Diet soda may not be the guilt-free drink we'd all hoped it would be, according to mounting research. In fact, it's exact health effects aren't quite clear.
We talked to Dr. David Katz, the founding director of Yale University's Prevention Research Center and a HuffPost blogger, and Dr. Melina Jampolis, a board-certified physician nutrition specialist and author of "The Calendar Diet," to explain what we know about diet soda -- and why we probably shouldn't be giving the beverage a free pass. (Disclosure notice: Jampolis does consulting work for a soda company that uses Stevia, but not artificial sweeteners.)
Granted, the evidence of health risks is a lot clearer for sugary drinks; a recent study presented at a meeting of the American Heart Association linked them with 180,000 deaths around the world. But while there's a lot we don't know about the effects of diet soda, we can surmise some points based on the available research. Take a look at some reasons to pick water over diet soda when you want a calorie-free drink:
Despite its name, it may not really be that diet friendly.
If something's called "diet," it must help you while you're on a diet, right? Not necessarily. There's "no convincing proof that these things ever did what they were supposed to do, and the burden of proof is with [the soda companies], not us," Katz said.
"Fundamentally, we have no convincing evidence that diet soda or artificial sweeteners are actually helpful for people trying to lose weight," he said. Research has shown that even though removing sugar and calories in the short term is a good thing for weight loss, in the long term, those sugar and calories can sneak right back into the diet.
Some observational research has linked weight gain and diet soda consumption, including a study presented at a meeting of the American Diabetes Association in 2011 which showed that waist circumference was 70 percent greater for diet soda drinkers than non-diet soda drinkers. And in a recent review of studies conducted by researchers at Purdue University, an association was found between obesity and artificially sweetened drinks.
However, the direction of these associations is a little less clear. Jampolis points out that it's possible the results of these studies are intrinsically tied to the fact that overweight people may be more likely to select diet sodas in the first place in order to lose weight. Katz agrees, but thinks the association is likely bidirectional -- overweight people may drink more diet soda, and diet soda could be having some sort of effect on weight. That brings us to the next point...
It confuses our brains.
When a person consumes a zero-calorie artificial sweetener, it's telling the brain, "I am eating sweet, expect calories." However, no calories come.
Sugar addiction researcher Nicole Avena, Ph.D., who is an assistant professor in the College of Medicine at the University of Florida, explains that in the short term, we're getting that satisfaction of sweet without the calories. But in the long run, it's a little more complicated. "If you're consuming beverages without calories and [you're] not getting fullness from sugar-sweetened beverages, you could be priming the brain to want to eat more," she tells HuffPost. "That’s one of the limitations of artificial sweeteners: In the long term, it could stimulate appetite, versus provide a benefit in the sense they're reducing calorie intake ... Over time, it's not helping the brain get over wanting sugar."
At this point, more studies are needed to confirm that consuming artificial sweeteners really causes people to consume more calories. It's unknown if that calorie-free sweetness actually quells our desires, or if it just makes us want to eat more, Jampolis said.
But Katz pointed out that artificial sweeteners are often super sweet (sucralose, also known as Splenda, is 600 times sweeter than sucrose, table sugar).
"They keep your preference for sugar at a high level, and encourage you to seek out those foods," he said. This could lead to poor dietary choices, which could in turn lead to being overweight, obesity and a number of other health ills.
If you're really trying to lose weight or eat healthier, Katz said the better way to do so is to "rehabilitate" your taste buds by cutting out hidden sugar in foods like salad dressings, pasta sauces and crackers, so that you're more sensitive to sweetness and thereby prefer less.
"Then we can solve the problem without relying on chemistry," he said. "These chemicals have uncertain, unpredictable effects, and so when you have the option to avoid them, I would prefer that."
It's been linked to scary conditions like heart attack, stroke and Type 2 diabetes (though its exact role is still not totally clear).
Researchers from the University of Miami and Columbia University found that people who drink diet soda every day have a 43 percent higher risk of experiencing a vascular event over a 10-year period, compared with people who didn't drink soda. Plus, this association held true even after taking into account known stroke and heart risk factors like diabetes and high blood pressure. And in a study published earlier this year in the American Journal of Clinical Nutrition, French researchers found an association between Type 2 diabetes and self-reported diet soda consumption. Plus, when comparing the diabetes risk of drinkers of diet with drinkers of regular sodas, researchers found that diet drinkers had the higher diabetes risk.
But again, these studies are observational. It's unknown if the diet soda is actually causing these conditions, or if people who are already at high risk for a heart attack, stroke and Type 2 diabetes tend to drink diet soda in an effort to lead a healthier lifestyle. Research on diabetes and diet soda consumption has been mixed so far; a review of studies from Harvard researchers published in 2011 showed no link between diet soda consumption and increased Type 2 diabetes risk.
As Katz explains, if diet soda really was causing heart attacks and strokes, there would have been spikes in these conditions in recent years. Rather, he thinks that it's more an effect of people who tend to eat wholesome diets may steer clear of artificial sweeteners to begin with, while people who eat a lot of artificial sweeteners may not have the healthiest diet. "At that point, the less healthier the diet, the more prone you are to cardiovascular disease," he says. "It's a sign that there's something wrong with the dietary pattern overall."
There's just so much we don't know.
This might just be the biggest issue with diet soda. Studies aren't perfect. Observational studies are purely that -- observational -- and don't prove cause-and-effect. Research based on food-recall questionnaires can be inaccurate because who really remembers every single thing they ate last week, anyway? And studies in rats will never be a perfect comparison for studies in humans; as Katz puts it, humans are "sophisticated animals and we can track calories. We look at nutrition labels. Rats don't read nutrition labels."
Plus, there's a lot we don't know about how diet soda can affect humans in the long run. For instance, do artificial sweeteners have any effect on hunger hormones? Could they contribute to the development of insulin resistance, which is a risk factor for diabetes? Jampolis notes that there have been some studies showing potential effects of diet soda on hormones and appetite, but more research needs to be done to paint a clearer picture.
"We don’t really know a whole lot about what these specific artificial sweeteners do to the brain reward system. We know their safety -– they're FDA-approved -- but don’t know enough about the long-term effects on appetite," Avena said .