America's sweet tooth is growing. Like many other mammals, we are hooked on sugar because it is packed with energy and our bodies have evolved ways of encouraging us to consume more of it.
The trouble is, foods and beverages with added sugars are plentiful today and usually cheaper on a per-calorie basis than vegetables or naturally sweet fruits. Between 1970 and 2005, consumption of added sugars in the typical American diet increased by 19% to a total of 64 kilograms per year. Last week, the American Heart Assn. issued a statement calling on Americans to cut back on added sugars of all types.
Foods are sweetened with various sugars: sucrose, fructose, honey, corn syrup and more. Is there much to choose between them? Passions burn fiercely here. Some people are convinced that high fructose corn syrup has properties that link it to the fattening of America -- partly for that reason, today regular sugar is almost achieving health-food status in some circles. Others swear by less-purified brown sugars or honey.
And many people don't know what all this sweet stuff even is.
Here's a primer on common sweeteners, as well as some not-so-common ones.
Table sugar, or sucrose, is the familiar stuff we use in cubes or by the spoonful. We sweeten our coffee with it, bake with it and know its flavor so well that it is the yardstick to which we compare other sweet flavors.
"When you say sweet, you have the image in your mind of sucrose," says Sidney Simon, a professor of neurobiology at Duke University who studies taste.
Most commercial sucrose comes from sugar beets and sugar cane. The natural sugar content of the plants is refined to varying degrees to produce granulated, powdered, brown and specialty sugars, such as demerara and muscovado. Molasses, a byproduct of the refining process, flavors and moistens the darker sugars. Crystals in these sugars range in size and flavor, but the sweetness in each is provided by sucrose.
Chemically, sucrose is a disaccharide, meaning that it is composed of two simple sugars linked together. In the case of sucrose, the two are fructose and glucose. During digestion, the bond between the two is cut and they are absorbed separately by the small intestine.
Sucrose from any source -- brown or white, beet or cane -- contains 4 calories per gram, as do other sugars. In other words, equal amounts of different sugars provide the same amount of energy to the body. However, some sugars taste sweeter than others, so you don't need to add as much to get the same level of sweetness.
When glucose is added to foods, it appears on nutrition labels as glucose, corn sugar or dextrose.
And even if it isn't added to foods, we end up with a lot of it. Many carbohydrates and sugars are ultimately converted by our bodies into glucose. Simple sugars such as fructose and galactose can be converted to glucose by the liver. More complex carbohydrates are digested down to glucose in the gut before being absorbed into the bloodstream.
These include the disaccharide maltose, which is made up of two linked molecules of glucose; maltodextrins or dextrins, which are chains of maltose molecules, and starches, which are chains of maltodextrins.
Once digested, glucose supplies the energy most parts of the body need to work. The amount of glucose in the bloodstream -- the blood sugar level -- is known to affect athletic performance, brain function, appetite and emotions.
Because this sugar is so critical, levels of available glucose are tightly regulated by hormones such as insulin; errors in this system can lead to disorders such as diabetes. Diabetics inject insulin to keep their blood sugar from going too high and, when necessary, take easily absorbed glucose tablets to quickly bring it back up to healthy levels.
Fructose is often called fruit sugar, which is a bit of a misnomer. Although fruit and fruit juice contain fructose, they also contain glucose and sucrose. And these days, the main source of dietary fructose is added sweeteners, not fruit.
"The average American gets 10% of their calories from fructose," says John Bantle, professor of medicine at the University of Minnesota. That's instead of the 3% they would get just from natural sources such as fruits and vegetables.
Fructose, which is sweeter than glucose, was once thought to be a possible diabetic-friendly sweetener because it doesn't cause spikes in blood sugar. "The rub was that fructose-sweetened foods tended to have adverse effects on lipids like cholesterol and triglycerides, and that's not a good thing," Bantle says. "That makes sense -- because we know that some of the fructose is converted to other things, like fat."
Fructose may, indeed, have slightly different metabolic effects on the body. In a 10-week study of 32 obese or overweight people published in May, UC Davis researchers found that those who drank fructose-sweetened beverages (accounting for 25% of their daily energy requirements) had increased levels of blood triglycerides and LDL, or "bad" cholesterol, compared with those who drank similar amounts of a glucose-sweetened beverage. They also had lowered insulin sensitivity, meaning they required more insulin to regulate their blood sugar levels.
Although both groups gained about three pounds during the course of the study, the fructose-drinking group tended to gain that weight in the abdominal cavity, while the glucose group tended to gain fat just below the skin.
Abdominal-cavity fat, elevated triglycerides and lowered insulin sensitivity together place a person at higher risk of developing cardiovascular disease, stroke and type 2 diabetes.
But the story is far from complete. Fructose may have different effects depending on gender, age and body type. For example, the researchers noticed larger effects of fructose on men than women. They are now working on a five-year study to see how sugar consumption affects younger and slimmer subjects.
The findings shouldn't be interpreted as a recommendation against eating fruit or drinking juice in moderation, says study author Peter Havel, a UC Davis professor in the departments of molecular sciences and nutrition.
"Consuming an eight-ounce glass of orange juice with breakfast is not the same as consuming three 32-ounce Big Gulps," he says. "You wouldn't want to discourage people from consuming fruit juices in moderation or from consuming whole fruit because they contain other good things."
Corn syrup and high fructose corn syrup
Starch in corn can be broken down into glucose-rich corn syrup. Manufacturers favor this sweetener since it keeps food moist and is cheap and abundant.
Much of the glucose in corn syrup is chemically converted to the comparatively sweeter-tasting fructose, and the resulting high fructose corn syrup packs a sweeter punch than regular corn syrup or dehydrated corn syrup (also known as corn syrup solids).
Typically, high fructose corn syrup contains 55% fructose and 45% glucose, a composition very similar to the 50-50 fructose and glucose content in sucrose.
The introduction of high fructose corn syrup to a wide variety of foods and beverages around 1970 coincides with the rise in obesity levels in the United States, which cast suspicion on the sweetener as a possible direct cause of the weight gain.
Registered dietitian Suzanne Murphy, a professor at the Cancer Research Center of Hawaii, was asked to review nine studies on fructose at a March 2008 conference co-sponsored by the International Life Sciences Institute North America and the U.S. Department of Agriculture.
"I didn't feel there was evidence saying that fructose or high fructose corn syrup was metabolically any different than sucrose," Murphy says of her review, published recently in the Journal of Nutrition. Rather, she says, the problem is excessive consumption of calories from all kinds of sweeteners.
Still, those extra sugar calories we're getting may be due in part to the addition of high fructose corn syrup to many foods that were not always sweetened, such as crackers, mustard, bread and peanut butter.
This is the sugar found in milk. Like sucrose, lactose is a disaccharide formed from simple sugars, in this case glucose and galactose.
Babies can all digest lactose, but by adulthood a significant percentage of people have lost the ability to make the digestive enzyme that breaks lactose into its constituent parts.
Excess undigested lactose is passed to the colon, where it prevents the normal uptake of water and provides fuel for gas-producing bacteria. Together, these factors cause the intestinal distress characteristic of lactose intolerance.
For much of human history, honey was the one abundant source of relatively pure sugar. This bee-made sweetener is a mixture of fructose, sucrose and glucose, with up to 40% water content.
Some research shows that less-refined sweeteners, including honey, contain more antioxidants and other potentially beneficial compounds than refined sucrose. A study published in January in the Journal of the American Dietetic Assn. showed that using less-refined sweeteners instead of white sugar could add the same amount of antioxidants found in a serving of nuts or purple fruits, but that molasses and date sugar contained the highest levels of antioxidants. Other studies have shown that the antioxidant content of honey depends on what sort of plant nectar it is made from.
However, as far as the sugar content goes, honey is metabolized in essentially the same way as other sugars are. "It's still caloric and you can still eat too much of it," Murphy says.
This sweetener, made from the same plant as tequila, has become popular in recent years because of its purported mellow flavor and relatively low glycemic index, the amount by which a food or drink item raises blood sugar levels in the two hours after it is eaten.
However, low glycemic index foods can still have copious amounts of sugars other than glucose; agave nectar can contain up to 90% fructose (the rest is glucose). This high level of fructose keeps it from spiking blood sugar the way sucrose or pure glucose do.
"For people with diabetes, modest amounts are OK," Bantle says. But he doesn't recommend overdoing it because of the possible link between too much fructose and atherosclerosis.
Research on sweeteners has a long way to go before nutrition scientists will be able to say for certain whether some are less healthful than others. There's debate, too, over whether the body is more apt to put on weight when sugars are slurped down in soft drinks than when consumed in solid foods.
For now, there's agreement on one thing -- we're eating too much sugar, regardless of which kind we're talking about.
"It's difficult to blame the obesity incidence on any particular sugar," Murphy says. "The best advice we can give to consumers is just cut down on sugars -- sugars of all kinds."