Physiology Friday #126: Do Non-nutritive Sweeteners Negatively Affect Blood Sugar Regulation?
Diverse and highly individual effects on the human gut microbiome and metabolism occurred after a 2-week diet rich in calorie-free sweeteners.
Happy Physiology Friday!
In case you missed it: On Monday, I released episode 52 of the Science & Chill podcast. I chat with Nick Norwitz, Ph.D., about some of the promises and controversies surrounding the use of continuous glucose monitoring (CGM) in healthy individuals.
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Quick finding of the week: Standing desks may be useless for improving cardiometabolic health. In a 12-month trial investigating the effects of adjustable desks on sitting time and physical health variables, there were no changes in waist circumference, BMI, body fat %, blood glucose, cholesterol, triglycerides, or cardiometabolic risk — despite a reduction in sitting time by ~50 minutes/day.1
Non-nutritive sweeteners: are they good or bad for your health?
We’re told on a regular basis to avoid sugar at all costs. While some of the caution is likely overblown, there’s no doubt that an excessive intake of sugar can lead to a number of deleterious health effects.
In recent years, similar concerns have been raised about “artificial” or so-called non-nutritive sweeteners (sweeteners that don’t contain calories). While non-nutritive sweeteners are “inert” from an energetic perspective, they may exert unique and surprising effects on the gut microbiome and other aspects of physiology.
Many people regularly consume products containing non-nutritive sweeteners with the assumption that they don’t affect blood glucose and therefore, are totally harmless. Very little research has been done to investigate whether this is so.
A new study published in the journal Cell2 provides a comprehensive look into the effects of non-nutritive sweeteners on the human microbiome and blood glucose regulation, as well as the highly individualized responses to these products.
120 healthy adults were randomized to 1 of 6 different conditions (20 participants per condition) in which they consumed Stevia, Saccharin, Aspartame, Sucralose, Glucose (sugar), or no sweetener (control group).
Participants consumed 6 sachets per day of their assigned sweetener — an amount that’s below the acceptable daily intake of non-nutritive sweeteners for adults.
At baseline, 1 week, 2 weeks, and follow-up, participants had their blood glucose tolerance assessed during an oral glucose tolerance test (OGTT). An OGTT measures the blood glucose response to the ingestion of a large amount of glucose (50g), with a larger and more prolonged glucose spike indicating worse glucose tolerance.
Fecal samples were also provided by all participants and “transplanted” into mice who were lacking a microbiome (known as gnotobiotic mice). These mice were then subjected to an OGTT to measure their glucose tolerance. This portion of the study allowed the researchers to determine whether the effects of non-nutritive sweeteners on glucose tolerance were mediated by the microbiome. If mice displayed similar metabolic responses to humans, then the microbiome-mediated effects of the sweeteners could be confirmed.
Saccharin and Sucralose, but not Aspartame or Stevia, impaired glucose tolerance in the human participants starting after the first week of exposure and lasting through week 2. However, glucose tolerance returned to normal during the follow-up period.
A particularly interesting finding was that the individual participant responses to each of the sweeteners were all over the place. Some participants were “responders” in whom sweetener consumption impaired glucose tolerance. Others were “non-responders” in whom sweetener consumption had no effect on glucose tolerance. It also appeared as if some of the participants who were “non-responders” at week 1 began to creep into the “responder” territory during week 2. Given enough time, would they have become susceptible to the effects of non-nutritive sweeteners?
All of the sweeteners were found to impact the stool and oral microbiome in the participants. When microbiome samples were taken from participants in the upper and lower ends of the responder categories and transplanted into microbiome-free mice, the mice exhibited similar glycemic responses to their human donors! This confirmed that the metabolic effects of non-nutritive sweeteners appear to be mediated by the microbiome.
Does this mean that you should cut out artificial and non-nutritive sweeteners from your diet? Are Stevia and Aspartame safe to ingest?
Well…it depends (sorry!) The individual responses to non-nutritive sweeteners suggest that for some, non-nutritive sweetener consumption may negatively impact glucose regulation. While non-nutritive sweeteners may not impact your blood glucose per se, they may affect your body’s ability to metabolize glucose or alter your insulin sensitivity.
This means (maybe) that ingesting artificial sweeteners along with a high-carb meal could be a harmful combination. However, the results of this study don’t directly suggest this.
For others, non-nutritive sweeteners exert neutral or perhaps even beneficial effects on blood glucose regulation (though the “benefits” weren’t shown in this study).
The bad news is that, unless you’ve got access to sophisticated testing methods, it’s going to be hard to figure out which group you fall into.
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It’s worth noting that this study was only 2 weeks in length and therefore, doesn’t say much about the chronic effects of non-nutritive sweetener consumption. Maybe the metabolic effects of the sweeteners dissipate after 3 weeks of use, or perhaps they become even worse!
The effects seen in this study do seem to be reversible — as suggested by the normalization of glucose tolerance during the follow-up period when participants had stopped their consumption of each sweetener.
From this, we might be able to speculate that the occasional moderate intake of non-nutritive sweeteners is probably harmless. But what defines “moderate?” The daily consumption in this study was the equivalent of around a single can of diet coke, which really isn’t that much. Limiting consumption to less than this amount would seem pertinent.
The larger message here — aside from the information that non-nutritive sweeteners are not as inert as we might think — is that nutrition should be taken as a highly personalized endeavor. No, this doesn’t mean you have to eat for your blood type or start a diet that’s recommended for your genome. Personalized nutrition means that how I respond to one food is totally different than how you’ll respond to the same exact food. Because of this, making blanket statements about “good” and “bad” food is moot.
The only way to find what works for you is, like most things, to run the experiment yourself. You might be surprised at what you find.
Thanks for reading. See you next Friday.