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As a registered dietitian, I hear some version of this confession almost every week: “I know I should stop, but I really like my diet soda.” » This is usually accompanied by a guilty look, as if that can of fizz is somehow a moral failing rather than a beverage choice.
And this 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 them toxic, and a constant stream of alarming headlines linking them to everything from weight gain to heart disease. No wonder people feel like they should be ashamed of it.
But are diet sodas really that bad for you? Naturally, it’s complicated. Here’s what the research actually shows — and what it doesn’t show — so you can make an informed decision about whether you should open that second box.
First of all, what is actually in diet soda?
To understand the debate over 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 little to no calories. The most common in soda are aspartame, sucralose, and acesulfame potassium (often called acesulfame K). Some brands also use plant-based sugar substitutes like stevia.
Beyond sweeteners, many diet sodas contain sparkling water, acids (like phosphoric or citric acid), flavorings, preservatives and sometimes caffeine. Nutritionally, a diet soda doesn’t add much, but flavor-wise, it can be quite satisfying to sip on.
Are artificial sweeteners safe?
Sweeteners undergo safety reviews before reaching store shelves. In the United States, the FDA evaluates and approves high-intensity sweeteners as food additives before they can be used, and sets an acceptable daily intake for each. This is the amount considered safe to consume every day throughout your life. Most people drink much less than that. That said, some concerns persist in the public debate, particularly regarding aspartame.
You may remember the scary headlines about aspartame and cancer risk in 2023. A World Health Organization research group said aspartame could possibly increase cancer riskbut that is not the same as proving that it causes cancer. The evidence was limited. At the same time, the FDA’s guidelines for safe consumption have not changed.
Some groups need to be careful. For example, people with phenylketonuria (PKU), a rare hereditary disease, should avoid aspartame because their body cannot break down any of its components. And some sugar alcohols, like sorbitol and xylitol, can cause digestive upset in large quantities.
Are diet sodas healthy?
The short answer: it’s complicated. Studies on diet soda have produced conflicting results for years, and no single title gives the complete picture. Here’s what the evidence actually indicates.
Weight and metabolism
When it comes to swapping sugary drinks for diet drinks, the data is generally reassuring in the short and medium term. A Network meta-analysis 2022 found that replacing sugary drinks with low- or no-calorie sugary drinks was associated with small reductions in body weight, body fat percentage, and liver fat. The benefits were modest, but they were going in the right direction.
A 12-month randomized trial found something similar: Among people with the most belly fat, those who continued to drink sugary drinks gained significantly more weight than those who switched to diet drinks or water. For most people, however, swapping one for the other didn’t produce dramatic changes in all cases.
Heart health
This is where things get murkier. A Meta-analysis 2024 of 12 studies involving more than 1.2 million people found that daily consumption of one or more diet drinks was associated with higher risks of death from any cause, cardiovascular disease and stroke. A general review in Advances in nutrition have been similarly reported regarding trends in obesity, type 2 diabetes, hypertension, and incidence of cardiovascular disease.
The important caveat: These are associations, not evidence of cause and effect. People who drink more diet soda may be managing existing health conditions, making it difficult to determine whether diet soda actively contributes to poorer health or is simply common among people who are already at higher risk.
Gut health and blood sugar
An active area of research focuses on 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 certain non-nutritive sweeteners, particularly saccharin and sucralose, were associated with worse blood sugar responses in healthy adults, with effects on the gut microbiome that appeared to vary between people.
Diet soda vs. regular soda: which is healthier?
If the choice is between routine and diet, diet usually comes out on top. THE 2018 American Heart Association Scientific Advisory noted that diet drinks can provide a reasonable stepping stone for habitual consumers of sugary drinks who are trying to reduce their consumption. A Meta-analysis 2022 supports this, finding small but significant improvements in cardiometabolic markers when people made this change.
That said, unsweetened drinks, especially water, seem to offer benefits that diet soda doesn’t, giving you the benefits of hydration with fewer open questions. To get the most accurate recommendation on whether diet soda is better for you than other drinks, meet with a registered dietitian for personalized advice.
Who should avoid diet soda?
Consuming diet soda won’t cause a health crisis for most people, but it may be worth considering reducing consumption if you:
Drink several cans per day, as observed links appear at higher intakes
Notice how it crowds out water, milk or other nourishing drinks
Rely on it for caffeine and find it affects your sleep
You’re working on reducing sugar cravings and want to reset your taste buds
You have tooth sensitivity or enamel problems
You suffer from PKU (in which case aspartame-sweetened drinks are no longer on the table)
The essentials
Diet soda isn’t a drink that dietitian would proactively tell you to drink multiple times a day, but it’s also not the bad guy some headlines suggest. For someone moving away from sugary drinks, this can be a useful bridge. The research raises questions worth taking seriously, especially at higher intakes, but it doesn’t prove that diet soda is directly harmful.
My advice? Consider diet soda an occasional treat rather than your primary source of hydration. Rely on water and other unsweetened beverages most of the time and enjoy that guilt-free can of fizz whenever you want. Your overall eating habits matter much more than the occasional Diet Coke.
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