What science really says about the sweeteners in your tea (2023)

In a time of confusing messages, yet another foodstuff we thought was “healthy” – or at least “healthier” – turns out to be quite the opposite. According to the World Health Organisation (WHO), artificial sweeteners are potentially bad for us.

Earlier this week, the WHO announced that using artificial sweeteners “does not confer any long-term benefit” in reducing body fat in adults or children. They then went one step further, saying that sweeteners such as saccharin, sucralose and aspartame could actually increase the risk of conditions such as type 2 diabetes and cardiovascular diseases. (The above does not apply to people who already have diabetes, of either type.)

As sugar is increasingly demonised, many of us turn to artificial sweeteners for a quasi-sugar hit. And these are everywhere from the Diet Coke you swig at 4pm to the pasta sauce you heat for dinner. They are also in sneaky places like low-fat yoghurt (there’s no such thing as a free lunch: that delicious “mouth-feel” has to be replaced by chemicals) and instant porridge.

Artificial sweeteners are big business. In January 2023, the publisher researchandmarkets.com predicted the global market will reach $9.35 billion (£7.5 billion) by 2028, as we aim to lose weight and look after our teeth. North America is the fastest-growing artificial sweetener market, owing to a combination of wellness-chasing consumers and stringent food safety regulations.

The WHO report comes on the back of a number of similar studies. In March this year, a paper from the Cleveland Clinic Lerner Research Institute revealed that patients with high levels of a zero-calorie sweetener called erythritol in their blood were increasingly likely to have a heart attack or a stroke. This followed a 2022 French study reported in the BMJ with similar results about a broader range of sweeteners.

“Humans have always loved sweet things – we historically sought them out, largely because we didn’t have to kill them,” says TC Callis, author of The Building Blocks of Life: A Nutrition Foundation for Healthcare Professionals. “Back when we were hunter-gatherers, the amount of natural sugar we ate was not a problem – we’d come across some honey, or fruit, when it was available. But we didn’t eat sugar in anything like the quantities we do now.”

Confronted with a limited amount of natural sugar, our bodies knew how to respond, she says. “But the additives in modern foods are new and different. There are so many chemicals, we don’t fully understand their mode of action.” Scientists, including ZOE’s Professor Tim Spector – who recently tweeted that artificial sweeteners “need a health warning” – are concerned about the effect they can have on the microbiome, or the ‘friendly’ bacteria in our digestive system.

Callis agrees with his approach. “Artificial sweeteners stimulate inflammation of the gut,” she says. “Inflammation messes up your cell structures and is linked to all sorts of chronic auto-immune conditions, including cardiovascular conditions, type 2 diabetes and cancer. Sweeteners won’t necessarily cause these things, but they can increase your risk.”

It’s fully accepted that an excess of natural sugar, or sucrose, does the same. So given a choice of the full sugar and the diet option, which should you choose?

Bridget Benelam, a nutrition scientist and spokesperson for the British Nutrition Foundation, explains that, “The WHO report is actually based on a study of all the studies. They looked at long-term research over time and asked: ‘Are artificial sweeteners associated with weight gain and its associated conditions?’ It’s true that some studies have shown an association. The problem is, we can’t see whether the sweeteners caused these problems, or whether the illnesses were a correlation.”

Benelam points to the phenomenon of ‘reverse causality’ – in other words, that it tends to be overweight people who may be more likely to choose diet foods – hence it appears that the products cause weight gain and related illnesses rather than actually these being a result of people eating badly at other times, or not exercising enough.

Callis agrees. “Many of these people may already have been overweight,” she says. “Their biochemistry already wasn’t functioning. Adding in an artificial sweetener would mess it up even more.”

But could artificial sweeteners actually cause weight gain on their own?

A 2021 study from the University of Southern California showed that foods containing the artificial flavour sucralose caused increased appetite and weight gain.

“While some studies show artificial sweeteners may be helpful, others show they may contribute to weight gain, type 2 diabetes and other metabolic disorders,” said Kathleen Page, lead author of the research. But again, the science behind this is not straightforward.

“To lose weight, you need a calorie deficit – it’s as simple as that,” says Bridget Benelam. “And one way to do this is to reduce your sugar intake. The problem is that this isn’t dependent on one behaviour.”

So, a person may consume a diet drink (with lower calories than the full-strength version) but then, feeling virtuous, eat a chocolate bar that has twice as many calories as the original sugary drink may have had.

Should you have diet drinks or the ‘fat’ version?

“In an ideal world, the WHO would prefer people to drink only water or other unsweetened drinks, but generally, people used to fizzy drinks may find it difficult to make the complete switch,” says Benelam. “Since the 2018 Soft Drinks Industry Levy – or “sugar tax” – it’s actually very hard to find a full-sugar drink. A lot of work has been done to replace sugar with artificial sweeteners.”

On balance – and within reason – she says, this has been a positive step. “Switching to the diet option is a straightforward way to lower your sugar intake,” says Benelam. “A full-sugar drink can have over 100 calories a can; a diet cola has zero calories. Making this change every day saves you from consuming a lot of sugar.”

Is a ‘normal’ flavoured yoghurt better than one with artificial sweeteners?

Next time you are in the supermarket, says Callis, take a low-fat yoghurt off the shelf and have a look at the list of ingredients. “The artificial sweeteners change the nature of the product – thickeners, gelling agents, preservatives,” she says. But neither is the ‘regular’ strawberry yoghurt a healthy option. “Choose a natural yoghurt,” she says. “We’ve been eating natural yoghurt for 6,000 years. Add sunflower seeds or strawberries for that kick of sweetness.”

Can natural sugars ever be better than artificial ones?

“It’s understandable that people are concerned about E numbers and chemicals they don’t recognise,” says Benelam. “But the idea that other, “natural”, alternatives such as agave, nectars or the natural sweetener stevia are “better” for you isn’t true. They can still cause tooth decay and weight gain.”

Artificial sugars are also less likely to cause tooth decay. “This is caused by the fermentation of sugars. Manmade sweeteners don’t have this result,” says Benelam. “However, all acidic and fruit drinks can contribute to dental erosion if consumed frequently.”

What’s a sensible approach?

A slice of real mango beats the dried and sweetened version. Instead of apple juice, eat an apple. “There are only so many apples a person can eat in one day, whereas you can drink a lot of sweetened apple juice,” says Benelam. “The fibre in the whole fruit also supports your digestive system.” Callis advises having a good look through your kitchen cupboard, and taking extra care during the supermarket shop.

“Think about what you are eating. Anything that wouldn’t be found in nature, put it back on the shelf,” she says. “Stay away from all processed food as much as possible; if you are short on time, batch cook instead of buying ready meals.” She accepts that not everyone is going to do this all the time – deadline biscuit cravings come to us all. “Inevitably, we are going to eat some sugar. But peeling an orange, or adding fruit to a yoghurt, takes seconds.”


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