The first artificial sweetener was developed in 1879, and despite being some of the most scientifically studied food substances on the market, their use remains controversial.  "Diet," reduced sugar, and sugar-free foods and beverages manage to maintain sweetness with the help of sugar substitutes like artificial sweeteners. Artificial sweeteners don’t raise blood glucose (also called blood sugar) levels and have been promoted as a way to reduce excess sugar intake and better manage chronic diseases like type 2 diabetes, overweight, and obesity.  But the question remains—are artificial sweeteners good or bad? Here’s what the science says on their effectiveness for weight loss, cravings, and the gut microbiome.
What are artificial sweeteners?
Artificial sweeteners are synthetically made and are structurally different from sugars found in grains and fruits like glucose and fructose. Though they activate the same taste buds and evoke a reward response from the brain as sugars, artificial sweeteners contain little to no calories and are referred to as non-nutritive or low-calorie sweeteners. They can achieve the same sweetness level as sugar using much smaller quantities and with negligible calories. For example, an artificial sweetener may require 1/200th or less of an amount of sugar to achieve the same sweetness. 
And that difference is taken into account in the formulation of artificial sweetener packets. Those small yellow, blue, and pink packets are designed to be of similar sweetness levels to one packet of sugar. So whereas a sugar packet is 100% sugar, artificial sweeteners only comprise 1-3% of sugar substitute packets—the rest are filler ingredients. 
The most common artificial sweeteners include aspartame, saccharin, sucralose, and neotame. All of these sweeteners are approved for use in food and beverages by the Food and Drug Administration (FDA) and are frequently found in diet beverages, yogurt, jams, candy, and some baked goods. Each sweetener has an acceptable daily intake, meaning it’s considered safe to consume up to a specific amount on a daily basis. This limit, however, is often orders of magnitude higher than any person is likely to consume.
And just to note, high-intensity low-calorie sweeteners can also be natural—like stevia extracts and Lou Han Guo (monk fruit). The purpose of this article is to focus on the research behind synthetic sweeteners, and the terms synthetic sweeteners, artificial sweeteners, sugar substitutes, and low-calorie sweeteners will be used synonymously.
Can artificial sweeteners help with weight loss?
The biggest potential benefit of sugar substitutes is to help regulate body weight. Since these sweeteners contain negligible calories, swapping sugar-rich foods and beverages for these lower calorie alternatives seems to be a great option for people looking to reduce their caloric intake. And many clinical trials have found this swap to in fact be beneficial for measures of metabolic health.
A 2014 systematic review and meta-analysis of 15 randomized-controlled trials and 9 prospective cohort studies investigated the relationship between low-calorie sweeteners, body weight, and body composition.  Findings showed that the substitution of low-calorie sweeteners for sugars results in modest but significant reductions in body weight, body mass index (BMI), fat mass, and waist circumference. Consistent results are shown across other clinical studies: when low-calorie options are used in place of sugar or as part of a calorie deficit diet, the reduced calorie intake results in weight loss. [6,7,8]
Conversely, large observational studies have found an association between the consumption of low-calorie sweeteners and increased BMI. [5,7] It’s hard to decipher what’s driving that connection. Do people who consume more artificial sweeteners follow less healthful lifestyles, which in turn drive up BMIs? Do those who mostly drink water have more favorable BMIs than both soda and diet beverage drinkers? Or, do people with higher BMIs try to choose more diet sodas/artificial sweeteners as a weight management option.
Key takeaway: Clinical trials show that consuming foods or beverages containing low-calorie sweeteners in place of sugar-sweetened ones can help reduce caloric intake and promote weight loss by creating a calorie deficit. However, other lifestyle factors may influence the extent of that potential weight loss.
Do artificial sweeteners increase sugar cravings or appetite?
Humans are designed to like sweet foods.  And there’s a hypothesis that eating sweet foods will increase the preference and desirability of sweets.  So might artificial sweeteners—which were designed to curb sugar intake—be fueling sugar cravings instead?
Results from a 2013 study suggest that artificial sweetener use actually does not drive sugar consumption. The study, published in the American Journal of Clinical Nutrition, examined whether calorie consumption and food patterns shifted when people who regularly drank sugary beverages either continued that pattern or substituted two servings per day for either water or a diet beverage.  After six months, both the people in the water and the diet beverage groups reduced daily calorie intake as well as carbohydrate, fat, protein, saturated fat, total sugar, and added sugar intake. Furthermore, compared to those who just consumed water, those who instead drank diet beverages ate less dessert by the end of the trial. So within six months, artificial sweeteners from diet beverages did not increase preference for consumption of sweet foods.
Other randomized controlled studies have not found a definitive link between artificial sweeteners and sweet cravings. In fact, most clinical trials have found that low-calorie sweeteners reduce the intake of sugar-containing foods. 
Key takeaway: Consumption of artificial sweeteners doesn’t appear to result in an intensified desire for sweets.
Can artificial sweeteners alter the gut microbiome?
This is a relatively new area of research, and few human studies to date have investigated the impact of artificial sweeteners on gut health.
Animal studies have shown that saccharin and sucralose can shift the composition of the gut microbiome. Saccharin in particular may impact pathways involved in blood sugar tolerance and dysbiosis (an imbalance of good and bad gut microbes). 
A 2014 study in humans also found a correlation between the use of artificial sweeteners and the presence of harmful bacterial strains in the gut.  A new study of 54 participants published in Microbiome in January 2021 found that participants who received the maximum acceptable daily intake of saccharin for two weeks did not present altered activity or composition of gut microbes. 
More research is needed to fully understand the relationship between artificial sweeteners and gut health. However, what is well known is that excess sugar is detrimental to good gut health. High sugar intake can cause low-grade inflammation and shift the composition of the gut microbiome to more harmful species.  Meal timing, probiotics, and sleep are also habits that can impact gut health.
Key takeaway: More human trials are needed to determine how artificial sweeteners impact the gut microbiome.
What's the consensus? Are artificial sweeteners bad for you?
While artificial sweeteners continue to be a contentious topic, the majority of the research indicates that, when used in place of sugar-sweetened food and beverages, they may be beneficial for weight loss. There is also a lack of convincing evidence that they increase sugar cravings. And while research on artificial sweeteners and the gut microbiome is evolving, negative changes may only be elicited by extremely high doses on a frequent basis.
But just like sugar, artificial sweeteners shouldn't be consumed in excess. Moderation is key when it comes to the consumption of all sweeteners. And remember, water is always the best choice for low-calorie hydration.
- Artificial sweeteners are synthetically produced, contain little to no calories, and are much sweeter than sugar.
- Clinical trials indicate that substituting sugary food and beverage for those with low-calorie sweeteners may help reduce calorie intake and promote weight loss.
- Observational studies have found an association between low-calorie sweetener intake and higher BMI.
- Artificial sweeteners have not been shown to increase preference or consumption of sweet foods.
- Current evidence does not yet support the theory that moderate use of artificial sweeteners can impact microbiome composition.
- More research is needed on the impact of artificial sweeteners
Molly Knudsen, MS, RDNMolly is a Content Writer and Team Nutritionist at InsideTracker. As a Registered Dietitian, Molly enjoys connecting people to the food they eat and how it influences their biomarkers. When she’s not writing about the latest nutrition science, she’s likely in the middle of a yoga flow or at the beach with a good book.