Stability of plasma fatty acids at -20 degrees C and its relationship to antioxidants

The fatty acid composition of cholesteryl esters (CE), triglycerides (TG) and phospholipids (PL) was analysed with gas chromatography before and after 3 years' storage of EDTA plasmas at -20 degrees C. In the three lipid fractions the proportion of polyunsaturated fatty acids (PUFA) with 3 or more double bonds decreased by 14% to 46%, while the proportions of saturated and monounsaturated fatty acids and also of linoleate (18:2 omega 6) showed an increasing trend. The changes tended to be relatively greatest in TG and smallest in PL. The initial concentration of vitamin A correlated negatively with reductions of all 20- to 22-carbon PUFA in CE and with that of arachidonate (20:4 omega 6) and docosahexaenoate (22:6 omega 3) in TG. The change in CE-18:2 omega 6 tended to be inversely correlated with vitamin A. The initial concentration of beta-carotene and the change in CE- and TG-18:3 omega 3 and CE-22:6 omega 3 showed also inverse correlations. Vitamin C, alpha-tocopherol and selenium had only occasional and mostly insignificant associations with the fatty acid alterations. In freshly analysed samples the concentration of vitamin A correlated negatively with the percentage of 18:2 omega 6 in plasma CE, TG and PL and with that of 20:4 omega 6 in platelets, and beta-carotene and alpha-tocopherol had positive correlations with 18:2 omega 6 in most plasma lipid fractions and platelets. Vitamin C and selenium correlated positively with 22:6 omega 3 in plasma, and selenium also with that in platelets.(ABSTRACT TRUNCATED AT 250 WORDS)     

Time-course effects of protein malnutrition on hepatic fatty acids delta 6 and delta 5 desaturation in the growing rat

1. In growing rats, the time-course effects of giving a normal-protein diet (200 g casein/kg; NP) for 52 d, a low-protein diet (20 g casein/kg; LP) for 52 d and a LP diet for 26 d followed by balanced refeeding (200 g casein/kg; BR) for 26 d, on the fatty acid composition of liver total lipids and microsomal phospholipids were investigated together with delta 6- and delta 5-microsomal desaturase activities. 2. The oleic acid content (mg/g tissue) of liver total lipids increased progressively with the LP diet, while linoleic acid was increased only at days 7 and 52. 20:3 omega 6, 20:4 omega 6, 22:5 omega 6 and 22:6 omega 3 fatty acids decreased during the period on the LP diet. BR for 7 d was sufficient to restore the fatty acid composition of total lipids to control values. Changes in the fatty acid composition of liver microsomal L-alpha-phosphatidylcholines were observed only after 52 d on the LP diet; the proportions (% w/w total fatty acids) of 18:0, 20:3 omega 6 and 20:4 omega 6 fatty acids decreased while oleic acid increased. The fatty acid composition of L-alpha-phosphatidylethanolamines was less affected. 3. delta 6- and delta 5-desaturase activities decreased to 20-30% of their original values after 2 d on the LP diet; a smaller deficit prevailed after 14 d but disappeared after 25 d, to appear again after 52 d. As early as day 2 of BR, desaturase activities were greatly recovered and returned to control values at day 13. 4. The present work shows that modifications in microsomal delta 6- and delta 5-desaturase activities are not strictly paralleled by the changes in the composition of fatty acids of liver total lipids and microsomal phospholipids.     

Long-term storage of red blood cells and correlations between red cell and dietary fatty acids: results from a pilot study.

Levels of red blood cell (RBC) fatty acids were determined at baseline and 12 months after storage at -70 degrees C in 15 postmenopausal women to determine whether storage had a detrimental effect on the stability of fatty acids. Four-day diet records were also completed at baseline, allowing comparisons between RBC fatty acid levels and fatty acid levels computed from recent dietary intake. The major fatty acid composition of RBCs did not change substantially during 12 months of storage, and, in particular, for n-6 and n-3 fatty acids most correlations between baseline and 12-month values were greater than 0.90. We also found strong positive correlations between RBC and dietary fatty acids, including oleic, linoleic (18:2n-6), total n-6, and the polyunsaturated-to-saturated fat ratio. We concluded that frozen RBCs may be a useful measure of recent dietary intake for epidemiological studies.     

Fatty acid composition of human milk in Western Iran

OBJECTIVE: To investigate the fatty acid composition of mature human milk in Western Iran with special focus on trans fatty acids. DESIGN: Observational study. METHODS: Milk samples were collected from 52 lactating mothers aging 19-39 y, from Western Iran. Subjects were asked to complete a diet questionnaire. Milk fatty acids were measured as 2-nitrophenylhydrazide derivatives by high-performance liquid chromatography. RESULTS: Saturated fatty acids were the main fraction of human milk (41.3%). Medium-chain fatty acids (C8:0-C14:0) constituted 24%, oleic acid (C18:1omega9) accounted for 30.9% and elaidic acid (C18:1T), the trans isomer of oleic acid, comprised 11.3% of the total milk fatty acids. Linoleic (C18:2omega6) and linolenic (C18:3omega3) acid contents were 13.8 and 1.1%, respectively. The level of the polyunsaturated fatty acids was 1.4% for arachidonic (C20:4omega6) and 0.2% for eicosapentaenoic (C20:5omega3) acid. CONCLUSIONS: The milk from Iranian lactating mothers, as compared to that from the American or European mothers, contained high levels of medium-chain and trans fatty acids. This difference may be attributed to the maternal diet with low animal protein and animal fat but with high carbohydrate and partially hydrogenated vegetable oils that carry large amounts of trans fatty acids. As the detrimental effects of trans fatty acids on blood lipids and cardiovascular diseases have been emphasized in the literature, a reduction of trans fatty acid content in the diet of Iranian mothers is suggested. SPONSORSHIP: Kermanshah University of Medical Sciences.     

n-3 fatty acids in human fat tissue aspirates are stable for up to 6 y

OBJECTIVES: The content of n-3 (omega-3) polyunsaturated fatty acids in fat tissue is a valid indicator of their long-term consumption. We studied the stability of n-3 fatty acids in human subcutaneous fat microbiopsies after 6 and 11 y of storage. DESIGN: Microbiopsies were taken from a lump of human adipose tissue and stored at +20 and -80 degrees C. SETTING: Laboratory study. RESULTS: After 5.6 y at -80 degrees C the proportion of six out of seven highly polyunsaturated fatty acids varied between 91 and 102% (mean 97%) of their baseline values. Storage at +20 degrees C yielded recoveries between 82 and 105%. After 11 y at -80 degrees C the proportions in the original lump of tissue ranged from 88 to 101% (mean 94%). CONCLUSION: n-3 fatty acids in stored fat tissue aspirates are stable for 6-11 y, and are suitable markers of baseline diet in long-term epidemiological studies. SPONSORSHIP: Wageningen Centre for Food Sciences.     

Composition of phospholipid fatty acids in red blood cell membranes of patients in intensive care units: effects of different intakes of soybean oil, medium-chain triglycerides, and black-currant seed oil.

Fatty acid composition of phospholipids in red blood cell membranes was studied in 32 severely head-injured or cerebral stroke patients receiving enteral nutrition for 3 weeks. During this study the effects of three diets differing only by their lipid composition were investigated. The daily energy intake of each patient amounted to 2950 kilocalories, of which the lipid fraction represented 45.7%. Diet A contained only soybean oil, diet B consisted of a 50% soybean oil and 50% medium-chain triglycerides mixture, and diet C was an emulsion of 50% soybean oil, 42.5% medium-chain triglycerides, and 7.5% black-currant seed oil. Our results showed no biochemical signs of fatty acid deficiency in red blood cell membranes for the patients at the beginning of the study, after a comparison with a control group of 20 healthy adults. Inhibition of delta 6-desaturase activity on linoleic acid (C18:2 omega 6) after diet A was suggested by an increase of linoleic acid without a corresponding increase of dihomo-gamma-linolenic acid (C20:3 omega 6). Replacing 50% of soybean oil by with medium-chain triglycerides (diet B) prevented this enzyme inhibition. Supply of black-currant seed oil rich in gamma-linolenic (C18:3 omega 6) and stearidonic (C18:4 omega 3) acids (diet C) induced significant increases of dihomo-gamma-linolenic and eicosapentaenoic (C20:5 omega 3) acids, without influencing arachidonic acid (C20:4 omega 6) levels. This balance was evaluated through the ratio (C20:3 omega 6 + C20:5 omega 3)/C20:4 omega 6.     

Evolution of fatty acid profile and lipid oxidation during enteral formula storage

BACKGROUND: Enteral formulas can be stored for up to 2 years. Fat oxidation during storage can lead to the loss of nutritive value and generation of toxic products such as lipid peroxides. METHODS: Two standard enteral formulas were stored for short periods at high temperatures (1-4 weeks at 32-55 degrees C) or for long periods at low temperatures (12-36 weeks at 4 degrees C, 20 degrees C, or 30 degrees C). The present study included the assessment of lipid oxidation by measuring related fluorescent compounds and the evolution of fatty acids profile. RESULTS: Enteral formula fat was oxidized under all assayed conditions, including storage at 4 degrees C. The loss of essential fatty acids (linoleic and linolenic acids) was always higher when time and temperature were increased. The omega6/omega3 ratio was increased by storage from 5.6 to 7.8, which could exacerbate the inflammatory response in critically ill patients. Fluorescence intensity increased with time and temperature of storage and was correlated with the decrease in essential fatty acids (lineal correlation between -0.9416 and -0.9996). CONCLUSIONS: Enteral formula fat was oxidized during storage, leading to a loss of nutritional value. These formulas should be stored under refrigeration to minimize this loss. Finally, fluorescence measurement proved to be a fast and easy method to assess fat oxidation status.     

Serum levels of polyunsaturated fatty acids and risk of colorectal cancer: a prospective study

To examine the relation between serum fatty acids and risk of colorectal cancer, the authors conducted a nested case-control study of 169 colorectal cancer cases and 481 controls matched by age and enrollment area as part of the Japan Collaborative Cohort Study. Serum samples were donated by subjects at baseline (between 1988 and 1990) and were stored at -80 degrees C until 2002. Serum fatty acid levels were measured by using gas chromatography and were expressed as the weight percentage of total lipids. Conditional logistic regression analyses adjusted for lifestyle factors revealed that total omega-3 polyunsaturated fatty acids (odds ratio = 0.24, 95% confidence interval: 0.08, 0.76), alpha-linolenic acid (odds ratio = 0.39, 95% confidence interval: 0.16, 0.91), docosapentaenoic acid (odds ratio = 0.30, 95% confidence interval: 0.11, 0.80), and docosahexaenoic acid (odds ratio = 0.23, 95% confidence interval: 0.07, 0.76) all showed a significantly decreased risk for the highest versus the lowest quartile levels for colorectal cancer in men. For women, a weak negative association was observed between docosapentaenoic acid and colorectal cancer risk, although it was not statistically significant. No adverse effects of high serum levels of omega-6 polyunsaturated fatty acids on colorectal cancer risk were detected.     

Reliability of fatty acid composition in human serum phospholipids

OBJECTIVE: We examined the reliability of the fatty acid composition of serum phospholipids in the New York University Women's Health Study, a prospective study of sex hormones, diet and breast cancer. DESIGN: Non-fasting serum samples collected at three yearly visits, in 46 healthy women, and stored at -80 degrees C for 7-12 y, were included in the study. Serum phospholipid fatty acid composition was measured by capillary gas chromatography. RESULTS: For the 20 individual fatty acids measured, the reliability coefficients were less than 0.50 for four, between 0.50 and 0.70 for nine, and greater than 0.70 for seven. Among the major fatty acids, arachidonic and alpha-linolenic acids had high reliability coefficients (0.71 and 0. 72, respectively), palmitic, oleic, linoleic, eicosapentaenoic and docosahexaenoic acids had intermediate coefficients (0.57, 0.69, 0. 62, 0.64 and 0.66, respectively), whereas stearic acid had the lowest coefficient (0.15). The reliability coefficients for total monounsaturated fats, omega-6 and omega-3 fatty acids were moderately high (0.66, 0.53 and 0.66, respectively), whereas the coefficients for total saturated fats and total polyunsaturated fats were low (0.31 and 0.43, respectively). CONCLUSIONS: These results indicate that the fatty acid composition of serum phospholipids can be a useful tool in epidemiologic studies, although for most fatty acids a single determination is associated with some error in measurement that should be taken into account at the design and analysis stages. Storage for up to 12 y at -80 degrees C preserved polyunsaturated fatty acids from oxidation very well.     

Essential fatty acid status and fluidity of plasma phospholipids in cystic fibrosis infants

The fatty acid (FA) patterns of cord serum phospholipids (PLs) were examined in 4 cystic fibrosis (CF) newborns, 8 non-CF siblings, and 22 normal control subjects. Plasma from 27 newly diagnosed CF infants and 38 normal infants aged less than 2 y were studied for comparison. CF cord-blood PLs had patterns similar to those of CF siblings and to normal newborns, but the pattern for CF did not shift toward adult patterns during infancy as did patterns for normal infants. CF infants at diagnosis exhibited a deficiency pattern in which 18: 2 omega 6, 20:4 omega 6, 22:4 omega 6, an omega 3 polyunsaturated fatty acids (PUFAs) were significantly subnormal and 18:3 omega 6, total saturated fatty acids, and total monounsaturated fatty acids were significantly elevated compared with normal infants. In PLs in CF infants, although mean chain length of FAs was low, mean melting point was elevated 2.4 degrees C and double-bond index was low (both P less than 0.001), implying a significantly lessened fluidity. Nutritional supplements of both omega 6 and omega 3 PUFAs are cated.     

The effect of a fish diet on serum lipids in healthy human subjects

A cross-over study was done with 19 male and 23 female volunteers living in a monastery and a convent, respectively. The effect of a fat gish (mackerel) diet on the blood serum lipid composition was studied. As the normal diet of these volunteers was of the lacto-ovo-vegetarian type, a control diet in which the fish was replaced by full-fat cheese was used. Subjects consuming the fish diet had a daily uptake of polyunsaturated acids of the omega3 family of about 8 g; comparable amounts of linoleic acid were ingested with both diets. Both diets were consumed for a period of 3 weeks. Serum cholesterol was slightly but significantly (7.5%) lower and serum triglycerides considerably lower (35%) on the fish diet, whereas high density lipoprotein cholesterol increased slightly. Lipoprotein analysis showed a strong very low density lipoprotein decrease by the fish diet while, in the men, both low and high density lipoproteins increased. The fatty acid composition of serum lipids showed considerable differences; C20:5omega3 increased in all fractions and C22:6omega3 was found in the triglycerides and the phospholipids, but not in the sterol esters. These increases occurred chiefly at the expense of C18:1omega9 and, in particular, C18:2omega6, which indicates a replacement of omega6 by omega3 acids. Long-chain monoenoic acids which are abundant in the mackerel were not detected in any serum lipid fraction.     

Dietary and serum fatty acid compositions among six Japanese populations

Dietary and serum fatty acid composition and their relations were investigated in men aged 40-59 years from six geographical and occupational populations: fishermen, three farming populations, urban clerical and manual workers. 1. Mean dietary intake of saturated, monounsaturated and polyunsaturated fatty acids were higher in urban workers than in the other populations. Mean dietary intake of omega 3 polyunsaturated fatty acids was higher in fisherman than in other populations. There were no differences in dietary compositions of saturated, monounsaturated and polyunsaturated fatty acids among six populations. However, the proportion of dietary omega 3 polyunsaturated fatty acids to total fatty acids varied: 10% for fishermen, 7-8% for farming populations and 6% for urban workers. 2. There were no differences in serum compositions of saturated, monounsaturated and polyunsaturated fatty acids among six populations. However, the proportion of serum omega 3 polyunsaturated fatty acids to total fatty acids varied: 15% for fishermen, 9-10% for farming populations and 8-9% for urban workers. 3. Significant associations were observed between population means of the proportion of dietary and serum polyunsaturated fatty acids. Within each population, individual dietary intake of omega 3 polyunsaturated fatty acids was significantly associated with the proportion of serum omega 3 polyunsaturated fatty acids. Significant associations were also obtained for omega 6 polyunsaturated fatty acids. 4. Fishermen showed a higher population means of dietary and serum omega 3 polyunsaturated fatty acids and a higher incidence rate of cerebral infarction compared with the other populations. This result did not support the hypothesis that dietary and serum omega 3 polyunsaturated fatty acids contribute to prevent cerebral infarction.     

Dietary alpha-linolenic acid and prostaglandin synthesis: a time course study

A purified diet containing 10% linseed oil as the fat source was fed to rats over a 56-day period. After the 56th day the rats were fed the same basal diet but containing 10% corn oil in place of the linseed oil. Rats were killed and blood and liver samples were taken from four to six rats on 14 days of the feeding trial. Serum and liver fatty acid profiles were determined. The platelet prostaglandin E2 (PGE2) released in serum as a result of blood coagulation for 1 h at 37 degrees C was determined. Liver homogenates were incubated and PGF2 alpha synthesizing capacity was assayed. Both serum and liver fatty acid profiles reflected the high linolenic content of the linseed oil. There was a progressive increase in fatty acids of the omega 3 series and a decrease in the omega 6 series. Notably the PG-2 series precursor, arachidonic acid (20:4 omega 6) was decreased and the precursor of the PG-3 series timnodonic acid (20:5 omega 3) was increased. These changes were reversed when corn oil was fed. PGE2 content of serum and PGF2 alpha synthesis by liver homogenates progressively decreased as the 20:4 omega 6 levels fell and the 20:5 omega 3 levels increased. PG synthesis was quickly increased in both when corn oil diets were fed. This study has implications for dietary manipulation of PG synthesis by blood components and may provide a basis for manipulation of PG synthesis in systems in which they are regulatory.     

Fatty acid composition of serum cholesteryl esters in 3- to 18-year-old Finnish children and its relation to diet

The composition of fatty acids in serum cholesteryl esters (CE) was analyzed gas chromatographically in 1348 boys and girls aged from 3 to 18 yr. A dietary survey was carried out simultaneously using the 48-h recall method. The dietary P/S ratio had highly significant correlations with CE fatty acids: positive with linoleate (0.567) and total omega 6 fatty acids and negative with saturated, monounsaturated, and omega 3 polyunsaturated fatty acids. The highest mean percentage of CE-linoleate was found in 15-yr-old girls (52.7, SD 4.68%) and lowest in 3-yr-old girls (48.1, SD 5.00%). Age, sex, and the degree of puberty had no independent effect on CE-linoleate after it had been adjusted for the effect of dietary P/S ratio by analysis of covariance. These results indicate that the fatty acid composition of serum CE depends on the quality of dietary fat and that CE-linoleate is a useful reflector of the dietary P/S ratio. The negative correlation between CE omega 3 fatty acids and dietary P/S ratio may be due to displacement of the omega 3 acids in serum CE by the much higher proportion of dietary linoleate.     

Differential oxidation of saturated and unsaturated fatty acids in vivo in the rat

The oxidation rates of lauric, myristic, palmitic, stearic, oleic, alpha-linolenic, linoleic, kappa-linolenic, dihomo-gamma-linolenic and arachidonic acids were studied by use of a radioisotope tracer technique in weanling rats at rest in a metabolism chamber over 24 h. Of the saturated fatty acids, lauric acid (12:0) was the most efficient energy substrate: the longer the chain length of the saturated fatty acids, the slower the rate of oxidation. Oleic acid (18:1) was oxidized at a remarkably fast rate, similar to that of lauric acid. Of the omega 6 essential fatty acids studied, linoleic acid (18:2 omega 6) was oxidized at a faster rate than any of its metabolites, with arachidonic acid (20:4 omega 6) being oxidized at the slowest rate. The rate of oxidation of gamma-linolenic acid (18:3 omega 3) was almost as fast as that of lauric and oleic acids.     

Effect of a moderately energy-restricted diet on obese patients with fatty liver.

The effects of a moderately energy-restricted (25 kcal/kg) diet on liver-function tests, anthropometric measurements, mononuclear-cell phospholipid fatty acid, lymphocyte blastogenesis, and plasma prostaglandin E2 and alpha-tocopherol levels were observed at weeks 0, 8, and 24 in 14 obese patients with fatty liver. Serum aminotransferase levels were improved significantly, with decreases in the body mass index and waist circumference. Decreases in energy intake from carbohydrate and increases in intake of vitamin A, vitamin C, and vegetables were observed at week 24. In mononuclear-cell phospholipids, linoleic acid (18:2omega 6), which was significantly lower in patients than in controls at week 0, was increased at week 24. In contrast, arachidonic acid was decreased. Plasma prostaglandin E2 levels were significantly lower in patients than in controls at week 0 and increased at week 24. The mononuclear-cell response for phytohemagglutinin correlated with 18:2omega 6 in mononuclear-cell phospholipids (r = 0.692, P < 0.01). Improvement of the serum alanine-aminotransferase level correlated with an increase in the plasma alpha-tocopherol level (r = -0.667, P < 0.01) and increases in consumption of vitamin A, omega 3 polyunsaturated fatty acids, and vegetables. These findings suggest that a hypoenergetic diet rich in omega 3 polyunsaturated fatty acids and antioxidants might be beneficial for obese patients with fatty liver.     

Obesity and weight loss alter serum polyunsaturated lipids in humans

Serum omega 6 (n-6) fatty acids were assessed in 12 obese women during an outpatient very-low-calorie diet (VLCD). Ten subjects (S10) achieved a mean weight loss of 17 kg over 3-5 mo (initial weight-for-height 157%). Serum was obtained before (baseline) and monthly during the VLCD and from five of them (S5) after 2-3 mo of weight stability (refed) at 21 kg of loss. At baseline for S10, the serum phospholipid (PL) 20:4 omega 6 was 9.16 wt% and differed from normal (12.81 wt%) by P less than 0.0001, but cholesterol ester (CE) 20:4 omega 6 did not differ from normal. During 3 mo of VLCD, the S10 serum PL and CE 18:2 omega 6 fell (P less than 0.005 and 0.0001, respectively). Serum PL 20:4 omega 6 rose to normal during VLCD months 1-3 (P less than 0.01) while the serum CE 20:4 omega 6 rose above normal (P less than 0.0002). During the VLCD, S5 results paralleled S10. However when refed, S5 PL and CE 18:2 omega 6 and 20:4 omega 6 all reverted to baseline (PL 20:4 omega 6 below normal, P less than 0.001). Serum PL 20:4 omega 6 is low in moderate obesity, corrects to normal during a VLCD, but regresses to the predict abnormality after weight loss.     

The influence of a maternal diet rich in linoleic acid on brain and retinal docosahexaenoic acid in the rat

Female rats were given throughout pregnancy and lactation a semi-synthetic diet, in which the fat was provided entirely by a soft margarine rich in linoleic acid (18:2 omega 6) or by mixture of butter and lard, and the influence on the fatty acid composition of fetal and pup brain and retinal phosphoglycerides was studied. The percentage of docosahexaenoic acid (22:6 omega 3) was much lower but that of docosapentaenoic acid (22:5 omega 6) was correspondingly higher in the brains of the day-22 fetuses and the 21-d-old pups from the margarine group compared with those from the group given the animal fats. Similar changes were noted in the synaptosomal and retinal phosphoglycerides, being most marked in the ethanolamine phosphoglycerides. The remaining pups from two groups were weaned on day 21 post partum on to the same stock diet that contained preformed 22:6 omega 3. After 9 weeks of this diet, the differences between the two groups in the fatty acid composition of the brain phosphoglycerides were barely discernible. The percentage of 22:5 omega 6 had decreased and had been replaced by 22:6 omega 3. It is concluded that the consequences of consuming a diet rich in linoleic acid and almost devoid of 22:6 omega 3 on brain fatty acid composition deserve consideration in man.     

Intensification of essential fatty acid deficiency in the rat by dietary trans fatty acids

Two studies were conducted using male rats to assess the effect of trans fatty acids upon essential fatty acid (EFA) deficiency. In the first study 5% corn oil (CO), hydrogenated coconut oil (HCNO) or margarine stock (MS, partially hydrogenated soybean oil) were fed, and the levels of trans fatty acids in tissue lipids were measured. The trans fatty acids present in MS were found to intensify EFA deficiency and to be retained in tissue lipids to a high degree, especially in heart phospholipids (PL). In the second study, as the level of trans fatty acids increased in the diet, increasingly higher levels of trans fatty acids were deposited in the heart PL. As dietary trans acid increased, a decrease in total omega 6 fatty acids, and a decrease in the sum of 18:2 omega 6 + 20:4 omega 6 - 20:3 omega 9 fatty acids in heart PL occurred, both criteria indicating a shift toward an increasing EFA deficiency state. Studies of delta 5 desaturase activity of liver microsomes in selected groups showed an increase in the conversion of 20:3 omega 6 to 20:4 omega 6 as the trans fatty acid level in the diet increased.     

Omega-3 fatty acids in health and disease and in growth and development

Several sources of information suggest that man evolved on a diet with a ratio of omega 6 to omega 3 fatty acids of approximately 1 whereas today this ratio is approximately 10:1 to 20-25:1, indicating that Western diets are deficient in omega 3 fatty acids compared with the diet on which humans evolved and their genetic patterns were established. Omega-3 fatty acids increase bleeding time; decrease platelet aggregation, blood viscosity, and fibrinogen; and increase erythrocyte deformability, thus decreasing the tendency to thrombus formation. In no clinical trial, including coronary artery graft surgery, has there been any evidence of increased blood loss due to ingestion of omega 3 fatty acids. Many studies show that the effects of omega 3 fatty acids on serum lipids depend on the type of patient and whether the amount of saturated fatty acids in the diet is held constant. In patients with hyperlipidemia, omega 3 fatty acids decrease low-density-lipoprotein (LDL) cholesterol if the saturated fatty acid content is decreased, otherwise there is a slight increase, but at high doses (32 g) they lower LDL cholesterol; furthermore, they consistently lower serum triglycerides in normal subjects and in patients with hypertriglyceridemia whereas the effect on high-density lipoprotein (HDL) varies from no effect to slight increases. The discrepancies between animal and human studies most likely are due to differences between animal and human metabolism. In clinical trials eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in the form of fish oils along with antirheumatic drugs improve joint pain in patients with rheumatoid arthritis; have a beneficial effect in patients with ulcerative colitis; and in combination with drugs, improve the skin lesions, lower the hyperlipidemia from etretinates, and decrease the toxicity of cyclosporin in patients with psoriasis. In various animal models omega 3 fatty acids decrease the number and size of tumors and increase the time elapsed before appearance of tumors. Studies with nonhuman primates and human newborns indicate that DHA is essential for the normal functional development of the retina and brain, particularly in premature infants. Because omega 3 fatty acids are essential in growth and development throughout the life cycle, they should be included in the diets of all humans. Omega-3 and omega 6 fatty acids are not interconvertible in the human body and are important components of practically all cell membranes. Whereas cellular proteins are genetically determined, the polyunsaturated fatty acid (PUFA) composition of cell membranes is to a great extent dependent on the dietary intake.(ABSTRACT TRUNCATED AT 400 WORDS)