A comparison of the metabolism of eighteen-carbon 13C-unsaturated fatty acids in healthy women

Abstract

) and oleate ( cis -18:1n-9) are the two predominant unsaturated fatty acids in the diet and are associated with several health benefits (1). ␣ -Linolenate ( cis -18:3n-3) is much less common in the diet but also has well-known health benefits, particularly against coronary artery disease and mortality (2-5). Elaidate, the main trans -isomer of oleate ( trans -18:1n Ϫ 9), which is mainly formed by food industry hydrogenation of vegetable oils, is associated with health concerns, particularly an increased risk of hypercholesterolemia (6-8). Despite their different abundances in the diet and different health implications, structurally, these four fatty acids are broadly similar in having 18 carbons and one to three double bonds. Nevertheless, comprehensive, comparative information is lacking about their metabolism that could help account for their differing health attributes in humans. This could be especially helpful in identifying potential reasons why trans -fatty acids may be hypercholesterolemic.The overall objective of this study was to gain insight into the differential health effects of these four common 18-carbon dietary unsaturated fatty acids by tracing their metabolism in healthy women using uniformly carbon-13 labeled (U-13 C) stable isotope tracers. This was a crossover study in which free-living healthy subjects consuming a self-selected diet orally ingested a tracer dose of [U-13 C]oleate, [U-13 C]elaidate, [U-13 C]linoleate, and [U-13 C] ␣ -linolenate in random sequential order with washout periods between each tracer. 13 C was measured in breath ( ␤ -oxidation), plasma fatty acids, and adipose tissue (storage) by high-precision gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS). Thus, the amount of each tracer used for energy, esterified to different lipid classes in plasma, desaturated and chain-elongated to long-chain PUFAs or stored in adipose tissue, was measured over a period of 8 days. MRI was used to quantify adipose tissue volumes to obtain pool size. Relationships between abdominal subcutaneous fat volume, blood lipids, plasma fatty acid profiles, and the metabolism of these tracers were also determined to identify conAbbreviations: AP, atom percent; APE, atom percent excess; AUC, area under the curve; CE, cholesteryl ester; GC-C-IRMS, gas chromatography-combustion-isotope ratio mass spectrometry; PL, phospholipid; U-13 C, uniformly carbon-13 labeled.

Suckling Rats Actively Recycle Carbon from α-Linolenate into Newly Synthesized Lipids Even During Extreme Dietary Deficiency of n-3 Polyunsaturates

“…Following saponification of the total lipid extracts, fatty acid methyl esters were prepared using BF 3 -methanol and analyzed by capillary gas chromatography (GC) (6). Total sterols (mainly cholesterol) from the brain were extracted and derivatized for analysis by GC (15). 13 C enrichment in individual fatty acids in the liver and brain and in brain cholesterol was determined by GC-combustion isotope ratio mass spectrometry as previously described (15).…”

Metabolism and functional effects of plant-derived omega-3 fatty acids in humans

“…McCloy et al followed ALA -oxidation for 7 days following consumption of labelled ALA and showed a progressive increase in appearance of labelled CO 2 which accounted for ~70% of dietary ALA over a seven day period [54]. In comparison, LA oxidation at 9 hours after consumption accounted for 12% of the LA consumed and at 7 days after consumption ~40% of LA consumed [54].…”

“…Studies using tracers report that conversion of ALA to carbon dioxide via -oxidation over the first hours following its consumption accounts for 15-35% of ALA consumed [30,31,54,56,57]. McCloy et al followed ALA -oxidation for 7 days following consumption of labelled ALA and showed a progressive increase in appearance of labelled CO 2 which accounted for ~70% of dietary ALA over a seven day period [54]. In comparison, LA oxidation at 9 hours after consumption accounted for 12% of the LA consumed and at 7 days after consumption ~40% of LA consumed [54].…”

“…Storage within adipose tissue is an important disposal route of dietary ALA [54]. The higher percentage of adipose tissue in women (average of 23% of body mass compared to 15% in men [42]) may suggest the storage of ALA in women is greater than in men.…”

Dietary n-6- or n-3-rich vegetable fats and α-tocopheryl acetate: effects on fatty acid composition and stability of rabbit plasma, liver and meat

“…In liver, linoleic acid content was 1.5-fold higher than in meat, but the content of linolenic acid was only half that in meat (Tables 2 and 3). This could be due to liver preferentially accumulating linoleic acid rather than linolenic acid; to a reduction in the content of linolenic acid due to its preferential use by D6-desaturase in the biosynthesis of longchain PUFA (Burdge and Calder, 2005a); and to preferential use of linolenic acid instead of linoleic acid for b-oxidation (McCloy et al, 2004). Consequently in liver, the ratio between the amount of long-chain n-3 PUFA derived from linolenic acid and the content of linolenic acid was much higher than the ratio between the amount of long-chain n-6 PUFA derived from linoleic acid and the content of linoleic acid (Figure 1).…”