TORONTO (Reuters) -- A bran muffin and a flavored Coffee drink are not unusual choices for a breakfast on the run. But along with fiber and caffeine, you may be getting something you hadn't bargained for: a day's worth of added sugar in just one small early morning meal.

We shouldn't consume more than 40 grams -- about 10 teaspoons -- of sugar a day, based on a 2,000-calorie diet, said Andy Bellatti, a graduate student at New York University's department of nutrition and food studies who blogs about diet and health at Small Bites. "It's very easy, though, to go way above that because that's basically one can of soda," Bellatti said. "So although 10 teaspoons sounds like a lot, it's actually not really that much."

Though the World health Organization recommends that added sugar should make up no more than 10 percent of our daily caloric intake, the average American eats about double that. A muffin could have 11 teaspoons of sugar added, and a grande vanilla latte at Starbucks has about seven teaspoons.

There are a few different chemicals we may be referring to when we talk about sugar, although teaspoon-for-teaspoon their calorie content is virtually the same. Sucrose is essentially table sugar. Lactose is a naturally occurring sugar found in milk. Fructose is also found naturally in fruits and some vegetables -- it's what makes an apple sweet -- but it's probably best known, and most maligned, as high fructose corn syrup (HFCS), an inexpensive sweetener used in many processed foods made by changing the sugar in corn starch into fructose.

"Currently we're eating about three times as much fructose as we should," said Dr. Richard Johnson, a researcher at the University of Florida. In the 1920s, when obesity rates were 5 to 7 percent of the population instead of the approximately 30 percent they are today, Americans ate about a third the fructose they now do.

Much of our excess fructose comes from HFCS found in a host of foods, from obvious offenders like soda and candy to more surprising culprits like bread and cereal. A Clif energy bar has five teaspoons of sugar, Belatti said, while a Luna energy bar has three. Many canned tomato sauces are high in added sugar, and other condiments like ketchup and salad dressing often contain HFCS. Even some breads have fructose from the corn syrup additive. Fruit-flavored yogurts that may be labeled low-fat are often high in sugar, because they get their sweetness from HFCS and concentrated fruit syrups.

There is some evidence that HFCS behaves differently in the body than naturally occurring sugars. Unlike other sugars, it bypasses the pancreas and heads for the liver, Bellati said. But that organ can't process the sugar effectively and some studies show that HFCS metabolization doesn't affect satiety in the normal way, making it easier to overeat.

As well, the more fructose you eat, the more the enzymes that metabolize fructose will increase, Johnson said. Problems like insulin resistance can result. "The trouble is, if you're eating lots of sugar and high fructose corn syrup, you may end up having very high levels of these enzymes," he said, "and that will make you more and more sensitive to fructose."

Research done by Johnson and others has tied fructose consumption to the production of uric acid, which studies have linked to hypertension, diabetes and obesity. Uric acid goes up rapidly after fructose in consumed, Johnson said, which has been shown to cause obesity in animals. It also seems to create conditions in the body that increase insulin resistance and triglycerides and predispose people to Diabetes or kidney disease. In a recently finished clinical trial that is currently under review for publication, Johnson and the research team found that lowering uric acid showed notable improvements in blood pressure in adolescents with previously high levels.

In his book, "The Sugar Fix", Johnson outlines a plan for reducing the number of those enzymes, which he says will help with weight loss. He advises cutting dietary fructose to a bare minimum for two weeks, then adding it back once your enzyme levels have gone down to normal -- but only to one-third of the previous intake, and preferably from natural sources like fruit instead of added sugars in foods such as sodas.

"One of my hopes is that focusing attention on fructose as a bad carbohydrate when taken in excess might increase public awareness of the hazards of excessive fructose," Johnson said. He also hopes to see better food labeling, where customers will not only be told that a product contains HFCS, but how much it has as well.

Journalist Joanne Chen researched North Americans' affinity for HFCS-containing sweet foods for her book "The Taste of Sweet". Chen says that to some degree, sugar has been unfairly demonized as the cause of the obesity epidemic -- the issue is not sugar itself, she said, but the large quantities in which we eat sweet foods, which are often also high in fat.

"I think that sugar or the taste of sweet is kind of this scapegoat for the obesity crisis," said Chen. "Sweet is making us fat because we're eating so much of it." She pointed out that many foods that are high in sugar are also high in fat and therefore high in calories; it may be that particular combination of sugar and fat that is problematic, Chen said, and not sugar alone.

There is no reason to avoid fruit because it naturally contains fructose, Johnson advised -- along with that sugar, you're also getting vitamins, antioxidants and fiber, which dulls the effects of fructose on blood sugar. But anything sweetened with fructose -- even if it's called "fruit sugar" -- is just sugar, he said, without the benefits. And instead of replacing sugary foods with artificial sweeteners, which can have side effects such as gas, we should reduce our portions and consumption of high-sugar items and replace candy with fruit when we crave something sweet.

Moderation is the key, Bellatti said. Large quantities of added sugar and large portions of the foods that contain it are the real problem, but an occasional treat is fine. "Sugar in and of itself isn't bad for you," he said.

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