With Washington U. in St. Louis
Sweeteners such as aspartame, found in Equal packets, sucralose (Splenda) or sugar alcohols are often seen as healthier alternatives to refined sugar (glucose) foods.
But that assumption is being challenged by new scientific research, including the recent finding that the sugar alcohol sorbitol is not as harmless a sugar substitute as we once thought.
The study in Scientific Signalingfollows a series of research detailing the harmful effects of fructose on the liver and other systems from Gary Patti’s lab at Washington University in St. Louis.
Patti, a professor of chemistry and genetics and medicine at WashU Medicine, has previously published research on how fructose processed in the liver can be hijacked to overload cancer cells. Previous research has also found that fructose is a major contributor to steatotic liver disease, affecting 30% of the adult population worldwide.
The most surprising finding from the current work is that because sorbitol is essentially “a transformation away from fructose,” it can cause similar effects, Patti says.
The research included experiments with zebrafish that showed that sorbitol, often used in “low-calorie” candy and gum and commonly found in stone fruits, can be naturally made by enzymes in the gut and eventually converted to fructose in the liver.
Patti’s team found that there are multiple pathways to fructose in the liver and possible detours, depending on a person’s sorbitol and glucose consumption patterns, along with the bacterial populations that colonize their gut.
For starters, although most research on sorbitol metabolism has focused on its production due to glucose overload in pathological settings like diabetes, sorbitol can be produced naturally in the gut from glucose after eating, Patti says.
The enzyme that produces sorbitol has a low affinity for glucose, so glucose levels must be high for it to work. This is why sorbitol production has mostly been associated with diabetes, where blood glucose levels can rise. But even under healthy conditions, gut glucose levels become high enough after feeding to drive sorbitol production within the gut, according to the team’s zebrafish experiments.
“It can be produced in the body at significant levels,” says Patti. “But if you have the right bacteria, it turns out, it doesn’t matter.”
Degradation of sorbitol Aerosol bacterial strains convert the sugar alcohol into a harmless bacterial byproduct.
“However, if you don’t have the right bacteria, then it’s problematic. Because in those conditions, sorbitol doesn’t break down and as a result, it’s transmitted to the liver,” he says.
Once it enters the liver, it is converted into a fructose derivative. It is important to determine whether alternative sweeteners provide a healthy alternative to table sugar, as people with diabetes and other metabolic disorders may rely on them as “sugar-free” products.
Gut bacteria do a good job of cleaning up sorbitol when it’s present in moderate levels, such as those found in fruit. But problems arise when the amounts of sorbitol become greater than the gut bacteria can break down. This can happen when excessive amounts of glucose are consumed in the diet, leading to high levels of glucose-derived sorbitol, or when dietary sorbitol itself is too high.
The more glucose and sorbitol consumed, then even if one has the friendly bacteria to clean it up, those gut microbes can be overwhelmed with the task.
Avoiding both sugar and alternative sweeteners is becoming more and more complicated as many foods are packed with many varieties of all of the above. Patti was baffled to discover that his favorite protein bar was chock full of sorbitol.
The lab will need to do more research to understand the specific mechanisms of how the bacteria clean up sorbitol, but the basic idea that these sugar alcohols, called polyols, are harmlessly excreted may not be true.
“We absolutely see that sorbitol given to animals ends up in tissues throughout the body,” he says.
Bottom line: it’s becoming increasingly apparent that “there’s no such thing as a free lunch” when trying to find sugar alternatives, with multiple roads leading to liver dysfunction.
This work was supported by the National Institutes of Health.
Source: Washington University in St. Louis
Original Study DOI: 10.1126/scisignal.adt3549
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Previously Posted at future.org with Creative Commons license
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