Concerning new research suggests that sorbitol, a common sweetener found in many sugar-free products, could significantly increase the risk of developing metabolic dysfunction-associated steatotic liver disease (MASLD). This condition, previously known as non-alcoholic fatty liver disease, is not linked to heavy alcohol consumption and is becoming a growing health concern.

The study, published in the journal Science Signalling, investigated the gut microbiome of zebrafish and its reaction to compromise. The gut microbiome is a complex ecosystem of beneficial bacteria and fungi crucial for digestion and nutrient absorption. Researchers observed that when the zebrafish's gut microbiome was depleted, they developed liver disease, even when on a normal diet. This critical finding shed light on the metabolic pathway involved. During natural digestion, the body converts glucose into fructose via sorbitol in the intestine. Normally, the gut bacteria efficiently break down this sorbitol, preventing its accumulation. However, when these vital gut bacteria were removed using antibiotics, sorbitol accumulated, traveled to the liver, and subsequently caused fatty liver disease. The study further confirmed this by showing that directly adding sorbitol to the fishes' diet produced the same detrimental effect. Conversely, preventing sorbitol production or introducing sorbitol-degrading bacteria successfully protected against liver damage.

These findings led researchers to conclude that gut bacteria play a protective role against sugar-related liver disease and that dietary sorbitol, commonly used as a sweetener, may elevate the risk of fatty liver. Experts have warned that these revelations suggest 'sugar free' alternatives might be as, if not more, harmful to liver health than previously assumed, prompting calls for a reevaluation of their place in a healthy diet.

Dr. Gary Patti, a professor of chemistry, genetics, and medicine at Washington University, highlighted that sorbitol is "one transformation away from fructose." Fructose has been previously linked to supercharging cancer cells and contributing to steatotic liver disease. While most research on sorbitol processing has focused on its production due to glucose overload, Dr. Patti pointed out that sorbitol can also be produced by the gut after eating. While it has long been known that consuming too much sugar can lead to a number of health problems, there is a growing body of evidence that sweeteners aren't necessarily the healthy alternative we're led to believe.

For sorbitol to become problematic, blood glucose levels typically need to be high, hence its association with conditions like diabetes. Dr. Patti explained that while sorbitol can be produced in significant levels in the body, the presence of the right sorbitol-degrading bacterial strains in the gut converts this sugar alcohol into a harmless byproduct. However, he cautioned that if an individual lacks these protective bacteria, sorbitol is not degraded and is instead passed on to the liver, leading to issues. This depletion in gut bacteria can occur when excessive amounts of sugar, or sorbitol itself, are consumed in the diet, potentially overwhelming even robust microbial populations and shifting the burden of processing to the liver. Once in the liver, sorbitol is converted into a fructose derivative, which results in increased fat accumulation in the organ. Known medically as metabolic dysfunction-associated steatotic liver disease (MASLD), the condition is not linked to heavy drinking, the more commonly known cause of liver problems.

The researchers collectively stated, "Together, these findings show that sorbitol-degrading bacteria in the gut protect against steatotic liver disease and suggest that excessive intake of dietary sorbitol may pose a risk for the development of MASLD." While acknowledging the need for further studies to fully understand the specific mechanisms of bacterial sorbitol clearance, they emphasized that the common belief that 'healthier' alternatives are harmlessly expelled from the body might not hold true. Dr. Patti confirmed that sorbitol given to animals "ends up in tissue all over the body."

The British Liver Trust estimates that MASLD could now affect up to one in five people in the UK, with some experts warning the true figure could be as high as 40 percent. Alarming statistics show that approximately 80 percent of affected individuals remain undiagnosed, largely because the disease often presents with no obvious symptoms or symptoms that are easily mistaken for less severe conditions. Diagnosis is typically made incidentally during routine blood or liver function tests performed for unrelated health issues. Professor Philip Newsome, Director of the Roger Williams Institute of Liver Studies at King's College London, highlighted the rising incidence of liver disease in the UK, noting that symptoms often go unnoticed until the disease has progressed significantly, particularly among overweight individuals or those with diabetes.

Beyond sorbitol, broader concerns about the impact of artificial sweeteners, also found in products like yogurt and certain cereals, on heart and brain health have been circulating for years. For instance, Brazilian experts found in September that consuming just one fizzy drink daily could rapidly increase the risk of brain decline. Higher consumption of 'added sugars' (including those from diet drinks) was linked to a 62 percent higher risk of brain aging, with this risk being particularly elevated in diabetic individuals who frequently use sugar substitutes. Furthermore, in 2023, the World Health Organization (WHO) controversially classified aspartame, an artificial sweetener found in Diet Coke, as "possibly carcinogenic to humans." However, the UN agency clarified that this risk only applies to massive consumption, estimating that an 11 stone (70kg) adult could safely consume about 14 cans a day. Similar to the recent sorbitol study, experts are keen to point out that the potential risks of artificial sweeteners should be viewed in context and not necessarily overblown compared to the known harms of the sugar they replace.