Food and diet

Research casts doubt on aspartame sensitivity

"Sweetener linked to cancer is safe to use," reports the Mail Online.

Aspartame – a commonly used artificial sweetener – has been dogged by controversy, despite being deemed safe by food regulators in the UK, EU and US.

Some believe they are sensitive to the sweetener. Anecdotal reports suggest it can cause headaches and stomach upsets.

This study recruited 48 "aspartame-sensitive" individuals and tested whether giving them a cereal bar with or without aspartame would elicit the suspect symptoms. The study was a gold-standard double blind randomised controlled trial (RCT), meaning neither the participants nor those analysing the results knew which bar they had eaten. This made it a fairer and more rigorous test.

It showed that there was no difference in the symptoms reported after eating the aspartame-laced bar compared with the normal bar.

This provides evidence that aspartame fears may not be warranted in some people who believe they are sensitive to the ingredient. However, the study may have failed to recruit those most fearful of the sweetener, so we can’t rule out aspartame-related symptoms in this group.

This study also can’t tell us whether regular aspartame consumption may have any health effects in the longer term.

To find out more, read "The truth about aspartame".

Where did the story come from?

The study was carried out by researchers from the University of Hull, the Food Standards Agency (FSA), Imperial College London, University College Dublin, Institute of Food Research (UK) and Weill Cornell Medical College, Qatar.

It was funded by the Food Standards Agency.

The study was published open-access in the peer-reviewed medical journal PLOS One. This means it is free to view and download this aspartame research.

The Mail Online reported the story accurately. However, in stating that aspartame does not cause harm, it would be better to make clear that this study has only looked at short-term effects. This study also had nothing to do with verifying aspartame’s safety in regards to cancer, despite what the headlines may lead you to believe.

What kind of research was this?

This was a double-blind randomised control crossover study looking at whether aspartame causes any harmful symptoms in people who report sensitivity to it.

Aspartame is a commonly used artificial sweetener that is around 200 times sweeter than normal sugar. Since its introduction in the 1980s, there have been concerns over whether aspartame is safe. There are many anecdotal reports of it causing stomach upsets, headaches and other problems. However, this concern doesn’t match the evidence.

Aspartame has been approved as a safe food ingredient after assessment of the evidence by regulators in the UK, EU and US, all of which have independently assessed the best available evidence. Despite the regulatory assurance, some people report they are sensitive to aspartame and are convinced that it causes them problems. The current study wanted to investigate this "aspartame-sensitive" group, to see if the claims were true.

A double blind RCT like this is the gold standard of single study research. It is one of the best ways to investigate whether aspartame is affecting people who report being sensitive to it. Neither the study participants nor those analysing the results knew whether they were consuming aspartame. This helps to eliminate bias caused by pre-conceived ideas of whether it is harmful or not. The only thing more convincing in the evidence stakes than an RCT like this is a meta-analysis of many of them.

What did the research involve?

Researchers gave 48 UK adults who said they were sensitive to aspartame two cereal bars, at least one week apart. One of the bars was laced with 100mg aspartame. This is equivalent, the researchers say, to the amount found in a can of diet fizzy drink. The other was a normal cereal bar. After eating each bar, standard questionnaires were used to assess psychological condition, and 14 symptoms were rated repeatedly over the next four hours. Blood samples were also taken immediately after eating and four hours later – the same was done for urine samples, but at four-, 12-, and 24-hour intervals.

One of the cereal bars was laced with aspartame and one was not. However, neither the participant nor the person analysing the results knew which was which, making the test more objective and eliminating many sources of bias.

Individuals volunteering were classified as "aspartame-sensitive" if they reported suffering one or more symptoms on multiple occasions, and as a consequence were actively avoiding consumption of any aspartame in their diet.

A further 48 people who didn’t report aspartame sensitivity (controls) repeated the same experiment under the same conditions. This group was chosen to match the characteristics of the aspartame-sensitive group in terms of age and gender. The aspartame-sensitive group had 21 men and 31 women; the control group had 23 men and 26 women. The groups did not differ significantly for age (around 50), weight, BMI, waist or hip circumference.

The 14 aspartame sensitivity symptoms assessed were:

  • headache
  • mood swings 
  • hot or flushed 
  • nausea 
  • tiredness 
  • dizziness
  • nasal congestion 
  • visual problems 
  • tingling
  • bloating 
  • hunger 
  • thirst 
  • happiness
  • arousal

The researchers’ main analysis looked for differences in symptoms after eating the aspartame-laced bar in those reporting aspartame sensitivity, compared with those reporting no sensitivity.

What were the basic results?

The main finding was that none of the rated symptoms differed between aspartame and control bars, or between sensitive and control participants.

They also found aspartame and control bars affected levels of chemicals in the blood (GLP-1, GIP, tyrosine and phenylalanine levels) equally in both aspartame-sensitive and non-sensitive subjects.

However, there were intriguing differences between the aspartame-sensitive group and the aspartame non-sensitive group. For example, the aspartame-sensitive people rated more symptoms, particularly in the first test session, whether this was after eating the placebo bar or the aspartame bar.

The two groups also differed psychologically in how they handled feelings and perceived stress.

How did the researchers interpret the results?

The authors’ conclusion was firm: "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."


This study shows that an aspartame-laced cereal bar caused no more adverse symptoms than a bar without aspartame in a group or people who said they were sensitive to aspartame. It also had no more adverse symptoms in a control group of people who did not think they were sensitive to aspartame.

The effects were monitored up to four hours after eating. This provides compelling evidence that aspartame doesn’t cause any short-term symptoms, even in people who think they are particularly susceptible to it, and report avoiding it as a result.

Limitations with the study include some missing symptom data, because not everyone was able to complete the ratings scale after eating the bars. However, you might expect someone with symptoms to fill it in, so not filling it in might signal a lack of symptoms. The sample size of around 90 participants was also relatively small. A larger sample size would have increased the conviction of the results.

The study authors reported problems recruiting participants, which brings us to the biggest limitation to consider. They anticipated 48 aspartame-sensitive people would be recruited within a year, but it took 2.5 years, despite high-level media coverage. A lot more non-aspartame-sensitive people (147 individuals) initially volunteered for the study before just one aspartame-sensitive individual participated. The researchers say this may reflect their genuine fear of aspartame consumption. Consequently, the 48 who participated may not be representative of the population of people who believe they are aspartame-sensitive, but it was impossible to recruit those most fearful, as they avoid taking part.

A further limitation is that the study looked only at short-term effects and cannot exclude the possibility of long-term, cumulative effects of aspartame on biological parameters and on a person’s psychological state. The dose given was also reported to be smaller than the daily intake of many individuals, but was greater than the intake at which the people reporting aspartame sensitivity believe they suffer symptoms.

Overall, this study provides evidence that aspartame fears may not be warranted in some people who believe they are sensitive to the ingredient. However, the study probably failed to recruit those most fearful of the sweetener. We don’t know if this group have symptoms caused by aspartame.

The conclusions of this study, and aspartame’s approval by food safety agencies in the US, UK and EU, provide quite robust reassurance that aspartame is safe for the vast majority of people. As with any ingredient, you can’t say for sure that some individuals won’t react badly to it. However, the findings from this study suggest this may be a perception of harm that is not necessarily borne out when tested rigorously.

The FSA website says that in December 2013, the European Food Safety Authority (EFSA) published an opinion on aspartame: "following a full risk assessment after undertaking a rigorous review of all available scientific research on aspartame and its breakdown products, including both animal and human studies. The EFSA opinion concluded that aspartame and its breakdown products are safe for human consumption at current levels of exposure".

NHS Attribution