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The Boston Globe

Health & wellness

What sugar really does to your body

How bad is sugar really? The Coca Cola company would have you believe in its new anti-obesity commercial that a calorie is just a calorie whether it’s from a sugar grain or sesame seed. But new research suggests otherwise.

In the study funded by the World Health Organization, New Zealand researchers analyzed 68 studies that compared added sugar intake in sweetened beverages and other foods with weight changes and found that when study participants were advised to lower their sugar intake -- without changing anything else in their diet -- they lost an average of nearly two pounds over six to eight months. When they were told to increase sugar, they gained nearly two pounds, according to the study which was published Tuesday in the British Medical Journal.

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That’s a very small change, but it’s significant, and it makes the case for government recommendations to lower added sugar intake, wrote Dr. Walter Willet, chair of nutrition at Havard School of Public Health, and Boston Children’s Hospital pediatrician Dr. David Ludwig in an editorial that accompanied the study.

The WHO commissioned the study, in fact, to see whether they should keep their decade-old advice to eat no more than 10 percent of calories from added sugars. The U.S. government recommends that added sugars make up no more than 15 percent of calories, whereas the American Heart Association’s recommendation is no more than 5 percent.

Following the strictest 5 percent guidelines would mean that women should eat no more than 100 calories a day of added sugars (equivalent to 6 teaspoons) and that men should eat no more than 150 calories per day (equivalent to 9 teaspoons).

One serving of my favorite high-fiber cereal -- which has 12 grams or 48 calories of added sugar -- and one serving of my favorite Chobani Greek vanilla yogurt -- which has 17 grams or 68 calories of added sugar -- would put me over my daily limit. Clearly, the AHA guidelines are really, really tough to follow, which is why Willet and Ludwig recommended a 10 percent goal as a “realistic practical goal” while 5 percent would be a goal for “optimal health.”

But why all the fuss when reducing sugar-sweetened foods -- and presumably replacing those calories with sugar-free foods -- won’t do much to prevent excess weight gain?

“Sugar isn’t the cause of obesity; it’s a cause of obesity,” said Dr. Robert Lustig, a pediatric endocrinologist and author of the best-selling new book Fat Chance. “What makes sugar so problematic is how it’s handled by the body.”

Too many sweet sips of a Starbucks Caramel Macchiato causes a surge in the hormone insulin and also alters the way the liver metabolizes the simple form of sugar, glucose. Too many giant spikes in insulin over time due to a high consumption of sugar or other refined carbohydrates, Lustig said, can lead to insulin resistance, liver problems, and ultimately Type 2 diabetes in those who are susceptible.

He believes that the reason diabetes rates have surged over the past two decades has more to do with our increased sugar and processed food intake than our expanding waistlines -- though, no doubt, the two go hand in hand.

In the 19th century, Americans consumed less than 30 grams of sugar per day -- about 6 percent of their total calories -- but by 1977, sugar consumption had increased to 75 grams per day on average. Teens now average 150 grams per day or roughly 30 percent of their total calories.

But it’s not all about sugar: Any carbohydrate that’s stripped of fiber can lead to a quick insulin rise. In a 2011 study that analyzed dietary surveys, Harvard School of Public Health researchers determined that potato chips and French fries were a leading cause of weight gain among Americans followed by sugar-sweetened beverages.

Consumption of whole grains, vegetables, and fruit were found in the 2011 study to be associated with weight loss -- even though they’re also carbohydrates.

I asked Lustig to explain the contradiction.

“You can drink a glass of orange juice and still be hungry,” he told me, “but if you eat the three oranges needed to make that glass of juice, you’d probably be unable to do it since you’d feel too full.” His point? The fiber and pulp in the whole orange prevents us from eating to the point of a giant insulin spike.

The fiber in unprocessed carbohydrates also enables the body to break down the food more slowly so insulin doesn’t rise and fall as quickly, which is good from a hormonal standpoint and also satiates hunger for longer so we eat fewer calories.

Foods to aim for? You can certain read labels for fiber and sugar content, but Lustig suggested something easier. “Just eat food that’s not in a package,” he said. That would leave you in the fresh produce, fish, and butchery aisles, and steer you away from processed foods like pasta, pretzels, soda, and candy.

“A high fiber, low sugar diet is real food,” Lustig said. “That’s what people should eat.”

Deborah Kotz can be reached at dkotz@globe.com. Follow her on Twitter @debkotz2.

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