Shf. Vermunt et al., Effects of dietary alpha-linolenic acid on the conversion and oxidation ofC-13-alpha-linolenic acid, LIPIDS, 35(2), 2000, pp. 137-142
The effects of a diet rich in alpha-linolenic acid vs. one rich in oleic ac
id on the oxidation of uniformly labeled C-13-alpha-linolenic acid and its
conversion into longer-chain polyunsaturates (LCP) were investigated in viv
o in healthy human subjects. Volunteers received a diet rich in oleic acid
(n = 5) or a diet rich in alpha-linolenic acid (n = 7; 8.3 g/d) for 6 wk be
fore and during the study. After 6 wk, subjects were given 45 mg of C-13-al
pha-linolenic acid dissolved in olive oil. Blood samples were collected at
t = 0, 5, 11, 24, 96, and 336 h. Breath was sampled and CO2 production was
measured each hour for the first 12 h. The mean (+/- SEM) maximal absolute
amount of C-13-eicosapentaenoic acid (EPA) in plasma total lipids was 0.04
+/- 0.01 mg in the alpha-linolenic acid group, which was significantly lowe
r (P = 0.01) than the amount of 0.12 +/- 0.03 mg C-EPA in the oleic acid gr
oup. Amounts of C-13-docosapentaenoic acid (DPA) and C-13-docosahexaenoic a
cid (DHA) tended to be lower as well. The mean proportion of labeled a-lino
lenic acid (ALA) recovered as (CO2)-C-13 in breath after 12 h was 20.4% in
the ALA and 15.7% in the oleic acid group, which was not significantly diff
erent (P = 0.12). The cumulative recovery of C-13 from C-13-ALA in breath d
uring the first 12 h was negatively correlated with the maximal amounts of
plasma C-13-EPA (r = -0.58, P = 0.047) and C-13-DPA (r = -0.63, P = 0.027),
but not of C-13-DHA (r = -0.49, P = 0.108). In conclusion, conversion of C
-13-ALA into its LCP may be decreased on diets rich in ALA, while oxidation
of C-13-ALA is negatively correlated with its conversion into LCP. In a fe
w pilot samples, low C-13 enrichments of n-3 LCP were observed in a diet ri
ch in EPA/DHA as compared to oleic acid.