PurposeThe ketogenic diet (KD) has gained popularity due to its ability to improve type 2 diabetes, weight loss, antioxidant and anti-inflammatory activity. However, long-term use of the KD might not be safe due to its adverse effects. This study examined the effects of the KD alone or in combination with Zamzam water (holy water for Muslims) on glucose homeostasis, lipid parameters and oxidant-antioxidant variables in rats.Design/methodology/approachBased on the diet given for ten weeks, three groups of adult male Wistar rats were made (12 rats/group): (1) rats which fed on a chow diet and ordinary water, (2) rats which fed on KD and ordinary water and (3) rats which were given KD along with Zamzam. Fasting blood glucose (FBG), serum insulin, insulin resistance (HOMA-IR), LDL cholesterol, HDL cholesterol, superoxide dismutase and malondialdehyde were compared by one-way ANOVA followed by post-hoc Tukey’s HSD test among groups.FindingsRats which fed on KD and Zamzam water had significantly reduced FBG and LDL cholesterol compared to the rats which fed on a chow diet and ordinary water (p-values 0.001), and KD and ordinary water (p-value 0.004 and 0.006, respectively). Serum insulin, insulin resistance, HDL cholesterol, superoxide dismutase and malondialdehyde did not differ significantly.Originality/valueConsumption of KD along with Zamzam for ten weeks significantly reduces FBG and LDL cholesterol. KD alone does not decrease these parameters in ten weeks duration.