YOU could be forgiven for being completely confused when it comes to consuming low-calorie or artificial sweeteners. Some days, the headlines are full of praise for their beneficial effects on health, helping people to lose weight by replacing their favourite sugary drinks and treats with similar-tasting diet versions. At other times, we are told low-calorie sweeteners are linked with serious health conditions, from raising blood pressure to an increased risk of type 2 diabetes. Just last month, claimed to have found an association between consuming sweeteners and an increased risk of heart disease.
, an associate professor in the department of exercise and nutrition sciences at George Washington University, Washington DC, is trying to unpick the science involved in this controversial topic. Her work is shedding light on whether artificial sweeteners can give us the sweet fix we seek while helping us to maintain our weight and prevent chronic disease, or whether they should be handled with care.
Helen Thomson: It is widely accepted that too much sugar is bad for you. Artificial sweeteners are a supposedly healthy replacement, so can you tell us some of their proposed benefits?
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Allison Sylvetsky: Sure. We know that too much added sugar is not good for our health. Artificial sweeteners provide a sweet and palatable alternative that has few or no calories. Until recently, it鈥檚 been the belief that these sweeteners don鈥檛 really do anything in the body because they don鈥檛 contain sugar or calories. So the benefit of replacing sugar with artificial sweeteners in foods and beverages is that this replacement lowers the product鈥檚 calorie and sugar content.
But now it seems that things aren鈥檛 so straightforward?
Lately, there鈥檚 been more and more evidence from both rodent and human studies showing that artificial sweeteners may contribute to metabolic abnormalities and various health problems. However, there are trials that show that, when used judiciously, may be helpful for weight management. That鈥檚 where the controversy is. [Part of the] challenge is that these may not reflect the way that sweeteners are actually used in real life and the studies showing associations between sweetener use and health problems cannot show causality.
What changes when we look at how people use sweeteners in real life?
Most artificial sweetener trials have relied on comparing diet beverages with those with added sugar. Until a couple of decades ago, diet beverages almost entirely contained either aspartame or saccharin. Now, there are newer artificial sweeteners on the market and they鈥檝e been incorporated into more and more foods and beverages. There鈥檚 not a lot of research that is specific to particular sweeteners, and studying them is challenging because they鈥檙e used in diet drinks, but also in yogurts and snack foods and even in ice creams. They鈥檙e also used in beverages that aren鈥檛 even considered diet drinks, and which also have added sugar. So, frankly, it鈥檚 unlikely that people are using sweeteners as one-to-one replacements for added sugars. And they might be saying: 鈥淚 had a diet soda, so I can have another cookie.鈥�
So are the potential negative effects of sweeteners down to how people are using them, or could sweeteners themselves be causing problems?
I would say potentially both. More and more, we鈥檙e seeing that these sweeteners are not inert 鈥� they don鈥檛 have calories and they are not sugar, but they do exert metabolic effects in the body. The big question is, how relevant are those mechanisms to human health? There鈥檚 a discrepancy in the data. Most of the randomised controlled trials of artificial sweeteners have focused on weight loss, but not on some of the other health outcomes. And the randomised controlled trials are relatively short term and the people in them might be already motivated to lose weight. Observational studies link consumption of various sweeteners to unfavourable health effects, including, for example, increased risk of diabetes, cardiovascular disease and stroke. They鈥檙e not randomised or controlled, but they may better capture real-life exposure to sweeteners in the context of how people actually eat.
Is there one type of sweetener that is worse for you than others? There seem to be different rules for which sweeteners are approved and which aren鈥檛, depending on the country you are in.
Most studies group different artificial sweeteners together when studying their effects. But given they are different compounds, they may have different effects. Sweeteners all have different chemical structures, different physical properties. They are all absorbed differently. Some are metabolised, some aren鈥檛. They鈥檙e excreted differently. And they鈥檙e not always consumed alone. Take sucralose, for instance. Taken in water, there is no effect on blood glucose levels. But there鈥檚 evidence to show that when it is consumed in combination with sugar, it alters the body鈥檚 glucose and insulin levels [differently than sugar alone]. If the mechanism that contributes to poor health outcomes is sweetness, then we would expect all artificial sweeteners to have similar effects, but if the mechanism is compound-specific, then sucralose might be different than aspartame and so on. And it might be a combination of the two 鈥� some effects being due to sweetness and some being compound-specific.
We have spoken a lot about artificial sweeteners. Do natural sweeteners like stevia have similar controversies around their use?
Unfortunately, there is not a lot of research on the metabolic and health effects of stevia in humans, and it is a really important question because the use of stevia in foods and beverages has increased markedly in recent years. The few studies that have been conducted report that stevia helps reduce inflammation, improves control of blood glucose and encourages weight management. Stevia may be a favourable alternative to other low-calorie sweeteners, but this is not yet clear and more studies in humans are needed.
Last month, a study of French adults claimed to show a direct association between higher artificial sweetener use and cardiovascular risk. What do you think it added to the debate?
It was a very well-done study. They enrolled a large cohort and it was unique in that they collected repeated and detailed estimates of food consumption and looked at different sweeteners separately. They also considered sweeteners from foods, beverages, packaged sweeteners, all different dietary sources. The results further justify the need to conduct experimental studies to better understand the metabolic effects of sweeteners in humans.
It is hard for a consumer to make sense of all this. Studies like the French one suggest there may be a link between sweetener use and poor health, but the website of England鈥檚 National Health Service says they are 鈥減erfectly safe to eat or drink on a daily basis as part of a healthy diet鈥�. Should we be using them or not?
I think it depends on what we mean by safe, because these sweeteners have been extensively tested and approved by various regulatory bodies worldwide with regard to toxicity. But where the debate is focused is on metabolic effects and their role in weight management and chronic disease risk. In this case, the question is, are they helpful or harmful in terms of weight management and chronic disease? We don鈥檛 have a clear answer to that question yet, but more and more evidence suggests that these low-calorie sweeteners may not be helpful and may actually be counterproductive.
Your own research examines the consumption and effects of low-calorie sweeteners in children. What have you discovered?
We鈥檝e done several different studies on consumption of sweeteners among children. Studies have shown that the prevalence of consumption of low-calorie sweeteners has been increasing, and particularly in children. That鈥檚 not surprising, as there is more emphasis on reducing added sugar to food; there鈥檚 an increased presence of sweeteners, including those that are marketed to and widely consumed by children. This trend is being seen globally, not just in the US, and really highlights the importance of having a better understanding of how these sweeteners are impacting kids in terms of their weight and metabolic health. We have a couple of ongoing studies 鈥� one is in kids with type 1 diabetes, where we鈥檙e investigating how restricting their use of sweeteners affects their glucose levels and metabolic risk factors.
You鈥檙e still collecting data on this, but what do you expect to see?
In rodents, and now in humans too, studies show that repeated consumption of low-calorie sweeteners 鈥� specifically saccharin and, more recently, sucralose 鈥� led to impairments in the ability to keep blood glucose within an ideal range. So we hypothesise that removing sweeteners from the diets of children with type 1 diabetes might lead to improvements in the amount of time they are within the target blood glucose range relative to those who continue consuming sweeteners.
Have you got any ideas about possible mechanisms that might be involved?
One of the mechanisms being studied a lot right now is how sweeteners change the composition of the microbiota in our gut 鈥� the bacteria in our intestinal tract. Rodent data and a relatively in humans published recently showed that impairments of glucose tolerance are mediated by changes in the gut microbiome. They showed that repeated consumption of saccharin and sucralose causes changes in the gut microbiome composition that adversely impact glucose intolerance.
Given the mounting evidence, I am surprised there isn鈥檛 more nuanced advice on the consumption of sweeteners.
It鈥檚 still a highly controversial topic and it鈥檚 a polarised field of research. Yes, there鈥檚 growing evidence suggesting there may be negative effects of prolonged low-calorie sweetener consumption on metabolism. But it鈥檚 not yet a conclusive body of evidence. It鈥檚 important to acknowledge the limitations and critiques of scientific studies 鈥� that鈥檚 how research works. And we want to make sure the science isn鈥檛 being sensationalised.
The study from Israel also showed how personalised the effects of low-calorie sweeteners are on the gut microbiome. It鈥檚 something that varies between individuals and is challenging to disentangle. There are likely some people who respond negatively to sweeteners and some that do not. The reality is that understanding how these things affect our health takes a lot of time. And we really need conclusive evidence to inform policy.
