Sugar free? Sweeteners may not be as ‘inert’ as we thought

Mon, 03 Nov, 2025 - 07:44

We need to cut down on sugar, but artificial substitutes may not be as effective as you think, writes DR CATHERINE CONLON

In recent weeks in a supermarket, I observed two boys landing a six pack of zero sugar cola into a trolley already laden with oven chips, crisps, and snack bars.

Their mother whisked it out, using Cristiano Ronaldo’s words ‘drink water’. “But it’s sugar-free,” one of them argued. The mother paused, six-pack in hand, accepted defeat with a sigh, and placed it back in the trolley.

Was she right? Are sugar free products living up to their image of, if not healthy, at least nutritionally inert, limiting the health effects of yet more sweetness on sugar-addicted palates?

What are artificial sweeteners, and what does the science say about the real health benefits of sugar alternatives?

Artificial sweeteners encompass a range of chemicals, mostly much sweeter than sugar, gram for gram. The industry claim that they are useful for weight management, diabetes control (because they have no impact on sugar levels) and for oral health because, unlike sugar, they do not promote tooth decay.

However, there is a mounting body of research linking the consumption of a lot of sweeteners to an increased risk of type 2 diabetes and heart disease, while people who consume a lot of sweeteners over the long term are more likely to gain weight.

Even in terms of dental care, a study in Weight, Diet and Physical Activity (2018) found children who consumed more that 250ml of artificially sweetened drinks a day were more likely to suffer from toothache than those who drank sugary drinks or energy drinks.

Based on the evidence, the World Health Organisation now advise that non-sugar sweeteners should not be used as a means of achieving weight control or reducing risk for chronic diseases such as diabetes or heart disease.

The industry claims sweeteners are metabolically ‘inert’ - in other words, that they do not lead to an increase in blood sugar. However, a study published in Cell (2022) has refuted these claims. In the study, 120 healthy adults were split into six groups. Four of the groups were assigned to receive a sweetener. One group was assigned to receive a sachet of glucose and one group received no sweeteners – artificial or otherwise. The study monitored participants’ blood sugar levels and microbes in their stool samples twice a day for two weeks.

The results were surprising. Two sweeteners (aspartame and stevia) were found to have no significant effects on participants’ blood sugar levels and microbes in their stool samples. The remaining two sweeteners (sucralose and saccharin) raised blood sugar in all participants who received them. In terms of the level of impact on blood sugar, this varied between participants – with some more prone to a raised blood sugar than others.

The results refute claims that artificial sweeteners are ‘inert’, with significant impacts found on both blood sugar and healthy gut bacteria.

One study found some artificial sweeteners were linked with raised blood sugars.

Now, a new study suggests that consuming artificial sweeteners is not so sweet for brain health, either.

Published in Neurology last month it found that middle aged and older adults who consumed the highest amounts of these sweeteners had a 62% faster decline in overall thinking and memory skills, equivalent to 1.6 years of ageing, compared to the those consuming the lowest amount.

The link was found in people younger than 60, but not in older adults, and was stronger for people with diabetes. The results were more pronounced in people with diabetes, particularly for memory decline, suggesting a heightened vulnerability in this group.

“The key message is that dietary exposures in midlife may impact long term brain health, and artificial sweeteners may not be the harmless alternatives to sugar that many assume,” says study author, Claudia Kimie Suemoto from the University of São Paulo in São Paulo, Brazil.

The research is important because it is the largest and longest prospective study to date, investigating the link between consumption of artificial sweeteners and cognitive decline. The study included 12,772 adults participating in the Brazilian Longitudinal Study of Adult Health. As part of it, they underwent cognitive tests every four years across three study waves (2008-2010, 2012-2014 and 2017-2019).

Participants were divided into three groups based on the total amount of sweeteners consumed. The lowest groups consumed an average of 20mg /d and the highest group consumed an average of 191mg/d. For aspartame, this amount is equivalent to one can of a diet fizzy drink.

After a median follow-up of eight years, participants in the two highest sweetener consumption groups had a 35% and 62% higher rate of decline in cognition compared to the participants in the lowest consumption group. That decline corresponded to between 1.3 and 1.6 year of cognitive ageing.

The findings highlight the need to look more critically at what we are using to replace sugar in our diets, and they underscore that dietary choices in midlife have consequences for brain health later in life.

So, the next time you reach for a diet cola or an artificial sweetener to add to you tea, remember that the combination of chemicals replacing sugar is not as inert as we once thought.

Whenever possible, consider adding natural options such as fruit, honey or spices, or even training our sugar-addicted palates to do without.