Artificial sweeteners sound like a dream come true for weight control. Even for people who generally eat a Paleo diet and scrupulously avoid real sugar, there’s always that temptation to give artificial sweeteners a pass. After all, they have no calories! Sure, they might not be the healthiest thing in the world, but at least they won’t make you gain weight, right (and we all know that’s what’s really important; who cares about that silly “health” stuff)? Surely it’s better to have Equal in your coffee than to have actual sugar, isn’t it?
Well first of all, weight and health are two different things. You can be thin and still be very, very sick. Paleo is a diet designed to make you healthy: for some people, that means weight loss as part of the package, but the weight loss itself isn’t the end goal. The end goal is health. So if artificial sweeteners help you lose weight but destroy your gut flora or cause other problems, then they’re not Paleo regardless of what the scale says.
But do they really even help you lose weight? It’s true that they don’t have calories, and it’s true that calories ultimately drive weight gain or loss, but “calories” includes both “how many calories you eat” and “what your body decides to do with those calories” – and the second category is not something you can measure just by tallying up a number.
If artificial sweeteners cause metabolic or gut flora damage that makes you (a) absorb more calories from the food that you eat, (b) store more calories as fat instead of burning them as fuel, or (c) both, then they might still cause weight gain even though the sweeteners themselves have no calories.
To clear that up, here’s a look at some common artificial sweeteners. This article doesn’t look at stevia (which is a natural product, so it isn’t an artificial sweetener) or at sugar alcohols (e.g. xylitol and erythritol, which are in a class of their own). It’s just about 0-calorie artificial sweeteners:
- Saccharin (Sweet’n’Low)
- Sucralose (Splenda)
- Aspartame (Equal, NutraSweet)
- Neotame (NutraSweet)
- (outside the US) Cyclamtes*
*Cyclamates are not approved by the FDA for human consumption, but they’re common in Europe.
Consumption of artificial sweeteners is associated with obesity. Does this mean that the sweeteners cause obesity, or does it mean that people who are obese tend to eat more artificial sweeteners because they’re trying to lose weight?
It’s hard to say whether these sweeteners do or don’t contribute to weight gain and loss – for one thing, the studies are full of conflicts of interest. Scroll down to the bottom, and you’ll often see that the authors have some kind of professional involvement with the artificial sweetener industry – of course they’re going to find that artificial sweeteners don’t cause weight gain. But here’s a look at the research we have on the topic.
Artificial Sweeteners: Effects on Insulin and Blood Sugar
One theory for how artificial sweeteners might contribute to weight gain revolves around insulin. Insulin is a hormone that helps clear glucose (sugar) from your bloodstream. If artificial sweeteners trigger the release of insulin but don’t provide any extra sugar for it to remove, you might end up with a dangerous low blood sugar crash. Then you feel hungry because you’re sugar crashing, so you reach for the simple carbs and end up gaining weight.
It makes sense as a theory, and it makes sense if you only look at rodent and test-tube studies, but the effects in humans are less clear. This study found that in healthy subjects sucralose lowered blood glucose (implying some kind of insulin action), but aspartame did not; in subjects with Type 2 Diabetes, neither had an effect. This study found that tasting aspartame, saccharine, or sucrose did not cause any greater insulin release than tasting plain water.
A review concluded that the insulin theory doesn’t actually pan out in actual human beings, but the authors of that study had serious conflicts of interest (one worked for the International Sweeteners Association, and the other one works for the company that makes Splenda). This review, where the authors had no conflicts of interest, concluded that “Further research is needed to determine whether non-nutritive sweeteners have physiologically significant biological activity in humans.”
The bottom line: It’s unlikely (but not conclusively proven false) that artificial sweeteners cause weight gain through an insulin response.
Artificial Sweeteners: Effects on Appetite
But what if it isn’t insulin at all? Another theory is that artificial sweeteners confuse your body by separating the taste of sweetness from the caloric reward. As a baby, your body learned to associate sweet taste with calories. By eating them, it un-learns that instinctive association, and learns that taste and calories are unrelated. This impairs your natural ability to “eat when you’re hungry and stop when you’re full,” and makes you more susceptible to external cues (e.g. food advertising).
In this study, rats fed a saccharin-sweetened yogurt ate more calories and gained more weight and body fat than rats fed a glucose-sweetened yogurt. The researchers speculated that this was because the artificial sweetener separated the taste of sweetness from the physiological intake of calories, effectively confusing the rats’ hunger signals.
So does it work the same way in humans? Some evidence does show that artificial sweeteners and real sugar have different effects on the brain. This study put healthy, non-obese men in an MRI after drinking either plain water (control), sugar water, or water sweetened with aspartame. Drinking the sugar water had a noticeable effect on brain activity in the hypothalamus, while the aspartame water didn’t. In other words, the subjects’ brains didn’t really “register” that they’d drunk something sweet.
There’s not a lot of evidence that this change in brain activity causes increased hunger or weight gain in humans, though.
This study found that artificial sweeteners made the subjects feel subjectively hungrier, but they didn’t end up eating more to compensate
(to be fair, the authors also clarified that their study design might have caused this). This study found that 280ml (just under a standard soda can) of an aspartame-sweetened soft drink had no effect on appetite, while 560ml (that’s roughly the size of a bottle you get from a vending machine) actually reduced appetite.
This review examined the role of artificial sweeteners on appetite regulation in humans, and found that hunger and satiety ratings after drinking sugar-sweetened soft drinks and artificially-sweetened drinks are basically the same. If you give study subjects a drink and then later give them a meal, they’ll eat about the same amount regardless of how the drink was sweetened.
The authors concluded that humans are so lousy at compensating for liquid calories that there’s basically no difference between compensation for sugar-sweetened drinks and artificially-sweetened drinks. We don’t compensate for liquid calories anyway, so there’s no real difference. The result is that in blind taste-tests, using artificial sweeteners results in a slightly lower calorie intake overall.
That accounts for the most popular use for artificial sweeteners: in drinks. It’s not clear whether this effect extends to artificial sweeteners in foods (like the yogurt in the rat study).
The bottom line: artificial sweeteners in drinks probably don’t increase appetite by confusing your body’s regulation mechanisms. In solid foods, it’s not clear.
Artificial Sweeteners: Effects on the Gut
The last potential problem is the gut: a recent study found that mice who ate a reasonable dietary amount of artificial sweeteners developed gut problems that impaired their carb tolerance and made them gain weight. Saccharin in particular caused significant changes in the gut flora of the mice (aspartame had no effect).
When they tested the same thing in humans, about half the people eating the saccharin had impaired glucose tolerance and about half of them showed no change.
In other words, some people may be sensitive to changes in gut flora caused by artificial sweeteners, but other people may not be. Hopefully more research will clear this up: it's an interesting question!
Summing it Up
Various overall studies on artificial sweeteners and weight gain have come to different conclusions:
- This review of artificial sweeteners on body weight concluded that there really is no evidence for significant benefit or drawback. In other words, switching from sugar to Splenda probably won’t help most people lose a lot of weight, but it won’t make them gain a lot of weight either.
- This study found that replacing sugary soft drinks with artificially-sweetened soft drinks (without any other intervention) had no significant effect on BMI after two years. This is a valuable study, because it's a real-world situation, not a blinded taste-test, so it controls for the "I got Diet Coke, so I get to have this cheesecake" effect - that might be one big reason why artificial sweeteners aren't very useful for weight loss in the real world.
- This review concluded that artificial sweeteners have a very slight tendency to reduce body weight, but if you look at the Acknowledgements section at the bottom, you’ll see “We acknowledge the International Life Sciences Institute Low-Calorie Sweetener Committee for providing feedback and review of the study protocol and manuscript.”
In other words, artificial sweeteners likely don’t do a lot for body weight either way, possibly because they’re really just a junk-food crutch that doesn’t address the reasons why we crave sugar and processed foods in the first place. They might not cause weight gain, but they’re not a sustainable strategy for weight loss, either.
It’s also worth reiterating that just because something doesn’t cause obesity doesn’t make it healthy. Especially considering the recent work on artificial sweeteners and the gut flora, it might be wise to hold off on eating them. The 2014 study just started to scratch the surface – we know a little bit about sugar alcohols and the gut, but very little about artificial sweeteners.
Instead of trying to reduce the calories in your junk food, a better plan for weight loss is to stop eating junk food full stop. Tackle any sugar cravings or emotional eating head-on instead of masking it with artificial sweeteners. That’s the way to create sustainable lifestyle changes and develop a healthy relationship with food in the long run.