How sweet it isn’t?

First it was fats, then carbohydrates. Now sugar has joined the ranks of nutritional villainy.

With Christmas approaching on a tidal wave of candy canes and gingerbread, one can’t help wondering: Is it OK to indulge in a little sweetness, or is sugar entirely bad?

There’s no denying a certain amount of hysteria when it comes to sugar. Critics claim sugar causes everything from hyperactivity to premature aging. A common – and inaccurate – belief about cancer is that cancer cells feed on sugar.

Some of this is hyperbole but there’s also a considerable amount of science that has examined the effects, both good and bad, of sugar consumption. Sugar has been linked, for instance, to increased risk of weight gain, diabetes and heart disease. Earlier this year, some U.S. health experts went so far as to declare that sugar is as addictive and dangerous as alcohol or tobacco and should be regulated accordingly.

Unfortunately it’s not always clear whether sugar itself is the culprit or whether something more complex is going on.

At least part of the reason why higher sugar consumption is linked to weight gain may simply be the extra calories. One of the issues with sugar-sweetened sodas and other beverages isn’t just that they contain lots of sugar, it’s that they often end up replacing water or milk in someone’s diet. Processed foods high in sugar also can be higher in fat and sodium, which are associated with negative health effects of their own.

A certain amount of sugar is necessary in order for the human body to function, but moderation seems to be called for here. Consuming large quantities of sugar each day also tends to be a marker for an overall diet that may not be optimal for health.

This brings us to the real vexation: the proverbial sweet tooth. Why do so many people love sugar and why can it be so hard to consume less of it?

I admit to not totally understanding the whole sweet tooth thing. If you were to invite me to your holiday buffet, I would go directly to the spinach dip and the shrimp cocktail. Cookies and candy, not so much. But this wouldn’t necessarily be the case for other guests.

There’s debate about whether so-called sugar addiction is real or imagined. Some studies have found clinical similarities between food cravings and drug dependence. A study published this year in the Journal of Psychoactive Drugs found, for instance, that when people binge on sugar-dense foods, it increases the amount of extracellular dopamine in their brain which has the potential to lead to addiction.

The authors wrote, “There appear to be several biological and psychological similarities between food addiction and drug dependence, including craving and loss of control.” They also note that for some people, consuming these foods is comforting and therefore might be regarded as a form of self-medication.

So far, however, the sugar addiction theory has mostly been tested on rats and mice, with implications for human behavior that are unclear at best. A 2010 review in the Clinical Nutrition journal examined the evidence and concluded there’s nothing yet in the literature suggesting that humans can become addicted to sugar or that sugar addiction plays a role in obesity or eating disorders.

The bottom line is that when it comes to “sugar addiction,” the jury still seems to be out.

In the meantime, here’s some guidance. The U.S. Department of Agriculture’s 2010 dietary guidelines recommend limiting consumption of added sugars and solid fats to somewhere between 5 and 15 percent of total daily calories. The American Heart Association suggests no more than 100 calories a day of added sugar for most women and no more than 150 calories a day for most men. That’s about 6 teaspoons for women and 9 for men.

Here’s something else to keep in mind. For most Americans, the main source of the sugar they consume isn’t in that spoonful they dump into their coffee, or a homemade dessert or even a Christmas cookie. Most of our dietary sugar comes in the form of added sugar – sugars and sugar-based syrups that are added to food during processing. Although the tendency is to single out highly sugared products, such as sodas, as the problem, added sugar can show up in a variety that may not be readily recognized – chicken nuggets, for instance, or ketchup or children’s breakfast cereals, all of which are often surprisingly high in sugar.

So go ahead and have that reindeer-shaped holiday cookie if you want. If you’re worried about the sugar, just take one.