Do No-Calorie Sweeteners Make Us Fat?

The Bitter Truth about Observational Studies

Are artificial sweeteners making us chubby? That’s what you might think if you skim the headlines or glance at study titles. Here’s the truth.

If you glance at the research on artificial sweeteners, or rather, the headlines about the research, you’ll think they’re best avoided.

“Just have regular sugar,” the normies will say. Too bad they don’t question what journalists tell them. Because, in truth, most regular journalists don’t know how to interpret scientific studies either.

When research shows that artificial sweeteners cause XYZ problems, you must ask. “How was the research done?” Is there an actual causation, or is it merely correlation?

So to cut to the chase, no, artificial sweeteners and the soft drinks they’re in do NOT cause weight gain. But read on to understand science a little better so you’re not duped in the future.

A Scary Study

Researchers recently found an association between several sweeteners and fat mass (1). Case closed, right? Not quite.

The weakness of observational studies is that they’re not able to show causation and are prone to many confounders. In this case, it’s quite clear that the associations found are due to a phenomenon known as “reverse causation.” In this case, those who are overweight or obese are more likely to consume non-nutritive sweeteners than sweeteners causing weight gain.

What did the researchers actually find?

They followed a group of adults over 25 years and gave them food questionnaires to gauge their intake of non-nutritive (artificial) sweeteners while also assessing their body weight and composition. Throughout the study period, total consumption of artificial sweeteners as well as consumption of aspartame, saccharin, and diet beverages, were positively associated with fat mass volumes, body mass index, body weight, and waist circumference.

However, interestingly, sucralose (Splenda) intake had no association with any of these variables.

How Do We Explain These Results?

If we take these results as the authors insist, total artificial sweetener intake can cause fat gain while sucralose does not.

That sounds great if you’re a big consumer of sucralose. Just keep in mind that when the media reports these findings, they’ll lump all sweeteners together and just tell you to consume the “real deal,” which is sugar-laden junk food and soft drinks.

Going back to the study, though, the most likely explanation for their findings is the association they neglected to consider between exercise habits, diet, and consumption of sweeteners. Granted, the researchers relied on self-reported food and physical activity questionnaires, which are notoriously unreliable. People forget, exaggerate, and often paint a very different picture of their own habits.

Nonetheless, when we evaluate the baseline characteristics of the study participants, we see that those consuming the highest amount of sweeteners were also the heaviest and had the greatest waist circumference. These were also the individuals who – if we believe the questionnaire’s accuracy – had the highest level of activity while also consuming the greatest amount of calories.

In the real world, these are likely the people who struggle with their weight. They try to out-exercise a bad diet and justify over-consuming calories – like eating brownies every night but justifying it because it was made with a sugar-free sweetener. Or the person who eats McDonald’s five times per day but has a Diet Coke each time to “balance it out.”

This is consistent with data from other studies where the majority (around 55%) of individuals regularly consuming diet soda were classified as obese (2).

In short, overweight people use more artificial sweeteners, but artificial sweeteners were not the cause of their fat gain.

Randomized Controlled Trials (RCTs)

How can we be so sure that this association is due to reverse causation rather than the sweeteners causing fat or weight gain?

In the hierarchy of scientific evidence, interventional studies consisting of randomized, placebo-controlled trials are the strongest. And unlike observational studies, these randomized controlled trials (RCTs) allow us to make conclusions about cause and effect.

When we look at what the RCTs find, it’s consistent that these sweeteners (including the “natural” sweetener stevia) either have no effect on variables such as fat mass or they actually decrease these variables (sucralose), especially when compared to those ingesting table sugar or sucrose (3-5).

This is also the case with meta-analyses of these RCTs, further strengthening the conclusions.

Take Home Points

  • Don’t give much credence to observational studies that find an association between artificial sweeteners and body fat.
  • The results from these observational studies are likely confounded by reverse causation.
  • Randomized, controlled trials consistently show either no effect on body weight and fat mass or, in some cases, a decrease, especially when substituted for sugar.

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  1. Steffen BT, Jacobs DR, Yi SY, Lees SJ, Shikany JM, Terry JG, Lewis CE, Carr JJ, Zhou X, Steffen LM. Long-term aspartame and saccharin intakes are related to greater volumes of visceral, intermuscular, and subcutaneous adipose tissue: the CARDIA study. Int J Obes (Lond). 2023 Jul 13. doi: 10.1038/s41366-023-01336-y. Epub ahead of print. PMID: 37443272.
  2. Rusmevichientong P, Mitra S, McEligot AJ, Navajas E. The Association between Types of Soda Consumption and Overall Diet Quality: Evidence from National Health and Nutrition Examination Survey (NHANES). Calif J Health Promot. 2018;16(1):24-35. PMID: 30906234; PMCID: PMC6428592.
  3. Rogers PJ, Appleton KM. The effects of low-calorie sweeteners on energy intake and body weight: a systematic review and meta-analyses of sustained intervention studies. Int J Obes (Lond). 2021 Mar;45(3):464-478. doi: 10.1038/s41366-020-00704-2. Epub 2020 Nov 9. Erratum in: Int J Obes (Lond). 2021 May 27;: PMID: 33168917.
  4. Movahedian M, Golzan SA, Asbaghi O, Prabahar K, Hekmatdoost A. Assessing the impact of non-nutritive sweeteners on anthropometric indices and leptin levels in adults: A GRADE-assessed systematic review, meta-analysis, and meta-regression of randomized clinical trials. Crit Rev Food Sci Nutr. 2023 Jul 13:1-18. doi: 10.1080/10408398.2023.2233615. Epub ahead of print. PMID: 37440689.
  5. Miller PE, Perez V. Low-calorie sweeteners and body weight and composition: a meta-analysis of randomized controlled trials and prospective cohort studies. Am J Clin Nutr. 2014 Sep;100(3):765-77. doi: 10.3945/ajcn.113.082826. Epub 2014 Jun 18. PMID: 24944060; PMCID: PMC4135487.

If theres any sweetener that ive always had issues with, its Stevia. It always messed with me hormonally and made me crave sweets more than anything. After a little research, i figured out that it is indeed an endorcrine disruptor. That may just be the extract that was doing this to me. Never had it in its natural form, though.

Love Stevia and Monk Fruit sweeteners.

I drank a ton of Diet Coke when I was preparing for bodybuilding competitions. I continued to lose weight. Non calorie sweeteners don’t make us fat.

As a personal anecdote and “n of one,” I was never a coffee drinker, so before I discovered green tea, I used to drink a lot of caffeinated diet sodas - probably 5-6 per day. It got to the point where I was essentially an addict, meaning I would get a headache and not feel well if I went too long without a diet soda. I didn’t like the feeling of dependence, so over a 3-day weekend I decided to go cold turkey. The first 24 hours were really miserable and the next 24 weren’t much better, but by the 3rd day, I was more or less over it. This was over 10 years ago, and I haven’t gone back. I did notice that I had lost a little fat about a month after I stopped the diet sodas, but I would attribute this to my sleeping much better and strangely, the significant improvement of my allergies.

I’m not sure what was going on with the diet sodas. I do have caffeine occasionally through green tea, but it doesn’t seem to have the same addictive effect that the diet sodas did. There’s probably some combination of the caffeine, the artificial sweeteners and maybe the carbonation that made it both really addictive as well as bad for my sleep and allergies. Again, this is just my own experience, but whenever I see friends that are diet soda addicts, I always try to share my story and encourage them to try drying out. If you can make past the first week, you’ll start feeling so much better that you won’t go back through force of habit.

One of the issues with Sucralose in particular that is never really discussed in articles and posts here is its effect on the gut biome.

There is more than anecdotal evidence about how sucralose negatively affects the gut biome which can lead to weight gain and obesity.

So it’s not really about cancer, insulin spikes, diabetes or things like that - it’s the potential for metabolic derangement.

Mark Sisson has an older article on his site that introduces some of the then-current research.

In my view, as always, pay attention to how you feel and whether or not your body comp is doing what it should.

Previous post regarding microbiome:

The gut microbiome issue is a complicated one. For one, it’s extremely difficult to study accurately in humans as there are so many variables (diet, lifestyle, body composition) that can influence the composition of microbes in the gut. Having said that, the studies with the strongest designs (RCTs) have produced conflicting results.

This is the most recent and comprehensive review I’ve seen and the author’s conclude that that it’s too difficult to determine whether these changes are occurring due to a given sweetener and what the significance of those changes would be. You also have data showing the complete opposite of effects in humans versus rodents.

Something else you’ll find is that the there are data showing changes regardless of the sweetener, natural or otherwise.

Also, a recent meta-analysis concluded that in humans, if sucralose alters the microbiome it results in weight loss, not weight gain. This is consistent with what has been shown in RCTs.

Thanks for the links, Cy. Will review.

So many confounding variables. Really, it’s like so much else in nutrition and fitness - how does the sum total of what you choose to do make you look, feel, and perform? Unhappy with something? Make a single discrete change that you can effectively measure, then tinker.

In an ideal world maybe people would eat less sugar less often (though this might be your ideal world, not mine). Since people have long been used to eating sweeter things, artificial sweeteners seem a reasonable alternative. The chemistry, metabolism, taste and effects differ for various non-nutritive sweeteners and sugar alcohols.

Many sweeteners have been well studied and used for decades in millions of people. Health organizations and studies come out periodically reporting drawbacks to sweeteners. But these drawbacks should sometimes be compared to the effect of sugar.

No one is going to drink 2000 diet colas in a day, or whatever unrealistic dose might increase the risk of mouse mutations. At a high enough dose, they might cause cancer. And this was the only impetus behind the stern sounding nothing-burgers the WHO recently came out with, saying in fearsome terms there is a possible dose of sweetener that is probably carcinogenic. No new info there.

That doesn’t mean every sweetener is ideal for every person. Some studies are better conducted than others (and some do compensate well for exercise and other demographics around who eats the sweetener, but as you rightly point out many studies do this badly). Sweeteners may not make you fat but they also might not help you lose weight if you consciously or unconsciously select other things or crave other foods. But eating the equivalent sugar probably won’t help you lose weight either, and metabolically “you can get fat from sweets, but you can’t get sweet from fat”. Does erythritol increase stroke and heart attack as the Cleveland Clinic reported in February 2023? Perhaps, but again this could easily be biased since bigger people may eat more sweeteners and be in worse shape if the study is poorly randomized. If the effect is real, is it significant enough for doses people might actually use? (I don’t eat this sweetener but the risks may be relatively mild for many people).

Other reports say sweeteners are not great for the gut. But doctors don’t really know that much about the gut microbiome. Hard to test, not the same in different parts, and hard to meaningfully measure. One dirty secret is that the world is full of untypeable bacteria and viruses. We know the names of microbes that cause disease in people and some animals and which you can grow in a Petri dish. But there are maybe millions which have no name and can’t be easily classified. Does sweetener affect the biome? Likely so, but it will be years before we know what that means.

It is messy. I have an issue with diverticulitis - a bacterial infection in the gut (Current science says it’s from squeezing too hard while poopin’ but I’ve never had that problem). I’ve quit sucralose for that. Even if it is questionable, for me, it is not worth it. Since quitting artificial sweeteners, I’ve not had another bout. But I’ve changed a lot of other stuff too, so this ain’t scientific at all.

I would hazard a guess that if you’re mostly healthy, stuff like this doesn’t matter that much. If you screwed up to have hard to pronounce issue, many minor or borderline and hard to reproduce research/problems might be the straw that breaks the camel’s back.