Diet soda is supposed to be a healthier option than its sugary counterpart: You get the delicious taste without all the calories. But recently, health officials at the World Health Organization (WHO) sounded the alarm on some of these fizzy beverages — specifically their key ingredient aspartame, labeling the popular sugar substitute as “possibly carcinogenic to humans.”

Aspartame is an artificial sweetener used since the early 1980s. While it’s not actually a zero-calorie sweetener — containing 4 calories per gram like sugar — it is 200 times sweeter, meaning you don’t need as much of it to get that sugary taste. Along with sodas such as Diet Coke and Pepsi Zero Sugar, aspartame is found in ice cream, breakfast cereals, cough drops, chewable vitamins, and other products, sometimes under the names Nutrasweet, Equal, and Sugar Twin.

Does this mean you should stop buying your favorite sugar-free soda? Not exactly. In fact, the U.S. Food & Drug Administration (FDA) released a statement publicly disagreeing with the WHO decision. Here’s what you need to know.

What did the WHO say about the sugar sweetener aspartame?

Together with the International Agency for Research on Cancer (IARC), the World Health Organization labeled aspartame as “possibly carcinogenic to humans.” Exposure to car engine gas and lead fall under this IARC category as well. In the case for aspartame, they found limited medical evidence linking the sweetener to cancer, with a low degree of certainty.

According to the WHO, aspartame is safe to use if you consume 0 to 40 milligrams per kilogram of body weight of aspartame. A 150-pound person would need to drink more than 9 to 14 cans of Diet Coke per day to exceed the recommended limit. 

“Some people might read this and think, ‘Well, no problem, I don’t drink twelve cans of soda per day, so I’m fine.’ However, here lies the problem,” says Megan Lyons, a clinical nutritionist and founder of The Lyons’ Share Wellness. “Even if the smaller dose itself is unlikely to cause cancer, when combined with all the other carcinogens we encounter through pollution and toxic food, it contributes to an overall higher risk.”

How does aspartame affect the body?

This widely-used sweetener produces three toxic byproducts when absorbed into the gut. At high doses, the metabolites — methanol, phenylalanine, and aspartic acid — are thought to contribute to the onset of cancer by damaging liver cells, interfering with protein function and other chemical reactions in the body. 

The WHO’s review of aspartame being a possible cancer-causing agent comes from several studies linking the sugar substitute to an increased risk for several cancers. One 2014 study, for example, followed over 470,000 people who regularly drank soda containing aspartame as a main ingredient. After an 11-year follow-up, people who drank more than six soft drinks a week increased the risk for a type of liver cancer known as hepatocellular carcinoma. More recently, a 2022 study found aspartame in sugary beverages was a contributor to liver cancer in people with diabetes. A separate 2022 study linked artificially sweetened beverages, particularly those with aspartame as a main ingredient, with an elevated pancreatic cancer risk.

“The research that the WHO has referenced to make their decision is based on high aspartame consumption,” says Melanie Murphy Richter, a registered dietitian nutritionist and instructor of nutrition physiology at the University of California, Irvine. “If consumers are more aware about these potential issues, they can choose to decrease or moderate their aspartame consumption.”

Beyond cancer, some research suggests aspartame may possibly contribute to the development of heart disease, Alzheimer’s, and stroke.

Why sucralose is not a good sugar alternative to aspartame

One alternative to aspartame is switching to a no-calorie sugar substitute like sucralose (the ingredient found in Splenda). Sucralose is found in a range of products such as baked goods, ice cream, and puddings. However, some research suggests this sugar substitute may also increase health risks.

Sucralose is created by fusing a chlorine molecule with a sugar molecule to make it 450 to 650 times sweeter than regular sugar. Lyons says the merger stops sucralose from being metabolized like a regular sugar molecule. However, the drawback is that the added chlorine puts the product at risk of becoming potentially toxic, making the liver work harder to detoxify it.

Early research suggests that sucralose may have health risks associated with it. A 2017 animal study sounded the alarm of sucralose being potentially damaging to the gut. After drinking sugar water for 6 months, the authors studied the guts of mice and observed the ingested sucralose promoted inflammation that hurt the gut lining. It also seems to disrupt normal gut function. More recently, a May 2023 study using human gut tissue showed sucralose promoting internal inflammation and damaging the gut barrier, resulting in ‘leaky gut’ syndrome. A weakened gut lining heightens the risk of chemicals and other harmful byproducts usually flushed out through the digestive system passing through and entering the bloodstream. The same study also found evidence of sucralose breaking up DNA, which in theory could lead to mutations and possible cancer.

Richter points out that like aspartame, these problematic outcomes are seen when consuming large amounts of the sweetener. She recommends low or moderate consumption of sucralose. Lyons, on the other hand, does not recommend using Sucralose at all as an alternative. “My suspicion is that as more research emerges, Splenda might be implicated in negative health outcomes.”

Nutritionists worry about possible food anxiety over sugar substitutes

As with all health decisions, individuals need to make the choice that right for them — and the benefit of lower-calorie products may outweigh the risks for some people. There’s concern that people who may have been using artificial sweeteners to lower sugar intake may turn to foods with high added sugar content, says Richter. “We still live in a society where added sugar is used in so many processed foods,” she explains. “It is one of the main drivers and causes of the top chronic illnesses our population faces — diabetes, heart disease, cancer and obesity, to name a few.

In its statement disagreeing with the WHO decision, the FDA emphasized that there is no research with a conclusive link to cancer and since the WHO did not recommend any guideline changes, not much has changed.

In an ideal world, people would lower their sugar intake and eat sugary foods in moderation. That’s not a realistic option for many people, says Irazema Garcia, a functional nutritionist and personal chef from Southern California. Instead, the WHO news and growing health research is meant to inform people of being mindful of how much sugar they’re putting into their body each day.

Are there healthier sugar substitutes nutritionists recommend?

Both Richter and Garcia recommend monk fruit as an all-natural sweetener. The tiny round fruit native is native to China and is 100 to 250 times sweeter than aspartame with zero sugar. It also does not spike up blood sugar levels, a benefit to people with type 2 diabetes. “You can use monk fruit 1-1 to regular sugar in most recipes,” explains Richter. 

If you’re looking for a more nutrient dense sugar substitute, other options include coconut sugar, Medjool dates, Manuka honey, or Grade A maple syrup. Richter says a lot of these sugars also contain vitamins, minerals, and fiber. While they do increase your blood sugar levels, Garcia says it is a very minimal bump up. However, since they have calories, you still need to be careful with portion servings. Garcia says the “key is using any type of sweetener sparingly.”

Before you go, check out these inspiring quotes to reshape your mindset on food.