The extent to which women of reproductive age are able to convert then−3 fatty acid α-linolenic acid (ALNA) to eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA) was investigatedin vivoby measuring the concentrations of labelled fatty acids in plasma for 21 d following the ingestion of [U−¹³C]ALNA (700 mg). [¹³C]ALNA excursion was greatest in cholesteryl ester (CE) (224 (SEM 70) μmol/l over 21 d) compared with triacylglycerol (9-fold), non-esterified fatty acids (37-fold) and phosphatidylcholine (PC, 7-fold). EPA excursion was similar in both PC (42 (SEM 8) μmol/l) and CE (42 (SEM 9) μmol/l) over 21 d. In contrast both [¹³C]DPA and [¹³C]DHA were detected predominately in PC (18 (SEM 4) and 27 (SEM 7) μmol/l over 21 d, respectively). Estimated net fractional ALNA inter-conversion was EPA 21 %, DPA 6 % and DHA 9 %. Approximately 22 % of administered [¹³C]ALNA was recovered as¹³CO₂on breath over the first 24 h of the study. These results suggest differential partitioning of ALNA, EPA and DHA between plasma lipid classes, which may facilitate targeting of individualn−3 fatty acids to specific tissues. Comparison with previous studies suggests that women may possess a greater capacity for ALNA conversion than men. Such metabolic capacity may be important for meeting the demands of the fetus and neonate for DHA during pregnancy and lactation. Differences in DHA status between women both in the non-pregnant state and in pregnancy may reflect variations in metabolic capacity for DHA synthesis.

The capacity for conversion of α-linolenic acid (ALNA) ton−3 long-chain polyunsaturated fatty acids was investigated in young men. Emulsified [U−¹³C]ALNA was administered orally with a mixed meal to six subjects consuming their habitual diet. Approximately 33 % of administered [¹³C]ALNA was recovered as¹³CO₂on breath over the first 24 h. [¹³C]ALNA was mobilised from enterocytes primarily as chylomicron triacylglycerol (TAG), while [¹³C]ALNA incorporation into plasma phosphatidylcholine (PC) occurred later, probably by the liver. The time scale of conversion of [¹³C]ALNA to eicosapentaenoic acid (EPA) and docosapentaenoic acid (DPA) suggested that the liver was the principal site of ALNA desaturation and elongation, although there was some indication of EPA and DPA synthesis by enterocytes. [¹³C]EPA and [¹³C]DPA concentrations were greater in plasma PC than TAG, and were present in the circulation for up to 7 and 14 d, respectively. There was no apparent¹³C enrichment of docosahexaenoic acid (DHA) in plasma PC, TAG or non-esterified fatty acids at any time point measured up to 21 d. This pattern of¹³Cn−3 fatty acid labelling suggests inhibition or restriction of DHA synthesis downstream of DPA. [¹³C]ALNA, [¹³C]EPA and [¹³C]DPA were incorporated into erythrocyte PC, but not phosphatidylethanolamine, suggesting uptake of intact plasma PC molecules from lipoproteins into erythrocyte membranes. Since the capacity of adult males to convert ALNA to DHA was either very low or absent, uptake of pre-formed DHA from the diet may be critical for maintaining adequate membrane DHA concentrations in these individuals.

BACKGROUND AND OBJECTIVE: Infants born preterm are significantly lighter and shorter on reaching term equivalent age (TEA) than are those born at term, but the relation with body composition is less clear. We conducted a systematic review to assess the body composition at TEA of infants born preterm. METHODS: The databases MEDLINE, Embase, CINAHL, HMIC, “Web of Science,” and “CSA Conference Papers Index” were searched between 1947 and June 2011, with selective citation and reference searching. Included studies had to have directly compared measures of body composition at TEA in preterm infants and infants born full-term. Data on body composition, anthropometry, and birth details were extracted from each article. RESULTS: Eight studies (733 infants) fulfilled the inclusion criteria. Mean gestational age and weight at birth were 30.0 weeks and 1.18 kg in the preterm group and 39.6 weeks and 3.41 kg in the term group, respectively. Meta-analysis showed that the preterm infants had a greater percentage total body fat at TEA than those born full-term (mean difference, 3%; P = .03), less fat mass (mean difference, 50 g; P = .03), and much less fat-free mass (mean difference, 460 g; P < .0001). CONCLUSIONS: The body composition at TEA of infants born preterm is different than that of infants born at term. Preterm infants have less lean tissue but more similar fat mass. There is a need to determine whether improved nutritional management can enhance lean tissue acquisition, which indicates a need for measures of body composition in addition to routine anthropometry.

Efficient isolation of individual lipid classes is a critical step in the analysis of plasma and lipoprotein fatty acid compositions. Whilst good separations of total lipid extracts are possible by TLC, this method is time consuming and a major rate-limiting step when processing large numbers of specimens. A method for rapid separation of phosphatidylcholine (PC), non-esterified fatty acids (NEFA), cholesterol ester (CE) and triacylglycerol (TAG) from total plasma lipid extracts by solid-phase extraction (SPE) using aminopropyl silica columns has been developed and validated. Following initial separation of polar and neutral lipids, individual classes were isolated by application of solvents with increasing polarity. Recoveries for combined plasma extraction with chloroform–methanol and SPE were (%): PC 74·2 (SD 7·5), NEFA 73·6 (sd 8·3), CE 84·9 (sd 4·9), and TAG 86·8 (sd 4·9), which were significantly greater for TAG and NEFA than by TLC (P<0·001). Both GC–flame ionisation detector and GC-MS analysis of fatty acid methyl esters demonstrated that there was no cross-contamination between lipid classes. Measurements of repeatability of fatty acid composition for TAG, PC, CE and NEFA fractions showed similar CV for each fatty acid. The magnitude of the CV appeared to be related inversely to the fractional fatty acid concentration, and was greatest at concentrations of less than 1 g/100 g total fatty acids. There was no evidence of selective elution of individual fatty acid or CE species. In conclusion, this method represents an efficient, rapid alternative to TLC for isolation of these lipid classes from plasma.

Background: Reduced fetal growth is associated with differences in body composition in adult life that may predispose to cardiovascular disease and diabetes. Most published data are based on simple anthropometric measures, which incompletely describe body composition. Objective: The objective was to assess body composition and fat distribution by using dual-energy X-ray absorptiometry (DXA). Design: This was a case-control study of 64–72-y-old white men (n = 32) with a low (x̄: 2.76 kg) or high (x̄: 4.23 kg) birth weight. Results: Compared with the high-birth-weight group, after adjustment for weight and height, the low-birth-weight group had a higher percentage body fat (29.31% compared with 25.33%; P = 0.029) and fat mass (P = 0.039) but a lower fat-free soft tissue (56.32 compared with 59.22 kg; P = 0.024), muscle mass (27.25 compared with 29.22 kg; P = 0.022), and muscle-to-fat ratio. Low birth weight was also associated with a higher trunk-to-limb fat ratio after control for total fat mass (1.42 compared with 1.16; P = 0.005) or percentage body fat (P = 0.041). The same body mass index predicted a greater percentage body fat (P = 0.019) in the low- than in the high-birth-weight group, and the same ratio of trunk-to-limb skinfold thickness (or waist-to-hip ratio) predicted a higher trunk-to-limb fat ratio (P < 0.01). Conclusion: Lifelong differences in adult body composition and fat distribution between the low- and high-birth-weight groups are consistent with programming in early life. The use of BMI to predict percentage body fat and the use of the trunk-to-limb skinfold thickness ratio (and waist-to-hip ratio) to predict the trunk-to-limb fat ratio measured by DXA can be misleading when low- and high-birth-weight groups are compared.

The effect of increased dietary intakes of α-linolenic acid (ALNA) or eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) for 2 months upon plasma lipid composition and capacity for conversion of ALNA to longer-chain metabolites was investigated in healthy men (52 (SD 12) years). After a 4-week baseline period when the subjects substituted a control spread, a test meal containing [U-¹³C]ALNA (700 mg) was consumed to measure conversion to EPA, docosapentaenoic acid (DPA) and DHA over 48 h. Subjects were then randomised to one of three groups for 8 weeks before repeating the tracer study: (1) continued on same intake (control,n5); (2) increased ALNA intake (10 g/d,n4); (3) increased EPA+DHA intake (1·5 g/d,n5). At baseline, apparent fractional conversion of labelled ALNA was: EPA 2·80, DPA 1·20 and DHA 0·04 %. After 8 weeks on the control diet, plasma lipid composition and [¹³C]ALNA conversion remained unchanged compared with baseline. The high-ALNA diet resulted in raised plasma triacylglycerol-EPA and -DPA concentrations and phosphatidylcholine-EPA concentration, whilst [¹³C]ALNA conversion was similar to baseline. The high-(EPA+DHA) diet raised plasma phosphatidylcholine-EPA and -DHA concentrations, decreased [¹³C]ALNA conversion to EPA (2-fold) and DPA (4-fold), whilst [¹³C]ALNA conversion to DHA was unchanged. The dietary interventions did not alter partitioning of ALNA towards β-oxidation. The present results indicate ALNA conversion was down-regulated by increased product (EPA+DHA) availability, but was not up-regulated by increased substrate (ALNA) consumption. This suggests regulation of ALNA conversion may limit the influence of variations in dietaryn-3 fatty acid intake on plasma lipid compositions.