If you do a search about sugar, you may become convinced that it’s evil and addictive — and that your sweet tooth will lead you to ruin. You’ll also see plenty of advice for how to curb your craving for sugary goodness.

But what do we really know about how sugar affects us? Does eating sugar make us want to eat more of it?

First things first. Sugar is a carbohydrate, a category that includes starches. In addition to tasting sweet on your tongue, a spoonful of table sugar — in a cup of coffee, for example — will cause the sugar, or glucose, level in your blood to rise.

Your body responds differently to eating an apple, which is loaded with fruit sugars. For the same amount of carbohydrate, table sugar will prompt a much bigger spike in blood glucose than a few bites of apple. That’s because the apple’s sugars are “in natural form, in the whole fruit,” said David Ludwig, a physician and professor of nutrition at the Harvard T.H. Chan School of Public Health. “The sugar is sequestered in the structure of the fruit, and it leaches out slowly.” In contrast, the sugar in sodas and candy, he said, “slams into the liver and raises blood glucose.”

This is what nutritionists are talking about when they cite a food’s glycemic index. A food with a high glycemic index raises blood glucose more than a food with a medium or low glycemic index. A rule of thumb is that the more processed, or refined, a food is, the higher its glycemic index, the American Diabetes Association said.

It’s not just sugary foods, either: White bread is a high glycemic index food, and potato chips fall in the medium category.

Scientists said they believe that the rise in blood glucose is responsible for food cravings.

“Sugary foods and refined carbohydrates cause a blood-sugar spike,” said Ashley Gearhardt, a psychologist at the University of Michigan. “And then three to four hours later, a blood-sugar crash. That cycle primes your brain and makes you want more of those foods.”

Ludwig imaged the brains of 12 overweight or obese men four hours after a high-glycemic-index snack and found increased activity in regions of the brain that respond to drugs of abuse.

Gearhardt asked 120 college students to identify foods that they “eat more and more of … to get the feeling I want, such as reduced negative emotions or increased pleasure.” Chocolate was No. 1, followed closely by ice cream, French fries, pizza, cookies, chips and cake.

Highs and crashes and priming and wanting. That’s the language of addiction.

“Addictive substances usually have high potency and a rapid rate of absorption,” Gearhardt said. She said there’s a parallel with foods that are highly processed and rapidly digested, “the foods that people struggle to eat in a manageable way.”

People may say they’re addicted to sugar, and the addictive model may be useful for researchers as they study cravings and overeating. But Larry Cheskin, director of the Johns Hopkins Weight Management Center, said candy is not the same as heroin. Eating and overeating are not only a result of physiological cues, he said. We also eat because we’re bored, we’re stressed, we’re celebrating or we’re with friends who are eating.

Jennifer Temple, director of the Nutrition and Health Research Laboratory at the University of Buffalo, tested whether eating sugar begets more eating of sugar. Participants chose a favorite item and were directed to eat it every day for a week. Then they were given a chance in the lab to earn another one. She reported that “40 percent of people who are already overweight or obese, when they’ve eaten a favorite treat every day … will work three times harder for that same treat” than when they hadn’t eaten one every day for a week.

Do artificial sweeteners feed this addictive cycle? “There’s no scientific consensus on this,” Gearhardt said.

If you stop eating foods with added sugar, can you reduce your craving for sweets? Anecdotally, the answer seems to be yes. But there’s scant research.

Are there substitute foods that can help rein in your desire for sugary treats? Not really, but substituting a food with a lower glycemic index may stave off that spike-and-crash cycle of blood sugar that drives craving.

Cheskin advised behavioral routes to change. Keep a record of your eating patterns, and you might identify your own triggers and then manage them. “Do you snack when you come home from a stressful day at work? Substitute something else relaxing — maybe a walk.”