People might consume artificial sweeteners because they think it will help them curb real-sugar consumption and prevent weight gain, but the chemicals may actually have an opposite effect. A new study has found that zero-calorie sweeteners may alter metabolism and increase blood-sugar levels, at least in mice and some people.
The negative effects of artificial sweeteners on metabolism seen in the study may have to do with how the sweeteners interact with the bacteria living the gut, the researchers said.
The results don't mean that eating sugar is healthier than consuming artificial sweeteners, study co-author Dr. Eran Elinav, a researcher at the Weizmann Institute of Science in Israel, said at a news conference Tuesday (Sept. 16). However, the study does suggest that artificial sweeteners may be harmful, at least in some people, Elinav said.
In experiments, the scientists added an artificial sweetener — either saccharin, sucralose or aspartame — to mice's drinking water, and found the animals ended up having higher blood-sugar levels than the mice that drank sugar water, or just water. Saccharin is sold under the brand name Sweet'n Low, sucralose has the brand name Splenda and aspartame is found in NutraSweet, Equal and Spoonful brands.
The researchers also found that artificial sweeteners seemed to change the function of the gut bacteria in the rodents. When the researchers used antibiotics to suppress the bacteria, the differences in blood-sugar levels between groups of mice on different diets disappeared, according to the study, published today (Sept. 17) in the journal Nature.
Next, the researchers studied about 400 people, and found that the gut bacteria in people who consumed an artificial sweetener were different from the gut bacteria in the people who ate sugar. Participants who used artificial sweeteners also had higher blood-sugar levels than participants who used sugar. [5 Ways Gut Bacteria Affect Your Health]
"Artificial sweeteners were extensively introduced into our diets with the intention of reducing caloric intake and normalizing blood glucose levels without compromising the human 'sweet tooth,'" the researchers wrote in their study. "Our findings suggest that [artificial sweeteners] may have directly contributed to enhancing the exact [obesity] epidemic that they themselves were intended to fight."
Your personal gut bacteria
There are trillions of bacteria living in human guts. Collectively called the microbiome, these bacteria are crucial for the normal functioning of the intestines, and their composition could potentially influence diverse functions of the body. For example, previous studies have tied the balance of bacterial species in the gut to people's risk of conditions such as obesity and type 2 diabetes.
But people can have different compositions of bacterial species, and that could potentially contribute to how they respond to different foods, the researchers said.
In the study, the researchers also carried out another experiment. They added saccharin to diets of seven people who didn't normally consume sweeteners. After only four days, four of these participants showed increased levels of sugar in their blood and changes in the composition of their gut bacteria.
The gut bacteria composition of these participants differed from that of the other three participants, even before they consumed saccharin, the researchers found. This finding suggests that people may respond differently to artificial sweeteners depending on their gut-bacteria compositions, the researchers said.
"What was super striking and interesting to us was the fact that [people's] susceptibility to [the effects] of sweeteners could be predicted ahead of time, even before the individuals consumed the sweeteners," said study co-author Eran Segal, a computational biologist at the Weizmann Institute of Science.
It's not clear how, exactly, changes in the bacterial species in the gut could contribute to increased blood-sugar levels, but scientists have some ideas. For example, it could be that the consumption of artificial sweeteners causes people to have more bacterial species that extract fat from the diet, which would contribute to obesity, said Taylor Feehley and Cathryn Nagler, researchers at the University of Chicago who wrote about the new study in the same journal.
Should you ditch the diet soda?
Previous studies have looked at whether people who replace sugar with artificial sweeteners have a lower risk of developing the health problems linked with consuming too much sugar, such as obesity and diabetes.
But although some studies found artificial sweeteners to be beneficial, others yielded mixed results, the researchers said. Some studies even found links between consuming sweeteners and a higher risk of obesity and high blood sugar, but those studies were observational (and didn't have randomized control groups), and it remains unclear whether artificial sweeteners may cause metabolism changes, or if people who are obese to begin with consume more of the sweeteners, Elinav said.
The new study is not conclusive, either. The results need to be confirmed in future research before recommendations about consuming artificial sweeteners can be made, the researchers said. Still, the findings should provoke discussion among the scientific, medical and public communities.
"By no means do we believe that based on the result of this study are we prepared to make recommendations as to the use and dosage of artificial sweeteners," Segal said. "We simply point to the immense body of experiments that we carried out both in humans and in mice. In none of these experiments have we seen any beneficial effects for the use of sweeteners."
Live Science newsletter
Stay up to date on the latest science news by signing up for our Essentials newsletter.