Young Ju, Ph.D.

On July 14, 2023, two expert groups of the World Health Organization (WHO) independently released their evaluations on the safety of aspartame–with somewhat different conclusions. While their conclusions do not change current intake limits and guidelines for aspartame, they could cause confusion for consumers. The purpose of this article is to answer some questions that may have resulted, e.g., what is aspartame, how were these conclusions reached, and what does this mean for consumers.

Aspartame (1,2)

Aspartame is an artificial sweetener that was accidentally discovered in 1965. It is about 200 times sweeter than sugar without a bitter aftertaste. In 1974, the U.S. Food and Drug Administration (FDA) approved aspartame as a food additive. Food additives are any substances added to food to maintain or improve safety, freshness, taste, texture, or appearance. These substances are continuously monitored and evaluated for harmful effects on human health. Since its approval, aspartame (Nutrasweet® and Equal®) has been used in many foods including carbonated beverages, tea, coffee, fillings, and dairy products. Aspartame provides calories (4 calories/g) similar to sugar, but less aspartame is used in food products because it is so much sweeter than sugar. For example, a 12-oz regular Coke contains 39 g of sugar (~156 calories). Diet Coke contains only 200 mg of aspartame (~0.8 calories).

Metabolism of Aspartame (3)

Once ingested, aspartame is fully metabolized into amino acids (90%) and methanol (10%) by digestive enzymes in the intestine. The amino acids and methanol are further metabolized just as they are from other food sources. Because the amounts of these amino acids and methanol from aspartame-sweetened products are much less than those from other food sources, many agencies and countries consider aspartame to be a safe food additive. It’s also very difficult (or impossible) to detect aspartame in the blood due to its rapid metabolism.

Aspartame and Cancer (1, 2, 4)

The International Agency for Research on Cancer (IARC) and the Joint Expert Committee on Food Additives (JECFA) both operating under WHO separately evaluated the safety of aspartame, particularly any possible carcinogenicity.

One of the roles of the IARC is to determine if an agent could cause cancer or increase cancer risk in humans. The IARC classifies agents into four groups based on the strength of available research evidence (5).

This was the first time that IARC has evaluated aspartame and classified it as possibly carcinogenic to humans (Group 2B) (1). Their decision was based on limited evidence in humans and in experimental animals and limited evidence on possible mechanisms for causing cancer. Their conclusion reflects research findings suggesting that aspartame can cause cancer in humans. It does not prove aspartame causes cancer at a given exposure level, because the agency could not rule out other cancer-contributing factors in available studies.

The JECFA is an international expert scientific committee administered jointly by the Food and Agriculture Organization of the United Nations and WHO. This committee evaluates food additives in terms of risk assessment, safety, and exposure. This was the third time that JECFA evaluated aspartame. This committee disagreed with the IARC’s ruling and reaffirmed that  “there is no evidence for harm with aspartame consumption below the current Acceptable Daily Intake (ADI) limit of 40 mg/kg body weight/day” (1). The JECFA’s evaluation was based on analysis of cancer-causing genetic mutations in both animal studies and in cell culture studies. They did not find evidence of mutations caused by aspartame or relationships between aspartame intake and cancer risk.

The ADI is defined as the maximum amount of a substance that can be ingested daily over a lifetime with no adverse health effect. The JECFA set the ADI of aspartame at 40 mg/kg body weight/day in 1981. In 1983, the U.S. FDA set it to 50 mg/kg body weight/day. (To reach 40 mg/kg body weight, a person weighing 154 lbs has to drink 14 cans of Diet Coke per day.)

The U.S. FDA also disagreed with IARC’s conclusions. They said that the classification into possibly carcinogenic to humans does not mean that aspartame is actually linked to cancer.  

What Should Consumers Do?

Consumers, especially people who regularly use products containing aspartame and other artificial sweeteners, should try to:

• Use those products in moderation.

• Cut down intake of both added sugar and artificial sweeteners.

• Replace sugar-sweetened or aspartame-sweetened beverages with water or tea.

• Reduce/avoid exposure to foods or activities that are definitely classified as carcinogenic or probably carcinogenic. 

Although WHO’s Director of the Department of Nutrition and Food Safety noted that occasional consumption of aspartame should not be an issue, it is important to note that recent studies raise questions and concerns on whether artificial sweeteners (including aspartame) are even effective on:

• blood glucose control in patients with diabetes

• weight control in people with obesity

• intestinal bacterial population

• hormonal balance

Most of these studies suggest reconsidering the role of artificial sweeteners in various health conditions as well as addressing the need for more research on aspartame and other artificial sweeteners.

Who Should Avoid Aspartame?

People with phenylketonuria, a rare inherited condition, must avoid aspartame and food products that contain aspartame because they cannot metabolize phenylalanine, a major metabolite of aspartame.  This can lead to very serious medical issues. This is why products containing aspartame must carry the warning “PHENYLKETONURICS: CONTAINS PHENYLALANINE.”

Overall

WHO expert groups and the U.S. FDA reaffirmed that aspartame is safe when consumed below ADI levels, while studies are continuing to improve our understanding of the safety and efficacy of aspartame.  Meanwhile, as in many things, moderation and information can help us reduce our potential exposure to cancer-causing foods and beverages.

REFERENCES

1. World Health Organization. Aspartame hazard and risk assessment results released. https://www.who.int/news/item/14-07-2023-aspartame-hazard-and-risk-assessment-results-released

2. American Cancer Society. Aspartame and Cancer Risk. https://www.cancer.org/cancer/risk-prevention/chemicals/aspartame.html

3. Ahmad, S.Y., Friel, J.K., Mackay, D.S. Effect of sucralose and aspartame on glucose metabolism and hormones. Nutrition Reviews. 2020, 78(9):725.

4. Lewis, T. Aspartame declared ‘possible’ carcinogen. Here’s what that really means. Scientific American July 13, 2023 https://www.scientificamerican.com/article/aspartame-declared-possible-carcinogen-heres-what-that-really-means/

5. World Health Organization. Aspartame Questions and Answers. https://monographs.iarc.who.int/wp-content/uploads/2023/06/Meeting134-QA-June2023.pdf

6. International Agency for Research on Cancer. List of Classifications https://monographs.iarc.who.int/list-of-classifications/

People with any health problems should talk to their healthcare providers. This information is provided for your reference and you use at your own risk; you should rely on your medical professional for medical advice.