what the latest study found

what the latest study found

A recent study from Mexico was published that examines the potential impact that sucralose (commonly found as Splenda), has on our gut health, blood sugar, and insulin levels. The title quickly implies a link between sucralose, and something called ‘gut dysbiosis’.

You’ve probably heard this term in the wellness sphere (usually when someone is trying to sell you something), so coupled with the common belief that sucralose is horrible for our gut (I wrote about this here), this study got a lot of attention, especially from people who believed that it was going to confirm their suspicions that sucralose is the most horrible thing ever.

I feel like these studies are like a litmus test of who really knows their sh*t and can read research, and everyone else who just reads the headlines and then posts on social media about what they THINK they know (and don’t).

Sounds SCARY!! This is an older headline, but it’s consistent with the media’s portrayal of sucralose and the gut

Dysbiosis of the gut simply means the microbes living in our bowels are out of balance. This can play a role in digestive conditions such as irritable bowel syndrome, and chronic bowel syndromes like Crohn’s, and colitis. 

Our gut microbiome contains billions of bacteria; some are generally helpful, and some are not, although science around the links between certain bacteria and their effects on health is in its infancy. Our microbiome has been linked to bowel habits, neurologic function, mood, and even our weight. 

The food and drink we consume, genetics, and lifestyle factors such as physical and mental stress, travel, and infections, seem to have a strong influence on our microbiome. Because of how many bacteria we have, how many types of bacteria there are, and the numerous factors that can impact their levels, the gut microbiome can be tricky to study. 

These bacteria look like cupcake sprinkles. They don’t really look like that IRL, just saying.

We still have a lot to learn about this complex world inside of us. 

What is sucralose?

Sucralose has been approved for use as a general-purpose sweetener (sugar alternative) by the FDA since 1999. Sucralose is 600x sweeter than sucrose, but it doesn’t promote dental cavities or increase blood sugar levels.

On a molecular level, sucralose is produced by chlorinating sucrose, or table sugar (one molecule of glucose + one molecule fructose), by replacing three of its hydroxy groups. Sucralose is not broken down or readily absorbed by body (hence it contains no calories).

The latest sucralose study. 

This study is the first to test sucralose in humans over a long time period (10 weeks is relatively long for studies like these).

Here is the link to the paper.  

The primary focus of the study was to investigate the potential impact of sucralose on gut health, blood sugar, and insulin levels.

Researchers chose 40 young, healthy volunteers (‘normal’ body mass index, between 18 and 35 years old, with no pre-existing medical diagnoses, no alcohol or tobacco intake, and who were not pregnant or lactating – even people who had used antibiotics in the last six months were not allowed to participate – and split them into two groups.

In this study, one group (the control group) drank water each morning, while the experimental group drank a solution containing sucralose (comparable to 4 packets of Splenda), for 10 consecutive weeks. During the study, all participants were asked to avoid sweeteners not provided by the study, and to adhere to a monitored diet. 

The researchers tracked their intake and exercise levels. Data on gut bacteria, insulin levels, and glucose levels was collected before the experiment began, and again after ten weeks.

What did the sucralose study find? 

Everyone’s microbiome is different – what constitutes ‘dysbiosis’ for me, may not for you. We also don’t fully understand what the ‘optimal’ microbiome looks like….for anyone.

In fact, there is no set definition or criteria of gut dysbiosis as a ‘condition’, nor did the study authors define one.

This is red flag numero uno for this research.

Just because gut bacteria changes, doesn’t mean that it’s going to have a clinical outcome that translates into poor health for the host. 

That being said, researchers found that volunteers in the sucralose group had changes in one of the tested species in their gut microbiome – more specifically, an increase in the bacteria Blautia Coccoidis. 

That sounds scary, but it’s probably not a bad thing.

There are 17 different Blautia species, some of which have been associated in early (and older) studies with fatty liver and type 1 diabetes in children. However, more recent research has found a much more positive association between Blautia and health.

This 2021 study linked this species of bacteria with increased short-chain fatty acid production (SFA), (PMID: 33525961) which is a GOOD thing: SFAs feed our good gut bacteria and are associated with better overall health.

This 2020 study (PMID: 32209719) found that a lack of Blautia species is linked to increased inflammation and obesity-related complications. It was also associated with new-onset inflammatory bowel disease in this 2014 study (PMID: 24629344)

Let’s talk about what this study found in terms of sucralose, insulin and glucose.

When volunteers in the sucralose group were exposed to an oral glucose tolerance test (OGTT) – effectively consuming a large amount of sugar at once and then checking to see how their bodies handle it – their insulin spiked higher at one time point, and their blood glucose levels were temporarily higher than when they underwent the test before the study. 

This seems relevant, but it isn’t: the researchers state in the study that the Area Under the Curve (which is an assessment of the impact) is the same at 0 weeks and at 10 weeks for both control and intervention groups with glucose and with insulin.


In other words, there’s no new and exciting news about sucralose and gut health here.

What’s all of this kerfuffle about the scary effect of sucralose on our insulin levels, again?

The researchers also attempted to make a vague connection between sucralose, lactobacillus, and abnormal insulin and glucose behaviour by citing an older study that used subjects who already had type 2 diabetes and obesity. 

This is an attempt to find a relevant link by comparing two completely different things. How do we know that the participants in the sucralose group Lactobacillus counts aren’t still within a perfectly healthy range for Lactobacillus? Simply stating there was a decrease doesn’t actually tell us anything useful here. 

The researchers also concede that further clinical studies are needed to make clear how sucralose may reduce the intestinal amount of this bacteria in humans in a clinically significant way.

What about the way the sucralose and gut health study was conducted?

We can’t talk about a nutrition study and not look at methodology. Methodology makes or breaks the research.

This study had some substantial limitations. Firstly, it was small, with 20 patients in each group. 

The entry criteria and methods for the study were fairly restrictive, which (in addition to its small size) means that findings may or may not apply to the general population.

The participants weren’t blinded to which group they were in, a design limitation that can introduce bias into the study results. In other words, if someone knows that they’re consuming a test substance and not a placebo, their behaviours may inadvertently (or purposely) change to match their perceived outcome.  

As in many nutrition studies, diet information relies on the recall and honesty of participants (unless each mouthful is watched by a researcher, which would be hard to get approved by an ethics committee) which can lead to errors, or at least unaccounted for factors. 

Additionally, the study’s primary endpoint (usually the most important factor to evaluate to see if the study made a difference or not) was defined as a change in the four bacterial species tested for, representing the bacterial ‘families’ or phyla. 

A ‘change,’ is pretty low-hanging fruit, considering that something changing doesn’t necessarily mean anything important (see comment on lactobacillus, above).

Studies that word their endpoints this way can sometimes turn into ‘fishing expeditions’, where they seek to report any change at all, rather than causative or logical ones.

Reporting these findings as significant changes, and calling this ‘gut dysbiosis,’ is very misleading. 

Participants were asked to ingest the sucralose on an empty stomach, in the morning. While not incorrect methodology, the rationale for this was not explained – and is likely not the way most people would use their sucralose in the real world. Substance absorption, interaction with other food products, and our bodies metabolism changes throughout the day, and based on our intake. The researchers have captured a narrow and specific type of intake here. 

Lastly, the genetics, diets, and lifestyles (overall stress levels, etc.) of the participants could impact the results as well.  

What did the authors say about the findings?

The authors themselves acknowledge some limitations of the study, including small sample size. They acknowledge that other test types may be better suited to answering their research question. Advanced sequencing would have enabled them to test for changes in all gut bacteria. The OGTT is notorious for poor reproducibility of insulin and glucose in other tests but served as the basis for the bold conclusions the authors ended up making. 

Future studies on the topic would do well to incorporate better tests that can help to find the true answer, rather than ‘any’ answer.

There is nowhere in the study that outlines clearly how the diagnosis of gut dysbiosis was arrived at. There are no figures or data showing the symptoms the volunteers would have had (diarrhea, abdominal pain, gas, bloating, belching, etc.) as it was not captured in the study. 

This is a red flag. 

As I always ask, what’s the CLINICAL SIGNIFICANCE of this conclusion? Does the supposed ‘dysbiosis’ have any relevant health outcomes that we need to consider? 

In this case, we have no idea. It’s just a kerfuffle of assumptions and loose ends. 

At the same time, the researchers state that their clinical trial ‘demonstrates, for the first time, that consumption of 48mg of sucralose every day for 10 weeks induces gut dysbiosis.’

This implies that ingesting sucralose for an extended period will lead to a messed-up gut. Saying this would be fine if that’s actually what the study found, but it’s not.

Hyperbolic language? Red flag!

Which ‘health experts’ are they talking about?

This study did not demonstrate a relevant, causal link between sucralose and gut health or anything else. 

That’s not surprising. In other human studies, sucralose has failed to demonstrate negative health effects.

One of the many reasons why nutrition is difficult to study and make definitive claims about is because it is so individualized; what may contribute to a dysbiosis in one individual will likely not have the same effect on another. 

In other words? Nothing new to see here, people. Just another nutrition study blown right out of proportion by the media.

Do I recommend sucralose? If someone wants to cut down on their sugar intake, they can switch from sugar to sucralose. They don’t have to though – what I usually recommend is that you cut down whatever you’re using to as little as possible.

Co-written by Lise Wolyniuk