Do Artificial Sweeteners Cause Weight Gain?


Do Artificial Sweeteners Cause Weight Gain?

You’ve seen the little packs of blue, pink, and yellow sweeteners, conveniently packaged so you can quickly add one to your coffee or tea. Artificial sweeteners sound like a “sweet” deal. You get the taste of sugar with virtually no calories. However, some experts are concerned that these sweeteners, despite their lack of calories, might not be so sweet after all. In fact, there are questions as to whether these sweeteners fuel weight gain. Is this supported by science?

Are Artificial Sweeteners Associated with Weight Gain?

Studies looking at whether artificial sweeteners are linked to weight gain are conflicting. That’s not surprising since there are a number of artificial sweeteners on the market and many of the studies were done in mice. Plus, whether or not a sweetener causes weight gain likely depends on factors like how much you use them, how often, in what form you take them in (food or liquid), and whether you consume them with a meal.

For example, getting artificial sweeteners from soft drinks may impact your body differently than adding them to food or to a healthier beverage like coffee or tea. Many of the studies showing a link between weight gain and use of artificial sweeteners were animal studies and not necessarily applicable to humans. Plus, people who are overweight or obese may respond differently to these sweeteners than leaner folks.

What does science say? A meta-analysis, an analysis of a large group of studies, published in the International Journal of Obesity in 2016 looked at a number of human studies where participants used artificial sweeteners. According to this analysis, artificial sweeteners were actually linked with lower total energy intake and modest weight loss. Many of these were interventional studies too, rather than observational. This gives them more credibility.

Other high-quality, randomized controlled trials show a modest reduction in BMI and waist size in people who use artificial sweeteners in place of sugar – but, remember, most of these studies are short-term. However, based on current studies, there’s little DIRECT evidence that artificial sweeteners cause weight gain, at least over a short period of time. However, we can’t say these sweeteners aren’t problematic longer term or that they can’t cause weight gain indirectly. Let’s see why.

Artificial Sweeteners, Gut Bacteria, and Body Weight

Your gut is far from a barren. In fact, the surface of your digestive tract is teeming with trillions of bacteria. Thankfully, many of these bacteria aren’t “bad guys” but perform useful functions. For example, these tiny critters produce acids that keep the lining of your intestinal tract healthy. They also protect against disease-causing bacteria, as well as modulate the health of your immune system. If that isn’t enough, they also play a role in nutrient and vitamin absorption and some even make vitamins, including vitamin K and some B vitamins. Studies also show that people who are overweight or obese have gut bacteria that differ from those who are leaner. So, gut bacteria seem to indirectly impact body weight.

What does this have to do with artificial sweeteners? Some studies suggest that artificial sweeteners may be harmful to the gut microbiome, the bacteria that make up your intestinal tract. According to an Israeli study, artificial sweeteners can alter the types and quantities of bacteria that live in your gut. That’s important since these bacteria play a role in how your body processes the macronutrients you take in as well as your overall metabolic health.

As Dr. Jeffrey Gordon, a researcher and physician from Washington University in St. Louis, points out, over 90% of the bacteria in the gut are of two species: Firmicutes and Bacteroidetes. Obese mice have a higher ratio of Firmicutes to Bacteroidetes. That’s important because Firmicutes bacteria give the mice the ability to extract more calories from the food they eat. More calories extracted from food increases the potential for weight gain. Even more interesting, when you transplant the bacteria from obese mice into lean mice, the formerly lean rodents gain weight.

Does this happen in humans as well? It’s a little more complicated with humans. It’s harder to monitor and control what humans, as opposed to mice, eat. People who are obese or overweight tend to use artificial sweeteners more than slender people but that’s not surprising since they’re trying to control their weight. So, there’s likely a selection issue. Many obese people also have metabolic issues, like insulin resistance and scientists are asking whether artificial sweeteners are a contributor.

Some scientists believe that artificial sweeteners are harmful to metabolic health in humans as well. The question is whether they’re worse than sugar? If so, the only option is to eliminate all forms of sweeteners or use a natural, no-calorie sweetener, like a Stevia-based one. However, there’s at least one study showing Stevia alters a particular gut bacteria, Lactobacillus reuteri, a bacterium you find in the digestive tract of most healthy people.

Do Artificial Sweeteners Change Eating Behavior?

Another question is whether artificial sweeteners change how much we eat. As mentioned, a study in the International Journal of Obesity found that artificial sweeteners actually reduce total energy intake. Yet, we know that sugar stimulates dopamine receptors in the brain involved with reward. That’s why experts believe sugar is addictive in much the same way as drugs. Artificial sweeteners are even more potent than sugar. Do they also stimulate reward centers in the brain? If so, using artificial sweeteners does nothing to help sugar addiction. In fact, their intense sweetness may further reinforce the desire to consume foods that are sweet.

The Bottom Line

The verdict is still out on how artificial sweeteners impact metabolic health and weight control. Ultimately, it’s best to replace sweet foods and “fake” sugar sweeteners with real food. Learn to appreciate the natural sweetness of a piece of fruit over the chemically created sweetness of an artificial sweetener. You’ll be healthier if you do.



International Journal of Obesity (2016) 40, 381–394; doi:10.1038/ijo.2015.177; published online 10 November 2015.
Scientific American. “Artificial Sweeteners May Change Our Gut Bacteria in Dangerous Ways”
Lett Appl Microbiol. 2014 Mar;58(3):278-84. doi: 10.1111/lam.12187. Epub 2013 Nov 19.
Int J Pediatr Obes. 2010 Aug; 5(4): 305–312.doi: 10.3109/17477160903497027.
Harvard Health Publications. “Artificial sweeteners: sugar-free, but at what cost?”


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