Designing a series of sweetener trials seemed straightforward enough to us as behavioural scientists who specialise in human appetite and obesity. The plan was simple: replace the added sugar in a range of foods with different classes of alternative sweeteners, holding everything else constant.

We would start with a simple biscuit with a fruit filling and work from there. In each case we would measure the effects on participants’ eating choices, metabolism and health outcomes.

We put this to our collaborator, Alain Le Bail, a professor and senior food scientist in France with more than 30 years’ experience. He looked as if we’d asked him to build a bridge using marshmallows.

Sugar, he said, isn’t just sweet. It provides structure, texture, browning, moisture and mouthfeel. Removing it doesn’t just alter the biscuit; it breaks the rules that make it a biscuit in the first place.

If even we researchers on appetite and nutrition need to be educated on these complexities, what hope does the average consumer have?

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Sweeteners, as we’ll call the broad category of sugar alternatives and sweetness enhancers, were once fairly niche. They were used to lighten a soft drink or sweeten a low-calorie yoghurt, but not much more besides. Now, they are on almost every shelf of the supermarket.

They go to the heart of global debates on obesity, diabetes, child nutrition and ultra-processed foods. Whether it’s politicians deciding on sugar taxes, doctors helping diabetic patients manage their diets, or parents wrestling with product labels, sweeteners are unavoidable.

They attract endlessly conflicting headlines. While we try to reconcile our very human desire for a healthy win-win with our deep cultural unease over “artificial” additives, sweeteners are alternately framed as helpful diet liberators or harmful hormone disruptors. Far more rarely are they seen as ingredients with a specific, measurable function. It doesn’t help that the science in this area is still surprisingly thin on the ground.

Understanding what sweeteners can (and can’t) do for us requires looking beyond the binary of “good” or “bad” to more grounded questions. What are they replacing? In what context? For whom? According to what desired outcomes?

And beyond all this is the question of where sweeteners are heading. Will new technologies like artificial intelligence be transformational? Will we ever make the perfect sugar alternative? Look down the decades and you realise we’ve been trying for a very long time.

A brief history of sweeteners

For over a century, sweeteners have promised the same taste as sugar without the calories or health risks – guilt-free pleasure, in other words. But every breakthrough has been followed by a backlash, leaving a trail of safety scares and shifting public attitudes.

The modern story of sweeteners begins in the late 19th century with the accidental discovery of saccharin at Johns Hopkins University in Baltimore, USA. Derived from coal tar, saccharin is 300-500 times sweeter than sugar.

It quickly found favour among diabetic patients and later, calorie-conscious consumers. Critics questioned its taste, safety and “unnatural” origins, yet its presence grew – particularly amid sugar shortages during the world wars.

In the decades that followed, saccharin became widely used in diet drinks and tabletop products, before safety scares and the arrival of newer sweeteners reduced its popularity.

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In the early 20th century, other synthetic compounds such as dulcin and P-4000 also emerged, but safety concerns led to their withdrawal a few years later. More prominent was cyclamate, discovered in 1937, which gained popularity in the post-war years, especially in the US.

Marketed as a diet aid and used widely in soft drinks, cyclamate was abruptly banned in 1969 by the US Food and Drug Administration (FDA) following concerns about bladder cancer. Though the evidence was contested – rats in one pivotal study were consuming the equivalent of 550 cans of diet soft drink each day – the US ban was never lifted, leaving a lasting scar on public trust in sweeteners.

The next turning point came with FDA approval of aspartame in soft drinks in 1983, ushering in what might be called the Diet Coke era. It was also approved as a general purpose sweetener in 1996.

Compared to saccharin, aspartame tasted more sugar-like: in an early comparative study of soft drinks, those sweetened with aspartame were found to be statistically equivalent to sugar (sucrose) on every descriptive scale. Drinks sweetened by saccharin, with its bitter/metallic aftertaste, were among the most different from sucrose.

Aspartame does still taste somewhat different to sugar, but duly became the sweetener of choice for weight-conscious consumers and the food industry, especially in the US and UK. It has drawn negative comparisons to the alternatives, however. In one Canadian study from 2021, 52% of respondents rated aspartame as less healthy than table sugar, while more favourably judging other sweeteners they saw as more “natural”.

Aspartame’s chemical origins admittedly lead to relatively minor drawbacks. It contains the amino acid phenylalanine, which harms individuals with the rare metabolic disorder phenylketonuria. Products containing aspartame must therefore warn about this risk in many jurisdictions, including the US and UK.

Journalists have also amplified speculative risks around aspartame, such as brain cancer, albeit without robust evidence. Regulators including the FDA and the European Food Safety Authority (EFSA) continue to regard aspartame as safe at current permitted intake levels.

Yet consumer scepticism has persisted – and with commercial consequences. In 2015 PepsiCo reformulated Diet Pepsi in the US as “aspartame-free”. Yet the ingredient was not displaced more broadly, and Pepsi later reintroduced aspartame after the reformulated product performed poorly.

The next wave of sweeteners focused on improved sensory profile and functionality. Acesulfame-K (ace-K) and sucralose were adopted in the 1990s and 2000s because they generally tolerate heat and storage better. For example you can’t use aspartame for baking or making sauces because it breaks down at high temperatures. It’s also not useful for items with long shelf lives including certain condiments, dried mixes and confectionery because it can lose sweetness over time.

However, ace-K and sucralose tend only to work in combinations. Ace-K, for example, boosts upfront sweetness, but has a bitter aftertaste that other sweeteners can help “round out”.

In general, uptake of “artificial” sweeteners has varied. They appear more accepted in the UK and Germany, and less, for example, in Portugal and Romania. Influencing factors include regulatory approvals, cultural preferences and health attitudes.

In the 2010s, consumers came to favour natural sweeteners with more botanical origins. The first to become a big deal was stevia, a sweetener extracted from the leaves of Latin America’s Stevia rebaundiana plant (below). It was followed by monk fruit, from the Siraitia grosvenorii vine of southern China.

These too come with trade-offs, however. For........

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