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

Abstract

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.

Trial registration: ClinicalTrials.gov NCT00608049.

Figure 1

Change in plasma uric acid (mg/dL, 95% confidence intervals) between diets (N = 159). Comparisons are organized by dietary factor: glycemic index, proportion carbohydrate, or both factors. CG represents the high carbohydrate/high glycemic index diet. Cg represents the high carbohydrate/low glycemic index diet, cG represents the low carbohydrate/high glycemic index diet, and cg represents the low carbohydrate/low glycemic index diet.