Is diet soda unhealthy? That’s one of the more common nutrition questions I get. And I guess I wouldn’t categorize soda, diet or not, as ‘healthy’ or ‘physically nourishing,’ but if a person drinks a can – or three – of diet soda a day, a week, or a month, is that going to harm their health? What do I tell clients about diet soda? What does the research say?

What’s In Diet Soda?

There’s not much in diet soda except carbonated water, colorings, flavorings, and sweetener. I think people fear it because of its sweeteners, plus the fact that most of us have seen that video of the guy cleaning the toilet with Coke. 


Let’s go over some of the more controversial ingredients in diet soda.

Artificial Sweeteners in Diet Soda

It’s hard to write a piece about diet soda and not have the majority of it be about sweeteners. That’s because most peoples’ fears about diet soda lie with the fact that it contains aspartame, or sucralose, or something that somebody told them causes cancer/heart disease/increased appetite and a slow and torturous death.

To address these fears, I’m going to break down the sweetener thing as efficiently as I can.

The majority of the diet beverages made by Coca-Cola and PepsiCo contain aspartame and/or Ace-K.

Some other ones contain sucralose, otherwise known as Splenda, and stevia, a plant-based sweetener. I’m not going to cover saccharine here, because it’s not abundant in our food supply (unless you drink Tab…which I can’t believe is still around).

What Is Aspartame?

Aspartame is 200 times sweeter than sugar, and is sold under the names Nutrasweet and Equal. It has had a really long history of rodent studies that seem to show a link between the ingredient and blood cancers. The problem with these studies is that rodents and humans metabolize aspartame differently. The other problem is that in many of these studies, the poor rats were fed huge amounts of the sweetener. Nobody in their right mind eats that much aspartame. 

After extensive investigation, the FDA and The European Food Safety Authority have both concluded that current exposure rates to aspartame are completely safe. The EFSA’s acceptable daily intake for the sweetener is 40mg/kg/day, which equals 36 cans of diet soda for a 136lb person. 

The FDA’s acceptable daily intake for aspartame is a bit higher, at 50mg/kg/day.

My thinking is that if you’re eating that much of anything, it will probably cause you problems. And put it this way: if aspartame was carcinogenic at current intakes, a heck of a lot of diabetic people, who have be consuming aspartame-laced foods for decades, would have cancer right now. 

What is Stevia?

Known for its bitter taste that IMO overrides any of its sweet flavor, stevia is a plant-based sweetener. It is known to be safe in typically consumed amounts. 

What is Ace-K?

Acesulfame-potassium is 200 times sweeter than sugar. According to the FDA, the acceptable daily intake for ace-K is 15mg/kg/day, which would equate to around two gallons of sweetened beverage a day

Rodent studies like this one (and here, and here) that suggest that ace-K, sucralose, and saccharine mess with gut bacteria, leading to obesity and chronic diseases like diabetes and insulin resistance. Human studies are lacking in this area, and these rodent studies were done with unrealistically high doses of sweeteners. 

What is Erythritol?

Thanks to the keto diet and the recent study about erythritol and cardiovascular disease and stroke, I think most of us have heard about this sweetener.

Erythritol is a sugar alcohol found in many fruits, vegetables, cheese, wine, and beer. It’s also used as a non-nutritive sweetener in many products. You can buy erythritol in the grocery store to bake with.

Aside from being something we get from our diet, our bodies make erythritol when metabolizing glucose.

The average consumer eats around 16 grams of erythritol a day, with the higher end of consumption being around 32 grams a day.

One recent, well-publicized study apparently found that erythritol was linked to heart attacks and strokes. The media was quick to hype the study with fear-mongering headlines:

erythritol and heart attacks

But what did this study actually find? You’ll be surprised.

First of all, the study didn’t set out to look at the effects of erythritol at all; this was an incidental finding. This is problematic because when a study outcome doesn’t come about as the result of a specific question, certain steps may be missed. We see that here.

Many of the study participants were around age 65 and had a history of heart disease to begin with. They also had high blood erythritol levels, but because the researchers didn’t control for diet, they can’t say whether the participants’ erythritol levels were because of what they ate, or if their bodies made that erythritol. It’s important to note that our bodies make erythritol when we’re stressed or in response to oxidative damage – both things can also bring on heart attacks and strokes.

Erythritol is typically excreted from the body fairly quickly after consumption. Blood erythritol levels were taken only once during the study. Again, in participants with high levels, are these the result of food, or endogenous production?

For most people, erythritol is recognized as safe.

What is Sucralose? Is Sucralose safe?

The FDA says sucralose is safe, and has determined the acceptable daily intake as 5mg/kg/day. So for someone who is 140lb, that means 32 packets of Splenda a day. 

A very small, very very short 2013 study along with a longer, better constructed one published in Nutrition Journal in April 2020 both suggest that sucralose – and maybe other sweeteners – may cause insulin to spike. 

The theory behind this insulin spike is that when we eat sweeteners, our bodies release insulin in anticipation of the blood sugar rise that happens with sugar. 

But when that doesn’t happen, we end up with elevated insulin and eventually, insulin resistance. 

It’s a phenomenon that scientists haven’t figured out yet, and honestly, the collective research on it is conflicting. 

The latest study on sweeteners – done in 2022 and published in Cell – appeared to find that sucralose and saccharin alter our gut microbiome, leading to alterations that these scientists then linked to elevated blood glucose in some study subjects.

This is an interesting outcome, but this study had a lot of problems.

First of all, the people who they gave sweeteners to, were not regular consumer of them. Would people who regularly consume sweeteners have a different reaction? Is there an adjustment period after which the microbiota go back to normal? The study was tiny – 20 people in each arm – and short – two weeks. This isn’t nearly long enough to assess clinical relevance and effect.

The study found that microbiota appeared to be altered with a certain dosage of these sweeteners. What we don’t know, is what outcome of this alteration actually is. Does it impact health at all? The subjects in the study who had the most alteration also showed elevated blood glucose levels. Scientists theorized that these two things were related. But were they? Why were blood insulin levels not rising as a result of the higher glucose levels, as we’d expect (see above).

Confusing, right?

Lastly, the groups weren’t monitored while testing their glucose levels. What was the margin of error?

So many questions. Not many answers.

So Are Sweeteners in Diet Soda Safe?

All in all, what we know about the sweeteners in diet soda is this: All of them are safe in the amounts we typically consume, with a large buffer zone.

There’s very little human research on them

Most rodent studies that have been done on sweeteners have used large doses, in amounts and configurations that humans rarely if ever consume, such as straight sucralose. 

The insulin spike that may happen when we eat sweeteners is poorly understood, and as you see above, is sometimes not present at all.

Other concerns about Diet Soda:


Some sodas contain phosphoric and citric acid to give the drink tartness. Both of these ingredients can erode enamel and dentine and cause tooth decay, but so can any other acidic food or drink. Chase sodas with water and use a straw. Problem solved.

Appetite, weight gain, and other conditions.

Again, this concern is due more to the sweeteners in diet soda rather than the soda itself. There have been studies in animals that suggest an impact in hunger hormones with artificial sweeteners, but in humans, this hasn’t been proven at all. 

A really small, stupid study on fruit flies and mice found that sucralose can increase appetite. A study on fruit flies – and mice – that are fed pure sucralose (who eats Splenda out of the packet?) doesn’t resonate with me.

A recent review of studies found that artificial sweeteners fail to control weight, while another (industry funded) study (and here, not industry-funded) shows that they help with weight loss – although these studies don’t prove causation.

Other studies associate diet soda with weight gain, type 2 diabetes, and metabolic syndrome, as well as strokes, dementia, cancer, Parkinson’s disease, among other things, but we can’t establish causation here. And that’s the lesson with pretty much every study that tries to link diet soda with weight or health issues. This BMJ 2018 review of sweeteners found the same thing: there isn’t a link between sweeteners and health outcomes.

Let me float a few hypotheses for the above studies that did find a link between diet soda and health outcomes:

The first one is that when we believe we’re cutting calories in other ways, such as choosing diet soda over regular, we tend to eat more out of a sense of permissiveness, leading to weight gain. 

Or, people who drink more diet soda tend to have a lower-quality diet overall.

Or, people who drink more diet soda are more overweight and have other risk factors for the above conditions.

It also may be that when a person is consuming a substance that’s many times sweeter than sugar, it eventually blunts their perception of sweetness. This may lead them to crave foods that are sweeter than average, which in turn may lead to increased consumption of those foods versus foods like vegetables. 

Or, diet soda DOES cause these things. Hey, just because correlation doesn’t equal causation doesn’t mean we can’t be an equal opportunity employer with our hypotheses.

The truth is, we don’t know the answer here. It could be none of these, or it could be a bit of all of them.

The preponderance of evidence shows that sweeteners are fine in small doses, and that they do, in the long term when replacing high-sugar foods, help people lose weight.

Is diet soda unhealthy? In short, no.

Is there a diet soda health risk? In terms of proving diet pop unhealthy, the research overall is weak. Stuffing a rat full of pure sweetener and waiting for it to grow tumours, doesn’t prove a heck of a lot. 

Population studies that try to link sweetener and diet soda to conditions that subjects were probably at risk for anyhow, don’t prove anything to me. 

And sources like Mercola, Josh Axe, Dave Bulletproof Asprey, and whoever else is saying that diet soda will kill you, aren’t reputable or worth listening to. 

A dietitian’s recommendations around diet soda (and sweeteners in general)

My concerns about diet soda don’t really come from a disease-causing perspective as much as the fact that it contains nothing nourishing whatsoever. Sure, water doesn’t either, but here’s my point:

I do believe wholeheartedly that the consumption of large amounts of artificial sweeteners leads to an increased tolerance for sweet taste, which can then make naturally sweet foods taste not sweet enough. 

I also think we should be aware of the products we’re consuming that contain added sweeteners AND added sugar, and limit them. This is because many of these foods are ultra-processed, and may not be that physically nourishing. Can they be a part of our diet? Of course! But they probably shouldn’t comprise the majority of it.

If you’re eating a nourishing diet and enjoy a diet soda every once in a while, that’s fine. But if diet drinks are crowding out nourishing food or water in your diet, it’s time to reel it in.