We came across several posts on X circulating a video originally shared on Instagram that claims that storing diet soda in warm environments, such as garages where temperatures can exceed 30°C (86°F), could make it unsafe for consumption.

The claim focuses on aspartame, a low-calorie artificial sweetener commonly used in diet sodas and other sugar-free products. It alleges that at temperatures above 30°C, aspartame breaks down into toxic byproducts such as formaldehyde and formic acid. According to the claim, exposure to these compounds can trigger symptoms resembling neurological conditions, including multiple sclerosis, potentially leading to misdiagnoses.

Aspartame has frequently been the subject of misinformation, and we previously debunked a claim that the additive was being mislabelled as “AminoSweet” to mislead consumers.

Concerns over aspartame’s safety resurfaced in 2023, when the International Agency for Research on Cancer, together with the World Health Organisation (WHO) and the Food and Agriculture Organisation Joint Expert Committee on Food Additives (JECFA), found that aspartame could be carcinogenic to humans, particularly concerning liver cancer. However, the review concluded that there is a need for further research rather than confirming a direct causal relationship.

JECFA, which evaluated the real-world risk of consuming aspartame, reaffirmed that it is safe when consumed within established limits. The acceptable daily intake (ADI) remains at 40 milligrams per kilogram of body weight. This means that an adult weighing 70 kilograms would need to consume more than 9 to 14 cans of diet soda in a single day—each containing approximately 200 to 300 milligrams of aspartame—to exceed this limit, assuming no other sources of intake. As of today, the additive has been approved for consumption in over 90 countries, including Singapore.

With Singapore’s tropical climate, where daytime temperatures often exceed 30°C, this claim may raise concern for individuals who store beverages in non-air-conditioned, low-ventilated spaces such as storerooms. In light of this, we took a closer look at the claim to assess whether it holds up to scientific scrutiny.

Claims from an article circulated online

The social media post refers to an article titled “Aspartame: Soda Poison for Your Kids?” published in January 2012 by the Journal-Advocate, a local news publication based in Colorado, U.S. The article claims that aspartame is composed of aspartic acid, phenylalanine, and methanol, and alleges that at high temperatures, the methanol component breaks down into formaldehyde and diketopiperazine (DKP)—substances it describes as highly toxic to the nervous system.

It further suggests that this chemical breakdown poses serious health risks, such as blindness, lupus, and Alzheimer’s disease. The concern is framed around common storage practices, particularly during summer months, when people might keep diet sodas in warm, enclosed areas like garages, potentially exposing the beverages to temperatures above 30°C.

However, the article does not cite any peer-reviewed studies or medical evidence to support these claims. Despite making alarming assertions about aspartame’s breakdown products and links to severe illnesses, it lacks references to scientific data or established toxicological research. This absence of credible sources undermines the reliability of the article and makes it difficult to verify or substantiate its claims.

Scientific literature on aspartame

In contrast to the viral claim, scientific literature does not support the idea that storing diet soda above 30°C makes it toxic. The international peer-reviewed nutrition journal Nutrients published a comprehensive literature review on aspartame in 2021, including research on its impact on obesity, diabetes, as well as neurological damage. Overall, the literature of research did not find a clear causal link that aspartame breakdown causes or contributes to neurodegenerative diseases such as Alzheimer’s disease, multiple sclerosis and brain tumours.

While some individuals report mild adverse effects from aspartame, such as headaches, these have not been consistently observed in clinical trials, and none of these reported symptoms have been linked to heat-induced degradation specifically.

A 2018 study by researchers from India and Malaysia found that when consumed, aspartame breaks down in the gut into phenylalanine, aspartic acid, and methanol – all of which are naturally occurring in many foods, and which the body can safely process. These breakdown products may influence brain chemicals such as dopamine and serotonin—neurotransmitters that play key roles in mood, memory, and behaviour. The study suggested that these metabolic by-products may explain some of the anecdotal neurological symptoms, such as headaches. However, the authors stressed that more research is needed to fully understand the relationship between aspartame consumption, brain chemistry, and possible adverse effects, particularly in individuals who may be more sensitive to these compounds.

Furthermore, a 2002 study concluded that, while aspartame’s widespread use could lead to occasional overconsumption beyond regulatory guidelines, such levels remain harmless to human health.  This was supported by a study in 2007, which found that the amounts of these compounds from typical aspartame exposure, including potential degradation during storage, are far below thresholds that would cause toxicity.

Moreover, research does show that heat can accelerate the degradation of aspartame, especially above 30°C. However, the primary outcome of this breakdown is a loss of sweetness. There is no indication that such degradation produces toxic compounds at levels harmful to human health. Manufacturers are aware of this and typically recommend storing products like diet soda in cool conditions and consuming them before their expiry dates.

Therefore, while aspartame can degrade at elevated temperatures, current scientific evidence does not support the claim that this makes diet soda toxic. Regulatory bodies such as the WHO and JECFA continue to affirm the sweetener’s safety when consumed within recommended limits.

Hence, the claim that storing diet soda above 30°C makes it toxic is currently unproven.