Effects of Lowering Glycemic Index of Dietary Carbohydrate on Plasma Uric Acid Levels: The OmniCarb Randomized Clinical Trial.

OBJECTIVE The effects of carbohydrates on plasma uric acid levels are a subject of controversy. We determined the individual and combined effects of carbohydrate quality (the glycemic index) and quantity (the proportion of total daily energy [percentage of carbohydrates]) on uric acid levels. METHODS We conducted a randomized, crossover trial of 4 different diets in overweight or obese adults without cardiovascular disease (n = 163). Participants consumed each of 4 diets over a 5-week period, each of which was separated by a 2-week washout period. Body weight was kept constant. The 4 diets were high glycemic index (≥65) with high percentage of carbohydrates (58% kcal), low glycemic index (≤45) with low percentage of carbohydrates (40% kcal), low glycemic index with high percentage of carbohydrates, and high glycemic index with low percentage of carbohydrates. Plasma uric acid levels were measured at baseline and after completion of each 5-week period for comparison between the 4 diets. RESULTS Of the 163 study participants, 52% were women and 50% were non-Hispanic African American subjects; their mean age was 52.6 years, and their mean ± SD uric acid level was 4.7 ± 1.2 mg/dl. Reducing the glycemic index lowered uric acid levels when the percentage of carbohydrates was low (-0.24 mg/dl; P < 0.001) or high (-0.17 mg/dl; P < 0.001). Reducing the percentage of carbohydrates marginally increased the uric acid level only when the glycemic index was high (P = 0.05). The combined effect of lowering the glycemic index and increasing the percentage of carbohydrates was -0.27 mg/dl (P < 0.001). This effect was observed even after adjustment for concurrent changes in kidney function, insulin sensitivity, and products of glycolysis. CONCLUSION Reducing the glycemic index lowers uric acid levels. Future studies should examine whether reducing the glycemic index can prevent gout onset or flares.