Diabetes is a long-term health condition characterised either by the body’s inability to properly use glucose or by insufficient insulin production by the pancreas, insulin being the hormone responsible for managing blood sugar levels [1]. According to the 11th edition of the International Diabetes Federation (IDF) Diabetes Atlas (2025), about 589 million people aged 20–79 years old worldwide are living with diabetes, of which 90% are type 2 (T2D) and 10% type 1 diabetes (T1D) [2]. Characterised by deficient insulin secretion or, in some cases, excessive glucagon release, type 1 diabetes is associated with the presence of autoantibodies (anti-GAD [Glutamic Acid Decarboxylase], anti-insulin, anti-IA2 [Insulinoma-Associated Protein-2], anti-ZnT8 [Zinc Transporter 8]), which are typically absent in T2D, where insulin resistance together with reduced insulin secretion are predominant ^[3][4][3,4]. It is estimated that by the year 2050 the number would increase to 853 million adults (13%). Generally, diabetes is associated with multiple systemic complications, particularly metabolic disorders affecting the liver such as hepatic steatosis, inflammation and fibrosis. These types of diseases tend to affect the quality of life and can lead to mortality [2].

There are effective anti-diabetic drugs used for patient management (insulin, metformin, hypoglycaemic sulphonamides, GLP [Glucagon Like Peptide]-1 agonists and SGLT2 [Sodium-Glucose Cotransporter] inhibitors), depending on the type of diabetes [5]. However, these are lifelong treatment regimens that are not easily accessible, particularly in rural Sub-Saharan Africa, due to their high cost. In addition, the adverse effects of these drugs, such as hypoglycaemia, gastrointestinal disorders, heart failure, renal failure and genitourinary infections, can compromise patient adherence to treatment ^[6][7][6,7]. The challenges of using conventional treatments have prompted investigations towards finding alternative therapeutic strategies such as probiotic supplements, which have gained increasing interest due to their potential in diabetes management.

Discovered by Henri Boulard in 1920, S. boulardii was the first yeast to be recognised as a probiotic, and its health claims are based on the results of around 80 clinical trials ^[8][9][8,9]. However, the activities observed were strain-dependent. S. boulardii has properties that guide its application in humans. It grows optimally at 37 °C, and has up to 75% viability at a pH of 2 and in the presence of bile salts; it is therefore able to cross the chemical barriers of the digestive tract ^[8][9][8,9]. This is despite the bile salts and organic acids being identified as one of the main stressors of gut microbiome (GM) in the gastrointestinal tract. However, unlike other probiotics, such as Lactobacillus or Bifidobacterium, S. boulardii has poor adhesion to the intestinal wall. One of the advantages of using S. boulardii is its insensitivity to antibiotics and it can therefore be consumed by patients undergoing antibiotic therapy [10]. Its use in the clinical context has other beneficial effects such as restoring liver wounds, reducing digestive tract dysfunction, boosting immunity and reducing inflammation and oxidative stress ^[11][12][11,12], but their role in diabetes remains largely unclear. Generally associated with probiotics for their ability to stimulate their growth and beneficial effects, prebiotics are non-digestible food compounds, primarily of plant origin. In patients with chronic diseases, often characterised by dysbiosis and systemic inflammation (including diabetes), probiotic colonisation is frequently impaired [13]. Under these conditions, prebiotics help to overcome this barrier by improving the survival, adhesion, and proliferation of probiotics, while positively modulating immune response and inflammation [14]. By rebalancing the Firmicutes/Bacteroidetes ratio in favour of Bacteroidetes, a change often observed during supplementation with Lactobacillus and Bifidobacterium ^[1][2][1,2], an increase in the production of short-chain fatty acids (SCFA) can be noted, which contributes to enhancing the aforementioned effects and achieving better glycaemic control in patients with diabetes [3]. However, several factors such as drug treatments, the patient’s immune status, and the initial composition of the microbiota, influence the effectiveness of this prebiotic-probiotic synergy ^[15][16][15,16].

Traditionally studied for its anti-diarrhoeal and immunomodulatory properties, S. boulardii has now attracted attention as a promising therapeutic candidate for metabolic disorders such as diabetes ^[17][18][19][17,18,19], particularly characterised by stress related to an imbalance in antioxidant defence mechanisms, which is exacerbated by chronic hyperglycaemia, this stress is promoted through several mechanisms, including glucose auto-oxidation, protein glycation, activation of the polyol pathway, and overproduction of superoxide radicals by mitochondria and NADPH (Reduced form of Nicotinamide Adenine Dinucleotide Phosphate) oxidase ^[20][21][20,21]. Literature data clearly support the antioxidant properties of S. boulardii in response to stress by reducing the activity of key antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), malondialdehyde (MDA), and glutathione peroxidase (GPx), as well as by decreasing protein carbonylation ^{[19][21][22][23]}[19,21,22,23]. In this context, the question arises whether S. boulardii consumption as a probiotic would effectively eradicate clinical symptoms associated with diabetes and its complications. Thus, this review aims to find any existing evidence that demonstrates the anti-diabetic effect of S. boulardii.