title: Postprandial changes in glucose oxidation and insulin sensitivity in metabolic syndrome: Influence of fibroblast growth factor 21 and vitamin D status.
abstract: OBJECTIVE
  Metabolic inflexibility due to insulin resistance has been reported in metabolic syndrome (MetS). Fibroblast growth factor 21 (FGF21) and vitamin D status may improve insulin sensitivity. The aim of this study was to investigate glucose-induced thermogenesis and oxidation in MetS, and to examine whether changes in FGF21 or prevailing vitamin D status modulated defined metabolic parameters.
  
  
  METHODS
  Forty-eight overweight and obese older adults (14 men, 34 women; ages 51 ± 15 y) were studied. Resting metabolic rate (RMR) and respiratory quotient (RQ) were measured before and intermittently for 2 h after an oral glucose tolerance test (OGTT). The total area under the curve (TAUC) was calculated. Insulin sensitivity index (ISI) was determined as 104/(insulin × glucose) for fasting and 2 h venous blood. Fat mass (FM) and fat free mass (FFM) were measured by dual-energy x-ray absorptiometry. Participants were grouped by metabolic syndrome (MetS+ for disease presence; MetS- when no disease was present) and by median 25 hydroxyvitamin D (OHD) concentration as VD_low and VD_high. 25 OHD was also tested as a continuous variable. A parsimonious 2 × 2 analysis of variance included age, FM, FFM and MetS × sex interaction.
  
  
  RESULTS
  Adjusted RMR was similar between groups but an interactive effect of MetS and sex was noted. Fasting RQ was significantly different between vitamin groups (VD_low: 0.835 ± 0.008 versus VD_high: 0.810 ± 0.008; P = 0.024) and fasting ISI was significantly greater in MetS- compared with MetS+ (P = 0.037). Postglucose increases in thermogenesis, RQ, and FGF21 were significant, but ISI decreased. Adjusted postprandial TAUC_RQ (VD_low: 1.71 ± 0.01; VD_high: 1.74 ± 0.001; P = 0.041) and ISI_2 h (VD_low: 35.41 ± 0.21; VD_high: 101.90 ± 0.21; P = 0.001) were significantly different. Adjusted FGF21 was similar across all comparisons before and after OGTT.
  
  
  CONCLUSIONS
  Higher vitamin D status, but not FGF21, was associated with greater postprandial glucose oxidation and improved insulin sensitivity.
authors.affiliation: Food, Nutrition & Health, School of Public Health, Curtin Health Innovation Research Institute, Faculty of Health Sciences, Curtin University, Perth, Western Australia.
authors.forename: Kaveri
authors.initials: K
authors.lastname: Pathak
authors.affiliation: Food, Nutrition & Health, School of Public Health, Curtin Health Innovation Research Institute, Faculty of Health Sciences, Curtin University, Perth, Western Australia. Electronic address: m.soares@curtin.ed.au.
authors.forename: Mario J
authors.initials: MJ
authors.lastname: Soares
authors.affiliation: Occuptation and the Environment, School of Public Health, Faculty of Health Sciences, Curtin University, Perth, Western Australia.
authors.forename: Yun
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: Food, Nutrition & Health, School of Public Health, Curtin Health Innovation Research Institute, Faculty of Health Sciences, Curtin University, Perth, Western Australia.
authors.forename: Anthony P
authors.initials: AP
authors.lastname: James
authors.affiliation: Food, Nutrition & Health, School of Public Health, Curtin Health Innovation Research Institute, Faculty of Health Sciences, Curtin University, Perth, Western Australia.
authors.forename: Jillian L
authors.initials: JL
authors.lastname: Sherriff
authors.affiliation: School of Biomedical Science, Curtin Health Innovation Research Institute, Curtin University, Perth, Western Australia.
authors.forename: Philip
authors.initials: P
authors.lastname: Newsholme
mesh_terms: D015502:Absorptiometry, Photon; D000293:Adolescent; D000328:Adult; D000368:Aged; D001481:Basal Metabolism; D001786:Blood Glucose / Q000378:metabolism*; D001823:Body Composition; D015992:Body Mass Index; D005215:Fasting; D005260:Female; D005346:Fibroblast Growth Factors / Q000097:blood*; D005951:Glucose Tolerance Test; D006801:Humans; D007328:Insulin / Q000097:blood; D007333:Insulin Resistance; D008297:Male; D024821:Metabolic Syndrome / Q000097:blood*; D008875:Middle Aged; D009765:Obesity / Q000097:blood; D050177:Overweight / Q000097:blood; D019518:Postprandial Period; D056152:Respiratory Rate; D018401:Sample Size; D014807:Vitamin D / Q000008:administration & dosage / Q000097:blood*; D055815:Young Adult
chemical_list: D001786:Blood Glucose; D007328:Insulin; C414620:fibroblast growth factor 21; D014807:Vitamin D; D005346:Fibroblast Growth Factors
keywords: Fibroblast growth factor 21; Metabolic flexibility; Metabolic syndrome; Respiratory quotient; Vitamin D