Sweet Talk

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By Robert L. Wolke
Wednesday, March 29, 2006

After a time on the South Beach Diet, I started adding back carbs to my diet, but I still want to eliminate sugar. Boy, is that difficult to do! Everything has sugar in it. Please help me learn the different names used on food labels that indicate some kind of sugar. I know about high-fructose corn syrup, but what about all those words that end in "-ose" or "-ol" ? Are they sugars

as well?

Some are, some aren't.

Intentionally or not, you have asked for a chemistry lesson. So bear with me and all your fears will be assuaged. Except, perhaps, your fear of chemistry lessons.

Chemists assign names ending in "-ose" to all carbohydrates, whether sugars or starches. Many of the sugar "-oses" are unique chemical compounds and are known by unique names, although they are all sweet to varying degrees. Starches, on the other hand, are found in our foods as complex collections of many kinds of molecules without individual names, so they are generally listed simply as "starch."

Glucose is the simplest sugar of all. Sometimes known as dextrose, it is found in fruits and honey and is the ultimate small-molecule sugar. It can pass directly into the bloodstream to be carried to our cells, where it is "burned" for energy. Starch molecules are made up of as many as thousands of molecules of glucose. Before we can derive energy from a starch, our metabolism must break its large molecules down into glucose.

Fructose, found in fruits, is another simple sugar. High-fructose corn syrup is made by using enzymes to break cornstarch down into glucose, after which a large percentage of the glucose is converted to fructose, which is sweeter than glucose or sucrose.

Sucrose (table sugar), obtained from sugar cane or sugar beets, is not a simple sugar; its molecules consist of two simple-sugar molecules, glucose and fructose, bound together. Sucrose is therefore called a disaccharide -- from di , a Latin form of "double," and saccharum meaning "sugar." Other common disaccharide sugars are maltose and lactose.

Lactose, a disaccharide about which I'll have more to say further on, is found only in milk.

The bottom line: Any or all of these sugars might be lurking in your food, but they might not be listed separately. Look for ingredients such as honey, syrup, corn syrup, corn sweetener, molasses, fruit juice concentrate and the sneaky euphemism "cane juice."

Mercifully, the Food and Drug Administration lumps together all sugars as "sugars" in the Nutrition Facts chart on packaged foods. So you don't have to go on your own (go)ose chase. Just divide the number of grams of "sugars" by the serving size in grams, and you'll know the percentage of all sugars in the product.

I am a public health nutritionist and often need to recommend dairy alternatives or lactose-reduced products for clients who do not digest lactose well.

Here is my question: Why are the sugar levels of milk, yogurt and lactose-free milk all the same? It seems like the yogurt should have lower levels due to the consumption of milk sugar by the culture bacteria. And lactose-free milk should certainly have lower levels because of whatever they do to take the lactose out. However, the labels of all three products read about the same in terms of sugar.

It's puzzling, but true.

According to the U.S. Department of Agriculture's National Nutrient Database for Standard Reference, whole milk contains an average of 5.25 percent lactose by weight, while unflavored whole-milk yogurt contains 4.66 percent. Presumably, then, the culture bacteria have been allowed to consume only 0.59 percent of the milk's lactose before being forcibly restrained by cooling or killed by heat. By that time, the fermentation bacteria will have converted enough lactose into lactic acid to curdle the milk to the desired consistency.

The real head-scratcher, though, is lactose-free milk. If they've taken the lactose out of it, how come it still contains about 5 percent sugar -- the same as in whole milk?

The answer is that lactose-free milk is made not by removing the lactose but by adding the enzyme lactase. Just as sucrose is made of two simple sugars bound together, lactose is made of the two simple sugars glucose and galactose, bound together. The lactase enzyme splits the lactose into its two components, which are digestible by lactose- intolerant people.

But glucose and galactose are still sugars, and the FDA requires the aggregate amount of all sugars to be listed in the Nutrition Facts chart.

What are sugar alcohols, which are present in many food products? Do they count as sugars as far as diabetics are concerned?

A sugar alcohol (aka polyol) is a chemical compound that has some of the characteristics of both a sugar and an alcohol. Chemists name all alcohols with the suffix "-ol."

Sugar alcohols are natural products found in fruits and berries, but they can be commercially produced from carbohydrates. The ones you'll see most often on food labels are mannitol, sorbitol, xylitol, lactitol, erythritol and maltitol. Because they taste sweet and don't cause tooth decay, these alcohols are used in toothpastes, sugar-free candies and chewing gums.

Sugar alcohols are metabolized slowly, so they don't cause sudden increases in blood sugar, and that's good news for diabetics. (The American Diabetes Association recommends counting only half the number of grams of sugar alcohols in a food as carbohydrates.) The bad news is that sugar alcohols are not metabolized completely, so they might escape undigested from the alimentary canal. Those who consume immoderate amounts of sugar-free candies may therefore suffer the revenge of Montezuma.

Robert L. Wolke (http://www.robertwolke.com) is professor emeritus of chemistry at the University of Pittsburgh. His latest book is "What Einstein Told His Cook 2, the Sequel: Further Adventures in Kitchen Science" (W.W. Norton, 2005). He can be reached atwolke@pitt.edu.


© 2006 The Washington Post Company

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