The great debate over Diet Coke

First, a quick history of artificial sweeteners

Here’s a timeline of how they became ubiquitous:

First came saccharin: which was discovered accidentally by a scientist in 1897. He accidentally licked a coal tar derivative—and stumbled upon benzoic sulfimide which is 300X sweeter than sugar. It remained both widely used and controversial until after World War II.

Next, cyclamate: Its discovery coincided with the diet soda boom of the 1950s. By 1963, cyclamate was the #1 artificial sweetener—“costing a tenth of the price of sugar and with zero calories.” Its most popular version: the iconic Sweet’N Low packet. Unfortunately, cyclamate was found to cause bladder cancer—and was banned. Sweet’N Low went back to using saccharin. 

And finally, aspartame: In 1965, once again a scientist licked his fingers—this time while researching a new ulcer drug. That’s when he discovered aspartame—an amino acid compound—aspartic acid plus phenylalanine–that is 200X sweeter than sugar.

A very rocky start: Aspartame was not approved for general use until 1981—and here’s why:

When American pharmaceutical company G.D. Searle first tried to get aspartame approved by the US Food and Drug Administration (FDA) in 1973, it was denied: Independent scientists alleged the product could cause a range of neurologic disorders, and some alleged the company hadn’t been entirely above-board in its safety testing.

But in 1981, Ronald Reagan became president. And his transition team including the CEO of GD Searle—a guy called Donald Rumsfeld—yes, the architect of the Iraq War. Aspartame got its approval within months—and hit the market as Nutrasweet.

Data point to note: A 12 ounce (354 ml) can of Diet Coke contains no calories or sugar while regular Coke contains 140 calories from 39 grams of pure sugar. 

Where we are now: Aspartame replaced more than a billion pounds of sugar in the American diet during the 1980s—when Diet Coke was launched. Today, it is found in nearly 6,000 widely consumed products. 

• As a sugar substitute, it is sold as NutraSweet and Equal. 
• Most diet sodas contain aspartame including Diet Coke, Coke Zero, Pepsi Max, and 7 Up Free. It is also found in 90% of ready-to-drink teas.
• Most sugar-free gums like Trident have aspartame, as well.

Ok, so Diet Coke is bad for me?

Let’s say the evidence is mixed—as of now.

Tested and approved: First off, the FDA has reviewed aspartame five times since 1981—and found it safe to consume. It is approved for use by regulatory bodies in over 90 countries. In fact, even the WHO has said aspartame is safe to consume within accepted daily limits: 

For example, an adult weighing 60 kg (132 pounds) would have to drink between 12 and 36 cans of diet soda—depending on the amount of aspartame in the beverage—every day to be at risk.

The worrying research: Researchers first raised doubts about aspartame in the 1990s. First a neurologist published a paper suggesting it could cause brain cancer. But the more definitive studies were conducted in 1997 by the Ramazzini Institute—a nonprofit research lab in Italy. The institute looked at its effects on rats—and it “was particularly high-quality in that it included thousands of rats and gave them a range of aspartame doses.” Here’s what its scientists found:

The rats that consumed aspartame had higher levels of malignant tumours in multiple organs, including kidneys, breasts, and the nervous system. These findings were noted even at low doses of aspartame — exposures similar to what the US and European authorities consider the acceptable daily intake of the product.

Their findings sparked a fierce debate within the medical community—and many others published counter-evidence challenging them. However, many of them were funded by the artificial sweetener lobby. 

More recently: This year, the Institute published a review of its research—which “confirm and reinforce” their previous findings. Last year, an observational study in France revealed a “slightly higher” risk of cancer among those who consumed large quantities of artificial sweeteners, in general. But its critics say it does not establish a cause-effect relationship.

And what is the WHO saying?

It hasn’t said anything yet. But a leaked report in Reuters says that its cancer research wing will categorise it as a “possible carcinogen” this month. But what does that vague term mean? No one is really sure. 

The classification: The International Agency of Research into Cancer (IARC) is tasked with assessing whether something is likely to cause cancer. It has five categories:

The highest tier, Group 1, is reserved for established carcinogens, including smoking, asbestos, alcohol, and now processed meat. The next two tiers, 2A (“probably carcinogenic”) and 2B (“possibly carcinogenic”), are for things whose relationship to cancer is less certain. Group 3 is for substances that can’t be classified, due to lack of data.

But, but, but: Here’s the really important bit—these categories do not reflect how dangerous these substances are. They only assess the strength of the evidence linking it to cancer:

These classifications serve as a rough way to rank the strength of the evidence linking a substance to cancer in humans; this evidence includes studies of humans, human cells and tissues and lab animals, as well as studies of the substances' similarity to known or probable carcinogens. The rankings aren't related to how much a substance might increase cancer risk, but how conclusively the IARC can say it causes cancer at all.

So two substances could be in the same category—even if one triples the risk of cancer and the other increases it by a small fraction. Also this: 

When processed red meat was categorised as carcinogenic, it led to reports equating it to smoking. But the risk of giving 100 people an extra 1.7oz (50g) of bacon—on top of any they already eat—every single day for the rest of their lives would lead to one case of bowel cancer.

OTOH, the risk of getting lung cancer if you’re a smoker is anywhere between 10 to 20%. 

Defining category 2B: That’s the “possibly carcinogenic” category assigned to aspartame. Critics say the criteria is so vague that it “becomes a giant dumping ground for all the risk factors that IARC has considered, and could neither confirm nor fully discount as carcinogens.” As BBC News notes:

Many of the 94 items on the inventory are perhaps not particularly surprising: gasoline, infection with HIV type 2, working with asphalt. But it also includes a number of seemingly wholesome entities, such as bracken ferns, aloe vera extract and traditional Asian pickled vegetables. Even a spot of carpentry could land you on the wrong side of this register.

That’s because the criteria that lands a substance in 2B is confusing:

For Group 2B, it is necessary to have "limited evidence of carcinogenicity in humans and sufficient evidence of carcinogenicity in experimental animals", though there are some caveats. Items could also fall into this category even if there isn't any direct evidence of their cancer-causing properties in humans, as long as there is also strong evidence that the mechanism via which it does this in animals also applies to people.

A key point to note: Experts also concede that the WHO has higher standards for safety than regulatory authorities—be it in the US or Europe. 

The bottomline: Despite the blanket media coverage, the WHO actually has not released an official statement. But given a 2B classification, it is actually saying that there isn’t strong evidence that aspartame causes cancer. So keep that in mind when the announcement triggers the next round of frantic headlines 

Reading list

Saveur has a delightful piece on the history of artificial sweeteners. This Reuters exclusive triggered the fierce debate. BBC News has two good pieces: an overview of the likely IARC announcement and an analysis of how IARC classifies substances. The Atlantic offers scathing critique of the WHO’s confused messaging around cancer.  Vox has the most exhaustive overview of the research into aspartame.