Highlights

• Sucralose is a no-calorie sweetener.
• While sucralose is the most commonly used sugar substitute, most diet sodas are not sweetened with sucralose.
• A new study suggests that sucralose consumption produces metabolic dysfunction when it is consumed with a carbohydrate, but not without a carbohydrate.
• This study was not designed to assess sucralose metabolism. Research in humans that has studied sucralose metabolism has not found plausible mechanisms that support the findings of this new study.
• This single study need not change your personal approach to making healthy choices.

Low- and no-calorie sweeteners (LCS), like sucralose, are some of the most studied components in our food supply. They have been shown to be safe and approved for use in foods and beverages by top health authorities around the world. But a new study published in Cell Metabolism has challenged expert consensus based on decades of research on the human metabolism of low and no-calorie sweeteners. The study suggests that sucralose-sweetened beverages may interfere with the way healthy people digest carbohydrates. What does this new study tell us that previous research does not? Should we think differently about what we eat while we drink a diet beverage? Here’s our take.

How was the study done?

This study set out to test a concept known as the “sweet uncoupling hypothesis,” which in simple terms states that since LCS deliver sweet taste without calories, the body changes its normal ways of responding to sweetness. If the hypothesis proved true, the results would indicate that people consuming LCS would have changes in glucose metabolism and reduced brain and sensory responses to sweet taste.

Study participants were 39 healthy adults (ages 20–45 years old) who did not regularly consume LCS (for this study, that meant they drank less than three 12-ounce (355 mL) servings per month). Initially, researchers had planned to conduct a similar study in adolescents ages 13–17. However, that study was terminated early due to increased plasma insulin concentrations in two Combo group participants.

Participants underwent baseline measurements that included an oral glucose tolerance test (OGTT) to look at how the body breaks down glucose and a functional magnetic resonance imaging (fMRI) scan to measure brain activity. Then, each participant drank seven 12-ounce (355 mL) drinks over the course of two weeks. The type of beverage they drank depended on the group they were randomized into: Sugar (sucrose, commonly known as table sugar), Sucralose, or Combo (sucralose plus maltodextrin, a type of sugar that contains the same amount of calories and is broken down just like table sugar but does not taste sweet). After finding differences in outcomes in the Combo group compared with the others, researchers covered their bases by adding another group that consumed drinks with maltodextrin only. Each time they drank their assigned beverage, participants had measurements taken on their taste perception and taste preference. After the two weeks were over, participants had another OGTT and fMRI to see how their responses changed compared with their baseline measurements. The main outcomes of interest were glucose tolerance, taste perception, and brain response to sweet, sour, savory and salty tastes.

What were the results?

The results of the study seemed somewhat unexpected to the researchers. No key differences were seen in any measurement between the Sugar or the Sucralose groups. The surprises came when looking at the Combo group: These participants had a more sustained concentration of insulin in their bloodstream in the OGTT that was completed after they drank all seven beverages compared to their baseline measurement; and combined with the fMRI imaging, a relationship was found between the brain’s responses to sweet taste and insulin concentrations. However, taste perception and preference did not change in any of the groups. Together, these results refuted the uncoupling hypothesis.

In essence, the study’s results showed that there were differences in the body’s glucose response when sucralose was consumed with a carbohydrate source when compared with sugar or sucralose alone.

Study strengths and limitations

The design of this research was complex. It aimed to touch on many aspects of eating and drinking: how our brain responds, how our body is impacted and how our personal preferences weigh into the physiology of it all. And while it was ambitious, it is apparent that methodological issues plagued the study and hindered the interpretation of its results. Here are a few key limitations:

• Small sample size. Of 55 people initially recruited for the sugar, sucralose and Combo groups, only 39 completed the study. Almost a full third of subjects didn’t finish, based on both personal preference and methodological issues requiring their removal. Only 13 people were included in each of these groups, which means that the variability in the endpoints is higher than if more people had been studied.
• Study length. This study’s intervention lasted just two weeks. In this amount of time, it’s difficult to draw strong conclusions after people drink seven 12–ounce beverages.
• Diet history was not assessed, or at least not included. While information on LCS use was collected, there was no mention of collecting information on other foods and beverages that participants ate and drank during the study. The effect of 84 ounces of a beverage is difficult to assess when everything else that was consumed during these two weeks was not fully accounted for. The total diet matters—it’s always an important factor to consider in nutrition studies.
• Lots of mechanisms were discussed, but most were not actually tested. Study authors wrote quite a bit about possible mechanisms that may explain the results they found. However, the study was not designed to confirm or refute any of them. Much more research is needed to be able either to draw clear lines between the findings or to erase them.

Media Interpretation

As is usually the case, many media outlets were off to the races with a new study on LCS, and not in an accurate, fact-checked kind of way. Headlines like “Mixing diet soda and fries has a dangerous effect on the brain” and “If you’re eating carbs, have a regular fizzy drink rather than a diet version” immediately materialized, showcasing perfect examples of how research results can be woefully misinterpreted. When little care is taken to stick to the science, it’s no wonder that readers are confused by the health impact of LCS and nutrition science in general.

We’re no stranger to the media attention paid to LCS research—we’ve written several Fast Takes similar to this one. A common thread among them is the fact that often, the headlines don’t align with the science. Taking the leap from people drinking sucralose and maltodextrin to having a diet soda with french fries is wholly inaccurate. Sucralose itself is not often used in most diet sodas (in most cases, it’s acesulfame potassium (ace-K) and aspartame). And maltodextrin is definitely not the same as an order of fries. While we don’t advocate for french fries as a health food by any means, they do consist of a multitude of food components—protein, fats, carbohydrates, vitamins and minerals. Maltodextrin, on the other hand, is a pure carbohydrate—a fast-metabolizing sugar source. The impact that a whole food will have on the body is markedly different from that of a pure sugar. To say that this study’s results lead us directly to the message of “don’t drink diet soda and eat fries at the same time” is an irresponsible way to interpret the science.

Closing thoughts

Sucralose’s impact on health has been extensively studied, with decades of research showing that sucralose is safe to consume and does not raise blood sugar or affect blood glucose control in humans. Despite these conclusions, some studies periodically raise questions about sucralose impairing normal blood glucose control. Stronger, more well designed research studies do not support such hypotheses.

What most people will likely want to have answers for is, “Should I change the way I eat and drink because of this latest study?” The short answer is no. If you use choose foods and beverages that contain sucralose and/or other low-calorie sweeteners, you can safely continue doing that. If you prefer not to use low-calorie sweeteners, that’s fine too. Whatever helps you stick to a healthy diet and lifestyle is the approach you should take.