How Sugar Substitutes Affect Your Gut Health

Food producers throughout the world use numerous artificial and natural low-calorie sweeteners. According to one representative survey of Americans between 2009 and 2012, 25 percent of kids and 41 percent of adults were consuming low-calorie sweeteners, and these intake rates represented a 200 percent surge in consumption for kids and a 54 percent increase among adults from just ten years earlier. Although similar studies conducted on athletes are hard to come by, they are likely, on average, consuming more artificial and low-calorie sweeteners than in years past.

People have all sorts of questions and concerns about these supposedly guilt-free sweeteners. Alas, we don’t have time to debate all the pros and cons of said sweeteners. Instead, this article aims to review how these sweeteners can potentially impact gut function and symptoms from an athlete’s perspective.

Types of Sugar Substitutes

There are many different energy-free and low-calorie sweeteners, so before we can discuss how they might affect your gut, it will be valuable to briefly review some of them individually.

Saccharin

Saccharin, the original artificial sweetener, is several hundred times sweeter than table sugar (sucrose) but has a somewhat unpleasant aftertaste. Sweet’N Low® is probably the most recognized brand of saccharin-based sweetening products.

Aspartame

Aspartame is another popular synthetic sweetener that was unearthed in 1965. While working on anti-ulcer drug candidates and related chemicals, a chemist named Jim Schlatter accidentally detected aspartame’s sweetness after licking his finger before picking up a piece of paper. Aspartame goes by the brand names Nutrasweet® and Equal® and is about 200 times sweeter than regular sugar.

Sucralose

Another artificial sweetener, sucralose, or Splenda®, is even sweeter than saccharin and aspartame, coming in at 600 times the potency of sugar.

While the Food and Drug Administration has approved several other artificial sweeteners, such as acesulfame potassium and neotame, we will focus on saccharin, aspartame, and sucralose because they are the most popular.

Stevia

Aside from the manmade sweeteners listed above, natural low-calorie sweeteners are also found in athletes’ foods and beverages. Stevia is one such natural sweetener and is often touted as being safer than artificial sweeteners. Stevia sweeteners usually come from the Stevia rebaudiana Bertoni plant, which is native to South America. Like aspartame, they are about 200 to 300 times sweeter than sugar.

Sugar Alcohols

Sugar alcohols—otherwise known as polyols—are an additional type of sweetener used to replace real sugar in certain foods. Many polyols are considered natural because they are found in plant foods such as fruits and vegetables.

In contrast to the other sweeteners mentioned so far, most polyols provide some energy, albeit less than sugar. Most contain about 1.5 to 3.0 kilocalories per gram, whereas sugar supplies 4 kilocalories per gram. When it comes to sweetness levels, polyols tend to be somewhat less potent than sugar.

What’s the Link Between Artificial Sweetener Consumption and Overall Health?

It’s important to acknowledge that numerous aspects of physiology influence overall gut health. Energy-free/low-calorie sweeteners could impact anything from gut hormone secretion to intestinal motility to the microbiome (i.e., the population of microbes living in your gut). That means we should avoid making overly simplistic conclusions about whether these sugar substitutes are good or bad for your gut’s overall fitness.

Animal Studies

With that caveat aside, let’s look at some relevant research on these sweeteners. In animals, feeding them artificial sweeteners like sucralose and aspartame sometimes increases the secretion of gut-produced hormones (e.g., gastric inhibitory peptide, peptide YY), which impact hunger and intestinal motility.

In addition, a study that fed mice sucralose, aspartame, or saccharin for 11 weeks found alterations in the gut microbiome, which caused intolerance to a standardized glucose feeding. This isn’t an isolated finding, as other studies have found compositional shifts in the gut microbiome post-artificial sweetener consumption.

Still, mice aren’t humans, and many of these animal experiments used dosages (relative to body weight) that were way higher than the amounts most people consume on a daily basis. As a result, it is tough to say how well some of these findings apply to people who consume modest amounts of manmade sweeteners.

Human Studies

For example, although some animal research suggests that artificial sweeteners could negatively affect hunger, body weight, and glucose metabolism, most experiments in humans have not found this to be true. In fact, a meta-analysis of clinical trials published this year found that consuming non-caloric/low-calorie sweeteners instead of sugar led to modest reductions in body weight in humans. Likewise, another review of human experiments found that replacing sugar-sweetened beverages with artificially-sweetened versions prompted modest decreases in body weight, body fat, blood triglycerides, and liver fat.

On the other hand, eating loads of artificial sweeteners could potentially lead to problems metabolizing carbohydrates in the body, but these effects probably only occur at very high doses. In one study, volunteers consumed the equivalent of ten Sweet’N Low packets’ worth of saccharin per day for a week, yet only four of seven volunteers developed any carbohydrate metabolism issues at this extreme dose. The point is, dosage matters.

Overall, if sugar in your diet is replaced with a reasonable amount of artificial sweetener, your metabolic health will likely not be significantly impacted. Although artificial sweeteners can certainly alter the gut microbiome, we don’t yet know what the long-term implications of those changes are.

Gut Problems Related to Sugar Substitute Consumption in Athletes

The surest thing we know about this topic is that eating loads of polyols is akin to dropping a bomb in your gut. About half to three-quarters of ingested polyols get absorbed, meaning that a portion of them hang around in the gut’s lumen.

Bloating, Gas, and Diarrhea

The fact that polyols are incompletely absorbed is precisely why they contain less energy than sugar. While a gram or two of unabsorbed polyols isn’t a big deal, larger amounts sitting in the gut can wreak havoc. In one experiment, about half of the people who ate chocolate bars containing 32 grams of a polyol called sorbitol suffered from diarrhea, flatus, stomach aches, and bloating. Likewise, in a study of children who ate hard candies with 25 grams of the polyol isomalt, stomach aches and watery stool were more frequent than when they ate candies with regular sugar. These are just a couple of the many studies that have shown polyols can be disagreeable to the gut if 20 grams or more are eaten in a single sitting.

On a mechanistic level, unabsorbed polyols draw water out of your body and into your gut lumen, resulting in loose, watery stools. Bacteria in the latter half of your gut also ferment these unabsorbed polyols, provoking gas and bloating.

Some good news: very few classic sports drinks marketed to endurance athletes contain polyols, so you probably need not worry about them when drinking those beverages.

Some not-so-good news: other products like diet and meal replacement bars are much more likely to be chock-full of polyols. One potential red flag to look for is a product that markets itself as “sugar-free” but still has a semi-sweet flavor like chocolate, vanilla, or strawberry. Look at the ingredients list to see whether any polyols are listed. For some products, you can figure out the exact quantity by looking for sugar alcohols under the total carbohydrate section of the Nutrition Facts panel.

Stevia, Aspartame, and Sucralose May Cause the Least Gastrointestinal Discomfort

As for Stevia, there is little reason to think that the amounts found in most products would cause notable gut issues. In an experiment involving eating cookies (how fun!), adding Stevia didn’t result in any digestive complaints compared to standard Stevia-free cookies.

Likewise, there is little evidence from animal or human experiments that consuming modest amounts of artificial sweeteners like aspartame or sucralose causes gut discomfort, gas, or stool abnormalities. There are always exceptions, though, and a small subset of athletes may want to avoid artificially sweetened foodstuffs before and during exercise if they know, from experience, that consuming them triggers GI issues.

Should I Be Worried About How Much Sugar Substitutes Can Affect My Gut?

Eating excessive amounts of artificial sweeteners like aspartame, saccharin, and sucralose can have undesirable effects on the body, but the dosages required for this to occur are quite high. In other words, downing a six-pack of diet soda or a dozen Sweet’N Low packets every day is much more likely to lead to problems than a once-a-day diet soda habit.

Scientists can’t provide a 100 percent guarantee that there will be no long-term adverse effects from eating modest amounts of artificial sweeteners. Still, the probability that doing so will cause lasting harm is pretty low for most people.

When it comes to natural sweeteners, polyols are the type you should be most careful of as they’re more likely to negatively affect the gut than other sugar substitute types.

Want more of Outside’s Health stories? Sign up for the Bodywork newsletter.