Objective: To evaluate the change in potassium after initiating a low-carbohydrate or low-fat weight loss diet.
Methods: Participants randomized to a low-carbohydrate (low-CHO) or a low-fat diet had serum potassium measured at baseline, 3 days, 1 week, 2 weeks, and 1 month after dietary initiation. Paired t tests and repeated measure analysis of variance (ANOVA) compared changes within each subject and between groups.
Results: Mean potassium (4.29 mmol/L + 0.41) was similar in both groups at baseline. The low-CHO arm (n = 48) had a mean decrease of 0.16 mmol/L +/- 0.49 (P = 0.03) over one month, and the low-fat arm (n = 47) had a reduction of 0.19 +/- 0.45 (P = 0.006). Serum potassium decreased within 3 days of diet initiation in the low-CHO arm, and at one week in the low-fat arm. Five participants (3 in low-CHO arm) required potassium supplementation for serum potassium <3.5 mmol/L.
Conclusions: Minor decreases in potassium occurred after initiating both diets, and was more rapid after the low-CHO diet. These decreases may be clinically meaningful in some patients.