Whole to body retention of alpha linolenic acid and its apparent conversion to other n3 PUFA in growing pigs are reduced with the duration of feeding alpha linolenic acid
Whole to body retention of alpha linolenic acid and its apparent conversion to other n3 PUFA in growing pigs are reduced with the duration of feeding alpha linolenic acid
Year: 2014
Authors:
Publication Name: Br J Nutr.
Publication Details: Volume 111; Number 8; pages 1382-93. doi:10.1017/S0007114513003991
Abstract:
In the present study, fifteen growing pigs were used to determine the whole to body oxidation, retention efficiency (RE) and apparent conversion (AC) of alpha linolenic acid (ALA,18 3n3) to n3 highly unsaturated fatty acids (HUFA), including EPA (20 5n3) and DHA (22 6n3). The pigs were fed a diet containing 10 percent flaxseed for 30 d. Whole to body fatty acid composition was determined at initial (27•7 kg), intermediate (day 15; 39•2 kg) and final (45•7 kg) body weight. On day 12, four pigs were fed 10 mg/kg of uniformly labelled 13C to ALA (single to bolus dose) to determine the oxidation of ALA. Expired CO2 samples were collected for 24 h thereafter. The whole body content of n3 PUFA increased linearly with time; however, the content of DHA exhibited a quadratic response with a peak occurring at 15 h. As a proportion of intake, the RE of ALA tended to reduce with time. The AC of ingested ALA to the sum of n3 HUFA was reduced with time (12•2 v. 7•53 percent for days 0–15 and days 15–30, respectively). The AC of ALA to EPA and DHA was lower than that to EPA, both for days 0–15 (1•14 or 1•07 v. 7•06 percent) and for days 15 to 30 ( 1•51 or 0•33 v. 4•29 percent). The direct oxidation of ALA was 7•91 percent and was similar to the calculated disappearance of ALA between days 0 and 30 (8•81 percent). The oxidation of ALA was much lower than that reported in other species. The AC of ALA to n3 HUFA was reduced over time and that to EPA in the present study was much higher than that reported in other species and should be explored further. (Authors abstract)
Effective manipulation of the fatty profile in pork products to provide human health benefits of ALA and n3 highly unsaturated fatty acids (HUFA) and all n3 PUFA minus ALA) requires a quantitative understanding of the n3 PUFA metabolism in growing pigs. Most mammalian species, including pigs, are able to metabolise ALA to n3 HUFA such as EPA, docosapentaenoic acid and DHA. The objective of the present study was to determine the whole to body RE of ALA and its AC to n3 HUFA in growing pigs fed a 10 percent FS to containing diet, utilising the mass balance approach and serial slaughter observations.
In addition, the oxidation of ALA was measured directly by feeding a single to bolus dose of uniformly labelled 13C to ALA (U to 13C to ALA). The purpose of the present study was to determine changes over time in the RE of ALA and its AC to EPA, DPA and DHA and intermediary n3 HUFA metabolites on a whole to body basis in growing pigs fed a diet containing 10 percent FS. The design of the present experiment is in contrast to that of human studies in which no attempt was made to adapt the subjects to the experimental diet before determining the oxidation of ALA. Moreover, in most of the human studies, breath is not sampled continuously. The latter can lead to inaccuracies in the estimates of CO2 production, and consequently FA oxidation, especially when breath is sampled during periods that are less than 5 min in duration and at 2 or 3 h intervals.
In the present study, the whole to body masses of SFA, MUFA, and n3 and n6 PUFA increased over time in the pigs when fed modest amounts of FS. Relatively few experiments have reported increasing contents of EPA in tissues after feeding FS to pigs. Moreover, the AC of ALA to EPA in mammals has not been reported in the literature. In the present experiment, EPA was the largest contributor to total n3 HUFA in the body (8 percent). Pigs fed FS appear unique in their ability to elongate ALA to EPA via chain elongation process, which differs from previous views of FA metabolism. The AC of ALA to DHA was low in the present study. It has been suggested that the initial conversion of ALA to stearidonic acid (SDA) by the action of D6 to desaturase and the conversion of SDA to EPA by the action of D5 to desaturase are the two main rate to limiting reactions in the Sprecher pathway.
The observed oxidation of ALA appears to be lower in the present study (approximately 8 percent) when compared with observations in other mammalian species, including adult humans. Highly variable results highlight the need to better understand animal and dietary factors that influence ALA utilisation in growing pigs and other species. Moreover, the experimental methodology should also be considered carefully, including between to animal variability and analytical procedures to quantify FA contents in diets and animal tissues. Quantitative information concerning the increasing rates of oxidation of ALA with age is not available for either pigs or humans. Whether there is a particular time period during pigs’ development when the RE and AC of ALA to n3 HUFA are more efficient, as well as the effect of whole to body FA composition on the RE and AC of ALA, remains to be explored further.
In conclusion, on a whole to body basis, the RE and AC of dietary ALA to n3 HUFA decreases with the duration of feeding a diet containing 15•5 g/kg of ALA to growing pigs with a low initial whole to body n3 PUFA content. Direct measures of ALA oxidation (7•91 percent of tracer dose; based on feeding a single bolus of labelled ALA) and indirect estimates of ALA oxidation (8•81 percent disappearance of intake; based on mass balance) yield similar values; these values are lower in pigs when compared with those in other mammalian species. Feeding modest amounts of ALA leads to a significant increase in the content of EPA, DPA and DHA in the pigs’ body, thus providing health benefits to n3 PUFA to enriched pork consumers. Pigs appear to be unique in that they elongate and store SDA, an intermediate between ALS and EPA, which deserves to be explored further. (Editors comments)
