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Is Diet Coke bad for you?

two pint glasses of diet soda with ice
(Image credit: Getty Images)

Diet cola is one of the most popular soda options for those who want to enjoy a refreshing drink without the extra calories and sugar. But studies have found that diet sodas might not be as healthy as they're portrayed. So is Diet Coke bad for you, and should we avoid it completely? The answer isn't clear cut — and as with most things, it comes down to moderation. Diet soda is certainly a better option than regular soda in terms of calories, but studies suggest that everyday consumption might be harmful to our health.

In fact, according to the Centers for Disease Control and Prevention (opens in new tab), the number-one source of added sugars in the U.S. diet is sugar-sweetened beverages such as soft drinks, tea and fruit drinks. Hence, as a population, we need to look at reducing the amount of added sugars we’re taking in. 

On one hand, switching from regular Coke to Diet can help with this, allowing people to enjoy a soft drink without added sugar. Regular soda also contains empty calories that offer no nutritional benefit. Since Diet Coke is a low calorie alternative, it can be a better option.

This being said, Keri Gans, registered dietitian and spokesperson for the American Dietetic Association, noted that it would be a better choice to choose a beverage with nutritional benefits. "[Like] a glass of low-fat milk or 100% fruit juice, if we're talking about calories," she said. "Ideally, if you want to consume something with zero calories, water is your best choice."

And just because diet soda is 'diet,' doesn’t make it a so-called 'health food,' added Sharon Fowler, epidemiologist at the University of Texas Health Science Center at San Antonio. "In fact, it's not a food at all, it's simply a slurry of chemicals, a number of which may have deleterious effects on the body," she said.

Sharon Fowler, MPH

Sharon Parten Fowler is an adjunct assistant professor in the Department of Medicine, School of Medicine, at UT Health San Antonio. She earned a BA from Rice University and an MPH from the UTSPH in Houston. 

A study in the American Journal of Clinical Nutrition (opens in new tab), for example, found that cola (but not other carbonated beverages) was associated with low bone mineral density in women, because of the phosphoric acid it contains. Similar results were seen for regular and Diet Cola. 

Fowler also noted that caramel coloring in colas contains substances which have been associated with an increased risk of a number of chronic diseases. Meanwhile, the safety of artificial sweeteners, especially aspartame and sucralose, is debatable, with recent research in the International Journal of Molecular Sciences (opens in new tab) suggesting they may negatively impact gut health.

"Individuals vary widely in their reactions to these substances," added Fowler. "Because of the very real possibility that irreversible cumulative effects [occur]… I'm convinced that we're in the middle of a very large-scale experiment, and that the whole story of the potential impact of diet sodas on health may not be known for years to come."

man sitting next to a glass of diet soda

(Image credit: Getty Images)

A 2012 study published in the Journal of General Internal Medicine (opens in new tab) also found that people who drank diet soda every day had a 61% higher risk of blood vessel diseases, such as stroke and heart attack, than those who reported not drinking any soda (diet or regular) at all. 

Speaking to Live Science, co-author Dr. Mitchell S. V. Elkind, associate chairman of Neurology for Clinical Research and Training at Columbia University in New York, said: "Based on our research, it looks like, at least for the blood vessels, diet soda is not good for people. [But] there've been other studies that have looked at this and not found the same result after they accounted for other confounding risk factors.

Mitchell Elkind
Dr. Mitchell S. V. Elkind, MD, MS, MPhil

Mitchell Elkind is a tenured professor of neurology and epidemiology at Columbia University Irving Medical Center, and Chief of the Division of Neurology Clinical Outcomes Research and Population Sciences (Neuro CORPS) in the Neurology Department. Dr. Elkind received his medical degree from Harvard Medical School, and he trained in Internal Medicine at Brigham and Women’s Hospital and in Neurology at Massachusetts General Hospital, both in Boston, Massachusetts. 

"So I wouldn't say our study has proven there's a causative link, but what it does, in my mind, is raise the question that there might be some risk here that we need to study further."

Elkind went on to add that there is also the theory that people who drink sugar-sweetened beverages have an increased risk of diabetes and obesity. “So, one might suggest that perhaps you can avoid this by drinking diet soda,” he said. “We would argue that you may not be entirely correct — there's still risk associated with diet soda, which could be due to other factors that are associated with drinking diet soda."

The bottom line? Diet Coke does have fewer calories and sugar than regular soda, and therefore some experts think it’s fine in moderation. But others point out that diet soda can increase the risk of stroke and metabolic syndrome. Its long term effects are also unclear.

Originally published on Live Science. This article contains additional reporting done by Amanda Chan in 2013.

Alice Ball
Health Editor

Alice Ball is the Health Editor for Future Plc. With more than five years of experience working in health journalism, she's covered everything from why we should 'kill' the calorie, to destigmatizing the menopause. Alice also specializes in nutrition and supplements. She's a self-confessed running fanatic, having completed five marathons. She enjoys documenting her progress on her Instagram account, @aligoesrunning. Alice works across a number of Future's sites, including LiveScience and Fit&Well.