Last week, Pepsi announced they will be removing aspartame, the artificial sweetener, from Diet Pepsi (in the US), and replacing it with another artificial sweetener, sucralose. This reignited the discussion on aspartame, probably one of the most maligned substances in fizzy drinks – but what does the science say on its safety? This graphic looks at the evidence behind aspartame’s bad reputation, and whether it makes sense to remove it from drinks.

There’s no shortage of material when it comes to aspartame research – the FDA has described it as one of the most studied food additives currently approved. We’re talking a huge number of studies, more than 500, so you’d justifiably think that this is an issue that the research can weigh in on pretty heavily, and with good authority. Even if we cast an overly suspicious eye, and exclude studies funded by soft drinks manufacturers and the like, there are still hundreds of studies that have been carried out on aspartame.

You could be forgiven for thinking that, if Pepsi are removing it from their drinks, there must be some pretty damning evidence behind their decision. That, sadly, is where you’d be wrong. In fact, Pepsi have admitted as much: they state that their decision is a ‘response to consumer preferences’, and cite aspartame as the number one reason customers aren’t buying diet sodas.

In the public sphere, there isn’t much that aspartame hasn’t been accused of – opponents of its use have linked it with cancers, seizures, neurotoxicity, and more besides. Despite this, it’s still present in a number of soft drinks, and if you examine the wide body of evidence, the reasons for this become clear.

Firstly, let’s consider what happens when aspartame is ingested. Your body breaks down aspartame into three different components: two amino acids, aspartic acid and phenylalanine, and methanol. Most people have heard of methanol – also known as wood alcohol, it’s a substance that’s poisonous to humans in sufficient quantity. However, as regular readers of the blog will appreciate, the dose makes the poison, and methanol is no exception.

Of course, the idea that aspartame is broken down into a product that is toxic is initially an alarming one, but let’s pause and think about this in more detail. Firstly, not all of the aspartame in a soft drink will be converted into methanol. In fact, it’s only about 10%, which translates to around 55 milligrams of methanol produced per litre of fizzy drink. 55 milligrams isn’t a lot, but any amount of methanol is bad, right?

Well, as it turns out, aspartame isn’t the only thing in your diet that contributes to your methanol intake. In fact, a lot of substances you might not initially expect contain methanol in small amounts. Most alcoholic drinks will contain a degree of methanol – for example, red wine can contain anywhere between 99 and 271 milligrams per litre. In fact, fruits have higher levels of methanol than even the most aspartame-loaded drink could produce; for example, tomato juice contains up to 218 milligrams per litre. Whether you drink aspartame-containing beverages or not, you’re being exposed to methanol on a daily basis.

Generally, then, aspartame is a pretty measly contributor to our daily methanol exposure. Though methanol is also metabolised in the body, into formaldehyde and then formate, much higher levels of these chemicals than produced by aspartame have been shown to have no negative health effects. The same is true for its other breakdown products, phenylalanine and aspartic acid, amino acids that are present in other foods we eat on a daily basis, and in higher levels. With that said, one of these isn’t completely without its dangers. Phenylalanine intake can pose risks, but only for a specific subsection of the population: those suffering from phenylketonuria.

Phenylketonuria is a rare genetic condition, that affects only 1 in every 10,000 people. People with this condition are unable to break down the amino acid phenylalanine, and as a result it can build up in their bodies to toxic levels. Obviously, for sufferers, aspartame-containing drinks pose a very real risk, as high levels can lead to brain damage, which is why any beverage containing aspartame must be clearly labeled as such. However, it must be emphasised that for the normal population, this isn’t a concern, as they can break down phenylalanine well before it reaches these levels.

The spectre of cancer is often one that looms over food additives. Aspartame has been studied for decades concerning whether or not it can have carcinogenic effects, and the vast majority of studies have found no causal link. In the mid-2000s, an Italian institute did claim to have provided evidence linking aspartame with cancers. However, the methods of these studies were criticised for a number of reasons, including using dosages that didn’t reflect normal human exposure levels, the presence of infection in the test animals prior to the tests with aspartame, and other issues.

Of course, the study was greeted with concern when published – however, in trying to ascertain the quality of the data produced, the FDA asked to be supplied with aspects of the data. The institute in question was unwilling to release the majority of the data, and other agencies later further criticised their methods, further devaluing their ‘results’. It’s now widely accepted that the data they collected on aspartame and cancer is highly unreliable, and has not been replicated.

So, it seems that the evidence supporting serious health effects from aspartame is largely spurious. But how about milder unpleasant effects? A lot of people claim that aspartame-containing drinks give them headaches. Surely all of these people can’t be wrong?

Whilst the science hasn’t conclusively ruled out a link, it’s been noted that headaches are one of the most commonly reported placebo symptoms. Some studies have suggested that those who identify as sensitive to aspartame do experience more headaches with aspartame under controlled conditions, compared to a placebo. It’s worth noting, however, that aspects of this study were criticised.

Others, meanwhile, have found no correlation between aspartame and headaches. A study in the 1980s found a group with self-reported sensitivity to aspartame experienced headaches 100% of the time when they knew they were ingesting aspartame, compared to only 35% of the time when they didn’t know. Additionally, they experienced headaches 45% of the time with a placebo, with the study ultimately finding aspartame to be no better at inducing headaches than a placebo. In other more general studies,the reactions of subjects who identified as sensitive to aspartame have not been reproducible.

So, with all of this evidence backing up the safety of aspartame, why is Pepsi removing it? The answer brings us back full circle: it’s aspartame’s reputation. There are other, less maligned artificial sweeteners out there, and Pepsi’s move is little more than a marketing one – and one that’s got them no small amount of publicity, to boot. Regardless of the evidence, the tide of public opinion affects sales, and Pepsi has clearly judged that kicking aspartame into touch will be good for business.

Of course, this isn’t to say that people shouldn’t be free to choose not to consume aspartame, or other artificial sweeteners, for that matter. But we should be honest about the reasons for its gradual disappearance from the products on shop shelves, which has little to do with health, and more to do with money.

Note: the original version of this article didn’t clarify that Pepsi themselves have stated their removal of aspartame is a purely commercial decision, and unrelated to health concerns. The text has since been amended to reflect this.

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