Sorbitol, a popular sugar substitute, has been linked to liver disease

However, new data casts doubt on this. A study by scientists from Washington University in St. Louis, published in Science Signaling, has found: sorbitol may be involved in the development of fatty liver disease.

Why sorbitol came under suspicion

Biochemist Gary Patti's group had previously demonstrated that fructose, which is processed in the liver,

• contributes to steatotic liver disease,

• and can even fuel the growth of cancer cells.

Now researchers have turned their attention to sorbitol, a sugar alcohol that:

• is widely used in "low-calorie" candy and chewing gum,

• naturally occurring in stone fruits,

• and has been shown to be easily converted in the body into fructose derivatives.

"Sorbitol is essentially just one step away from fructose," the authors explain, and so can trigger similar unfavourable processes in the liver.

What the experiments showed

The scientists worked on a model using danio rerio (zebrafish). They found that:

• Sorbitol can naturally be formed in the intestine from glucose after a meal, not only in severe metabolic disorders like diabetes.

• This sorbitol then enters the liver and is converted into fructose-type compounds involved in the development of fatty liver disease.

Previously, it was thought that significant sorbitol formation was predominantly the province of diabetic patients with severely elevated glucose levels. But data show that even in healthy people after a meal, the concentration of glucose in the intestine can be high enough to trigger its synthesis.

The role of gut bacteria

A key factor is the microbiota.
Some bacteria in the gut (such as Aeromonas strains) are able to break down sorbitol to harmless products.

• If such bacteria are present and there is little sorbitol (as with moderate fruit consumption), the body is generally successful.

• But if the necessary microflora is not present, or if there is too much sorbitol and glucose, the system is overloaded:

  • sorbitol doesn't have time to break down in the gut,

  • part of it goes to the liver,

  • where it's converted into fructose-like compounds that affect liver metabolism.

Even in the presence of the "right" bacteria, excess sugars and sugar alcohols can simply outweigh the compensatory capabilities of the microbiota.

Why this is important for nutrition and medicine

Sorbitol and other polyols are commonly used in "sugar-free" or "for diabetics" products. But:

• people with obesity, metabolic disorders and diabetes often actively rely on such sweets as a safe substitute for sugar;

• while the new findings show that the 'safety' of polyols is far from absolute, and some of them may contribute to liver dysfunction.

The authors emphasise: the notion that sugar alcohols are simply "not digested and excreted" needs to be reconsidered. In the experiments, sorbitol injected into animals was found in different tissues of the body, not only excreted in transit.

The scientists' final conclusion sounds pretty harsh:

There is no such thing as a free lunch when looking for a "harmless" substitute for sugar - many pathways lead to liver overload anyway.