title: A novel extrinsic reference method for assessing the vitamin A value of plant foods.
abstract: BACKGROUND
  The amounts of vitamin A that are metabolically derived from specific carotene-containing foods are largely unknown.
  
  
  OBJECTIVE
  We sought to develop an improved method for estimating the metabolic vitamin A potential of provitamin A carotenoids by using [2H4]retinyl acetate (d4-RA) as an extrinsic reference standard.
  
  
  METHODS
  Healthy subjects consumed a standardized test meal containing 6 mg beta-carotene as either raw carrot or spinach, either 20 or 1 g added fat, and 6.0 micromol d4-RA. Concentrations of unlabeled (d0) retinyl esters (RE), labeled (d4) RE, and carotenoids in the plasma triacylglycerol-rich lipoprotein fraction (d < 1.006 kg/L) were determined in serial blood samples with HPLC and gas chromatography-mass spectrometry. Baseline-corrected areas under the curve for d0-RE, d4-RE, and carotenoids were calculated, and the masses of absorbed d0-retinol and carotenes were estimated assuming 80% absorption of the d4-RA reference dose.
  
  
  RESULTS
  In trials with ample (20 g) fat (n = 6), 7 +/- 4% of the 6 mg beta-carotene ingested was taken up as beta-carotene plus RE with 0.3 +/- 0.1 mg as retinol. Test meals without carotenes yielded no beta-carotene or d0-RE response and there was no effect of treatment (either fat amount or vegetable, n = 6) on the mean d4-RE area under the curve. The lower-than-expected vitamin A yields were attributed to poor intestinal uptake rather than to low conversion of beta-carotene to RE.
  
  
  CONCLUSIONS
  The triacylglycerol-rich lipoprotein and d4-RA method, which controls for variation in chylomicron kinetics in vivo and RE recovery during analysis, is useful for obtaining quantitative estimates of the vitamin A potential of single meals.
authors.affiliation: Division of Nutritional Sciences and the Department of Food Science, Cornell University, Ithaca, NY 14853, USA.
authors.forename: A J
authors.initials: AJ
authors.lastname: Edwards
authors.forename: C S
authors.initials: CS
authors.lastname: You
authors.forename: J E
authors.initials: JE
authors.lastname: Swanson
authors.forename: R S
authors.initials: RS
authors.lastname: Parker
mesh_terms: D000328:Adult; D000975:Antioxidants / Q000032:analysis / Q000378:metabolism / Q000493:pharmacokinetics; D019540:Area Under Curve; D001682:Biological Availability; D002851:Chromatography, High Pressure Liquid; D018552:Daucus carota / Q000737:chemistry; D004224:Diterpenes; D005260:Female; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D007408:Intestinal Absorption; D007553:Isotope Labeling; D008297:Male; D009753:Nutritive Value; D010945:Plants, Edible / Q000737:chemistry*; D012015:Reference Standards; D000084562:Retinyl Esters; D018724:Spinacia oleracea / Q000737:chemistry; D014280:Triglycerides / Q000097:blood / Q000737:chemistry; D014801:Vitamin A / Q000031:analogs & derivatives / Q000032:analysis / Q000378:metabolism / Q000493:pharmacokinetics*; D019207:beta Carotene / Q000032:analysis / Q000378:metabolism / Q000493:pharmacokinetics*
chemical_list: D000975:Antioxidants; D004224:Diterpenes; D000084562:Retinyl Esters; D014280:Triglycerides; D019207:beta Carotene; D014801:Vitamin A; C009166:retinol acetate