Availability Of Essential Fatty Acids Research Articles

Diatom-mediated food web functioning under ocean artificial upwelling

Enhancing ocean productivity by artificial upwelling is evaluated as a nature-based solution for food security and climate change mitigation. Fish production is intended through diatom-based plankton food webs as these are assumed to be short and efficient. However, our findings from mesocosm experiments on artificial upwelling in the oligotrophic ocean disagree with this classical food web model. Here, diatoms did not reduce trophic length and instead impaired the transfer of primary production to crustacean grazers and small pelagic fish. The diatom-driven decrease in trophic efficiency was likely mediated by changes in nutritional value for the copepod grazers. Whilst diatoms benefitted the availability of essential fatty acids, they also caused unfavorable elemental compositions via high carbon-to-nitrogen ratios (i.e. low protein content) to which the grazers were unable to adapt. This nutritional imbalance for grazers was most pronounced in systems optimized for CO2 uptake through carbon-to-nitrogen ratios well beyond Redfield. A simultaneous enhancement of fisheries production and carbon sequestration via artificial upwelling may thus be difficult to achieve given their opposing stoichiometric constraints. Our study suggest that food quality can be more critical than quantity to maximize food web productivity during shorter-term fertilization of the oligotrophic ocean.

Microalgae technology for polishing chemically-treated fish processing wastewater

The development of cost-effective treatment methods for nutrient-rich effluents is of great importance. In this study, microalgal-based technology was investigated as a final polishing stage for fish processing wastewater (FPWW) after fat and oil removal, with the purpose of facilitating wastewater reuse and nutrient recovery. First, the effect of FPWW filtration on the growth of two microalgal species (Chlorella sorokiniana and Selenastrum sp.) was investigated under batch mode. For both microalgae, the final biomass concentration and nutrient removal levels were higher in unfiltered FPWW than in filtered FPWW. Chlorella sorokiniana growth was notably greater than that of Selenastrum sp. Chlorella sorokiniana was further cultivated in a semi-continuous mode, which lead to stable microalgae growth and high nutrient uptake in unfiltered wastewater with no need to eliminate indigenous microorganisms and contamination. However, based on biochemical analysis, filtration increased the availability of essential fatty acids and carotenoids from Chlorella sorokiniana, thus increasing the commercial value of the algal biomass.

Quality of the food of flatfish larvae: requirements, supplies and availability of essential fatty acids in coastal marine areas

Quality of the food of flatfish larvae: requirements, supplies and availability of essential fatty acids in coastal marine areas

Alterations in hepatic fatty acids reveal depletion of total polyunsaturated fatty acids following irinotecan plus 5-fluorouracil treatment in an animal model of colorectal cancer

Fatty liver is a side effect of chemotherapy that limits the ability to treat colorectal cancer (CRC) patients in the most effective way. The aim of this study was to determine hepatic fatty acid composition and expression of genes involved in lipid metabolism at two time points following sequential chemotherapy treatment with Irinotecan (CPT-11)+5-fluorouracil (5-FU), agents commonly used to treat human colorectal cancer. Female Fischer 344 rats were provided a semi-purified AIN-76 basal diet with modified fat component. One cycle of chemotherapy consisted of CPT-11+5-FU and was initiated 2 weeks after tumor implantation (D0); a second cycle was given one week later. Two days after each cycle (Day 2 and Day 9), animals were euthanized, and livers collected. Triacylglycerol (TAG) and phospholipid (PL) fractions were isolated using thin layer chromatography and fatty acids (FAs) were quantified using gas chromatography. Expression of 44 lipid metabolism genes were analyzed by qPCR. Total liver TAG level was lowest after the second cycle D0 and D2 (P = 0.05) characterized by lower content of n-6 and n-3 polyunsaturated fatty acids (PUFAs). N-6 PUFAs significantly declined with subsequent treatments. Of 44 genes analyzed, 13 genes were altered with CPT-11+5-FU treatment. Expression of genes VLCAD and DGAT1, involved in fatty acid oxidation as well as DGAT1 in TAG synthesis, were significantly elevated after each cycle, whereas expression of genes ELOVL2 and FADS2, involved in fatty acid elongation and desaturation were significantly lower at D9 compared to D2 and D0 (P < 0.03). Hepatic total TAG PUFA was depleted, and genes involved in pathways of PUFA synthesis were down-regulated by chemotherapy treatment. This observation suggests impediments in lipid metabolism in the liver that could potentially impact peripheral availability of essential fatty acids.

Temperature-induced changes in fatty acid dynamics of the intertidal grazer Platychelipus littoralis (Crustacea, Copepoda, Harpacticoida): Insights from a short-term feeding experiment

Dietary lipids, and in particular the essential fatty acids (EFA), EPA (20:5ω3) and DHA (22:6ω3), guarantee the well-being of animals and are recognized for their potential bottom-up control on animal populations. They are introduced in marine ecosystems through primary producers and when grazed upon, they are consumed, incorporated or modified by first-level consumers. As the availability of EFA in the ecosystem is affected by ambient temperature, the predicted rise in ocean temperature might alter the availability of these EFA at the basis of marine food webs. Despite the FA bioconversion capacity of certain benthic copepod species, their lipid (FA) response to varying temperatures is understudied. Therefore, the temperate, intertidal copepod Platychelipus littoralis was offered a mono and mixed diatom diet at 4, 15 °C (normal range) and at 24 °C (elevated temperature) to investigate the combined effects of temperature and resource availability on its FA content and composition. P. littoralis showed a flexible thermal acclimation response. Cold exposure increased the degree of FA unsaturation and the EPA%, and induced a shift towards shorter chain FA in the copepod’s membranes. Furthermore, a mixed diet reduced the impact of heat stress on the copepod’s membrane FA composition. Temperature affected the trophic transfer of EPA and DHA differently. While dietary resources could fully compensate for the temperature effects on total lipid and EPA content in the copepods, no such counterweigh was observed for the DHA dynamics. Heat stress lowered the DHA concentration in copepods regardless of the resources available and this implies negative effects for higher trophic levels.

Interspecific competition in phytoplankton drives the availability of essential mineral and biochemical nutrients.

The underlying mechanisms and consequences of competition and diversity are central themes in ecology. A higher diversity of primary, producers often results in higher resource use efficiency in aquatic and terrestrial ecosystems. This may result in more food for consumers on one hand, while, on the other hand, it can also result in a decreased food quality for consumers; higher biomass combined with the same availability of the limiting compound directly reduces the dietary proportion of the limiting compound. Here we tested whether and how interspecific competition in phytoplankton communities leads to changes in resource use efficiency and cellular concentrations of nutrients and fatty acids. The measured particulate carbon: phosphorus ratios (C:P) and fatty acid concentrations in the communities were compared to the theoretically expected ratios and concentrations of measurements on simultaneously running monocultures. With interspecific competition, phytoplankton communities had higher concentrations of the monounsaturated fatty acid oleic acid and also much higher concentrations of the ecologically and physiologically relevant long-chain polyunsaturated fatty acid eicosapentaenoic acid than expected concentrations based on monocultures. Such higher availability of essential fatty acids may contribute to the positive relationship between phytoplankton diversity and zooplankton growth, and may compensate limitations by mineral nutrients in higher trophic levels.

Aquatic hyphomycetes: a potential source of polyunsaturated fatty acids in detritus-based stream food webs

Abstract To date, aquatic hyphomycetes have mainly been considered as a source of carbohydrates, mineral elements and proteins for detritivores in detritus-based headwater streams. Yet, consumers are highly dependent on other molecules, such as essential fatty acids, to complete their biological cycle. These molecules might be limiting in detritus-based ecosystems since they are primarily synthesized by autotrophic organisms. We investigated: (i) if aquatic hyphomycetes are able to synthesize polyunsaturated fatty acids (PUFAs); and (ii) if the abundance of phosphorus, often considered as a limiting factor in headwater streams, could affect the proportions of PUFAs in aquatic hyphomycetes. All hyphomycete species tested synthesized high amounts of PUFAs (C18 ω3 and ω6) and the proportions of these essential fatty acids varied with P availability. This study sheds new light on the importance of aquatic hyphomycetes in the detritus-based stream food web, but also on potential co-variations between mineral nutrient limitation and the availability of essential fatty acids for consumers.

Temporal changes in essential fatty acid availability in different food sources in the littoral macrophyte zone

In littoral environments, different food resources are available for zooplankters. In addition to seston, species may feed on biofilms growing on sediments, plants (epiphyton), and at the air-water interface (neuston). However, despite a growing interest in these different biofilms, little is known about their food quality for microcrustaceans. In a field study, we measured changes in the food quality over time in terms of the essential fatty acid (EFA) content of different potential food sources for littoral consumers. The food quality of seston, neuston, and epiphyton growing on three different aquatic macro- phytes were assessed. Our results showed that there is an important seasonal variability within each food source. However, in the system studied, epiphytic biofilms, especially those of Ludwigia and Callitriche offered the highest food quality, in terms of EFA content, throughout the year. As the highest EFA concentrations in each food source were found con- secutively, high concentrations of these physiologi- cally important compounds are maintained in the system throughout the year. Therefore, greater diver- sity of food resources could affect ecosystem productivity.

Changes in consumption of omega-3 and omega-6 fatty acids in the United States during the 20th century

The consumption of omega-3 (n-3) and omega-6 (n-6) essential fatty acids in Western diets is thought to have changed markedly during the 20th century. We sought to quantify changes in the apparent consumption of essential fatty acids in the United States from 1909 to 1999. We calculated the estimated per capita consumption of food commodities and availability of essential fatty acids from 373 food commodities by using economic disappearance data for each year from 1909 to 1999. Nutrient compositions for 1909 were modeled by using current foods (1909-C) and foods produced by traditional early 20th century practices (1909-T). The estimated per capita consumption of soybean oil increased >1000-fold from 1909 to 1999. The availability of linoleic acid (LA) increased from 2.79% to 7.21% of energy (P < 0.000001), whereas the availability of α-linolenic acid (ALA) increased from 0.39% to 0.72% of energy by using 1909-C modeling. By using 1909-T modeling, LA was 2.23% of energy, and ALA was 0.35% of energy. The ratio of LA to ALA increased from 6.4 in 1909 to 10.0 in 1999. The 1909-T but not the 1909-C data showed substantial declines in dietary availability (percentage of energy) of n-6 arachidonic acid, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). Predicted net effects of these dietary changes included declines in tissue n--3 highly unsaturated fatty acid status (36.81%, 1909-T; 31.28%, 1909-C; 22.95%, 1999) and declines in the estimated omega-3 index (8.28, 1909-T; 6.51, 1909-C; 3.84, 1999). The apparent increased consumption of LA, which was primarily from soybean oil, has likely decreased tissue concentrations of EPA and DHA during the 20th century.

Climate regime shifts and reorganization of fish communities: the essential fatty acid limitation hypothesis

Climate regime shifts force fish communi- ties through rapid transitions between alternate species assemblages, but little is known about the role that bio- chemical ecology plays in these transitions. We docu- ment a biochemical effect of climate-induced commu- nity transitions in boreal oceans: opposite population trajectories of lipid-rich and lipid-poor fish species. We compared published estimates of fish lipid content and population trajectories following climate shifts in 4 areas (Bering Sea, Gulf of Alaska, Scotian Shelf and North Sea). In all cases, total lipid content differed between species that increased and decreased in abundance, and the resulting relatively lipid-rich or lipid-poor com- munities persisted for decades. We hypothesize that these changes in fish community lipid content are the result of climate-mediated changes in the availability of essential fatty acids (EFAs), which are required by fish as components of hormones and cell membranes. EFAs are produced only by plants and must be obtained by fish through their diet, and ecosystem EFA availability is sensitive to physical forcing mechanisms. Using original data from 5 species of northeast Pacific fish (total lipid 1.0 to 28.9% wet mass) and published data for 29 species of myctophids (total lipid 0.5 to 46.3% wet mass), we found that the content of 2 important EFAs was positively correlated with total lipid content. This result suggests the possibility of species differences in EFA requirements that are related to total lipid content, and possible differences in susceptibility to changing EFA availability in lipid-rich and lipid-poor fish species.

Compartmental modeling to quantify α-linolenic acid conversion after longer term intake of multiple tracer boluses

To estimate in vivo alpha-linolenic acid (ALA; C18:3n-3) conversion, 29 healthy subjects consumed for 28 days a diet providing 7% of energy from linoleic acid (C18:2n-6) and 0.4% from ALA. On day 19, subjects received a single bolus of 30 mg of uniformly labeled [(13)C]ALA and for the next 8 days 10 mg twice daily. Fasting plasma phospholipid concentrations of (12)C- and (13)C-labeled ALA, eicosapentaenoic acid (EPA; C20:5n-3), docosapentaenoic acid (DPA; C22:5n-3), and docosahexaenoic acid (DHA; C22:6n-3) were determined on days 19, 21, 23, 26, 27, and 28. To estimate hepatic conversion of n-3 fatty acids, a tracer model was developed based on the averaged (13)C data of the participants. A similar tracee model was solved using the averaged (12)C values, the kinetic parameters derived from the tracer model, and mean ALA consumption. ALA incorporation into plasma phospholipids was estimated by solving both models simultaneously. It was found that nearly 7% of dietary ALA was incorporated into plasma phospholipids. From this pool, 99.8% was converted into EPA and 1% was converted into DPA and subsequently into DHA. The limited incorporation of dietary ALA into the hepatic phospholipid pool contributes to the low hepatic conversion of ALA into EPA. A low conversion of ALA-derived EPA into DPA might be an additional obstacle for DHA synthesis.

Changes of Fatty Acid Composition of Human Milk during the First Month of Lactation: A Day-to-Day Approach in the First Week

Background: Fatty acid composition of human milk (HM) is known to change considerably during lactation. However, we were unable to find data on changes of fatty acid composition of HM during the very early phase of lactation, i.e. in the first week of life. Subjects and Methods: HM samples were obtained from 18 healthy lactating women every day during the first week and thereafter on the 14th and 28th days of lactation. Fatty acid composition of colostrum and mature HM samples was determined by high-resolution capillary gas-liquid chromatography. Results: Values of the n-6 essential fatty acid, linoleic acid, in HM did not change significantly during the first month of lactation, whereas values of the n-3 essential fatty acid, α-linolenic acid, showed significant increases during the first 2 weeks of lactation (1st day: 0.49 [0.12], % weight/weight, median [ranges from the 1st to the 3rd quartile], 14th day: 0.69 [0.31], p < 0.05). In contrast, values of the n-6 long-chain metabolites, eicosadienoic-, dihomo-γ-linolenic- and arachidonic acid, as well as the values of the n-3 long-chain metabolites, eicosatrienoic-, and eicosapentaenoic acid exhibited significant decreases during the entire period investigated. The principal n-3 long-chain metabolite, docosahexaenoic acid, showed a significant increase between the 3rd and 14th days, but a significant decrease between the 14th and 28th days (3rd day: 0.15 [0.13], 14th day: 0.28 [0.11], p < 0.05, 28th day: 0.19 [0.12], p < 0.01). There were statistically significant positive correlations between arachidonic and docosahexaenoic acid values on the 1st (r = 0.67, p < 0.01), 5th (r = 0.56, p < 0.05) and the 6th (r = 0.53, p < 0.05) days of lactation. Conclusion: Fatty acid composition of HM changes significantly even during the first week of lactation. The lack of positive correlation between essential fatty acids and their long-chain metabolites suggests that it is not only the availability of essential fatty acids that influences the fatty acid composition of human colostrum.

Effects of protein-energy malnutrition and human immunodeficiency virus-1 infection on essential fatty acid metabolism in children

This report summarizes data on the availability of essential fatty acids (EFAs) and their long-chain polyunsaturated fatty acid (LCPUFA) metabolites in protein-energy malnutrition (PEM), in human immunodeficiency virus-1 (HIV-1) infection for which less information is available, and the combination of both PEM and HIV-1. The contribution of different EFAs and LCPUFAs to the fatty-acid composition of plasma and erythrocyte membrane lipids was found to be reduced in children with PEM in comparison with well-nourished children. In addition to limited dietary EFA supply, reduced bioconversion of EFAs to their respective LCPUFA metabolites and/or peroxidative degradation of LCPUFAs may contribute to the reduction of LCPUFA status in malnourished children. Restoration of normal energy, protein, and EFA intakes does not appear to readily correct abnormalities of plasma and erythrocyte membrane LCPUFA values. Enhanced dietary supply of LCPUFAs and/or improved supply of antioxidant vitamins may represent novel therapeutic modalities in severe PEM. With and without PEM, HIV infection was related to altered availability of various EFAs and LCPUFAs in HIV-seropositive children. The plasma total lipid fatty-acid profiles seen in well-nourished children with HIV infection were compatible with an HIV infection–related enhancement of the metabolic activity of the conversion of EFAs to their respective LCPUFA metabolites. However, the plasma phospholipid EFA and LCPUFA profiles seen in severely malnourished children with HIV infection more closely resembled those seen in children with PEM but without HIV infection than in those in children with HIV infection but no PEM. Metabolic studies using stable isotope-labeled fatty acids may contribute to better understanding of the HIV-related changes in EFA metabolism and clearly are needed before therapeutic conclusions can be drawn.

Olestra Ingestion and Dietary Fat Absorption in Humans , ,

The effect of olestra, a zero-calorie fat replacement, on the absorption of dietary fat was determined with a dual-isotope technique in 67 healthy male subjects. After a 30-d adaptation period in which they consumed potato chips which delivered either 10 g/d olestra or 10 g/d triglyceride under free-living conditions, the subjects were housed in a metabolic ward and given 0, 8, 20 or 32 g olestra in potato chips. The chips were eaten as part of a breakfast containing about 38 g of fat, about 0.16 mg of 14C-triolein, and a nonabsorbable marker, 51CrCl3 . Feces were collected for 7 d, and aliquots of the two daily collections containing the highest levels of 51Cr were oxidized. The CO2 was collected, and 14C content was determined by liquid scintillation spectrometry. The fractional absorption of 14C-triolein was calculated from the average ratios of 14C/51Cr dosed and measured in the feces. Olestra had a slight but significant dose-response effect on triglyceride absorption: the highest olestra dose (32 g) reduced absorption by 1.2%. This effect is not nutritionally significant with respect to either availability of essential fatty acids or energy intake.

Hepatic storage and transport of n-3 and n-6 polyunsaturated fatty acids by very-low-density lipoproteins in growing rats fed low- or adequate-protein diets with sunflower, soybean, coconut, and salmon oils

Protein and essential fatty acid (EFA) deficiencies may both occur in chronic malnutrition and have common symptoms. To determine the interactions between dietary protein intake and EFA availability, rats were fed purified diets containing 20% or 2% casein and 5% as one of four fats (sunflower, soybean, coconut, or salmon oil) that differed particularly in their n-6 and n-3 polyunsaturated fatty acids (PUFAs). Protein malnutrition enhanced hepatic triacylglycerol and cholesterol concentrations while decreasing hepatic protein and phospholipid contents and mass and components of very-low-density lipoprotein (VLDL). The ratio of PUFAs to saturated fatty acids (SFAs) was consistently depressed by protein malnutrition in liver and VLDL triacylglycerol and phospholipid. Total n-6 and n-3 fatty acids were diminished by protein malnutrition, except with salmon oil, with which a decrease in 20:5n-3 was compensated for by an increase in 22:6n-3. The ratio of 20:4n-6 to 18:2n-6 was enhanced in liver phospholipid and VLDL triacylglycerol, and modified little in liver triacylglycerol. Generally, the ratio of 20:3n-9 to 20:4n-6, an index for EFA deficiency, was raised with protein malnutrition in liver triacylglycerol and phospholipid and in VLDL triacylglycerol. The extent of changes in each fatty acid proportion varied according to the oil fed. Overall, VLDL-apolipoprotein concentrations were, in general, strongly reduced with protein malnutrition. In conclusion, protein malnutrition may accelerate marginal EFA deficiency and decrease long-chain PUFA bioavailability and thus increase EFA requirement.

Essential Fatty Acid Rich Shell Eggs are Beneficial in the Diets of Dyslipidemic Males Dependent of a low fat diet

LEARNING OUTCOME: The health professional will be able to assess the impact of egg consumption on blood lipids of dyslipidemic males.Recent data from the Framingham Cohort suggests that low fat diets may increase heart disease risk by limiting the availability of essential fatty acids (EFA). The current study was designed to determine if eggs modified to be EFA-rich could positively influence blood lipids of dyslipidemic males independent of a low fat diet. Participants were nonsmoking individuals exhibiting plasma triglycerides (TG) between 200–400 mg/dl, high-density lipoprotein cholesterol (HDL-C) below 35 mg/dl; a BMI < 29; and not currently involved in drug or diet therapies. The test period included a two week lead-in free from EFA eggs, followed by a 10 week period of daily EFA or typical egg consumption (2/day; 5 days/week). Throughout the 12 week test period, breakfast and lunch meals were administered under controlled conditions while individuals self-selected evening and weekend meals. Initial three-day diet records from study participants indicated that their typical diets contained 28–44% of calories from fat, with a mean of 36%. Therefore, controlled and self-selected diets were designed to contain 36% of calories from fat for consistency among participants. Regardless of egg treatment, risk factor (RF=total plasma cholesterol/HDL-C) significantly (p<.003) decreased from 7.4 at week -2 to 5.8 at week 10. RF declined as HDL-C significantly increased and plasma cholesterol remained unchanged. Individuals consuming EFA eggs further benefited from significant reductions in low density lipoprotein cholesterol (LDL-C) and a 6% decrease (p<.07) from week -2 to week 10 in plasma TG. These data indicate that consuming up to 10 eggs per week does not adversely influence blood lipids of dyslipidemic males even in the absence of a low fat diet. Furthermore, EFA supplied in the form of shell eggs improves plasma markers of heart disease in dyslipidemic males.

Alterations in plasma and tumour levels of fatty acids with weight loss in an experimental cachexia model

Growth of the MAC16 tumour in NMRI mice was accompanied by a decrease in host body weight, adipose tissue and liver weight in proportion to the tumour mass. The total plasma concentration of fatty acids also increased with increasing weight loss, while the linoleic acid: arachidonic acid ratio decreased. The liberated fatty acids were taken-up both by the tumour and the liver. However, since liver weight decreased in proportion to weight loss the accumulation of fatty acids increased as liver weight decreased. This suggests that the small liver mass had an increased capacity to accumulate fatty acids. The concentration of stearic, palmitic, oleic palmitoleic and arachidonic acids all increased with increasing tumour weight, while the stearic acid: oleic acid ratio, a measure of unsaturation in the tumour increased. Thus mobilization of adipose tissue reserves during cancer cachexia ensures a constant availability of essential fatty acids for tumour growth.

28-Day continuous dosing study in minipigs with a SALATRIM structured triacylglycerol composed of stearate, acetate, and propionate

SALATRIM 23SO lot A026 belongs to a family of structured triacylglycerols with lower caloric availability than corn oil. Male and female minipigs were divided into five groups of four pigs of each sex and fed diets containing 0%, 3%, 6%, and 10% SALATRIM or 10% corn oil, as a reference for the high fat content of the SALATRIM diets, for 28 days. Diets were supplemented with 2% corn oil to ensure adequate essential fatty acid availability. No effects on body weight, feed consumption, clinical observations, hematology, serum chemistry, bone mineral content, serum and liver levels of fat-soluble vitamins, and organ weights were detected. Focal hepatocellular vacuolation was observed in treated and control groups. The incidence was similar among groups

The metabolism and availability of essential fatty acids in animal and human tissues.

Essential fatty acids (EFA), which are not synthesized in animal and human tissues, belong to the n-6 and n-3 families of polyunsaturated fatty acids (PUFA), derived from linoleic acid (LA, 18:2n-6) and alpha-linolenic acid (LNA, 18:3n-3). Optimal requirements are 3-6% of ingested energy for LA and 0.5-1% for LNA in adults. Requirements in LNA are higher in development. Dietary sources of LA and LNA are principally plants, while arachidonic acid (AA, 20:4n-6) is found in products from terrestrian animals, and eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are found in products from marine animals. EFA are principally present in dietary triacylglycerols, which should be hydrolyzed by lipases in gastric and intestinal lumen. DHA seems to be released more slowly than the others. Its intestinal absorption is delayed but not decreased. Long-chain PUFAs are incorporated in noticeable amounts in chylomicron phospholipids. However, their uptake by tissues is no more rapid than uptake of shorter chain PUFA. In tissues, LA and LNA, which constitute the major part of dietary EFA, should be converted into fatty acids of longer and more unsaturated chain by alternate desaturation (delta 6, delta 5, delta 4)-elongation reactions. Animal tissues are more active in this biosynthesis than human tissues. Liver is one of the most active organs and its role is critical in providing less active tissues, particularly the brain, with long-chain PUFA secreted in VLDL (very low density lipoprotein). In liver, many nutritional, hormonal and physiological factors act on the PUFA biosynthesis. Dietary fatty acids exert a great influence and are often inhibitory. Dietary LNA inhibits delta 6 desaturation of LA. The desaturation products AA, EPA, and DHA inhibit delta 6 desaturation of LA and delta 5 desaturation of DGLA (dihomo-gamma-linolenic acid). With regard to hormones, insulin and thyroxin are necessary to delta 6 and delta 5 desaturation activities, whereas other hormones (glucagon, epinephrine, ACTH, glucocorticoids) inhibit desaturation. Concerning the physiological factors, the age of individuals is critical. In the fetus, the liver and the brain are capable of converting LA and LNA into longer-chain EFA, but these are also delivered by the mother, after synthesis in the maternal liver and placenta. Just after birth, in animals, the delta 6 desaturation activity increases in the liver and decreases in the brain. In aging, the capacity of the whole liver to desaturate LA and DGLA is equal at 1.5 and 25 months of age in rats fed a balanced diet throughout their life and the AA and DHA content of tissue phospholipids is unchanged in aging.(ABSTRACT TRUNCATED AT 400 WORDS)

Unsaturated fatty acid bioavailability in growing rats fed low or adequate protein diets with sunflower or soybean oils

The relationship of serum very low density lipoproteins (VLDL) to hepatic lipid composition was studied after 28 days of protein depletion to determine the interactions between dietary protein levels and the essential fatty acid (EFA) availability. This was examined in rats using a dietary combination of 20% or 2% casein with 5% vegetable oils, variable in their n-6:n-3 fatty acid ratios. Rats were divided into four groups, SFC (20% casein + 5% sunflower oil); SFd (2% casein + 5% sunflower oil); SC (20% casein + 5% soybean oil); Sd (2% casein + 5% soybean oil). Dietary protein depletion decreased phospholipid and protein concentrations in liver and VLDL, whereas triacylglycerol amounts were enhanced in liver, but lowered in VLDL. Dietary protein depletion strongly depressed VLDL apolipoproteins. Protein-deficient groups (SFd and Sd) exhibited, in both liver and VLDL, decreased linoleic acid in triacylglycerol fractions and depressed both arachidonic and linoleic acids in phospholipid fractions. In spite of short periods of dietary treatment, protein depletion involved an impairment in EFA availability. Total n-6 polyunsaturated fatty acids contents were diminished in liver and VLDL lipids, while total n-3 polyunsaturated fatty acids contents were diminished in only VLDL triacylglycerol and phospholipid. Furthermore, sunflower oil amplified this impairment, and the lack of α-linolenic acid involved a greater diminution in n-3 polyunsaturated fatty acids and enhanced 20:3 n-9 and 22:5 n-6, especially in phospholipid fractions. In this experiment, in spite of a short period of dietary treatment, protein depletion strongly impairs EFA metabolism and accentuates the α-linolenic acid deficiency.