The rate of intestinal absorption of natural food folates is not related to the extent of folate conjugation.
BACKGROUND
Evidence is conflicting as to whether the bioavailability of food folates is influenced by the extent of their conjugation.


OBJECTIVE
The objective was to compare the bioavailability of 3 representative food folate sources with various degrees of glutamylation-ie, egg yolk, spinach, and yeast, whose polyglutamyl folate content measured 0%, 50%, and 100%, respectively.


METHODS
In a randomized crossover trial, 13 male subjects, after a prestudy folate saturation procedure, received in random order either placebo or 500 mug total folate, which was provided as concentrated freeze-dried extract removed from the normal food matrix of egg yolk, spinach, or yeast. Blood samples (n = 10) were collected before and up to 10 h after treatments, which were administered at weekly intervals.


RESULTS
A significant increase from baseline plasma folate concentrations was observed by 0.5 h after treatment with egg yolk folate or spinach folate and by 1 h after treatment with yeast folate, and the concentrations remained significantly elevated for 3-5 h; no plasma folate response was observed after placebo treatment. The overall responses, calculated as plasma folate area under the curve (AUC) for egg yolk, spinach, and yeast folate, were 122.6 +/- 23.6, 136.2 +/- 21.4, and 102.5 +/- 21.1 nmol . h/L, respectively. No significant differences in AUC were seen between monoglutamyl (egg yolk) folate and either of the polyglutamate-containing folates examined.


CONCLUSIONS
These results suggest that the ratio of monoglutamate to polyglutamate in natural folates is not a factor that limits the extent of intestinal absorption of food folate.
McKillop
Derek J
DJ
Northern Ireland Centre for Food and Health, University of Ulster, Coleraine, United Kingdom.
McNulty
Helene
H
Scott
John M
JM
McPartlin
Joseph M
JM
Strain
J J
JJ
Bradbury
Ian
I
Girvan
Jayne
J
Hoey
Leane
L
McCreedy
Richard
R
Alexander
Joy
J
Patterson
B Karen
BK
Hannon-Fletcher
Mary
M
Pentieva
Kristina
K
D000284:Administration, Oral; D000328:Adult; D019540:Area Under Curve; D001682:Biological Availability; D018592:Cross-Over Studies; D004311:Double-Blind Method; D004530:Egg Yolk / Q000737:chemistry*; D005492:Folic Acid / Q000008:administration & dosage / Q000097:blood / Q000737:chemistry / Q000493:pharmacokinetics*; D006801:Humans; D007408:Intestinal Absorption; D008297:Male; D018724:Spinacia oleracea / Q000737:chemistry*; D015003:Yeasts
D005492:Folic Acid