Essentiality of dietary ω3 fatty acids for premature infants: Plasma and red blood cell fatty acid composition

Pre-term infants, that are not breast-fed, are deprived of vital intrauterine fat accretion during late pregnancy and must rely on formula to obtain fatty acids essential for normal development, particularly of the visual system. Preterm infants (30 wk postconception) receiving human milk were compared to infants given one of the following formulae: Formula A was a commercial preterm formula with predominantly 18∶2ω6 (24.2%) and low (0.5%) 18∶3ω3; Formula B was based on soy oil and contained similar 18∶2ω6 levels (20%) and high 18∶3ω3 (2.7%); Formula C was also a soy oil-based formula (20% 18∶2, 1.4% 18∶3) but was supplemented with marine oil to provide ω3 long-chain polyunsaturated fatty acids (LCP) at a level (docosahexaenoic acid, DHA, 0.35%) equivalent to human milk. At entry (10 days of age), the fatty acid composition of plasma and red blood cell (RBC) membrane lipids of the formula groups were identical. By 36 wk postconception, the DHA content in lipids of group A was significantly reduced compared to that in the human milk and marine oil formula groups. Omega-3 LCP results were further amplified by 57 wk with compensatory increases in 22∶5ω6 in both plasma and RBC lipids. Provision of 2.7% α-linolenic acid in formula group B was sufficient to maintain 22∶6ω3 levels equivalent to those in human milk-fed infants at 36 wk but not at 57 wk. Effects on the production of thiobarbituric acid reactive substances and fragility of RBC attributable to the marine oil supplementation were negligible. The results support the essentiality of ω3 fatty acids for preterm infants to obtain fatty acid profiles comparable to infants receiving human milk. Formula for preterm infants should be supplemented with ω3 fatty acids including LCP. Based on a paper presented at the Symposium on Milk Lipids held at the AOCS Annual Meeting, Baltimore, MD, April 1990.     

Δ15, 18-tetracosadienoic acid content of sphingolipids from platel and erythrocytes of animals fed diets high in saturated or polyunsaturated fats

The effect of diets high (15%) in saturated (beef tallow) or polyunsaturated (corn or cottonseed oil) fatty acids on the fatty acid composition of sphingomyelin from canine erythrocytes and platelets and sphingomyelin and neutral glycosphingolipids of swine erythrocytes was determined. Sphingolipids of platelets and erythrocytes from animals fed high levels of corn or cottonseed oil exhibited a dramatic alteration in their fatty acid composition, most notable of which was a 50% reduction in nervonic acid (24∶1ω9) as compared to levels observed in control or tallow fed animals. This decrease was compensated for by a quantitatively similar increase in a C₂₄ dienoic acid. The long chain dienoic acid was isolated by silver nitrate thin layer chromatography and determined by analysis of its oxidation products to be Δ15, 18-tetracosadienoic acid (24∶2ω6). When the animals were fed the diets high in polyunsaturates, the 24∶2ω6 represented 13, 20, and 9% of the sphingomyelin fatty acids from canine erythrocytes, platelets, and swine erythrocytes, respectively, and 5% of the neutral glycosphingolipid fatty acids of swine erythrocytes. In contrast, the 24∶2ω6 represented less than 4% of the total cellular sphingolipid fatty acids in animals fed the control or high beef tallow diets. The 24∶1ω9 in the sphingolipids of the animals fed the polyunsaturated diet was roughly equal to that of 24∶2ω6, whereas in the sphingolipids of animals fed the control or saturated fat (beef tallow) diet, the 24∶1ω9 was twice these values. Since sphingomyelin is a membrane component, the increase in unsaturation (24∶2ω6) in its fatty acid moiety induced by dietary polyunsaturates may affect membrane fluidity and may alter membrane properties. Dr. Nelson’s current affiliation is with the Lipid Metabolism Branch, Division of Heart and Vascular Diseases, National Heart, Lung, and Blood Institute.     

trans fatty acids. 4. Effects on fatty acid composition of colostrum and milk

trans Isometric fatty acids of partially hydrogenated fish oil (PHFO) consist oftrans 20∶1 andtrans 22∶1 in addition to thetrans isomers of 18∶1, which are abundant in hydrogenated vegetable oils, such as in partially hydrogenated soybean oil (PHSBO). The effects of dietarytrans fatty acids in PHFO and PHSBO on the fatty acid composition of milk were studied at 0 (colostrum) and 21 dayspostpartum in sows. The dietary fats were PHFO (28%trans), or PHSBO (36%trans) and lard. Sunflower seed oil (4%) was added to each diet. The fats were fed from three weeks of age throughout the lactation period of Experiment 1. In Experiment 2 PHFO or “fully” hydrogenated fish oil (HFO) (19%trans), in comparison with coconut oil (CF) (0%trans), was fed with two levels of dietary linoleic acid, 1 and 2.7% from conception throughout the lactation period. Feedingtrans-containing fats led to secretion oftrans fatty acids in the milk lipids. Levels oftrans 18∶1 andtrans 20∶1 in milk lipids, as percentages of totalcis+trans 18∶1 andcis+trans 20∶1, respectively, were about 60% of that of the dietary fats, with no significant differences between PHFO and PHSBO. The levels were similar for colostrum and milk. Feeding HFO gave relatively lesstrans 18∶1 andtrans 20∶1 fatty acids in milk lipids than did PHFO and PHSBO. Only low levels ofcis+trans 22∶1 were found in milk lipids. Feedingtrans-containing fat had no consistent effects on the level of polyenoic fatty acids but reduced the level of saturated fatty acids and increased the level ofcis+trans monoenoic fatty acids. Increasing the dietary level of linoleic acid had no effect on the secretion oftrans fatty acids but increased the level of linoleic acid in milk. The overall conclusion was that the effect of dietary fats containingtrans fatty acids on the fat content and the fatty acid composition of colostrum and milk in sows were moderate to minor.     

Hematological and lipid changes in newborn piglets fed milk replacer diets containing vegetable oils with different levels of n−3 fatty acids

To test if linolenic acid (18∶3n−3) from vegetable oils would affect bleeding times and platelet counts in new-borns, piglets were used as a model fed milk replacer diets containing 25% (by wt) vegetable oils or oil mixtures for 28 d and compared to sow-reared piglets. The oils tested included soybean, canola, olive, high oleic sunflower (HOAS), a canola/coconut mixture and a mixture of oils mimicking canola in fatty acid composition. All piglets fed the milk replacer diets showed normal growth. Bleeding times increased after birth from 4–6 min to 7–10 min by week 4 (P<0.001), and were higher in pigs fed diets containing 18∶3n−3, as well as in sowreared piglets receiving n−3 polyunsaturated fatty acids (PUFA) in the milk, as compared to diets low in 18∶3n−3. Platelet numbers increased within the first week in newborn piglets from 300 to 550×10⁹/L, and remained high thereafter. Milk replacer diets, containing vegetable oils, generally showed a transient delay in the rise of platelet numbers, which was partially associated with an increased platelet volume. The oils showed differences in the length of delay, but by the third week of age, all platelet counts were >500×10⁹/L. The delay in rise in platelet counts appeared to be related to the fatty acid composition of the oil, as the effect was reproduced by a mixture of oils with a certain fatty acid profile, and disappeared upon the addition of saturated fatty acids to the vegetable oil. There were no alterations in the coagulation factors due to the dietary oils. Blood plasma, platelets and red blood cell membranes showed increased levels of 18∶3n−3 and long-chain n−3 PUFA in response to dietary 18∶3n−3. The level of saturated fatty acids in blood lipids was generally lower in canola and HOAS oil-fed piglets as compared to piglets fed soybean oil or reared with the sow. The results suggest that consumption of milk replacer diets containing vegetable oils rich in 18∶3n−3 does not represent a bleeding risk, and that the transient lower platelet count can be counterbalanced by the addition of saturated fatty acids to the vegetable oils.     

Dietary saturated,monounsaturated, n−6 and n−3 fatty acids,and cholesterol influence platelet fatty acids in the exclusively formula-fed piglet

Platelet lipid composition is important to normal platelet morphology and function, and is influenced by dietary fatty acids and cholesterol. The fatty acid composition and cholesterol content of infant formulas differs from those of human milk, but the possible effects on platelet lipids in young infants is not known. This was studied in piglets fed from birth to 18 d of age with one of eight formulas differing in saturated fatty acid chain length, or content of 18∶1, 20∶5n−3 plus 22∶6n−3, or cholesterol. A reference group of piglets fed sow milk was also studied. Sow milk has a fatty acid composition and cholesterol content similar to that of human milk. Piglets fed formulas high in 18∶1 (34.9–40.8% wt fatty acids) and low in 16.0 (≤6.5% wt fatty acids) had lower platelet counts and greater platelet size than piglets fed sow milk (40.4% 18∶1, 30.7% 16∶0). Piglets fed formulas high in 16∶0 (27–29.6%) and 18∶1 (40–40.6%), or low in both 16∶0 (5.9–6.1%) and 18∶1 (10.8–11.2%), had similar platelet counts and size to piglets fed sow milk. Platelet phospholipid % 20∶4n−6 was lower in all the groups of piglets fed formula than in the group fed sow milk. Addition of fish oil with 20∶5n−3 plus 22∶6n−3 to the formula further decreased platelet phospholipid 20∶4n−6. Addition of cholesterol to the formula increased the platelet phospholipid % 20∶4n−6 and platelet volume.     

Influence of dietary linoleic acid andtrans fatty acids on the fatty acid profile of cardiolipins in rats

Cardiolipins (CL) have unique fatty acid profiles with generally high levels of polyunsaturated fatty acids, primarily 18∶2n−6, and low levels of saturated fatty acids. In order to study the effect of dietary fatty acid isomers on the fatty acid composition of cardiolipins, rats were fed partially hydrogenated marine oils (HMO), rich in 16∶1, 18∶1, 20∶1, and 22∶1 isomeric fatty acids, supplemented with linoleic acid at levels ranging from 1.9% to 14.5% of total fat. Although the dietary fats contained 33%trans fatty acids, the levels oftrans fatty acids in CL were below 2.5% in all organs. The fatty acid profiles of cardiolipins of liver, heart, kidney and testes showed different responses to dietary linoleic acid level. In liver, the contents of 18∶2 reflected the dietary levels. In heart and kidney, the levels of 18∶2 also parallelled increasing dietary levels, but in all groups fed HMO, levels of 18∶2 were considerably higher than in the reference group fed palm oil. In testes, the 18∶2 levels were unaffected by the dietary level of 18∶2 and HMO.     

Influence of partially hydrogenated vegetable and marine oils on lipid metabolism in rat liver and heart

Partially hydrogenated marine oils containing 18∶1-, 20∶1- and 22∶1-isomers and partially hydrogenated peanut oil containing 18∶1-isomers were fed as 24–28 wt % of the diet with or without supplement of linoleic acid. Reference groups were fed peanut, soybean, or rapeseed oils with low or high erucic acid content. Dietary monoene isomers reduced the conversion of linoleic acid into arachidonic acid and the deposition of the latter in liver and heart phosphatidylcholine. This effect was more pronounced for the partially hydrogenated marine oils than for the partially hydrogenated peanut oil. The content oftrans fatty acids in liver phospholipids was similar in groups fed partially hydrogenated fats. The distribution of various phospholipids in heart and liver was unaffected by the dietary fat. The decrease in deposition of arachidonic acid in rats fed partially hydrogenated marine oils was shown in vitro to be a consequence of lower Δ6-desaturase activity rather than an increase in the peroxisomal β-oxidation of arachidonic acid. The lower amounts of arachidonic acid deposited may be a result of competition in the Δ6-desaturation not only from the C22-and C20-monoenoic fatty acids originally present in the partially hydrogenated marine oil, but also from C18- and C16-monoenes produced by peroxisomal β-oxidation of the long-chain fatty acids. Part of this work was presented at the ISF-AOCS Congress, New York City, 1980.     

Reduction of essential fatty acid deficiency in rats fed a low iron fat free diet

Young male rats were fed ad libitum for 8 weeks a low iron fat-free (FF-Fe) diet or a fat-free diet supplemented with iron (FF+Fe). The relative levels of 16∶1 to 16∶0 and 18∶1 to 18∶0 in the total fatty acids of liver and other tissues (plasma, erythrocytes and intestinal mucosa) were considerably decreased because of a lack of dietary iron. In rats fed the FF-Fe diet, the levels of essential fatty acids (18∶2ω6+20∶4ω6) in tissues were 2-to 3-fold greater than in the corresponding tissues of rats fed the FF+Fe diet. Eicosatrienoic acid (20∶3ω9) levels in tissue lipids from rats fed the FF+Fe diet were high (8–16%), whereas they were low (2–5%) in the case of animals fed the FF-Fe diet. The proportion of 20∶4 in total fatty acids of tissues was 2-to 3-fold greater in rats fed the FF-Fe diet than when they were fed the FF+Fe diet. Therefore, the relative levels of 20∶3ω9/20∶4ω6 varied from 1-2.9 in tissue lipids of rats fed the FF+Fe diet, while it varied only from 0.2–0.3 in animals fed the FF-Fe diet. These results suggest that a lack of dietary iron may reduce the synthesis of 16∶1, 18∶1, 20∶3 and 20∶4 and the metabolism of 20∶4.     

Diet-induced alterations in the discoid shape and phospholipid fatty acid compositions of rat erythrocytes

For eight weeks young male rats were fed diets rich in 18∶2 (stock diet, or 10% corn oil, CO) or those devoid of 18∶2 (fat free, FF, or 10% hydrogenated coconut oil, HCNO). The CO and HCNO diets were fed in the absence or presence of eicosa-5,8,11,14-tetraynoic acid (TYA). When 18∶2 was excluded, an increase in the level of 16∶1, 18∶1 and 20∶3 and a decrease in 18∶2 was observed in the fatty acids of red cells. On feeding TYA, an increase in 18∶2 and in the case of the HCNO+TYA diet, a decrease of 12∶0 and 14∶0 was also observed. In all cases the levels of 20∶4 in erythrocyte fatty acids were similar. Saturated fatty acids were predominant in phosphatidyl choline (PC), lysophosphatidylcholine, (LPC) and sphingomyelin whereas unsaturated acids were predominant in phosphatidyl ethanolamine (PE), (PS), and phosphatidyl inositol (PI). Acids containing three or more double bonds comprised about 90% of the total acids in PI. In all the phospholipids, the characteristic changes in the composition of fatty acids were observed due to the exclusion of 18∶2 from the diet. However, changes due to the feeding of TYA were found only in PC and LPC. In rats fed the 18∶2-rich diet, about 60% of the red cells were discocytes. In those fed the 18∶2-free diet, the level of discocytes decreased to about 23%, and the levels of echinocytes II and III increased. The exclusion of 18∶2 for even a few days decreased the proportion of discocytes. The loss of discoid shape was reversed in a few days by feeding an 18∶2-rich diet. Fatty acid analysis of erythrocytes of rats of the various dietary manipulations showed that the change in the proportion of discocytes followed the change in the level of 18∶2.     

Efficiency of transfer of polyunsaturated fats into milk

Polyunsaturated milk has been produced by feeding cows safflower oil enclosed in a casein coat protected with formaldehyde (SOC-F) or formaldehyde-treated soybean (SB) preparations. The efficiency of transfer of dietary 18∶2 ranged from 17 to 42% for various lots of SOC-F and was only 2–8% for SB (per cent transfer=18.2 in milk fat per dietary 18∶2×100). The 18∶2 content of the milk fat increased from basal levels of 2–3% of total fatty acids to 35% with certain SOC-F levels and 7% with SB. Major compensatory changes were noted in 14∶0 and 16∶0 fatty acids. Blood cholesterol, triglycerides and nonesterified fatty acids all increased markedly as cows were fed increasing amounts of SOC-F. There was no increase in cholesterol in the milk. Presented at the AOCS Meeting, Los Angeles, April 1972.     

Dietary linoleic acid and the fatty acid profiles in rats fed partially hydrogenated marine oils

The influence of the linoleic acid levels of diets containing partially hydrogenated marine, oils (HMO) rich in isomeric 16∶1, 18∶1, 20∶1 and 22∶1 fatty acids on the fatty acid profiles of lipids from rat liver, heart and adipose tissue was examined. Five groups of rats were fed diets containing 20 wt% fat−16% HMO+4% vegetable oils. In these diets, the linoleic acid contents varied between 1.9% and 14.5% of the dietary fatty acids, whereas the contents oftrans fatty acids were 33% in all groups. A sixth group was fed a partially hydrogenated soybean oil (HSOY) diet containing 8% linoleic acid plus 32%trans fatty acids, mainly 18∶1, and a seventh group, 20% palm oil (PALM), with 10% linoleic acid and notrans fatty acids. As the level of linoleic acid in the HMO diets increased from 1.9% to 8.2%, the contents of (n−6) polyunsaturated fatty acids (PUFA) in the phospholipids increased correspondingly. At this dietary level of linoleic acid, a plateau in (n−6) PUFA was reached that was not affected by further increase in dietary 18∶2(n−6) up to 14.5%. Compared with the HSOY- or PALM-fed rats, the plateau value of 20∶4(n−6) were considerably lower and the contents of 18∶2(n−6) higher in liver phosphatidylcholines (PC) and heart PC. Heart phosphatidylethanolamines (PE) on the contrary, had elevated contents of 20∶4(n−6), but decreased 22∶5(n−6) compared with the PALM group. All groups fed HMO had similar contents oftrans fatty acids, mainly 16∶1 and 18∶1, in their phospholipids, irrespective of the dietary 18∶2 levels, and these contents were lower than in the HSOY group. High levels of linoleic acid consistently found in triglycerides of liver, heart and adipose tissue of rats fed HMO indicated that feeding HMO resulted in a reduction of the conversion of linoleic acid into long chain PUFA that could not be overcome by increasing the dietary level of linoleic acid.     

The identity of the cholesteryl esters in human milk

Milk samples were collected from 11 mothers who were at least 4 weeks postpartum. The amounts of fat and the fatty acid compositions of cholesteryl esters (CE) and triacylglycerols (TG) in the milk were determined. The mean concentration of total milk lipid was 3.01 gm/100 ml of milk±.42 SD. The major fatty acids esterified with CE and TG were 16∶0,cis 18∶1 and 18∶2. The patterns were similar except for a greater proportion ofcis 18∶1 in the CE. The majortrans fatty acid detected was the 18∶1 isomer which accounted for 4.48% of the TG fatty acids and 2.96% of the CE fatty acids. Scientific Contribution No. 821, Storrs Agricultural Experiment Station, University of Connecticu, Storrs, CT. 06268     

Dietary saturated fat level alters the competition between α-linolenic and linoleic acid

Male weanling rats were fed semi-synthetic diets high in saturated fat (beef tallow) vs high in linoleic acid (safflower oil) with or without high levels of α-linolenic acid (linseed oil) for a period of 28 days. The effect of feeding these diets on cholesterol content and fatty acid composition of serum and liver lipids was examined. Feeding linseed oil with beef tallow or safflower oil had no significant effect on serum levels of cholesterol. Serum cholesterol concentration was higher in animals fed the safflower oil diet than in animals fed the beef tallow diet without linseed oil. Feeding linseed oil lowered the cholesterol content in liver tissue for all dietary treatments tested. Consumption of linseed oil reduced the arachidonic acid content with concomitant increase in linoleic acid in serum and liver lipid fractions only when fed in combination with beef tallow, but not when fed with safflower oil. Similarly, ω3 fatty acids (18∶3ω3, 20∶5ω3, 22∶5ω3, 22∶6ω3) replaced ω6 fatty acids (20∶4ω6, 22∶4ω6) in serum and liver lipid fractions to a greater extent when linseed oil was fed with beef tallow than with safflower oil. The results suggest that the dietary ratio of linoleic acid to saturated fatty acids or of 18∶3ω3 to 18∶2ω6 may be important to determine the cholesterol and arachidonic acid lowering effect of dietary α-linolenic acid.     

n−3 Fatty acid requirements of the newborn

Whether docosahexaenoic acid (22∶6n−3) is an essential nutrient for term or preterm infants, or if not, the quantity of dietary linolenic acid (18∶3n−3) needed to support sufficient synthesis of 22∶6n−3 for assimilation in the central nervous system is unknown. Infants fed formulas have lower plasma and red blood cell (RBC) levels of 22∶6n−3 than breast fed infants. No relationship between the intake of 18∶3n−3 in formula (0.8 or 4.5% of fatty acids, 18∶2n−6/18∶3n−3 ratio 35∶1 or 7∶1, respectively) and the infant's RBC 22∶6n−3 was found. Premature infants (<33 wk gestation) also showed a decrease in RBC 22∶6n−3 during feeding with formula containing 18∶3n−3 as the only n−3 fatty acid. However, a marked decrease in plasma and RBC 22∶6n−3 occurred between premature birth and the start of full enteral feeding at 1–2 wk of age. This was not reversed by breast milk or formula feeding. Piglets, which are appropriate for studies of infant lipid metabolism, had decreased brain synaptic plasma membrane, retina and liver 22∶6n−3 and increased 22∶5n−6 when fed formula with 0.8% fatty acids (0.3% of kcal) as 18∶3n−3. Formula with 4.0% fatty acids (1.7% of kcal) as 18∶3n−3 resulted in similar accretion of 22∶6n−3 in the organs compared to milk fed animals. The studies suggest the dietary requirement for 18∶3n−3 in term animals in energy balance exceeds 0.3% diet kcal. Studies in the premature infants suggest 18∶3n−3 may be oxidized rather than desaturated to 22∶6n−3 if energy requirements are not met, and that due to early lipid restriction and later rapid growth, premature infants may have higher dietary n−3 requirements than term infants. Based on a paper presented at the Symposium on Milk Lipids held at the AOCS Annual Meeting, Baltimore, MD, April 1990.     

Production of prostaglandins in homogenates of kidney medullae and cortices of spontaneously hypertensive rats fed menhaden oil

Menhaden oil (MO), whose polyunsaturated fatty acids consist mainly of (n−3) fatty acids, was fed to spontaneously hypertensive rats to determine the effect of (n−3) fatty acid on the in vitro production of prostaglandins produced from arachidonic acid (20∶4[n−6]). Capacity to form PGE₂ and PGF_2α was impaired in homogenates of kidney medullae and cortices from rats fed the MO diet compared to rats fed the control diet. The lower amounts of diene prostaglandins produced corresponded to the decrease in the amount of 20∶4 (n−6) in the tissue. Possibly changes produced in tissue lipids by dietary fatty acids affect prostaglandin production by reducing the availability of substrate in tissue lipids.     

Influence of dietary fat composition on intestinal absorption in the rat

Omega-3 fatty acids influence the function of the intestinal brush border membrane. For example, the omega-3 fatty acid eicosapentaenoic acid (20∶5ω3) has an antiabsorptive effect on jejunal uptake of glucose. This study was undertaken to determine whether the effect of feeding α-linolenic acid (18∶3ω3) or EPA plus docosahexaenoic acid (22∶6ω3) on intestinal absorption of nutrients was influenced by the major source of dietary lipid, hydrogenated beef tallow or safflower oil. Thein vitro intestinal uptake of glucose, fatty acids and cholesterol was examined in rats fed isocaloric diets for 2 weeks: beef tallow, beef tallow + linolenic acid, beef tallow + eicosapentaenoic acid/docosahexaenoic acid, safflower oil, safflower oil + linolenic acid, or safflower oil + eicosapentaenic acid/docosahexaenoic acid. Eicosapentaenoic acid/docosahexaenoic acid reduced jejunal uptake of 10 and 20 mM glucose only when fed with beef tallow, and not when fed with safflower oil. Linolenic acid had no effect on glucose uptake, regardless of whether it was fed with beef tallow or safflower oil. The jejunal uptake a long-chain fatty acids (18∶0, 18∶2ω6, 18∶3ω3, 20∶4ω6, 20∶5ω3 and 22∶6ω3) and cholesterol was lower in salfflower oil than with beef tallow. When eicosapentaenoic acid/docosahexaenoic acid was given with beef tallow (but not with safflower oil), there was lower uptake of 18∶0, 20∶5ω3 and cholesterol. The demonstration of the inhibitory effect of linolenic acid or eicosapentaenoic acid/docosahexaenoic acid on cholesterol uptake required the feeding of a saturated fatty acid diet (beef tallow). These changes in uptake were not explained by differences in the animals’ food intake, body weight gain or intestinal weight. Feeding safflower oil was associated with an approximately 25% increase in the jejunal and ileal mucosal surface area, but this increase was prevented by combining linolenic acid or eicosapentaenoic acid/docosahexaenoic acid with safflower oil. Different inhibitory patterns were observed when mixtures of fatty acids were present together in the incubation medium, rather than in the diet: for example, when 18∶0 was in the incubation medium with 20∶4ω6, the uptake of 20∶4ω6 was reduced, whereas the uptake was unaffected by 18∶2ω6 or 20∶5ω3. Thus, (1) the inhibitory effect of eicosapentaenoic acid/docosahexaenoic acid on jejunal uptake of glucose, fatty acids and cholesterol was influenced by the major dietary lipid, saturated (beef tallow) or polyunsaturated fatty acid (safflower oil); and (2) different omega-3 fatty acids (linolenic acid versus eicosapentaenoic acid/docosahexaenoic acid) have a variable influence on the intestinal absorption of nutrients.     

Triglyceride composition of bovine milk fat with elevated levels of linoleic acid

The effect of increasing the linoleic acid (18∶2) content of milk fat on the composition and structure of the triglycerides (TG) was investigated. Protected sunflower seed supplement was added to the diet of a cow grazing on pasture, and the structure and composition of the milk fat compared with the milk fat from its monozygous twin which had been fed a control diet. The relative proportions of TG fractions of high, medium, and low molecular weight in the milk fat with elevated levels of 18∶2 (15.5% 18∶2) were 43.0, 19.5, and 37.5 moles %, respectively, compared with 36.1, 19.7, and 44.2 moles %, respectively, in the milk fat from the cow fed the control diet. Separation of these three TG fractions of each milk fat into TG classes with different levels of unsaturation showed that the milk fat with elevated levels of 18∶2 contained higher proportions of diene, triene, and tetraene TG and correspondingly lower proportions of saturated and, to a lesser extent, monoene TG. The saturated and monoene TG from the two milk fats had similar fatty acid compositions. However, the diene TG of the 18∶2-rich milk fat included high proportions of the combination of 18∶2 with two saturated fatty acids (FA) which are minor constituents of normal milk fats. Likewise, the triene TG reflected the presence of 18∶2 in combination with 18∶1 and a saturated FA.     

Docosahexaenoic acid in developing brain and retina of piglets fed high or low α-linolenate formula with and without fish oil

Docosahexaenoic acid (22∶6n−3) can be synthesized in the liver and/or brain from α-linolenic acid (18∶3n−3) and is required in large amounts in structural membranes of developing brain and retina. The adequacy and efficacy of formulas containing 18∶3n−3 and/or fish oil in providing 22∶6n−3 for deposition was investigated in piglets fed formula from birth to 15 days. The test formulas contained high (HL) or low (LL) 18∶3n−3 (3.9 or 0.7% of the total formula fatty acids, respectively), or low 18∶3n−3 plus fish oil (LL+FO) to provide C₂₀ and C₂₂ n−3 polyunsaturated fatty acids (0.8% of total fatty acids). Fatty acid analyses of synaptic plasma membrane and retina ethanolamine phospholipids (EPL), which are especially enriched in 22∶6n−3, were compared to those of 15-day-old piglets fed sow milk (SM). Feeding LL resulted in lower 22∶6n−3 in synaptic plasma membrane. Fatty acid levels in HL and LL+FO piglets were equivalent to SM, with the exception of lower 22∶5n−3 in the synaptic plasma membrane of LL+FO and in the retina of HL and LL+FO-fed piglets. Levels of 22∶4n−6 were also lower in the retina of the LL+FO group. The results suggest formula 18∶3n−3 is at least 24% as effective as C₂₀ and C₂₂ n−3 fatty acids as a source of membrane 22∶6n−3. This study shows dietary 18∶3n−3, as the only n−3 fatty acid, can support deposition of comparable percentage of 22∶6n−3 to natural milk. Fish oil also supported tissue levels of 22∶6n−3 similar to natural milk; however, lower 22∶4n−6 may indicate possible inhibitory effects on n−6 metabolism. Recipient of the 1967 Science and Engineering Scholarship, Natural Sciences & Engineering Research Council of Canada.     

Lipid composition and prostaglandin synthesis in mouse lung microsomes: Alterations following the ingestion of menhaden oil

Three groups of male mice were fed a normal diet or a semisynthetic diet containing either 10% hydrogenated coconut oil (CO group) or 10% menhaden oil (MO group) for two wk. The synthetic diet altered the fatty acid composition of lung microsomal lipids. Mice ingesting menhaden oil contained greater amounts of eicosapentaenoic acid (20∶5 n−3), docosapentaenoic acid (22∶5 n−3) and docosahexaenoic acids (22∶6 n−3) and decreased amounts of n−6 fatty acids such as arachidonic and adrenic. Synthesis of prostaglandin E₂ and prostaglandin F_2α from exogenous arachidonic acid was significantly depressed in n−3 fatty acid-enriched lung microsomes. These studies indicated that dietary fish oil not only alters the fatty acid composition of lung microsomes but also lowers the capacity of lungs to synthesize prostaglandins from arachidonic acid.     

Fatty acid composition of black bear (Ursus americanus) milk during and after the period of winter dormancy

Black bears give birth and lactate during the 2–3-mon fast of winter dormancy. Thereafter the female emerges from the den with her cubs and begins to feed. We investigated fatty acid patterns of milk from native Pennsylvania black bears during the period of winter dormancy, as well as after den emergence. Throughout winter dormancy, milk fatty acid composition remained relatively constant. The principal fatty acids at all times were 14∶0, 16∶0, 16∶1, 18∶0, 18∶1, 18∶2n−6, 18∶3n−3 and 20∶4n−6. After den emergence, large changes occurred in almost all the fatty acids, particularly in 18∶2n−6 and 18∶3n−3. Large variability among the active free-ranging animals likely reflected differences in diet. In a carnivore, with apparently limitedde novo synthesis of fatty acids, milk fatty acid composition may be affected by factors such as transition from reliance on stored lipids to feeding, and by temporal changes in dietary intake. Based on a paper presented at the Symposium on Milk Lipids held at the AOCS Annual Meeting, Baltimore, MD, April 1990.