What to Know About Aspartame

Medically Reviewed by Jabeen Begum, MD on February 23, 2024
Written by WebMD Editorial Contributors
7 min read

Aspartame is a low-calorie sweetener, a substance that tastes sweet but doesn't contain natural sugars and is much lower in calories than sugar. This is because it's 200 times sweeter than sugar, so the amount of it you need to use is very small.

Aspartame is artificial, meaning it doesn't exist in nature. It's made of two naturally occurring amino acids: aspartic acid and phenylalanine. These can be found in food and your own body. But the phenylaniline in aspartame has been changed slightly to make it sweeter.

Since it was developed in 1965, aspartame has been widely tested by both government-funded and independent laboratories. But its safety is still being questioned, even though you can find it right now in thousands of food items around the world.

Aspartame is sold under brand names such as NutraSweet and Equal and is used to sweeten many low-calorie, zero-calorie, and diet products.

Common products that use aspartame include:

  • Diet soda
  • Juice and iced tea
  • Chewing gum
  • Breath mints
  • Powdered drink mixes
  • Flavored sparkling water beverages
  • Light yogurt
  • Low-sugar gelatin desserts

Aspartame’s use as an aid for weight loss is highly debated. The initial belief, supported by common sense and early marketing, was that a product that made things sweet like sugar but contained fewer calories would help you lose weight while still enjoying sweet foods and drinks. ‌

Over the decades, research has been divided. Some studies found that switching to aspartame from sugar led to successful weight loss in some people, but others did not lose any weight. And, some people even gained weight.‌

Some studies show that aspartame can slow down your metabolism. Your metabolism is how your body makes energy from the food you eat. A slower metabolism is directly related to weight gain. So, even if aspartame helps you eat fewer calories, you might still gain weight because your metabolism has slowed. But other studies didn't find this to be true.‌

In 2020, a study by Yale researchers found that consuming a low-calorie sweetener was not, by itself, responsible for slowing metabolism. But when it was combined with carbohydrates or fats, it did cause people's metabolism to slow. So, for example, if you drank a diet soda with aspartame, it might not have any effect on you. But if you drank that diet soda as you ate French fries, it could have negative effects on your metabolism. 

The results of this study were just early findings, and more research has to be done before scientists can truly understand how this works.

Research hasn't yet confirmed if aspartame is a good sugar substitute if you have type 2 diabetes. Aspartame islow-glycemic, meaning it doesn't spike your blood sugar levels like real sugar does. So, it would seem to be a safe alternative when you're craving something sweet.

But some studies have found that when you eat or drink products containing aspartame, it increases levels of a hormone called cortisol in your blood. This changes the activity of the microbes responsible for the breakdown of food in your digestive tract. One theory is that these changes may lead to weight gain and insulin resistance, both of which would have a bad effect on blood sugar control in those with type 2 diabetes. Using a lot of aspartame could make these effects worse.

Although it is considered safe in small amounts, aspartame does have a few possible risks and side effects to consider. If you eat a lot of aspartame, you have a greater chance of the following:

Addiction: Some scientists believe that sugar and noncaloric sweeteners such as aspartame can become somewhat addictive. Aspartame and sugar cause your brain to produce feel-good hormones, such as dopamine, which can make you want more of it. This doesn’t mean you’re physically addicted to aspartame, like drugs or alcohol, but it can lead you to crave it and consume more than is good for you.

Skin problems: If you eat or drink very large amounts of aspartame, it could cause contact dermatitis, an allergic reaction that results in an itchy rash.

Early menstruation: Young girls who regularly drink beverages sweetened with aspartame have a higher chance of starting menstruation before age 11.

Damage to kidney and liver: Studies suggest that if you regularly eat or drink a lot of aspartame over a long period, it could harm your kidneys. Scientists also think aspartame can cause toxic liver disease.

Mood swings: Aspartame can cause changes to your mood. In one study, people felt more irritable when following a diet high in aspartame compared to when they weren’t eating or drinking as much aspartame. Research has also linked aspartame to depression.

Aspartame and cancer

Scientific evidence suggests that aspartame may be associated with cancer, but that doesn’t mean it causes cancer.

For example, one large study found that people who ate or drank more aspartame than average were 15% more likely to get cancer. This doesn’t prove that it was the aspartame that made their risk go up, though. It's possible that the people who were more likely to eat and drink aspartame had other behaviors in common that increased their cancer risk, such as bad diet, smoking, or high stress.

The World Health Organization’s International Agency for Research on Cancer (IARC) puts aspartame in Group 2B for its cancer hazard classification, or “possibly carcinogenic to humans.” This is based on limited evidence that aspartame causes a type of liver cancer in humans. They also found limited evidence that it causes cancer in experimental animals and limited evidence of possible ways it causes cancer.

The FDA disagrees with the IARC’s classification of aspartame as possibly carcinogenic because of the low amount of evidence in the studies that the IARC used to make its decision.

Both the FDA and IARC agree that aspartame is safe to eat or drink in certain amounts, and those amounts aren’t small. A person who weighs 150 pounds can drink nine cans of diet soda a day and be considered safe.

Who should avoid using aspartame?

If you have an illness called phenylketonuria, you should avoid aspartame. Phenylketonuria causes phenylamine to build up in your body and can lead to serious health problems. Since aspartame is made from phenylalanine, it can be too much for your body to process. Also, if you are pregnant and have high levels of phenylalanine in your blood, you should avoid it.

Avoid aspartame if you have tardive dyskinesia, a side effect of some medications. The phenylalanine in aspartame can worsen its symptoms, such as involuntary muscle movements.

Aspartame isn’t the only low-calorie sugar alternative. There are many natural and artificial sweeteners you can try if you are concerned about aspartame:

Monk fruit extract: This is a natural sweetener that has no calories. It’s made from the sweetest part of the monk fruit, a small fruit native to southern China. According to the FDA, it is “generally recognized as safe,” with no reported side effects.

Allulose: This sugar is found naturally in certain foods such as figs, raisins, and maple syrup. Scientists have started creating it from fructose, so you can now buy it packaged as a sugar substitute. It has received the “generally recognized as safe” status from the FDA. It has a lot of pros: it tastes very similar to sugar, has almost no calories, does not affect your insulin, and does not cause tooth decay. The downsides are that it can be expensive and is not widely available.

Sucralose: This artificial sweetener is sold under the brand Splenda. It is 600 times sweeter than sugar and has zero calories. Considered safe by the FDA, it is found in many food products.

Stevia: This is a sweetener made from the leaves of a plant native to South America. It has zero calories and is “generally recognized as safe” by the FDA.

Sugar alcohols: This type of sweetener includes sorbitol, xylitol, lactitol, mannitol, erythritol, and maltitol. They have slightly fewer calories than sugar and do not cause tooth decay or a sudden blood sugar increase. Some people find that sugar alcohols can cause gastrointestinal problems such as gas and bloating.

You can enjoy aspartame in moderation as long as you don’t have certain health conditions. Aspartame has been studied for many years and is considered safe to eat in normal amounts. But if you feel uncertain about how it will affect you, there are many other low-calorie sweeteners you can try. There's still not enough evidence to confirm that aspartame can help you lose weight or control your blood sugar if you have type 2 diabetes.

Is aspartame harmful to the body?

The FDA considers aspartame safe to eat or drink within recommended amounts.

What artificial sweeteners should you avoid?

Cyclamates and their salts (such as calcium cyclamate, sodium cyclamate, magnesium cyclamate, and potassium cyclamate) are not allowed in the U.S. and should be avoided. Whole-leaf and crude stevia extracts (different from processed stevia that is considered safe) are also not allowed to be used as sweeteners in the U.S.

What is the safest artificial sweetener?

There are six artificial sweeteners that the FDA says are safe for most people: aspartame, acesulfame potassium (Ace-K), sucralose, neotame, advantame, and saccharin.

Is aspartame banned in Europe?

No, aspartame is not banned in Europe. Aspartame is authorized to be used as a food and drink sweetener in Europe just like it is in the U.S.