Is switching from regular soda to diet soda good for you?
I’ll admit: I started researching this topic for entirely selfish reasons. For years now, I’ve liked to have a Coke or three (if Dr. Pepper is available, I prefer that) before and during Utah Jazz games. I know that drinking sugary sodas is bad for me ... but I like the pick-me-up of the caffeine and the sweet taste that comes with them.
So is diet soda the answer? Or do I simply want to have my cake and eat it too? (Is there diet cake available?)
If you ask regular folks what they think about this, you’ll get somewhat surprising results. In a 2020 survey of 3,430 people, just 25.2% of respondents said that diet sodas were more healthy than their regular soda counterparts. Meanwhile, 26% said diet sodas were actually more unhealthy. The remainder said they were about the same.
Who’s right? I looked at the research. As always with everything in nutrition, the studies are frequently conflicting and confusing. A person’s health is determined by one trillion factors, and studying one switch alone is difficult. Much of what we know is from observational studies and surveys, which can be confounded by other factors. Diets are hard to stick to, even when being observed by science.
There’s also the unfortunate reality of the soda industry’s impact, which clearly works to promote soda acceptance, including via paid research. I did my best to filter the studies I used below to those with no such conflict of interest.
Here’s what I found.
Is aspartame carcinogenic?
You may have heard about the aspartame controversy of 2023.
It started when the World Health Organization put aspartame on its list of items considered possibly carcinogenic, i.e., possibly causing cancer. It turns out, though, that this list has a bunch of random items we’d probably consider benign: aloe vera, cell phones, ferns, pickled vegetables, and dry cleaning. A number of national health organizations, including the U.S. Food and Drug Administration, disagreed with the decision.
I see both sides. The WHO published a 697-page report on the research it looked at if you want to go as in-depth as I did, but there are a number of studies that do tie drinking diet sodas to higher rates of cancer.
Three smaller studies looked at liver cancer and aspartame in particular, and all three found a positive association. Some animal studies did as well. The best, most worrisome study, was a French study that asked more than 100,000 people to fill out randomly assigned 24-hour food intake diaries a few times a year between 2009 and 2021. Those who ingested aspartame were about 15% more likely to get all kinds of cancer compared to those who stuck with water.
However: There were larger studies, and more studies, that didn’t find a tie between aspartame and cancer generally. A study of 450,000 Europeans from 1992-2000 found no tie. A study of 117,000 American nurses found no tie. A study of 934,000 random American citizens from 1982-2016 found no tie.
And even that French study was agnostic on switching. It also looked at the cancer risk for those who drank regular soda — and found the same roughly 15% increase. Regular sugar is bad for you too.
So I understand why the WHO put aspartame on its list of possible carcinogens; it’s not that there’s nothing there. But it would be hard to argue from the evidence we have that drinking diet soda is more likely to lead to cancer than drinking regular, sugary soda.
It’s also worth noting that WHO didn’t edit its recommended acceptable daily intake as part of its decision. In fact, it reaffirmed its previous level. The WHO recommended people ingest no more than 40 milligrams per kilogram of their weight. To convert the units: a 150-pound person would need to consume more than 13 cans of Diet Coke per day in order to beat that marker.
So, you know, definitely don’t drink that much.
Weight loss, diabetes, and other considerations
There’s some evidence that switching from regular soda to diet soda can help lose weight in the short term.
A meta-analysis of 15 randomized controlled trials studying the use of diet sodas — all of which did their trials slightly differently — found an average weight loss of 1.7 pounds among people who switched to some sort of low-calorie sweetener. Another meta-analysis of 20 studies found about a 2.8-pound difference. A longer, 4-year study of more than 100,000 participants found a 1-pound decrease for those who replaced a serving of soda with a serving of artificially sweetened beverage.
In general, the evidence showed that participants who were already overweight or obese had a significantly larger chance of losing weight with diet soda than those who were in the normal range of BMI.
What about other factors? The WHO did a meta-analysis of 56 different studies. Among the findings:
• With regards to diabetes, slightly lower resting blood glucose levels (a good thing) when people began using diet soda when compared to sugary ones. No changes were detected in insulin levels, though.
• Lower blood pressure (by about five systolic points and three diastolic points).
• No significant changes in self-reported appetite or hunger levels. Calorie counts and sugar counts that people ended up consuming were lower among those who moved to diet beverages, as you’d expect.
• No effects on kidney disease, mood, behavior, headaches, or cognition.
That being said, all of these findings were classified by WHO with a “certainty of evidence” score between “very low” and “moderate.” There’s just a lot we don’t really know.
We do know that swapping sodas doesn’t appear to be a sticky solution. In observational studies and surveys, who consumed more diet beverages were reliably found to be more likely to be overweight or obese than their water drinking or their sugary-soda-guzzling counterparts. They were also found more likely to have diabetes, and even depression, as well. Why?
The prevailing theory on that is reverse causation. In this case: Generally, it’s unhealthy people who feel the need to switch to diet drinks. Since they can’t do enough to solve the underlying health problems, we see the negative correlation between diet drinks and health. Given that we don’t see these harms in smaller, more direct studies, that explanation makes the most sense — but we don’t know for sure.
So ...
What am I going to do?
For me, the investigation gave me relative peace of mind that diet soda isn’t going to hurt me when compared to regular soda — and indeed, it’s likely to be better in the short run in significant, but small, ways. But diet soda isn’t good for me, either. Yes, it’s a relatively low-willpower solution, but one with minor or non-existent results.
If I need a soda, diet soda’s probably the way to go ... but switching to diet soda doesn’t constitute a lasting health strategy.
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