title: Effect of type and amount of dietary carbohydrate on biomarkers of glucose homeostasis and C reactive protein in overweight or obese adults: results from the OmniCarb trial.
abstract: OBJECTIVE
  The glycemic index (GI) of dietary carbohydrate is thought to affect glucose homeostasis. Recently, the Effect of Amount and Type of Dietary Carbohydrates on Risk for Cardiovascular Heart Disease and Diabetes Study (OmniCarb) trial reported that a low-GI diet did not improve insulin sensitivity. We conducted this ancillary study of the OmniCarb trial to determine the effects of GI and carbohydrate content on glucose homeostasis and inflammation.
  
  
  METHODS
  OmniCarb was a randomized cross-over feeding study conducted in overweight or obese adults without diabetes (N=163). Participants were fed each of 4 diets for 5 weeks with 2-week washout periods. Weight was held constant. Diets were: high GI (GI≥65) with high carbohydrate (58% kcal), low GI (GI≤45) with low carbohydrate (40% kcal), low GI with high carbohydrate, and high GI with low carbohydrate. We measured glycated albumin (GA), fructosamine, and high sensitivity C reactive protein (CRP) at baseline and following each dietary period. These biomarkers were compared within-person between diets.
  
  
  RESULTS
  The study population was 52% female and 50% black. Mean age was 53 (SD, 11) years; mean body mass index was 32 (SD 6) kg/m2. Reducing GI had no effect on GA or fructosamine, but increased fasting glucose in the setting of a high-carbohydrate diet (+2.2 mg/dL; p=0.02). Reducing carbohydrate content decreased GA in the setting of a high-GI diet (-0.2%; p=0.03) and decreased fructosamine in the setting of a low-GI diet (-4 µmol/L; p=0.003). Reducing carbohydrate while simultaneously increasing GI significantly reduced both GA (-0.2%; p=0.04) and fructosamine (-4 µmol/L; p=0.009). Neither reducing GI nor amount of carbohydrate affected insulin or CRP.
  
  
  CONCLUSIONS
  Reducing carbohydrate, regardless of high or low GI, decreased GA and fructosamine. This suggests that reducing carbohydrate content, rather than GI, is a better strategy for lowering glycemia in adults at risk for diabetes.
  
  
  BACKGROUND
  NCT00608049.
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 , Baltimore, Maryland , USA.
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Juraschek
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 , Baltimore, Maryland , USA.
authors.forename: Edgar R
authors.initials: ER
authors.lastname: Miller
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 , Baltimore, Maryland , USA.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Selvin
authors.affiliation: Harvard T.H. Chan School of Public Health, Harvard Medical School, Brigham & Women's Hospital , Boston, Massachusetts , USA.
authors.forename: Vincent J
authors.initials: VJ
authors.lastname: Carey
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 , Baltimore, Maryland , USA.
authors.forename: Lawrence J
authors.initials: LJ
authors.lastname: Appel
authors.affiliation: University of Maryland School of Medicine , Baltimore, Maryland , USA.
authors.forename: Robert H
authors.initials: RH
authors.lastname: Christenson
authors.affiliation: Harvard T.H. Chan School of Public Health, Harvard Medical School, Brigham & Women's Hospital , Boston, Massachusetts , USA.
authors.forename: Frank M
authors.initials: FM
authors.lastname: Sacks
keywords: Carbohydrate(s); Glycated Proteins; Glycemic Index Diet; Randomized Controlled Trial