Artificial sweeteners may evict good gut microbes

To avoid the calories in sugar, dieters often sweeten foods and drinks with no-calorie substitutes, such as saccharin. But this fake sugar could have unexpected side effects, a new study finds. Its authors show that a high-saccharin diet causes changes in mice and people that could lead to obesity or type 2 diabetes. The sweetener did that by altering microbes in the gut. Other sweeteners would likely cause similar problems, the researchers say.

This research suggests “there could be unintended consequences” of using sugar substitutes, Robert Margolskee told Science News. He’s a neuroscientist at the Monell Chemical Senses Center in Philadelphia, Pa. He was not involved in the new work. “This is very interesting and scary if it really does hold for humans,” he says.

Until recently, most people thought artificial (no-calorie) sweeteners passed through the body without doing anything. That’s what makes them appealing. They add a sweet taste without the caloric cost. Many diet foods, from soft drinks to desserts, are sweetened with these substances. But that may come with a different cost.

To probe the sweeteners’ effects, Eran Segal and Eran Elinav  ran tests on mice. Segal is a computational biologist. Elinav is an immunologist. Both researchers work at the Weizmann Institute of Science in Rehovot, Israel. The researchers added artificial sweeteners to the animals’ drinking water. Those sweeteners included saccharin, aspartame and sucralose.

After 11 weeks, the animals showed problems with their metabolism. Unusually high levels of a type of sugar called glucose circulated in their blood after meals. This suggested the sweeteners impaired their bodies’ ability to process glucose. The most significant problems affected mice that drank water laced with saccharin.

Mice that drank water sweetened with glucose had no such problems.

In people, problems with glucose processing have been linked with diabetes and obesity. Being obese raises a person’s risk of serious health problems, including diabetes. Diabetes, a metabolic disease, affects how a person turns food into energy. If not well controlled, diabetes can be fatal.

Homing in on the ‘bugs’

To explain the results of their initial mouse study, the scientists looked at the animals’ intestines — or guts — for clues. They focused on the gut microbiota. These are the bacteria and other microbes growing in the intestines. Mice, like people, host many different bacteria and fungi in their intestines. That’s a good thing. Microbes can help digest food. Some supply nutrients. Many help by crowding out disease-causing germs. The scientists wondered whether the microbial community in the saccharin-fed animals was different than in those mice given water sweetened with glucose.

To probe this, they treated the saccharin-fed mice with antibiotics. That killed all bacteria in their intestines. Over time, new bacteria moved in to replace those that had died. By four weeks, the animals’ metabolism had returned to normal. That recovery suggested the change in the animal’s ability to use glucose was caused by bacteria. Follow-up tests confirmed that saccharin-fed mice had different types of gut bacteria than did mice getting sugar sweetened water.

The researchers kept experimenting. They put germs collected from the poop of saccharin-fed mice into the intestines of other mice. Before long, those mice developed the same metabolic problems seen in the saccharin-fed animals. Segal and Elinav reported their findings September 17 in Nature.

The new findings clearly show some bacterial change is behind the problems, Cathryn Nagler told Science News. “This is the home run experiment,” said this immunologist at the University of Chicago in Illinois. Nagler did not work on the new study. 

In a second study, also published September 17 in Nature, seven people volunteered to eat a high-saccharin diet. After only one week, four developed problems. Their bodies had trouble turning glucose into energy. That glucose began building up in their blood. Such high blood-glucose levels are an early sign of type 2 diabetes or of a risk for that disease.

Scientists now need to identify which gut microbes are the problem, Nagler said. But even without that information, she says, the new study points out that allowing a fake sugar to tinker with these microbes may pose serious health risks.

“We have to respect the power of the microbiota,” she says. “We need to step back and see what we are doing.”

Power Words

bacterium (plural bacteria)  A single-celled organism. These dwell nearly everywhere on Earth, from the bottom of the sea to inside animals.

computational biology    A field in which scientists use mathematics and computer programs to better understand living things.

germ   Any one-celled microorganism, such as a bacterium, fungal species or virus particle. Some germs cause disease. Others can promote the health of higher-order organisms, including birds and mammals. The health effects of most germs, however, remain unknown.

glucose    A simple sugar that is an important energy source in living organisms. It is half of the molecule that makes up table sugar (also known as sucrose).

gut  Common term for an organism’s stomach and/or intestines. It is where food is broken down and absorbed for use by the rest of the body.

immune    Able to ward off a particular infection. Alternatively, this term can mean to show no impacts from a particular poison or process. More generally, the term may signal that something cannot be hurt by a particular drug, disease or chemical. The field of biomedicine that deals with the immune system is known as immunology.

metabolism  The set of life-sustaining chemical reactions that take place inside cells. These reactions enable organisms to grow, reproduce, move and otherwise respond to their environments.

microbe  Short for microorganism.

microbiota  The microorganisms that live in a particular place or geological period.

microorganism  A living thing that is too small to see with the unaided eye, including bacteria, some fungi and many other organisms such as amoebas. Most consist of a single cell.

obesity  Extremely overweight. Obesity is associated with a wide range of health problems, including type 2 diabetes and high blood pressure.

saccharin A no-calorie sugar substitute.

type 2 diabetes   A disease caused by the body’s inability to effectively use insulin, a hormone that helps the body process and use sugars. Unless diabetes is controlled, a person faces the risk of heart disease, coma or death.