Here’s a scenario:

Me: (holding a diet coke, an aspartame containing beverage) Hey, how’s it going?


Me: Actually, that’s a pretty common misconception. The data suggests it’s quite safe.



If this has ever happened to you, don’t worry. You’re not alone. There are a ton of misconceptions out there about aspartame. Let me just name a few:

  1. Aspartame gives you cancer
  2. It causes weight gain
  3. It creates an insulin response, which is bad
  4. When aspartame breaks down, it creates carcinogenic (cancer causing) compounds

The purpose of this blog is to take a look at the current body of evidence and clear the air about a few of these misconceptions and hopefully give you some peace of mind.

What is aspartame?

Aspartame is an artificial sweetener that’s used in many foods and beverages such as Diet Coke and other popular zero calorie beverages. It was discovered by accident in 1965 by a chemist named James Schlatter. While working on an anti ulcer drug, Mr. Schlatter unknowingly contaminated his finger with a white substance. Later on, while James was reading, he licked his finger to flip the page and that’s when he noticed this white substance had a very sweet taste. And that was the birth of what we now know as aspartame.

Not many people know this, but aspartame actually isn’t calorie free. It contains 4 calories per gram just like sugar. The caveat is that since aspartame is about 200 times sweeter than sugar, the amount you need to sweeten a food makes it virtually calorie-free. When it comes to safety, the FDA has set the acceptable daily intake for aspartame at 50 mg/kg per day (1). That’s roughly 21 cans a day for a 175 lb person. Now that we have the basics out of the way, let’s start taking a look at some of the most popular misconceptions that are floating around the internet.

“Aspartame gives you cancer!”

This misconception all starts with a study that came out in 2005 that found higher cases of lymphomas and leukemia in rats fed very high doses of aspartame (2). So naturally, the media blew this one way out of proportion and everyone had this reaction:

However, upon looking at the study a few things stood out that made the cause for alarm seem a bit blown out of proportion. First thing, the rats were fed an ridiculously high amount of aspartame. It ranged from 4 mg/kg all the way up to 5000 mg/kg of body-weight. That’s the equivalent of giving the rats up to 10 cans of Diet Coke per day. While that may still not seem like a lot, let’s take a look at what that translates to for humans. Let’s take someone who weighs about 175 lbs. The dose in the study would be equivalent to about 2100+ cans of Diet Coke a day. Yes, I have seen people with some absurd Diet Coke habits but not 2100+ cans a day.

Also, while humans and rodents share some similarities, the mechanisms our body uses to process aspartame is different than rats so that kind of negates the relevance of this study for us.

Take that for data!

To further drive home the point that aspartame is actually quite safe, let’s take a look at the summary of a review from 2002 that was published in the peer reviewed journal titled Regulatory Toxicology and Pharmacology (3). In the review titled Aspartame: Review of Safety, the authors concluded that:

More than 30 years have elapsed since the foundations of today’s aspartame safety database were laid. Since that time the portfolio of studies assessing the safety of aspartame has continued to grow. A search of the scientific literature on the U.S. National Library of Medicine’s MEDLINE reveals almost 700 citations for aspartame with a number of these relevant to aspartame safety. The extensive body of research undertaken on aspartame clearly and overwhelmingly demonstrates its safety for its intended use. The aspartame safety data have been evaluated and found satisfactory by regulatory scientists in all major regulatory agencies and expert committees, including the U.S. Food and Drug Administration (FDA), the EU Scientific Committee for Food (SCF), and the Joint FAO/WHO Expert Committee on Food Additives (JECFA). 

Further, aspartame has been approved for human consumption by regulatory agencies in more than 100 countries and received wide consumer acceptance with consumption by hundreds of millions of people over the past 20 years, representing billions of man-years of safe exposure.”

That last part is pretty important. If aspartame was as dangerous as people make it out to be, there would have already been a ton of documented cases of death traced back to aspartame. That’s just not the case.

“I heard aspartame leads to weight gain!”

As the great Ron Burgandy would say:

I mean, how does something that is essentially calorie free cause weight gain? It just physiologically makes zero sense. Nonetheless, let’s take a look at what the data says.

A study done in 2002 investigated 41 overweight men and women who were split into two groups (4). The first group consumed a sucrose (sugar) supplement, while the other group consumed an aspartame supplement. The study found that the group consuming the sucrose supplement saw increases in energy intake, body weight, fat mass, and blood pressure while the same results were not found in the aspartame consuming group. Wait, so the group who consumed something with calories gained weight compared to the group who didn’t? Shocking right?

Let’s take a look at another study. A six month randomized control trial in which participants substituted caloric beverages with non caloric beverages found that the participants who made the switch resulted in weight loss of about 2-2.5% (5).

Another systematic review that looked at low energy sweeteners (aspartame, sucralose, etc.) and it’s relationship with energy intake and weight gain found similar results as the above study(6).

“Overall, the balance of evidence indicates that use of LES in place of sugar, in children and adults, leads to reduced EI and BW, and possibly also when compared with water.”

“I heard aspartame spikes insulin! Insulin makes us fat!”

There are a couple things wrong with the above statement but let’s just talk about the first part (I’ve covered the second part here). There is zero evidence that aspartame causes an insulin response. Let me clarify that. There is zero evidence that aspartame causes an insulin response in humans. Yes, there is a study that found that aspartame coupled with glucose created an insulin response in rats but we already covered why that’s pretty irrelevant to us (7).

“I heard aspartame breaks down into carcinogenic compounds!”

While there is some truth to this, it’s blown way out of proportion. When you consume aspartame, it’s broken down into three parts. Those parts are aspartic acid, phenylalanine, and methanol. The last one is where most of the concerns originate. Yes, methanol is converted into formaldehyde which is a known carcinogen but this is a case where the dose makes the poison. The amount of methanol found in aspartame is safe. Plus, other foods that are deemed as healthy, such as fruits and vegetables, also contain methanol but you don’t hear anyone freaking out about those.

 Summing it all up

As you can see, a lot of the popular misconceptions about aspartame are just simply not supported by the current body of evidence. Now, don’t get me wrong. There are still a few concerns that the jury is still out on. Here are a few:

  1. Some people report aspartame increases sugar cravings. If you feel that’s the case I would suggest either reducing or eliminating your intake. Same goes for those who report headaches when consuming aspartame.
  2. There is some research supporting aspartame having a negative effect on your gut microbiome in regards to glucose intolerance(8). This is something that I am paying a great deal of attention to so I will write about my findings once more data comes out.
  3. Regularly consuming sweet beverages or foods may lead to a change in your taste palate so again if you feel that is you, reduce or eliminate your intake.

All in all, a diet soda here or there will not cause immediate death like some people make it seem but I urge people to be mindful of their intake. I wouldn’t recommend that most of your fluid intake come from diet sodas. I would much rather prefer everyone just stick to water but don’t be afraid to crack open a Diet Coke in case you are craving something sweet.

Want more information about nutrition counseling and our Fuel program? Contact one of our registered dietitian nutritionists today!

Written by: Jesus Hernandez RDN, LD

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