Is Aspartame Bad For You? An Evidence-Based Guide

Reading media headlines about aspartame can be very confusing.

One month the sweetener is perfectly safe, the next it is linked to some scary health condition or another.

However, what does recent research on this artificial sweetener show?

This article will stick to the facts and summarize the current science in plain English.

What Is Aspartame?

Aspartame is one of many available sweeteners on the market.

This sweetener is mainly used for giving low-calorie, sugar-free foods and drinks a sweet taste.

Aspartame was approved for use in food back in 1981 by the Food and Drug Administration (FDA), and it has been a controversial food additive since that time (1, 2).

As an artificial sweetener, aspartame is of synthetic origin, meaning that it was made in a laboratory.

While many people are suspicious about foods or additives of synthetic origin, a synthetic origin does not automatically mean something is unhealthy.

How Is It Made?

Aspartame is the result of chemically combining two amino acids; aspartic acid and L-phenylalanine.

Producing these two amino acids requires the use of two types of bacteria; Brevibacterium flavum and Corynebacterium glutamicum. These bacteria are added to a tank containing all the things they need to grow, such as sugars and sources of carbon and nitrogen.

Once a large enough amount of bacteria is present, they are moved to a fermentation tank where they ferment/produce the amino acids aspartic acid and phenylalanine.

At this point, producers use a centrifuge to separate the amino acids from the bacteria.

Following this, the amino acids undergo a crystallization and drying process. Next, phenylalanine is mixed with methanol to produce the compound L-phenylalanine methyl ester.

After aspartic acid undergoes a modification of its own, the two amino acids are then left to mix in a reactor tank. During this process, the amino acids are heated, cooled, filtered, and dried.

Finally, the resulting compound is mixed with acetic acid to convert it into aspartame. The full (and more detailed) production process of aspartame is available here.

What Is the Acceptable Daily Intake For Aspartame?

The ‘acceptable daily intake’ (ADI) is an estimate of the safe amount of a substance for daily consumption over a lifetime.

In other words, if consumers stay under the ADI for aspartame, there should theoretically be no risk of harm (according to those who set the ADI).

According to the FDA, aspartame has an ‘acceptable daily intake’ (ADI) of 50mg per kilogram of body weight.

Elsewhere, the ADI is slightly stricter, and the World Health Organization (WHO) and European Food Safety Authority (EFSA) advise a maximum of 40mg per kilogram of body weight for aspartame (3, 4).

Using the EFSA’s lower 40 mg ADI, this infers that an individual weighing 60 kilograms could safely consume 2,400 mg of aspartame daily.

For the record, one standard can of diet coke contains about 125 mg of aspartame (5).

Is Aspartame Safe Or Is It Bad For You?

Many people—including the FDA—believe that aspartame is safe.

On the other hand, there are also individuals who believe aspartame may have adverse effects on health. For instance, some influential Internet voices claim that aspartame is a “toxic” and dangerous substance.

There are also thousands of articles on the dangers of aspartame on the Internet.

However, many of these sources mostly pick negative (primarily animal) studies to suit the narrative of the story rather than fairly looking at both sides.

This seems to be a common theme with all artificial sweeteners rather than aspartame alone, and sweeteners like sucralose are also hotly debated.

Why Do Some People Think Aspartame Has Dangers?

Common concerns people have about aspartame relate to the compounds it breaks down into within the body.

These breakdown constituents include;

• Aspartic acid
• Phenylalanine
• Methanol (which further breaks down into formaldehyde)

A common claim from those who are suspicious about aspartame is that high levels of aspartic acid may be capable of having a neurotoxic effect. Additionally, methanol is a toxin and formaldehyde is a known carcinogen, which also gets a lot of attention (6).

However, it is worth noting that the amounts of methanol present upon digestion of aspartame are minimal.

Furthermore, consuming aspartame does not raise methanol or formaldehyde concentrations above normal blood values (7).

Systematic Reviews and Randomized Clinical Trials On Aspartame

Here are some of the more recent and in-depth studies on aspartame.

Toews, I., Lohner, S., Kullenberg de Gaudry, D., Sommer, H., Meerpohl, J. (2019).

This was a systematic review of 56 studies, and some of the findings of the analysis were;

• There was no association between high consumption of aspartame and lymphoid cancers.

• Aspartame users appeared to have no significant differences in blood pressure compared to non-users.

• Children receiving aspartame had a similar or lower weight gain to children receiving sugar/placebos.

• There appeared to be no association between aspartame and brain cancer risk.

• One randomized trial found that aspartame increased total cholesterol levels and, rather interestingly, another controlled trial showed that preschool children receiving aspartame had larger blood glucose increases than those receiving sugar.

• Overall, this systematic review found no health benefits to aspartame intake, but it also couldn’t rule out potential negative effects.

Spencer, M., Gupta, A., Van Dam, L., Shannon, C., Menees, S., Chey, WD. (2016).

This systematic review on artificial sweeteners included four papers that focused on aspartame and its potential gastrointestinal effects. 

These studies showed that;

• In an animal study, adding aspartame to the drinking water of mice significantly impaired glucose tolerance. However, the doses used are unclear.

• In a controlled trial, rats were given 250 mg/kg of aspartame (5x the FDA’s ADI for humans). This dose had no negative effect on gastric secretion or gastrointestinal function.

• Giving rats mega-doses of aspartame (1000 mg/kg +) did not cause DNA damage.

• The authors concluded that the existing animal studies in this area are conflicting and that further research on human participants is necessary.

Santos, NC., de Arauio, LM., De Luca Canto, G., Guerra, ENS., Coelho, MS., Borin, MF. (2018).

This was a systematic review of 29 randomized clinical trials (human participants). 

The analysis demonstrated that;

• Aspartame intake did not affect cholesterol or triglyceride levels.

• There were no significant differences in body weight changes between participants using sugar-sweetened and aspartame-sweetened products.

• Blood glucose and insulin levels showed no changes between aspartame and control groups.

• Aspartame intake did not affect overall daily energy intake.

• Overall, this meta-analysis demonstrated neither benefits nor drawbacks of aspartame use.

Haighton, L., Roberts, A., Walters, B., Lynch, B. (2018).

This was a systematic review of 10 studies that provided complete histopathology (disease-related changes to body tissues).

The purpose was to analyze the potential carcinogenic effects of aspartame from animal feeding studies.

Here are the findings;

• Aspartame did not appear to cause brain tumors, and there was no statistically significant difference between aspartame-fed groups and control groups.

• Animals receiving high doses of aspartame had a lower growth rate than a control group. However, this effect was only seen in aspartame doses higher than 4000 mg/kg of body weight (a can of diet coke contains 125 mg).

• In lifetime animal studies, the survival rate of rats was “significantly reduced” (423 days) in animals fed this high dose (4000 mg/kg +) of aspartame. However, there was no difference between control groups and all other aspartame-fed groups for longevity (663 days).

• There were no indications that aspartame was associated with promoting bladder cancer, leukemia, or lymphoma.

• There were positive associations between aspartame and breast, kidney and ureteral cancers, as well as malignant Schwannomas. However, these were only in groups fed very high doses of the sweetener.

• Overall, the researchers concluded that the sum of the evidence suggests that aspartame in food and drinks does not have carcinogenic potential.

Mishra, A., Ahmed, K., Froghi, S., Dasgupta, P. (2015).

This systematic review examined studies looking at links between artificial sweeteners, including aspartame, and cancer.

The findings of this review related to aspartame included;

• In a prospective cohort study, results found an elevated risk of non-Hodgkin lymphoma in men as aspartame intake increased. However, this trend was not seen in female participants.

• A case-control study showed that individuals with brain cancer did not have increased consumption of aspartame compared to healthy individuals.

• The review concludes that there are indications that prolonged, high-dose artificial sweetener use could potentially increase the risk of specific cancers. However, the researchers state that there is nothing to conclusively support the idea that aspartame has carcinogenic properties.

Bernardo, WM., Sioes, RS., Buzzini, RF., Nunes, VM., Glina, FPA. (2016).

This systematic review focused on various potential adverse effects of artificial sweeteners.

The specific findings on aspartame are listed below;

• A population study of 473,984 people with 5-year follow up found that high daily doses of aspartame (600 mg >) had no association with brain or hematopoietic cancers.

• In a prospective cohort study, researchers found a higher relative risk (RR: 1.42) for leukemia from consuming more than one diet soda per day.

• The data from numerous neurotoxicity studies “do not support the hypothesis that aspartame in the human diet will affect nervous system function, learning, and behavior”.

• The systematic review found no association between aspartame consumption and cancers of the digestive and reproductive systems.

• There appeared to be no association between aspartame intake during pregnancy and childhood or later adulthood brain tumors.

Higgins, KA., Considine, RV., Mattes, RD. (2018).

This study was a randomized controlled trial featuring one hundred adults aged 18-60 years old. 

• Participants consumed either 0, 350, or 1050 mg of aspartame per day for 12 weeks.

• Results showed that there were no differences between the three groups for glucose and insulin levels.

• There were no changes in appetite or body weight between the groups.

Bernardo, WM., Sioes, RS., Buzzini, RF., Nunes, VM., Glina, FPA. (2016).

This double-blind, randomized clinical study compared the effect of aspartame on forty-eight self-reported ‘aspartame sensitive’ individuals compared to forty-eight age and gender-matched non-sensitive individuals.

• Participants were blindly given either a chocolate bar containing aspartame or a control bar. Prior taste tests showed that people could not tell which bars contained aspartame.

• After consuming the bars, blood samples were taken.

• There were no significant changes in health markers (glucose, insulin, lipids) in either group both before and after eating the bars.

• In the aspartame-sensitive group, individuals reported the same ‘sensitivity symptoms’ (such as perceived stress and headaches) whether they had consumed the aspartame or control bar.

Lindseth, GN., Coolahan, SE., Petros, TV., Lindseth, PD. (2014).

In this study, twenty-eight healthy adults were fed either a high-aspartame diet of 25 mg/kg body weight or a low-aspartame diet of 10 mg/kg for eight days.

For an individual weighing 70 kg, the high-aspartame diet would be equivalent to 1750 mg of aspartame (14 cans of diet coke) per day.

For the low-aspartame diet, it would be 700 mg aspartame (5-6 cans).

• Seven (25%) of the individuals experienced “clinically significant” neurobehavioral effects on the high-aspartame diet.

• Headaches were rare across both study groups (reported by one participant one time).

• Participants were “significantly more depressed” on the high-aspartame diet, with several indicating mild to moderate clinical depression.

• The researchers noted that their study was relatively small in size (28 individuals) and that the existing evidence is conflicting. As a result, more research in this area is necessary.

Is Aspartame a Safe Sweetener?

Based on the systematic reviews and clinical trials listed in this article, here is a summary of the findings;

• There is no conclusive proof from human trials that aspartame can have harmful carcinogenic effects.

• Epidemiological study results are inconsistent and show conflicting results.

• While some controlled animal studies show that aspartame may increase cancer risk, most of these trials are using mega-doses of aspartame well above the maximum ‘adequate daily intake’ for humans.

• Some (small) studies on human participants show potential neurobehavioral issues. For example, links with headache and depression in some individuals. However, once again, these effects only seem to be visible at very high intake levels.

• Looking at human trials, there does not appear to be any evidence that aspartame has adverse effects on blood glucose, insulin levels or other health markers.

Summary

Overall, the majority of the evidence for harm from aspartame comes from animal studies using extremely high doses of the sweetener.

Additionally, the general consensus from systematic reviews is that there is no evidence of aspartame’s carcinogenicity in humans.

However, some individual studies do find associations between specific health conditions and aspartame, but the evidence for this is conflicting, and an association does not automatically imply causation.

At this point, the totality of the evidence from large review studies suggests that aspartame is safe at human consumption levels, and there is no strong evidence to suggest otherwise.

That said, I think it is difficult to categorically state that aspartame is 100% safe, and the fact human trials are ongoing probably demonstrates that more research is deemed necessary.

Other Considerations

Here are some extra considerations about aspartame and the use of artificial sweeteners.

Phenylketonuria

PKU is a genetic and inherited condition that results in the inability of an individual—from birth—to break down the amino acid phenylalanine. As a result, phenylalanine can build up inside the body to potentially harmful levels (8).

Since phenylalanine is one of the compounds that aspartame breaks down into, aspartame intake should be avoided (9).

Artificial Sweeteners vs. Sugar Alcohols

For anyone who wishes to avoid artificial sweeteners like aspartame, it could be worth looking into a class of sweeteners called sugar alcohols.

While there are potential gastrointestinal distress issues at higher doses, sweeteners like erythritol have consistently shown no evidence for carcinogenicity in human or animal studies.

Further Resources

For more information on aspartame, here are some useful resources;

• Scientific opinion on the re-evaluation of aspartame as a food additive (European Food Safety Authority)

• The History of Aspartame (Harvard Library)