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.