose molecules. That's why all carbohydrates provide 4 calories of energy per gram.
Sucrose is also a disaccharide, made up of fructose and glucose. It's a chemical combination of the two, just as lactose is a chemical combination of galactose and glucose. Fructose metabolism is somewhat more complex than galactose metabolism, one reason that it is controversial as a sweetener. The big difference between sucrose and high fructose corn syrup (HFCS), though, is that sucrose is a chemical combination of glucose and fructose and HFCS is a physical combination of the two. There are several commercial mixtures of glucose and fructose that are sold as HFCS but the version that is 58% glucose and 42% fructose has the same sweetness as sucrose, which is why it's used as a substitute.
So what is the effect of HFCS? That same page I linked to above says there isn't one.
Studies that have compared high fructose corn syrup (an ingredient in nearly all soft drinks sold in the US) to sucrose (common table sugar) find that most measured physiological effects are equivalent. For instance, Melanson et al. (2006), studied the effects of HFCS and sucrose sweetened drinks on blood glucose, insulin, leptin, and ghrelin levels. They found no significant differences in any of these parameters. This is not surprising since sucrose is a disaccharide which digests to 50% fructose and 50% glucose; while the high fructose corn syrup most commonly used on soft drinks is 55% fructose and 45% glucose. The difference between the two lies in the fact that HFCS contains little sucrose, the fructose and glucose being independent moieties.
48. Melanson, K.; et al. (2006). "Eating Rate and Satiation.". Obesity Society (NAASO) 2006 Annual Meeting, October 20-24,Hynes Convention Center, Boston, Massachusetts. doi:10.1111/1467-9280.02452
Let the furious comments begin.
What about other sugars? Let's circle back to that Nutrition Action Healthletter article.
Agave syrup or nectar: 84% fructose, 8% glucose, 8% sucrose.
Apple juice concentrate: 60% fructose, 27% glucose, 13% sucrose.
Brown sugar: 97% sucrose, 1% fructose, 1% glucose.
Evaporated cane juice: 100% sucrose.
Dextrose: 100% glucose.
Grape juice concentrate: 52% fructose, 48% glucose.
High-fructose corn syrup: 58% glucose, 42% fructose or 55% fructose, 45% glucose.
Honey: 50% fructose, 44% glucose, 1% sucrose.
Maple syrup: 95% sucrose, 4% sucrose, 1% fructose.
Molasses: 53% sucrose, 23% fructose, 21% glucose.
Orange juice concentrate: 46% sucrose, 28% fructose, 26% glucose.
Raw sugar, Table sugar, Confectioner's sugar, Baker's sugar, Powdered sugar: 100% sucrose.
(If the percentages don't equal 100% the remainder are other carbohydrates.)
That's right. Agave nectar, the darling of coconut milk nondairy alternatives, is much higher in fructose than HFCS. So is apple juice content rate. And honey is basically the equivalent of HFCS.
If you want to scorn HFCS you're free to do so. Just be aware that the alternatives may have far more fructose that they aren't telling you about. It's not the food: it's how much you have of it and what percentage that plays in your overall diet. Please don't get fooled by phony claims of "organic" or "natural." First understand the chemistry and composition of food. Then make wise decisions.