Consumption of fructose- but not glucose-sweetened beverages for 10 weeks increases circulating concentrations of uric acid, retinol binding protein-4, and gamma-glutamyl transferase activity in overweight/obese humans

Abstract

Background: Prospective studies in humans examining the effects of fructose consumption on biological markers associated with the development of metabolic syndrome are lacking. Therefore we investigated the relative effects of 10 wks of fructose or glucose consumption on plasma uric acid and RBP-4 concentrations, as well as liver enzyme (AST, ALT, and GGT) activities in men and women.

Methods: As part of a parallel arm study, older (age 40-72), overweight and obese male and female subjects (BMI 25-35 kg/m2) consumed glucose- or fructose-sweetened beverages providing 25% of energy requirements for 10 wks. Fasting and 24-h blood collections were performed at baseline and following 10 wks of intervention and plasma concentrations of uric acid, RBP-4 and liver enzyme activities were measured.

Results: Consumption of fructose, but not glucose, led to significant increases of 24-h uric acid profiles (P < 0.0001) and RBP-4 concentrations (P = 0.012), as well as plasma GGT activity (P = 0.04). Fasting plasma uric acid concentrations increased in both groups; however, the response was significantly greater in subjects consuming fructose (P = 0.002 for effect of sugar). Within the fructose group male subjects exhibited larger increases of RBP-4 levels than women (P = 0.024).

Conclusions: These findings suggest that consumption of fructose at 25% of energy requirements for 10 wks, compared with isocaloric consumption of glucose, may contribute to the development of components of the metabolic syndrome by increasing circulating uric acid, GGT activity, suggesting alteration of hepatic function, and the production of RBP-4.

Figure 1

Circulating uric acid concentrations over 24-h in subjects before and after 10 wks of consuming (A) fructose- or (B) glucose- sweetened beverages. ***P < 0.0001 compared with baseline and P < 0.0001 for effect of sugar using PROC mixed 3-factor (sugar, gender, and presence of metabolic syndrome) ANOVA; glucose, n = 14; fructose, n = 16. Data represent mean ± SEM.

Figure 2

Percent changes of fasting RBP-4 concentrations after 10 wks of consuming fructose- or glucose-sweetened beverages in male and female subjects. Values are means ± SEM, n = 31 (fructose group, n = 16; glucose group, n = 15) PROC MIXED 3-factor (sugar, gender, and presence of metabolic syndrome) ANOVA; *P < 0.05 and **P < 0.01 for changes significantly different from baseline.

Figure 3

Correlations between the percent changes of 24-h TG exposure and percent changes of (A) RBP-4 levels and (B) GGT activity in subjects consuming fructose. Pearson’s correlation coefficients (r) were calculated using PROC CORR. Average 24-h TG exposure was determined as the mean of TG concentrations in the 33 postprandial samples. n = 31 (fructose group n = 16).