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One of the primary goals of SBM is to provide information to consumers regarding health decisions they make for themselves and their families. We make such decisions every day, and unfortunately the public sphere is flooded with misinformation about common health choices. Most non-experts I discuss these issues with, whether personally or professionally, are either uninformed or misinformed about common health topics. Frequently those who think of themselves as being highly informed are burdened with the most misinformation.

This is extremely unfortunate, because I find that people who are making the greatest effort to have healthy lifestyles are actively looking for information to help them do so, and are finding mostly slick narratives full of falsehoods. This often leads them to make changes to their habits that are useless or even counterproductive, while missing the real changes that have been shown to have a positive impact.

One of the most common questions I get about personal habits is the consumption of low calorie sweeteners (LCS, also called low energy sweeteners or LES in the literature), such as sucralose and aspartame. Just search on either of these terms and you will find a flood of fearmongering, conspiracy theories, and alternative nonsense. You will also find serious discussions of the research that are complex and confusing – hardly a remedy to the simple scary narratives sold by self-appointed gurus.

I reviewed the evidence in 2015, concluding:

In this case, despite confusing results from many types of studies, the best evidence consistently indicates that consuming LES results in reduced energy intake and reduced weight compared to either consuming sugar-sweetened beverages or even water. There does appear to be room for further rigorous studies, but this is the best conclusion we can currently make based upon all the evidence, and it is fairly consistent and robust.

It’s been a few years, and the conversation really hasn’t changed much, but I wanted to see if there was any new relevant evidence. To quickly review, the main reason for confusion is that observational studies consistent show that consuming LCS is correlated with an increased body mass index, BMI. However, this data is correlational only, and it is more likely that being overweight motivates people to consume LCS, rather than the other way around. Animal studies also suggest a correlation between weight gain and LCS consumption, but in these studies the results are mixed, and the data is very difficult to extrapolate to humans. Rats and mice simply appear to have different metabolisms than humans, and in most of these studies the diets fed to the experimental animals were unrealistic, adding further confounders.

As with many questions in medicine, animal, basic science, and observational studies are useful – but they are trumped by well-designed controlled clinical experiments. In such experiments variables can be controlled for, and we can make cause-and-effect conclusions. These studies consistently show that substituting LCS for sugar helps in weight loss. It may even help to substitute LCS for water. There also does not appear to be any negative effect from consuming LCS.

What new evidence is there on the question of LCS and weight control? A 2018 review, the most recent published I could find, concluded:

Low-calorie sweeteners provide a means to reduce energy density while largely preserving food or beverage reward value. Consistent with this, consumption of low-calorie sweeteners compared with consumption of sugars has been found to reduce energy intake and body weight.

This review focuses on an interesting point – the strategy of reducing the ratio of calorie intake to the physical and mental reward of eating. Energy intake and expenditure are not perfectly matched (which is why we have the problem of obesity in the first place). We evolved a host of reward sensations that influence how much we eat, by estimating the calorie density of food. LCS essentially trick the body into thinking the food we are eating is more energy dense than it is, and that can help reduce caloric intake. This works best as part of an overall strategy of eating foods that are rewarding compared to their energy density.

A 2016 review focusing on energy balance found:

Randomized controlled trials are consistent in showing a benefit of LCS which suggests that simple behavioral engagement by individuals attempting to control their weight is a sufficiently strong signal to overcome any potential mechanism that might act to promote energy intake and weight gain. Based on existing evidence, LCS can be a useful tool for people actively engaged in managing their body weight for weight loss and maintenance.

All the reviews I found came to the same conclusion – that controlled experiments in humans shows a weight loss benefit. However, some reviews decried the lack of studies looking at other metabolic outcomes. Personally I don’t think this is concerning, because weight control seems to be the dominant factor for most people in determining related metabolic factors, like glycemic control. Looking at them separately would be useful, but I consider it unlikely that we will be surprised. Still, it is always better to be sure.

To that end, there are recent studies (perhaps too recent for the reviews to have taken into consideration) that do look at metabolic outcomes. A 2018 study looked at the glycemic impact of consuming LCS (which they call non-nutritive sweeteners, or NNS):

In comparison with the baseline, NNS consumption was not found to increase blood glucose level, and its concentration gradually declined over the course of observation following NNS consumption.

So LCS did not have an adverse effect on insulin effectiveness (which some of the animals research suggested) and in fact had a positive impact on blood sugar over time. This is yet another example of why you cannot directly extrapolate from basic science to net clinical outcomes in humans – you have to study them directly.

There are still some sub-questions, such as the impact of LCS on young children. Perhaps it affects their reward system or metabolism adversely and has later negative consequences. A 2016 and 2018 review both concluded that there is no evidence for an adverse effect, but more research is needed to be sure.

The safety of the various LCS, long established, has also been recently reaffirmed by reviews of the published research.

However, for those dedicated to fearmongering about artificial sweeteners, there is always something new to worry about. It is, of course, legitimate to ask new questions as our medical knowledge advances, and we may find previously missed risks. But it is reassuring that we have years and even decades of clinical research looking at overall health outcomes, so if there were any real health risk, even from a completely unknown mechanism, we should have seen it.

Despite reassuring safety data, you can stoke fears anew by simply doing another basic science study and showing some new potential effect to worry about – in this case the new concern is over the gut microbiota. Studies in mice show changes to the bacterial flora of the gut, which can be used to speculate wildly about the possible health impacts. The gut microbiota is the new oxidative stress; it can be blamed on anything about which you want to stoke fears. We won’t know for decades what all of this preliminary evidence about our microbial friends really means, but it will serve as a fresh source of pseudoscience, fearmongering, and speculation for that time and beyond. At this point there is no clear evidence that LCS have an adverse effect on our gut microbiota leading to any adverse health outcome. Anyone quoting the basic science to suggest that there might be should be referred to the utter lack of correlation between the basic science and clinical outcomes on all the other false fears about LCS.

So in 2018 we are basically in the same place we were in 2015 – artificial sweeteners are safe, they do not cause obesity or any known metabolic or other health problems, and they can be very useful as part of a weight control strategy. People should not avoid them because of unwarranted fears.

Further, we should reject the offer of “all natural cane sugar” and other sugar gimmicks. Unlike the speculative an unknown risks of LCS, there are well-documented and clear health risks from consuming too much simple and refined sugars. I know many people who choose to consume cane sugar rather than sucralose or aspartame because they believe it is better for them. They are wrong, the victims of deliberate misinformation campaigns, fearmongering, and misguided narratives. But they are also poorly served by popular communication regarding a complex scientific literature. They are exchanging a small speculative risk for a large known risk, and patting themselves on the back for it.

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Posted by Steven Novella

Founder and currently Executive Editor of Science-Based Medicine Steven Novella, MD is an academic clinical neurologist at the Yale University School of Medicine. He is also the host and producer of the popular weekly science podcast, The Skeptics’ Guide to the Universe, and the author of the NeuroLogicaBlog, a daily blog that covers news and issues in neuroscience, but also general science, scientific skepticism, philosophy of science, critical thinking, and the intersection of science with the media and society. Dr. Novella also has produced two courses with The Great Courses, and published a book on critical thinking - also called The Skeptics Guide to the Universe.