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A funny thing happened over the past couple of decades: As we Americans cut our fat consumption, we not only got fatter, we also developed more obesity-related illnesses like diabetes. Not very funny if you're one of those Americans. Inactivity is largely to blame, but so may be our soaring sugar consumption, up 28 percent since 1983 (along with a 10 percent increase in calorie intake). And so much of that sugar is hidden, few of us know how much we're getting.

Why such a collective sweet tooth? Blame the oodles of advertising dollars spent each year to tempt us and the burgeoning sales of fat-free foods. "Manufacturers took the fat out of food and bolstered the sugar to give it flavor," says Alison Horton Eastwood, R.D., a clinical dietitian at the University of California, San Francisco-Stanford Medical Center. "Sugar is fat-free, so people think it's okay to eat as much as they want."

Eastwood also points to portion sizes: With 20-ounce beverages the norm, it's no surprise that 43 percent of our sugar intake comes from drinks. The average American teen-ager drinks twice as much soda as calcium-rich milk, setting herself up for osteoporosis later on.

It's tough to prove, but sugar is very likely a factor in the nation's obesity epidemic. "More sugar means more calories, and more calories means weight gain," says Marion Nestle, Ph.D., M.P.H., chair of the Department of Nutrition and Food Studies at New York University. Obesity in turn plays a role in the alarming rise in "adult-onset" diabetes among young people, even children.

For the average person, perhaps the greatest concern is that sweetened foods crowd out more-wholesome choices, says Leslie Bonci, R.D., M.P.H., director of sports medicine nutrition at the University of Pittsburgh Medical Center. U.S. Department of Agriculture data show that people whose diets are high in added sugar eat less protein, fiber, calcium, iron, folate and many other important nutrients.

The body metabolizes all sugars, whether "added" or "naturally occurring," the same. But that's where the similarity ends. "Orange juice and a soda may contain the same sugar and calories," Nestle says, "but orange juice has vitamins, minerals and phytochemicals you don't get in a soft drink."

You needn't swear off sugar entirely, but you should keep tabs on your intake. The USDA recommends no more than 10 teaspoons (40 grams) of added sugar a day for a 2,000-calorie diet, and six teaspoons (24 grams) for a 1,600-calorie diet. On average, we consume more than twice that much.

One reason is that most sugar we eat is hidden; much of the carbohydrates in many cereals, sports bars and gels are pure sugar. Check the ingredients. All of these terms indicate added sweeteners: sucrose, glucose, dextrose, maltose, fructose, molasses, barley malt, honey, raw, invert or brown sugar, and maple, fruit or corn syrup. Whatever the alias, except for molasses, which has some iron and calcium, they're all nutritional zeroes.

Sneaky sweets

Strawberry Passion Awareness Fruitopia

Serving size: 20 oz.

Sugar (tsp.): 17.75

Added sweeteners: High-fructose corn syrup and/or sucrose

Sunkist Orange Soda

Serving size: 12 oz.

Sugar (tsp.): 13

Added sweeteners: High-fructose corn syrup and/or sugar

Otis Spunkmeyer Almond Poppyseed Muffin

Serving size: 4-oz. muffin

Sugar (tsp.): 8.5

Added sweeteners: Sugar (first ingredient)

Low-fat fruit-flavored yogurt

Serving size: 8 oz.

Sugar (tsp.): 7

Added sweeteners: Any or all of the following: sugar, high- fructose corn syrup, corn syrup, honey

Honey Peanut Balance Bar

Serving size: 1.76-oz. bar

Sugar (tsp.): 4.25

Added sweeteners: High-fructose corn syrup, honey, sugar, high-maltose corn syrup, dextrose, oligofructose

Kellogg's Cracklin' Oat Bran Cereal

Serving size: 1 cup

Sugar (tsp.): 3.75

Added sweeteners: Brown sugar, sugar, corn syrup

SnackWell's Mint Creme Cookies

Serving size: 2 cookies

Sugar (tsp.): 3.25

Added sweeteners: Sugar, fructose, high-fructose corn syrup

Quaker Chewy Low Fat Chocolate Chunk Granola Bar

Serving size: 1-oz. bar

Sugar (tsp.): 2.5

Added sweeteners: Sugar, molasses, honey, corn syrup, corn syrup solids, high-fructose corn syrup