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As a registered dietitian, I hear some version of this confession almost every week: “I know I should quit, but I really love my diet soda.” It usually comes with a guilty look, as if that can of fizz were somehow a moral failing rather than a beverage choice.
And that guilt didn’t come out of nowhere. Over the years, diet soda has quietly taken on a lot of cultural baggage: concerns about “chemicals,” wellness influencers declaring it toxic, and a steady stream of alarming headlines linking it to everything from weight gain to heart disease. No wonder people feel like they should be ashamed of it.
But is diet soda really that bad for you? Naturally, it’s complicated. Here’s what the research actually shows—and what it doesn’t—so you can make an informed decision about whether you should crack open that second can.
First, what’s actually in diet soda?
To understand the debate of whether diet soda is bad for you, it helps to understand what you’re actually drinking. Diet soda gets its sweetness from non-nutritive sweeteners. These ingredients taste sweet but add few or no calories. The most common ones in sodas are aspartame, sucralose, and acesulfame potassium (often listed as acesulfame K). Some brands also use plant-based sugar substitutes like stevia.
Beyond sweeteners, many diet sodas contain carbonated water, acids (such as phosphoric or citric acid), flavorings, preservatives, and sometimes caffeine. Nutritionally, a diet soda doesn’t add much, but in the flavor department, it can be utterly satisfying to sip.
Are artificial sweeteners safe?
Sweeteners go through safety reviews before they reach store shelves. In the U.S., the FDA evaluates and approves high-intensity sweeteners as food additives before they can be used, and sets an acceptable daily intake for each one. That’s the amount considered safe to consume every day over a lifetime. Most people drink far less than that. That said, some concerns have lingered in the public conversation, particularly around aspartame.
You may remember scary headlines about aspartame and cancer risk in 2023. A World Health Organization research group said aspartame may possibly raise cancer risk, but that’s not the same as proving it causes cancer. The evidence was limited. At the same time, the FDA guidance on safe intake hasn’t changed.
A few groups do need to be careful. For example, people with phenylketonuria (PKU), a rare inherited condition, should avoid aspartame because their bodies can’t break down one of its components. And some sugar alcohols, like sorbitol and xylitol, can cause digestive upset in large amounts.
Is diet soda healthy?
The short answer: It’s complicated. Studies on diet soda have produced conflicting results for years, and no single headline captures the full picture. Here’s what the evidence actually points to.
Weight and metabolism
When it comes to swapping sugary drinks for diet ones, the data is generally reassuring in the short to medium term. A 2022 network meta-analysis found that replacing sugar-sweetened beverages with low- and no-calorie sweetened drinks was associated with small reductions in body weight, body fat percentage, and liver fat. The benefits were modest, but they pointed in the right direction.
A 12-month randomized trial found something similar: Among people with the most abdominal fat, those who kept drinking sugary beverages gained significantly more weight than those who switched to diet drinks or water. For most people, though, swapping one for the other didn’t produce dramatic changes either way.
Heart health
This is where things get murkier. A 2024 meta-analysis of 12 studies covering more than 1.2 million people found that drinking one or more diet beverages daily was associated with higher risks of death from any cause, cardiovascular disease, and stroke. An umbrella review in Advances in Nutrition flagged similarly concerning patterns for obesity, type 2 diabetes, hypertension, and cardiovascular disease incidence.
The important caveat: These are associations, not proof of cause and effect. People who drink more diet soda may be managing existing health conditions, and that makes it hard to untangle whether diet soda is actively contributing to worse health or simply common among people who are already at higher risk.
Gut health and blood sugar
One area of active research is how artificial sweeteners may affect the gut microbiome and blood sugar regulation. Some studies suggest that certain sweeteners, particularly sucralose and saccharin, may alter gut bacteria in ways that could affect how the body processes glucose. A study published in Cell found that some non-nutritive sweeteners, especially saccharin and sucralose, were linked to worse glycemic responses in healthy adults, with gut microbiome effects that appeared to vary from person to person.
Diet soda vs. regular soda: Which is healthier?
If the choice is between regular and diet, diet generally comes out ahead. The 2018 American Heart Association science advisory noted that diet drinks may be a reasonable stepping stone for habitual sugary drink consumers trying to cut back. A 2022 meta-analysis supports this, finding small but meaningful improvements in cardiometabolic markers when people made that switch.
That said, unsweetened drinks—especially water—appear to offer advantages that diet soda doesn’t, giving you the benefits of hydration with fewer open questions. For the most accurate recommendation about whether diet soda is better for you than other drinks, meet with a registered dietitian for personalized advice.
Who should avoid diet soda?
Drinking diet soda won’t cause a health crisis for most people, but scaling back may be worth considering if you:
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Drink several cans a day, since the observational links appear at higher intakes
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Notice it’s crowding out water, milk, or other nourishing drinks
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Rely on it for caffeine and find it’s affecting your sleep
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Are working on reducing sugar cravings and want to reset your taste buds
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Have dental sensitivity or enamel concerns
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Have PKU (in which case aspartame-sweetened drinks are off the table)
The bottom line
Diet soda isn’t a drink this dietitian would proactively tell you to drink multiple times a day, but it’s also not the villain some headlines suggest. For someone moving away from sugary drinks, it can be a helpful bridge. The research raises questions worth taking seriously, especially at higher intakes, yet it doesn’t prove that diet soda directly causes harm.
My advice? Think of diet soda as an occasional treat rather than your main source of hydration. Lean on water and other unsweetened drinks most of the time, and enjoy that can of fizz without the guilt when you want it. Your overall eating pattern matters far more than the occasional Diet Coke.
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