The Impact of Low and High Salt Intake on Insulin Resistance in Healthy Individuals

Hypertension is closely linked to insulin resistance, hyperglycemia, and hyperinsulinemia among non-communicable diseases, and individuals with insulin resistance are at increased risk of premature cardiovascular mortality. Modifying dietary salt intake may influence insulin resistance and related metabolic outcomes. This randomized crossover study assessed the effects of low-salt and high-salt diets on insulin resistance in healthy individuals. Fifty-one apparently healthy male medical students from the University of Medicine 2 participated. Each participant completed a 7-day low-salt diet (<50 mmol/day sodium) and a 7-day high-salt diet (>165 mmol/day sodium) in random order. Dietary compliance was verified by urinary sodium excretion, which was appropriately lower during the low-salt phase and higher during the high-salt phase. On the 8th day of each dietary period, fasting blood samples were collected to measure plasma glucose and serum insulin. Fasting plasma glucose did not differ significantly between the low-salt (5.32 ± 0.50 mmol/L) and high-salt (5.20 ± 0.42 mmol/L) diets. However, fasting serum insulin levels were significantly higher during the low-salt phase compared with the high-salt phase (17.32 ± 8.78 μIU/mL vs. 12.68 ± 5.69 μIU/mL, p<0.001). HOMA-IR was also higher with the low-salt diet (4.1 ± 2.14 vs. 2.9 ± 1.32, p<0.001), whereas QUICKI values were lower (0.32 ± 0.03 vs. 0.33 ± 0.02, p<0.001). These findings indicate that a low-salt diet is associated with greater insulin resistance and reduced insulin sensitivity compared with a high-salt diet. Consequently, recommending sodium intake <50 mmol/day may not be beneficial for improving insulin sensitivity in healthy individuals.