Brussels, 17th July 2026: The International Sweeteners Association (ISA) welcomes new research that contributes to our understanding of the interactions between low/no calorie sweeteners and the gut microbiota. However, the new study by Blasche et al. should be regarded as a mechanistic screening study rather than evidence that low/no calorie sweeteners adversely affect the human gut microbiota or human health under normal patterns of consumption.
The research was conducted entirely in vitro, using isolated bacterial cultures and a simplified synthetic microbial community, which cannot replicate the complexity of the human gut ecosystem or account for factors such as host physiology, diet and the diversity of the microbiota. Therefore, bacterial responses observed under these highly controlled conditions outside of the human body may not translate to meaningful changes in the human gut microbiota.
A further consideration is that all sweeteners were tested at the same concentration, despite substantial differences in how they are absorbed, metabolised and processed in the human body. As a result, the concentrations reaching the colon can vary considerably between sweeteners, meaning the experimental conditions may not reflect real-world patterns of human exposure.
Notably, none of the commonly consumed and approved low/no calorie sweeteners tested in this study, including aspartame, acesulfame-K, cyclamate, sucralose, and the steviol glycosides stevioside and rebaudioside A, showed confirmed direct effects on bacterial growth under the experimental conditions.Instead, the study’s strongest mechanistic findings were driven by isosteviol, a compound that is a derivative of steviol and not a normal steviol metabolite or a sweetener itself, making the relevance of these findings to typical human stevia exposure uncertain. In addition, recent randomised controlled trials have shown that consumption of steviol glycosides did not significantly affect gut microbiota composition, microbial diversity or faecal short-chain fatty acid concentrations compared with control treatments. These human data suggest that effects observed in simplified laboratory models do not necessarily translate into meaningful changes in the human gut microbiota.
The current body of evidence continues to support the safety of approved low/no calorie sweeteners when consumed within established acceptable daily intake levels.