Polyunsaturated fatty acids in the food chain in Europe.
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Intakes of partially hydrogenated fish oil and animal fats have declined and those of palm, soybean, sunflower, and rapeseed oils have increased in northern Europe in the past 30 y. Soybean and rapeseed oils are currently the most plentiful liquid vegetable oils and both have desirable ratios of n-6 to n-3 fatty acids. However, soybean and rapeseed oils are commonly partially hydrogenated for use in commercial frying to decrease susceptibility to oxidative degradation. This process leads to selective losses of alpha-linolenic acid (18:3n-3). Intake of linoleic acid (18:2n-6) has risen in many northern European countries. In the United Kingdom, intakes have increased from approximately 10 g/d in the late 1970s to approximately 15 g/d in the 1990s. The intake of alpha-linolenic acid is estimated to be approximately 1-2 g/d but varies with the type of culinary oil used. There are few reliable estimates of the intake of long-chain n-3 fatty acids, but those are generally approximately 0.1-0.5 g/d. The increased use of intensive, cereal-based livestock production systems has resulted in a lower proportion of n-3 fatty acids in meat compared with traditional extensive production systems. Overall, there has been a shift in the balance between n-6 and n-3 fatty acids over the past 30 y. This shift is reflected in the declining concentrations of docosahexaenoic acid and rising concentrations of linoleic acid in breast milk. (+info)
Safety considerations of polyunsaturated fatty acids.
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The n-6 and n-3 polyunsaturated fatty acids (PUFAs) are essential nutrients; intake of relatively small amounts of these fatty acids prevents nutritional deficiencies. Replacing dietary saturated fat with PUFAs may confer health gains. Experimental data support the notion that high intake of n-6 PUFAs may increase in vivo lipid peroxidation. This effect may be counteracted by dietary antioxidant supplementation. The influence of a high n-3 PUFA intake on measures of lipid peroxidation has been equivocal. In clinical trials, subjects who consumed diets rich in n-6 or n-3 PUFAs had fewer atherothrombotic endpoints than did control groups. In this report, data regarding the influence of PUFAs on lipid peroxidation as well as on cholesterol and glucose metabolism, hemostasis, and other aspects of interest are reviewed and discussed. Currently, daily intake of PUFAs as >10% of total energy is not recommended. Below this ceiling there is little evidence that high dietary intake of n-6 or n-3 PUFAs implies health risks. (+info)
Essential fatty acids in infant nutrition: lessons and limitations from animal studies in relation to studies on infant fatty acid requirements.
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Animal studies have been of pivotal importance in advancing knowledge of the metabolism and roles of n-6 and n-3 fatty acids and the effects of specific dietary intakes on membrane composition and related functions. Advantages of animal studies include the rigid control of fatty acid and other nutrient intakes and the degree, timing, and duration of deficiency or excess, the absence of confounding environmental and clinical variables, and the tissue analysis and testing procedures that cannot be performed in human studies. However, differences among species in nutrient requirements and metabolism and the severity and duration of the dietary treatment must be considered before extrapolating results to humans. Studies in rodents and nonhuman primates fed diets severely deficient in alpha-linolenic acid (18:3n-3) showed altered visual function and behavioral problems, and played a fundamental role by identifying neural systems that may be sensitive to dietary n-3 fatty acid intakes; this information has assisted researchers in planning clinical studies. However, whereas animal studies have focused mainly on 18:3n-3 deficiency, there is considerable clinical interest in docosahexaenoic acid (22:6n-3) and arachidonic acid (20:4n-6) supplementation. Information from animal studies suggests that brain and retinal concentrations of 22:6n-3 plateau with 18:3n-3 intakes of approximately 0.7% of energy, but this requirement is influenced by dietary 18:2n-6 intake. Blood and tissue concentrations of 22:6n-3 increase as 22:6n-3 intake increases, with adverse effects on growth and function at high intakes. Animal studies can provide important information on the mechanisms of both beneficial and adverse effects and the pathways of brain 22:6n-3 uptake. (+info)
Essential fat requirements of preterm infants.
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The interest in factors that modify early infant development has led investigators to focus on n-3 and n-6 long-chain polyunsaturated fatty acids (LCPUFAs) in the past 2 decades. The presence of docosahexaenoic acid (DHA) and arachidonic acid (AA) in breast milk, compared with their absence from infant formulas available in the United States, has prompted clinical trials designed to examine whether LCPUFA enrichment of infant formula has beneficial effects on maturational events of the visual system. These trials have shown significant functional advantages of LCPUFA supplementation for preterm infants, whereas benefits for full-term infants remain controversial. The growth and safety of preterm infants was not compromised by LCPUFA enrichment, although these issues remain to be resolved in clinical trials with full-term infants. (+info)
Long-chain polyunsaturated fatty acids, pregnancy, and pregnancy outcome.
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During pregnancy, essential long-chain polyunsaturated fatty acids (LCPUFAs) play important roles as precursors of prostaglandins and as structural elements of cell membranes. Throughout gestation, accretion of maternal, placental, and fetal tissue occurs and consequently the LCPUFA requirements of pregnant women and their developing fetuses are high. This is particularly true for docosahexaenoic acid (DHA; 22:6n-3). The ratio of DHA to its status marker, docosapentaenoic acid (22:5n-6), in maternal plasma phospholipids decreases significantly during pregnancy. This suggests that pregnancy is associated with maternal difficulty in coping with the high demand for DHA. The DHA status of newborn multiplets is significantly lower than that of singletons; the same is true for infants of multigravidas as compared with those of primigravidas and for preterm compared with term neonates. Because the LCPUFA status at birth seems to have a long-term effect, the fetus should receive an adequate supply of LCPUFAs. Data from an international comparative study indicated that, especially for n-3 LCPUFAs, the fetus is dependent on maternal fatty acid intake; maternal supplementation with LCPUFAs, their precursors, or both increased LCPUFA concentrations in maternal and umbilical plasma phospholipids. However, significant competition between the 2 LCPUFA families was observed, which implies that effective supplementation requires a mixture of n-6 and n-3 fatty acids. Further research is needed to determine whether higher LCPUFA concentrations in plasma phospholipid will have functional benefits for mothers and children. (+info)
Transport mechanisms for long-chain polyunsaturated fatty acids in the human placenta.
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To understand the placental role in the processes responsible for the preferential accumulation of maternal long-chain polyunsaturated fatty acids (LCPUFAs) in the fetus, we investigated fatty acid uptake and metabolism in the human placenta. A preference for LCPUFAs over nonessential fatty acids has been observed in isolated human placental membranes as well as in BeWo cells, a human placental choriocarcinoma cell line. A placental plasma membrane fatty acid binding protein (p-FABP(pm)) with a molecular mass of approximately 40 kDa was identified. The purified p-FABP(pm) preferentially bound with essential fatty acids (EFAs) and LCPUFAs over nonessential fatty acids. Oleic acid was taken up least and docosahexaenoic acid (DHA) most by BeWo cells, whereas no such discrimination was observed in HepG2 liver cells. Studies on the distribution of radiolabeled fatty acids in the cellular lipids of BeWo cells showed that DHA is incorporated mainly into the triacylglycerol fraction, followed by the phospholipid fraction; the reverse is true for arachidonic acid (AA). The greater cellular uptake of DHA and its preferential incorporation into the triacylglycerol fraction suggests that both uptake and transport modes of DHA by the placenta to the fetus are different from those of AA. p-FABP(pm) antiserum preferentially decreased the uptake of LCPUFAs and EFAs by BeWo cells compared with preimmune serum. Together, these results show the preferential uptake of LCPUFAs by the placenta that is most probably mediated via the p-FABP(pm). (+info)
Long-chain polyunsaturated fatty acids in children with attention-deficit hyperactivity disorder.
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Attention-deficit hyperactivity disorder (ADHD) is the diagnosis used to describe children who are inattentive, impulsive, and hyperactive. ADHD is a widespread condition that is of public health concern. In most children with ADHD the cause is unknown, but is thought to be biological and multifactorial. Several previous studies indicated that some physical symptoms reported in ADHD are similar to symptoms observed in essential fatty acid (EFA) deficiency in animals and humans deprived of EFAs. We reported previously that a subgroup of ADHD subjects reporting many symptoms indicative of EFA deficiency (L-ADHD) had significantly lower proportions of plasma arachidonic acid and docosahexaenoic acid than did ADHD subjects with few such symptoms or control subjects. In another study using contrast analysis of the plasma polar lipid data, subjects with lower compositions of total n-3 fatty acids had significantly more behavioral problems, temper tantrums, and learning, health, and sleep problems than did those with high proportions of n-3 fatty acids. The reasons for the lower proportions of long-chain polyunsaturated fatty acids (LCPUFAs) in these children are not clear; however, factors involving fatty acid intake, conversion of EFAs to LCPUFA products, and enhanced metabolism are discussed. The relation between LCPUFA status and the behavior problems that the children exhibited is also unclear. We are currently testing this relation in a double-blind, placebo-controlled intervention in a population of children with clinically diagnosed ADHD who exhibit symptoms of EFA deficiency. (+info)
Evening primrose oil and borage oil in rheumatologic conditions.
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Diets rich in arachidonic acid (20:4n-6) lead to the formation of 2-series prostaglandins (PGs) and 4-series leukotrienes (LTs), with proinflammatory effects. Nonsteroidal antiinflammatory drugs are used in rheumatoid arthritis to inhibit cyclooxygenase (prostaglandin-endoperoxide synthase), thereby decreasing production of 2-series PGs. Lipoxygenase activity remains intact, however, allowing LT production (eg, synthesis of LTB(4), a potent inflammatory mediator) to continue. Altering the essential fatty acid (EFA) content of the diet can modify some of these effects. Ingestion of a diet rich in evening primrose oil elevates concentrations of dihomo-gamma-linolenic acid (DGLA; 20:3n-6), which results in the production of 1-series PGs, eg, PGE(1). DGLA itself cannot be converted to LTs but can form a 15-hydroxyl derivative that blocks the transformation of arachidonic acid to LTs. Increasing DGLA intake may allow DGLA to act as a competitive inhibitor of 2-series PGs and 4-series LTs and thus suppress inflammation. The results of in vitro and animal work evaluating EFAs in inflammatory situations are encouraging, which has stimulated clinical workers to evaluate these compounds in rheumatoid arthritis. Several well-controlled, randomized clinical studies have now been completed in which various EFAs were evaluated as treatments. The results of most of these studies suggest some clinical benefit to these treatments; these data are reviewed here. (+info)