If only dropping pants sizes were as easy as switching from Coke to Coke Zero.

Sure, you're cutting out empty calories when you ditch the sugar-sweetened drinks in favor of artificially sweetened ones. But there's a growing body of research that suggests this isn't really helping in the battle of the bulge.

The latest ding against diet drinks? Researchers report this week that overweight and obese people who choose diet beverages eat about the same number of total calories as their counterparts guzzling sugary drinks — they're just getting more of their calories from solid food.

In other words, their drinks may be no-calorie, but they're making up for it at meal and snack times.

And that suggests that public health messages urging people to drop the sugar-sweetened drinks in favor of diet ones to combat obesity need to be tweaked, says the study's lead author, Sara Bleich, an associate professor at the Bloomberg School of Public Health at Johns Hopkins University.

"We need to go beyond telling them, 'You need to drink less sugary soda,' " Bleich tells The Salt. "That's because when people make the switch from regular to diet, they're not making many other changes" to what they consume.

Americans' diet soda habit has exploded in the past 15 years — 1 in 5 of us now consumes one on a daily basis. Overweight and obese adults are about twice as likely as their healthy-weight counterparts to drink diet beverages, according to Bleich's findings, which appear in the American Journal of Public Health. And it makes sense, she says, that this reflects a desire to shed excess weight.

But Bleich and her colleagues wanted to know how Americans' rising diet drink habit relates to overall calorie consumption. So they looked at data for adults 20 and older gathered between 1999 and 2010 by the National Health and Nutrition Examination Survey. It's an ongoing program that collects details on eating habits and other health-related information from a nationally representative sample of people in the U.S.

And what did they find? It turns out that overweight adults who drank artificially sweetened beverages ate on average 88 more solid-food calories per day than their weight counterparts who drank sugary beverages, while obese diet drinkers ate an extra 194 calories per day.

What's more, when they snacked, these heavier-set drinkers of diet sodas tended to get more of their calories from sweet treats, the researchers found.

That jibes with research that suggests artificial sweeteners may be messing with the body's feedback loop when it comes to sweet tastes.

"What we've seen from animal data is there is something metabolic that changes when you consume artificial sweeteners," says Bleich. "The brain is tricked into thinking it is less full."

So what's going on? Basically, when we eat sweet-tasting foods, that signals our brains to release hormones to process the sugar. It's part of a mechanism that tells the body how much energy it's just taken in, and when it's had enough.

But in people who are regular drinkers of diet sodas, the theory goes, the body gets confused and no longer releases enough hormones. As a result, researchers suspect, diet drinkers end up eating more — and gaining weight.

"For some individuals, that constant exposure to that sweet taste does drive appetite," says Sharon Fowler, an epidemiologist at the .

Fowler's own published research has found that, over a seven- to eight-year period, habitual diet soda drinkers were twice as likely to go from being healthy weight to overweight or obese as those who didn't down the artificially sweetened beverages.

And she points to other studies that have linked a diet soda habit to increased risk of metabolic syndrome, Type 2 diabetes, heart attack and stroke.

"So the question is: Are diet sodas innocent bystanders in the obesity epidemic, or are they accomplices?" Fowler tells me. "I don't think they are innocent — for some people, at least."

Of course, the case against diet soda isn't so clear-cut. For example, as we've previously reported, researchers from Boston Children's Hospital found that ditching the sugar-sweetened drinks for no-calorie options like diet soda helped overweight teens manage their weight.

And Bleich, for one, isn't ready to throw diet drinks under the bus.

"We need to make recommendations that work with life," she says. "If you are an obese person, and I get you to switch from regular to diet soda, I've made gains by getting you to switch. But the reality is, if you want to lose weight, you need to make other, better choices."

Copyright 2021 NPR. To see more, visit https://www.npr.org.