title: Effect of glycemic index and carbohydrate intake on kidney function in healthy adults.
abstract: Replacing carbohydrate with protein acutely increases glomerular filtration rate (GFR) but is associated with faster, long-term kidney disease progression. The effects of carbohydrate type (i.e. glycemic index, GI) on kidney function are unknown.
  
  
  
  We conducted an ancillary study of a randomized, crossover feeding trial in overweight/obese adults without diabetes or kidney disease (N = 163). Participants were fed each of four healthy, DASH-like diets for 5 weeks, separated by 2-week washout periods. Weight was kept constant. The four diets were: high GI (GI ≥65) with high %carb (58 % kcal) (reference diet), low GI (≤45) with low %carb (40 % kcal), low GI with high %carb; and high GI with low %carb. Plasma was collected at baseline and after each feeding period. Study outcomes were cystatin C, β2-microglobulin (β2M), and estimated GFR based on cystatin C (eGFRcys).
  
  
  
  Mean (SD) age was 52 (11) years; 52 % were women; 50 % were black. At baseline, mean (SD) cystatin C, β2M, and eGFRcys were 0.8 (0.1) mg/L, 1.9 (0.4) mg/L, and 104 (16) mL/min/1.73 m(2). Compared to the high GI/high %carb diet, reducing GI, %carb, or both increased eGFRcys by 1.9 mL/min/1.73 m(2) (95 % CI: 1.1, 2.7; P < 0.001), 3.0 mL/min/1.73 m(2) (1.9, 4.0; P < 0.001), and 4.5 mL/min/1.73 m(2) (3.5, 5.4; P < 0.001), respectively. Increases in eGFRcys from reducing GI were significantly associated with increases in eGFRcys from reducing %carb (P < 0.001). Results for cystatin C and β2M reflected eGFRcys.
  
  
  
  Reducing GI increased GFR. Reducing %carb by increasing calories from protein and fat, also increased GFR. Future studies on GI should examine the long-term effects of this increase in GFR on kidney injury markers and clinical outcomes.
  
  
  
  Clinical Trials.gov, number: NCT00608049 (first registered January 23, 2008).
authors.affiliation: The Johns Hopkins School of Medicine, The Johns Hopkins Bloomberg School of Public Health, and The Welch Center for Prevention, Epidemiology and Clinical Research, Johns Hopkins Medical Institutions, 2024 East Monument Street, Suite 1-500, Baltimore, MD, 21205, USA.
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Juraschek
authors.affiliation: Geisinger Health System, Danville, PA, USA.
authors.forename: Alex R
authors.initials: AR
authors.lastname: Chang
authors.affiliation: The Johns Hopkins School of Medicine, The Johns Hopkins Bloomberg School of Public Health, and The Welch Center for Prevention, Epidemiology and Clinical Research, Johns Hopkins Medical Institutions, 2024 East Monument Street, Suite 1-500, Baltimore, MD, 21205, USA.
authors.forename: Lawrence J
authors.initials: LJ
authors.lastname: Appel
authors.affiliation: University of California San Diego, San Diego, CA, USA.
authors.forename: Cheryl A M
authors.initials: CA
authors.lastname: Anderson
authors.affiliation: The Johns Hopkins School of Medicine, The Johns Hopkins Bloomberg School of Public Health, and The Welch Center for Prevention, Epidemiology and Clinical Research, Johns Hopkins Medical Institutions, 2024 East Monument Street, Suite 1-500, Baltimore, MD, 21205, USA.
authors.forename: Deidra C
authors.initials: DC
authors.lastname: Crews
authors.affiliation: The Johns Hopkins School of Medicine, The Johns Hopkins Bloomberg School of Public Health, and The Welch Center for Prevention, Epidemiology and Clinical Research, Johns Hopkins Medical Institutions, 2024 East Monument Street, Suite 1-500, Baltimore, MD, 21205, USA.
authors.forename: Letitia
authors.initials: L
authors.lastname: Thomas
authors.affiliation: The Johns Hopkins School of Medicine, The Johns Hopkins Bloomberg School of Public Health, and The Welch Center for Prevention, Epidemiology and Clinical Research, Johns Hopkins Medical Institutions, 2024 East Monument Street, Suite 1-500, Baltimore, MD, 21205, USA.
authors.forename: Jeanne
authors.initials: J
authors.lastname: Charleston
authors.affiliation: The Johns Hopkins School of Medicine, The Johns Hopkins Bloomberg School of Public Health, and The Welch Center for Prevention, Epidemiology and Clinical Research, Johns Hopkins Medical Institutions, 2024 East Monument Street, Suite 1-500, Baltimore, MD, 21205, USA. ermiller@jhmi.edu.
authors.forename: Edgar R
authors.initials: ER
authors.lastname: Miller
mesh_terms: D000328:Adult; D003404:Creatinine / Q000097:blood / Q000652:urine; D018592:Cross-Over Studies; D055316:Cystatin C / Q000097:blood; D004040:Dietary Carbohydrates / Q000008:administration & dosage*; D004041:Dietary Fats / Q000008:administration & dosage; D004044:Dietary Proteins / Q000008:administration & dosage; D002149:Energy Intake; D005260:Female; D005919:Glomerular Filtration Rate; D038321:Glycemic Index; D064368:Healthy Volunteers; D006801:Humans; D007668:Kidney / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000503:physiopathology*; D001613:beta 2-Microglobulin / Q000097:blood
chemical_list: D055316:Cystatin C; D004040:Dietary Carbohydrates; D004041:Dietary Fats; D004044:Dietary Proteins; D001613:beta 2-Microglobulin; D003404:Creatinine
keywords: Carbohydrate; Clinical trial; Creatinine; Cystatin C; Diet; Estimated glomerular filtration rate; Glycemic index; β2-microglobulin