Some people who rely on artificial sweeteners to cut their sugar intake in hopes of losing weight find that weight loss never comes. That could be as a result of what those sweeteners do inside the body. Researchers at the Keck School of Medicine at the University of Southern California found the artificial sweetener sucralose increases activity in a region of the brain that regulates appetite and body weight.
The resulting action is the body misses the signal that is had something sweet or is full. That leads to eating sugary foods or more than is necessary to reach satiety.
Surveys show about 40 percent of Americans regularly consume sugar substitutes like sucralose. The purpose is generally to reduce calories and/or sugar intake.
"But are these substances actually helpful for regulating body weight?" That's what USC's Kathleen Alanna Page wanted to know along with, "What happens in the body and brain when we consume them, and do the effects differ from one person to the next?"
Page and her colleagues wanted to see how sucralose affects brain activity related to hormone levels and hunger so they designed a randomized experiment to find out.
Previous research pointed to a link between calorie-free sweeteners and obesity in animal studies, but this study was designed to look for a link in humans.
A total of 75 participants took part in the study. They underwent functional magnetic resonance imaging brain scans before and after consuming water, a sucralose-sweetened drink and a sugar-sweetened drink. They also had blood samples evaluated and completed a hunger ratings survey.
Sucralose actually increased hunger and activity in the hypothalamus. This was especially true in people who were already obese. Sucralose changed the way the hypothalamus communicated with other brain regions and did not increase blood levels of hormones that create a feeling of being full like sugar did.
The findings show the artificial sweetener confused the brain. It provided a sweet taste, but it did not provide the expected caloric energy.
Page said this "mismatch" could be responsible for changes in cravings and eating behavior. "If your body is expecting a calorie because of the sweetness, but doesn't get the calorie it's expecting, that could change the way the brain is primed to crave those substances over time," she said.
When study participants had sugar it led to an increase in blood sugar along with the associated hormones that regulate it like insulin and glucagon-like peptide 1 (GLP-1). But sucralose did not have a similar effect.
"The body uses these hormones to tell the brain you've consumed calories, in order to decrease hunger," Page said. "Sucralose did not have that effect—and the differences in hormone responses to sucralose compared to sugar were even more pronounced in participants with obesity."