Who hasn't been in a relationship we know is bad for us, but one we just can't quit? For many people, it's like that with sugar.

Breaking up is hard to do.

"People generally know that sugar isn't good, but they don't appreciate how powerfully negative it really is," says Donald Hensrud, medical director of the Mayo Clinic Healthy Living Program. "If you look at all the things in our diet we can change, pulling away from refined or added sugar will do more good than anything else."

Nutritional experts don't suggest that you abandon the sugar that occurs naturally in fresh and frozen fruit. Rather, they're talking about the stuff that you add to cookie dough or sprinkle onto your morning oatmeal. Sugar has many forms (high-fructose corn syrup, maltose, dextrose, maple syrup, brown sugar, molasses, raw sugar and honey, among others), but it's still sugar. Manufacturers put it in countless processed foods, including soda, packaged cereals, ice cream, pastries, candy, flavored yogurt, granola bars and dried fruits. It's also added to such products as salad dressings, ketchup and pasta sauces.

Eating too much sugar contributes to numerous health problems, including weight gain, Type 2 diabetes, dental caries, metabolic syndrome and heart disease, and even indirectly to cancer because of certain cancers' relationship to obesity. It also can keep you from consuming healthier things. "Kids who are drinking sugar-sweetened beverages aren't drinking milk," Hensrud says.

Between 2003 and 2010, Americans consumed about 14 percent of their total daily calories from added sugars, much of it from sugar-sweetened beverages, according to the Centers for Disease Control and Prevention. But the 2015-2020 Dietary Guidelines for Americans recommend an intake of added sugar of less than 10 percent of calories. In a 2,000-calorie daily diet, that means less than 200 calories. Ten percent would amount to about 50 grams of sugar, according to Hensrud, who points out that food labels list sugar-per-serving in grams, making it easy to calculate. (With four grams to a teaspoon, that's about 12 teaspoons.)

While the World Health Organization also recommends a 10 percent limit, it stresses that 5 percent would be even better. That amounts to less than one serving (about eight ounces) of a typical sugary drink, according to WHO. "The lower the number, the better," Hensrud says.

Over the past 30 years, American adults' consumption of sugar increased by more than 30 percent, from 228 calories a day to 300, according to a study released last year. "This is equivalent to eating an additional 15 pounds of sugar a year," Hensrud sayes.

For many years, saturated and trans fats were regarded as the big dietary villains. While some fats are unhealthy, experts now believe it is wiser to focus on cutting back sugar than on paring fats.

"Quality sources of red meat, like grass-fed bison, beef and yak, are a great source of minerals, [conjugated linoleic acid] and protein, which will provide health benefits to our bodies," says Jessica Murgueytio, a clinical dietitian in Bethesda. Most people do better limiting saturated fat — red meat has high levels of saturated fat — than they do sugar, "primarily because saturated fats don't have the same addictive quality" as sugar, she adds.

Indeed, when people say they have a sweet tooth, they really are suffering from a "sweet brain" — because that's where sugar rules. Sugar resembles other abused substances in that "it is reinforcing and can change how you feel," says former Food and Drug Administration Commissioner David A. Kessler, whose 2009 book "The End of Overeating" describes the science behind Americans' obsession with sugar. "It's rewarding. And it's self-administered."

Past memory of eating sweet things produces cues that induce the craving for more, he adds. "I had that chocolate chip cookie in the past, and it changed how I feel. I had the momentary bliss from the consumption of sweetness, and that makes me want more," he says. "Sugar is an effective agent that produces excess calories and stimulates further eating. That's why the old saying 'A calorie is a calorie' is a fallacy." The source of that calorie matters, he says.

Animal studies have shown that sugar releases opioids and dopamine in the brain, which suggests that sugar dependence is real. "Consuming large amounts of added sugar activates the reward center and makes us want to eat that food again," Murgueytio says. When this happens, "you can have increased cravings for sugar, feel a lack of control when around sugar, and also increased tolerance for sugar, which causes one to eat more to feel the same impact."

Artificial sweeteners don't help, because they can have the same effect. "Artificial sweeteners in small amounts, like one pack in your coffee or tea, are safe and not harmful, but having large amounts, like in diet sodas and sugar-free candies daily, can make sweet cravings a lot worse," Murgueytio says.

Recent research suggests that a high intake of artificially sweetened products can result in increases in body fat, waist circumference and body mass index.

This is, of course, the best of times and the worst of times to end it with sugar — the best because most people have their biggest weight gain between Thanksgiving and New Year's (and often can't get rid of it) and the worst because there are so many holiday temptations.

Save the sweets for special days, like Christmas morning and New Year's Eve, and avoid them when they matter less, like at 3 p.m. in the office. At parties, don't stand by the buffet table. Freeze your leftover desserts, or send them home with family or friends. Try to stay out of grocery store food aisles that feature sugary holiday treats, and avoid gourmet and specialty shops whose shelves seem to be overloaded with them this time of year.

As for the remainder of the year, read the labels on your unopened processed foods. If they have high levels of added sugar per serving, several grams, for example, return them to the store. Use the store credit to buy fresh fruit.

If you drink fruit juice, dilute it with unflavored club soda or seltzer. Gradually reduce the amount of sugar you put in your coffee and tea. You'll get used to it. Make your own salad dressing. If you think you can stop with just one small piece of chocolate, great. But stick to the dark variety, which has less sugar than milk chocolate (and has some health benefits of its own).

Restaurant eating can be tough. Put olive oil and vinegar on your salad, and have grilled chicken or fish — no sauces. Skip the mixed drinks and cocktails and switch to a dry wine. Avoid baked goodies, and have fresh fruit for dessert.

You can live without sweetness, Kessler says. "If you moved to a continent where there was no sweetness, you would adapt," he says. "After a while, if you couldn't have access, you would stop wanting."

But if you must, retrain your palate to appreciate the sweetness of foods in their natural state. Fresh fruit has sugar, but it also has water, fiber and other nutrients. The average candy bar has 270 calories. A small piece of fruit has about 60. You can eat an apple, an orange, a pear and a peach and get fewer calories than in that one candy bar.

You can end that toxic relationship. "Sugar does have a powerful hold on us, but there are ways to separate gently," Hensrud says. "If you can't totally break up with sugar, consider finding a new partner — in fruit."

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