Does Aspartame Cause Anxiety? Only if You’re a Mouse

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Hello, it’s me, Rebecca Watson, science YouTube’s resident Diet Soft Drink Defender, logging on once again to address the rumors that the “Artificial sweetener aspartame linked to anxiety.” If you’re new here, let me address a few points before we dive in: first of all I have some important conflicts of interest. On the one hand, I think Coca-Cola is an evil corporation that is helping destroy the planet and I fully believe that if they could legally get away with marketing a more addictive substance that caused people to bleed from the anus they would absolutely do it. As I mentioned in a video last year, they’re the largest producer of plastic pollution who refuse to invest in sustainable packaging and instead spend their money lobbying politicians and supporting feel-good initiatives that do nothing to actually address the problem.

On the other hand, Coke Zero is delicious and I drink it every day.

Second of all, if you’re new here, please note that every video I make has a helpful link in the description that will take you to a full transcript available to view for free on Patreon, which has links to everything I discuss so you can learn more.

Okay, let’s get into it! These headlines about a “link” between aspartame (a very common artificial sweetener) and anxiety are all based on this study: “Transgenerational transmission of aspartame-induced anxiety and changes in glutamate-GABA signaling and gene expression in the amygdala,” published earlier this month in my favorite science journal, PNAS.

Some of the better headlines about this study manage to sneak in maybe the most important detail, which is that this study was done on mice. Not humans. Different animals can be good models for how people work, but they’re never perfect, so it’s worth noting.

The other important thing to note is that there have already been studies on aspartame IN HUMANS, and they have found no link between aspartame and anxiety IN HUMANS. As the FDA points out, “Aspartame is one of the most exhaustively studied substances in the human food supply, with more than 100 studies supporting its safety.” For instance, in 2015 a group of doctors, psychologists, and food safety specialists published a double-blinded randomized controlled trial of about 50 people who claimed to be sensitive to aspartame:

“Using a comprehensive battery of psychological tests, biochemistry and state of the art metabonomics there was no evidence of any acute adverse responses to aspartame. This independent study gives reassurance to both regulatory bodies and the public that acute ingestion of aspartame does not have any detectable psychological or metabolic effects in humans.”

That’s just one of literally hundreds of studies done over more than 50 years (before and after aspartame was approved by the FDA in 1981) showing absolutely zero negative effects in humans.

Despite that, the general public and a subset of researchers remain keen to find something, anything to be scared of in aspartame and other artificial sweeteners. That’s not to say I don’t think these studies should be done – I think this one did have an interesting result, which I will get to. But I also think that studies like this should have absolutely no impact on the behavior of the general public. Aspartame is safe for humans and you should not worry about it after this study.

So! In this most recent study, researchers at Florida State University College of Medicine gave mice the equivalent of what they point out is “below 15% of the FDA recommended maximum daily intake for humans.” That makes it sound like a really small amount but it’s actually not: because aspartame has been found to be so god damn safe, the FDA says you can consume absolute shit tons of it every day. “Below 15% of the FDA’s recommended daily intake” is actually about 64 ounces of Diet Coke per day, or about a 2-liter bottle. Are there people out there drinking that much? Absolutely! But it’s not exactly normal. Still, it’s absolutely worth studying that amount.

Mice who were given that amount of aspartame in water were more likely to show symptoms of anxiety. How do you tell when a mouse has anxiety? Well, you toss him into a field and see how much time he spends in the exposed center versus how much time he spends around the darker, less exposed border. Anxious mice, just like anxious people, are more likely to hide in the dark avoiding others and playing video games. Well, they didn’t test that last bit but I bet if you gave them the option they would. Future research opportunity? Perhaps!

And sure enough, mice that got the aspartame were more likely to show anxiety compared to mice who just got plain water. Here’s where the interesting result comes in: the researchers also found that the CHILDREN of those anxious mice were also more likely to be anxious despite not getting any aspartame, for up to two generations. This is due to something called “epigenetics,” which is the study of how our behavior and environment can change the way our bodies deploy the code that is our DNA. Smoking cigarettes, for instance, seems to “turn off” a certain gene. When you stop smoking, after some time that gene can click back on. And a lot of recent epigenetic research is finding that those changes can be passed down from parents to children.

In fact, this same Florida State University lab previously found that giving mice nicotine resulted in changes to the mouse sperm that affected behavior in future generations, which inspired this new aspartame study.

So THAT is the takeaway here: confirmation that what we eat and drink and do can be passed on to future generations.

Note that I’m not saying aspartame doesn’t have some effect on human anxiety. What I AM saying is that IF there is an effect, it’s far too small to actually show up in any human trials. And I’ll conclude the way I conclude every video about the supposed negative effects of aspartame, which is to compare it to the thing it is meant to replace: sugar. And unlike aspartame, researchers HAVE been able to detect a relationship between sugar and anxiety, as in this study published last year that looked at a cohort of more than 20,000 people and found “modest age-specific associations between anxiety status and sugar intake among adults.” Basically, they found that people under the age of 45 who had high anxiety were more likely to consume large amounts of processed sugar. There are also case studies of patients who reduced their anxiety by cutting out processed sugar, like this one in which a 15-year old changed her mostly-refined-sugar diet, which “resulted in a substantial decrease in anxiety symptoms…A brief return to her previous diet caused a return of her anxiety symptoms, followed by improvement when she restarted the prescribed diet.”

Smoking gun? Nope! But it’s way more evidence than we have for any supposed link between aspartame and anxiety. And don’t even get me started on the other chemical that we usually consume along with aspartame, which is caffeine, a substance that has an undeniable negative effect on anxiety and nervousness to the point that it has its own DSM–5 classification.

So if you do have bad anxiety and want to change your diet to help with it, you should probably start by reducing your intake of caffeine and sugar. Once that’s done, maybe consider dropping your 6-pack of Diet Coke-a-day habit because sure, it’s probably not doing you any favors anyway and then you’re giving less money to an evil corporation, which honestly probably would help my anxiety.

Rebecca Watson

Rebecca is a writer, speaker, YouTube personality, and unrepentant science nerd. In addition to founding and continuing to run Skepchick, she hosts Quiz-o-Tron, a monthly science-themed quiz show and podcast that pits comedians against nerds. There is an asteroid named in her honor. Twitter @rebeccawatson Mastodon Instagram @actuallyrebeccawatson TikTok @actuallyrebeccawatson YouTube @rebeccawatson BlueSky

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