Effects of 10-day medically supervised fasting on serum electrolytes and safety-related clinical variables in healthy women

Abstract Background: Fasting practices are gaining attention for their potential health benefits, yet comprehensive data on physiological effects, particularly regarding serum electrolytes and safety parameters in women, remain limited. This study evaluates the impact of a 10-day medically supervised fasting protocol on electrolyte balance and safety-related clinical variables in healthy female adults. Materials and Methods: Fifteen healthy female participants (age: 18–30 years, body mass index: 18–25 kg/m²) underwent a 10-day fasting regimen consisting of two preparatory days, 6 days of a low-carbohydrate diet (250–500 kcal/day) and two refeeding days. Measurements included serum electrolytes (sodium, potassium, chloride, calcium, phosphorus, magnesium), anthropometric parameters, vital signs, blood indices, urine composition, body composition and subjective well-being. Data were collected at baseline and at regular intervals throughout the fasting period. Results: Significant changes were observed in serum sodium ( P = 0.027), chloride ( P < 0.001) and magnesium ( P < 0.001), while potassium, calcium and phosphorus remained stable. Total protein, albumin and globulin levels showed significant alterations ( P < 0.001 for all). Cardiovascular parameters improved, with significant reductions in morning diastolic blood pressure ( P = 0.005), evening systolic blood pressure ( P = 0.033) and fasting blood glucose ( P < 0.01). Body weight decreased significantly ( P < 0.001), as did mid-arm circumference ( P < 0.001). Notably, body fat percentage increased ( P < 0.001) despite weight loss, while fat-free mass decreased ( P = 0.007). Basal metabolic rate decreased significantly ( P < 0.001), and visceral fat increased ( P = 0.023). Total leukocyte count and platelet count showed significant reductions ( P < 0.001 and P = 0.003, respectively). Conclusion: The 10-day fasting protocol yielded improvements in cardiovascular parameters and metabolic markers but raised concerns regarding body composition changes, particularly increased visceral fat and decreased basal metabolic rate. While fasting appears to be well-tolerated in the short-term, these findings suggest careful consideration of metabolic adaptations is warranted when implementing fasting interventions, especially in women. This study contributes to understanding the complex physiological responses to short-term fasting and highlights the importance of monitoring body composition alongside standard clinical parameters.