For anyone keeping an eye on their weight, it’s an easy win: switch regular Coke, Pepsi or Fanta for diet versions which have all the fizz and sweet taste but none – or barely any – of the calories or tooth-rotting sugar.
And with consumers always looking for healthier options in the supermarket, these drinks are soaring in popularity. Today, two-thirds of the fizzy drinks we buy are low or zero-calorie versions made with artificial sweeteners such as aspartame, acesulfame K, sucralose and saccharin.
A wave of trendy new brands, such as Dash, Nocco and Remedy, have joined the more familiar labels jostling for fridge space, and you’re as likely to see them sold in gyms and health-food stores as you are in supermarkets and corner shops. Meanwhile, other low or no-calorie foods are having their moment, with zero-sugar ice creams, cereal bars and yogurts, also laced with artificial sweeteners, all trading on similar health promises.
Sirin Kale, 27, from London, pictured, was addicted to Diet Coke, spending £500-a-year on the soft drink
So claims that surfaced – or rather, resurfaced – last month, warning that consuming these products might make us more likely to pile on the pounds, made alarming reading.
According to weight-loss nutritionist Susie Howe, artificial sweeteners hijack our hunger hormones, making us want to eat more. And Howe is not alone in her concerns.
Over the past two years, a number of studies have come to similar conclusions, with scientists suggesting that the additives, which are up to 200 times sweeter than sugar, prime our tastebuds to crave sweet things and eat when we’re not hungry.
In March 2020, a group of scientists from Yale University found that consuming drinks containing sweeteners might increase the amount of sugar we absorb from foods eaten at the same time.
And earlier this year a French study involving more than 100,000 people found those who consumed lots of low-calorie sweeteners, including those added to low-cal ice cream and sugar-free sweets, were more likely to be obese and more likely to suffer obesity-related cancers, such as breast and liver cancer.
Such is the worry that some British scientists are calling for the Government to ban one of the most widely used sweeteners, aspartame – which is found in Diet Coke and Coca-Cola Zero Sugar – because of concerns about its ‘adverse effects’.
Such is the worry that some British scientists are calling for the Government to ban one of the most widely used sweeteners, aspartame – which is found in Diet Coke and Coca-Cola Zero Sugar – because of concerns about its ‘adverse effects’
‘The accumulation of data so far suggests that, at best, food containing artificial sweeteners is unhelpful for weight loss and, at worst, they are counter-productive,’ says Erik Millstone, emeritus professor of science policy at the University of Sussex, who is backing the proposed ban.
‘There is strong evidence that sweeteners act as an appetite stimulant. I have scrutinised most of the studies on potential harms of many sweeteners, and I have yet to come across one that I would give a clean bill of health.’
Yet the NHS does not support this view. The official line is that there’s ‘little evidence’ from studies to show sweeteners cause weight gain in the long term. Meanwhile, dieticians who work with patients in GP surgeries and hospitals continue to recommend diet drinks to those who need to slim down.
So what’s the truth? Before we can answer that, it’s important to understand what artificial sweeteners are.
Broadly speaking, they are man-made chemical compounds – although, in many cases they are derived from natural sources – that stimulate sweetness taste receptors on the tongue, just as sugar does.
Importantly, they are many hundreds of times sweeter than sugar, so only minute amounts need to be used, and most are indigestible – hence, we absorb few or any calories from them.
Aspartame is made up of amino acids extracted from eggs and milk, while acesulfame K, often mixed with other sweeteners due to its slightly bitter taste, is made from potassium salt.
Others, such as sucralose, which is found in table-sugar substitute Splenda; polyols, used in sugar-free gum; and saccharin, found in Sweetex tablets, are less commonly used and make up a smaller fraction of the total sweeteners most people consume on a daily basis.
Since their widespread adoption by the food industry in the 1960s, they have been dogged by health-scare stories.
Aspartame when eaten, the compound is broken down and releases substances including methanol and formaldehyde, which are known carcinogens. But this doesn’t mean aspartame causes cancer
Aspartame, specifically, has been a target. When eaten, the compound is broken down and releases substances including methanol and formaldehyde, which are known carcinogens. But this doesn’t mean aspartame causes cancer.
Dr Duane Mellor, a dietician with the British Dietetic Association and a nutrition researcher, says: ‘The amount of methanol that is released when you drink a can of Diet Coke is about five to ten per cent of the amount that would be produced after eating an apple.’
In the 1970s, lab studies showed that mice fed aspartame developed tumours – but it was later revealed the animals had been fed the equivalent to 20 cans of Coke a day.
‘No one would ever consume this amount, and no similar effect has ever been found in humans,’ says Chris Corpe, nutrition expert at King’s College London.
Despite this, and no doubt aware of all the bad press, in 2015 drinks giant Pepsi removed aspartame from its diet drinks in the US, replacing it with sucralose – but it didn’t do this in the UK or anywhere else around the world.
Numerous reviews by public-health bodies over the past four decades have all concluded that sweeteners are safe. As for other studies that show people with diets high in sweeteners have an increased risk of cancer, Dr Mellor says: ‘These people tend to be the people who are also eating little fresh, home-cooked food and more processed, possibly high-calorie meals.
‘A lot of people turn to diet drinks and low-calorie products because they need to lose weight, which means they are at a higher risk of cancer anyway. Studies looking at people who eat lots of processed foods find the same relationship.’
So what of the claims that sweeteners, far from helping us stay slim, actually have the opposite effect?
Animal studies certainly seem to suggest this.
In 2016, Australian scientists found that rats fed a diet containing artificial sweeteners went on to consume more food when they were allowed to eat freely than those not given the sweetener diet.
Scans on the animals showed consuming sweeteners increased activity in areas of the brain associated with pleasure – more so than when they were fed normal sugar.
Professor Greg Neely from the University of Sydney, who led the research, explained that, long-term, consumption of an overly sweet artificial flavour increased the animals’ preference for high-calorie food – making them binge. Human studies have come to similar conclusions. Experiments involve participants fasting overnight, then being given drinks containing either artificial sweetener or sugar. After each drink, volunteers are allowed to choose snacks from a buffet – and the amount they eat is monitored.
In some studies, people consume more food after the sweetened drink than the sugary drink. Blood tests also show raised levels of hormones that trigger feelings of hunger, such as ghrelin, in those who had consumed drinks with sweeteners compared to those who had swallowed drinks with sugar.
But Dr Mellor says research such as this proves little. ‘Lab studies like these are not a fair representation of the way people eat,’ he says. ‘If you make people fast, they will eat more than they usually would when they’re allowed to – because they’ll be very hungry.
‘A sweetened drink like Diet Coke won’t provide any calories, so you’d expect people to be less satisfied by that than by a full-sugar version. In reality, most people won’t be drinking these drinks with nothing else in their stomach, having starved themselves for hours on end.’
So what about the blood tests showing raised hunger hormones after the artificially sweetened drink?
‘Some studies show this, but others show the total opposite, so it’s not clear what’s going on,’ answers Dr Mellor.
In the 1970s, lab studies showed that mice fed aspartame developed tumours – but it was later revealed the animals had been fed the equivalent to 20 cans of Coke a day
The latest theory is that sweeteners have a damaging effect on the trillions of bacteria that live in our gut. Pioneering this research is a team of Israeli scientists who used faecal samples to analyse gut bacteria before and after participants drank artificially sweetened drinks. They discovered that giving saccharin, sucralose or aspartame to people over the course of a few weeks disrupted the healthy bacteria in the gut. These bacteria feed off the partly digested food in the bowel, producing compounds that send signals to the brain which tell us if we’re hungry or full.
The sweeteners also seemed to increase levels of a type of bacteria linked to damaged bowel tissue.
But other scientists say these results need to be viewed with caution. Firstly, there is not yet consensus about the exact combination of gut bugs – out of the 100 trillion in an average bowel – that is needed for healthy appetite regulation.
‘The one thing we know about gut bacteria is that they are changing all the time and are never static,’ says Dr Mellor. ‘The bugs that are most likely to impact our health are the ones that remain there for a long period of time – not those that appear, or disappear, over a weekly period. The only way you can test this – and its impact on appetite – is by putting tubes in people’s bowels for weeks at a time as they eat, which is clearly impossible.’
Dr Mellor adds: ‘Some sweeteners, like aspartame, are absorbed into the bloodstream very quickly and do not even make it into the gut.’
So why do studies show that those who consume diet-drinks are more likely to be overweight?
For instance, one, in 2015, found that the average waist circumference of people who drank diet soda daily over a ten-year period was nearly four inches greater than those who didn’t drink them.
The most likely explanation is a scientific phenomenon known as reverse causality – or what some diet experts call ‘the Big Mac and Diet Coke theory’.
‘Essentially, this means the people who consume a lot of diet drinks are more likely to eat high-fat, high-salt and high-sugar foods, and are more likely to be overweight in the first place,’ says Dr Mellor.
So does that mean diet drinks do little to keep off the pounds?
Earlier this year, the World Health Organisation published one of the most conclusive reports on the health impact of artificial sweeteners to date.
The paper, which scrutinised 283 international studies, including controlled experiments and observational research on all common sweeteners, concluded that artificial sweeteners may lead to a ‘small reduction’ in body fat in the short term, with no significant impact on long-term heart health risk.
The authors noted some studies showed negative health effects but that evidence was ‘inconclusive’.
Banning certain commonly used sweeteners entirely might be equally as detrimental.
For instance, one, in 2015, found that the average waist circumference of people who drank diet soda daily over a ten-year period was nearly four inches greater than those who didn’t drink them.
Dr Sarah Berry, senior lecturer in nutritional sciences at King’s College London, says: ‘If you stop people having diet drinks, some of them may well switch to high-sugar, high-calorie drinks instead.’
Meanwhile, consultant dietician Rebecca McManamon is keen to highlight one important benefit of diet drinks that is rarely considered. ‘Currently we have a crisis in dental health across the UK – with record levels of tooth decay in children and huge waiting lists for dentist appointments,’ she says.
‘Although diet drinks increase the risk of some enamel erosion, because they are acidic, the absence of sugar makes them far less harmful. It is all very well telling people to drink water instead but, for many, these drinks are a staple part of their daily routine and they find it hard to give them up.
‘But if you can convince patients to switch to a non-fizzy version, you’re sparing them tooth damage, at the very least.’
