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,” says 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 says, “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, according the American Diabetes Association.
It’s not just sugary foods, either: White bread is a high glycemic index food, and potato chips fall in the medium category.
Scientists believe that the rise in blood glucose is responsible for the craving one feels for certain foods. “Sugary foods and refined carbohydrates cause a blood-sugar spike,” says 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.” Such language aimed to elicit foods eaten in an addictive way. 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 says. Think snorting cocaine rather than chewing coca leaves. (The leaves contain minuscule amounts of cocaine, and chewing activates the drug’s stimulant effects slowly.) Gearhardt says 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 food cravings and overeating. But candy is not the same as heroin, says Larry Cheskin, director of the Johns Hopkins Weight Management Center. For people, eating and overeating are not only a result of physiological cues, he says.
We also eat because we’re bored, we’re stressed, we’re celebrating, we’re with friends who are eating, or we see that it’s time to eat.
Jennifer Temple, director of the Nutrition and Health Research Laboratory at the University of Buffalo, tested whether eating sugary treats begets more eating of sugary treats.
Participants chose a favorite item and were directed to eat it every day for a week. Then they returned to the lab, where they were given a chance to earn another one. She reports finding that “not everybody, but 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 says.
If you stop eating foods with added sugar for a while, can you reduce your craving for sweets? Anecdotally, the answer seems to be yes. But there’s been little research on this.
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 researchers think drives craving.
(You can find a list of 100 foods and their glycemic index by searching for “Harvard Health glycemic list.”)
Cheskin advises behavioral routes to change. Keep a record of your eating patterns, and you might identify your own triggers for less-than-healthy snacking — a place, a mood, a response to stress. Then you can make a plan to manage those triggers, he says. “Do you snack when you come home from a stressful day at work? Substitute something else relaxing — maybe a walk.”