Linoleic acid intake and cancer risk: a review and meta-analysis

Replacement of saturated fat by the major dietary polyunsaturated fat linoleic acid reduces blood cholesterol concentrations and the risk of coronary artery disease. However, there is concern that long-term consumption of large amounts of linoleic acid might increase cancer risk. We reviewed the epidemiologic and experimental literature on linoleic acid intake and cancer risk and performed additional meta-analyses of risk estimates from case-control and prospective cohort studies. None of the combined estimates from within-population studies indicated a significantly increased risk of cancer with high compared with low intakes of linoleic acid or polyunsaturated fat. For case-control studies, the combined relative risks were 0.84 (95% CI: 0.71, 1.00) for breast, 0.92 (95% CI: 0.85, 1.08) for colorectal, and 1.27 (95% CI: 0.97, 1.66) for prostate cancer. For prospective cohort studies, combined relative risks were 1.05 (95% CI: 0.83, 1.34) for breast, 0.92 (95% CI: 0.70, 1.22) for colon, and 0.83 (95% CI: 0.56, 1.24) for prostate cancer. Ecologic comparisons of populations showed positive associations between cancer rates and per capita use of animal or saturated fat, but less so with per capita use of vegetable oil or polyunsaturated fat. Controlled studies of coronary artery disease in men did not, except for 1 study, show an increased cancer incidence after consumption of diets with a very high linoleic acid content for several years. Animal experiments indicated that a minimum amount of linoleic acid is required to promote growth of artificially induced tumors in rodents; but above this threshold, linoleic acid did not appear to have a specific tumor-promoting effect. Although current evidence cannot exclude a small increase in risk, it seems unlikely that a high intake of linoleic acid substantially raises the risks of breast, colorectal, or prostate cancer in humans.

Linoleic acid and alpha-linolenic acid lightens ultraviolet-induced hyperpigmentation of the skin

This study was conducted to evaluate the effects of unsaturated fatty acids on ultraviolet-induced hyperpigmentation of the skin. An efficient lightening effect was observed following topical application of linoleic acid or alpha-linolenic acid to UV-stimulated hyperpigmented dorsal skin of brownish guinea pigs. The number of melanocytes in the treated skin was similar to the number in the skin of the pigmented control, indicating that the pigment-lightening effect was not due to depletion of melanocytes. In vitro experiments using cultured murine melanoma cells showed that melanin production was inhibited most effectively by alpha-linolenic acid, followed by linoleic acid and then by oleic acid. Furthermore, the turnover of the stratum corneum, which plays an important role in the removal of melanin pigment from the epidermis, was accelerated by linoleic acid and by alpha-linolenic acid. Taken together, the results suggest that the pigment-lightening effects of linoleic acid and alpha-linolenic acid are, at least in part, due to suppression of melanin production by active melanocytes, and to enhanced desquamation of melanin pigment from the epidermis.

Long-chain polyunsaturated fatty acids in plasma and erythrocyte membrane lipids of children with phenylketonuria after controlled linoleic acid intake

It has been reported that children with classical phenylketonuria (PKU) have reduced levels of arachidonic acid (AA, 20:4 n-6) and docosahexaenoic acid (DHA, 22:6 n-3) in plasma and membrane phospholipids compared to controls and may therefore require supplementation. However, it is not established that these changes are specific for PKU. They may as well be attributed to the specific composition of a largely vegetarian diet used for dietary PKU treatment. We therefore investigated the fatty acid composition of plasma phospholipids (PL), plasma cholesterol esters (CE), red blood cell phosphatidylcholine (PC), and red blood cell phosphatidylethanolamine (PE) in two groups of PKU patients including 8 children between 1 and 6 years (group A), 9 adolescents between 11 and 18 years (group B), and 20 age-matched healthy controls. Group A had good dietary control (median plasma phenylalanine 272 mumol/L during the last 6 months before phospholipid analysis) while median phenylalanine in group B was 714 mumol/L (p < 0.001). When compared to age-matched controls, group A showed significantly lower DHA levels in PE (4.21 vs 5.85 weight% (wt%), p < 0.01), in PC (1.02 vs 1.25 wt%, p < 0.05) and in CE (0.25 vs 0.54 wt%, p < 0.05). There was no significant difference of DHA between group B and controls. AA levels were similar in phospholipids of all groups. We conclude that reduced levels of long-chain polyunsaturated fatty acids in PKU patients occur only in those patients with strict dietary therapy with respect to n-3 fatty acids, most probably caused by reduced intake of n-3 fatty acids.

Duodenal nutrient infusions differentially affect sham feeding and Fos expression in rat brain stem

Duodenal infusions of macronutrients inhibit sham and normal feeding. Neural substrates of this response were studied by infusing glucose, linoleic acid, an amino acid mixture, saline, or water into the duodenum of unanesthetized rats and then measuring sham feeding of 30% sucrose or Fos expression in the dorsal vagal complex. Linoleic acid and amino acids (both 1.5 kcal) and glucose (4.5 kcal) suppressed sham feeding relative to control infusions, and all three macronutrients triggered Fos expression in the nucleus of the solitary tract and area postrema. Although there were significant quantitative differences, the subnuclear distribution pattern of Fos-expressing neurons was not different for the three macronutrients and was largely localized to the medial, dorsomedial, and commissural subnuclei of the nucleus of the solitary tract and the area postrema. Linoleic acid suppressed intake and stimulated Fos expression similarly to glucose infusions of three times the caloric value. Amino acids strongly suppressed sham feeding but triggered relatively little Fos expression. These results indicate that the intake-suppressing potency of duodenal macronutrients is dependent on nutrient type, rather than simply caloric value, and that amino acids, although potent inducers of satiety, affect ingestion by processes different from those subserving lipids and carbohydrates. Furthermore, the similar patterns of neuronal activation after different duodenal infusions may indicate a large degree of convergence at the level of primary and second-order sensory neurons, whereas the distinctly different pattern obtained earlier with gastric distension indicates partially separate neural pathways for satiety signals generated by duodenal nutrients and gastric mechanoreceptors.

Effect of replacing a high linoleate oil with a low linoleate, high alpha-linolenate oil, as compared with supplementing EPA or DHA, on reducing lipid mediator production in rat polymorphonuclear leukocytes

The fatty acid composition of rat polymorphonuclear leukocytes (PMN) was modified by diets supplemented with a high linoleate (LA) safflower oil (76% LA), mixtures of eicosapentaenoate (EPA) and safflower oil (EPA(20) containing 20% EPA and 61% LA, EPA(40) containing 40% EPA and 46% LA), mixtures of docosahexaenoate (DHA) and safflower oil (DHA(20) containing 20% DHA and 61% LA, DHA(40) containing 40% DHA and 46% LA) or a high alpha-linolenate (alpha-LNA) perilla oil (57% alpha-LNA and 13% LA), and then lipid mediator production in casein-induced peritoneal PMN were compared. EPA and DHA were relatively ineffective in reducing platelet-activating factor (PAF) production; a statistically significant reduction was observed only in the DHA(40) group. In contrast, perilla oil reduced PAF production by 50% as compared with safflower oil. Arachidonate (AA) in the PAF precursor, 1-alkyl-2-acyl-glycerophosphocholine, was roughly correlated with PAF production, but EPA and DHA in the precursor lipid were relatively unrelated. On the other hand, both PGE2 and LTB4 production correlated positively with AA and negatively with EPA and DHA in PMN phospholipids; EPA tended to be somewhat more effective than DHA in reducing PGE2 and LTB4 formation; the activity of perilla oil was no less than EPA(20). Thus, replacing safflower oil with perilla oil was no less effective than supplementing safflower oil with EPA or DHA (at 40% of total fatty acids) in reducing lipid mediator production in rat PMN.

Opposite effects of linoleic acid and conjugated linoleic acid on human prostatic cancer in SCID mice

The relationship between dietary fat intake (level and type) and cancer development is a matter of concern in Western society. The purpose of this study was to determine the effect of three different diets on the local growth and metastatic properties of DU-145 human prostatic carcinoma cells in severe combined immunodeficient (SCID) mice. Animals were fed a standard diet or diets supplemented with 1% LA or 1% CLA for 2 weeks prior to subcutaneous (s.c.) inoculation of DU-145 cells and throughout the study (total of 14 weeks). Mice receiving LA-supplemented diet displayed significantly higher body weight, lower food intake and increased local tumor load as compared to the other two groups of mice. Mice fed the CLA-supplemented diet displayed not only smaller local tumors than the regular diet-fed group, but also a drastic reduction in lung metastases. These results support the view that dietary polyunsaturated fatty acids may influence the prognosis of prostatic cancer patients, thus opening the possibility of new therapeutic options.

Inhibitory effect of linoleic acid on chain elongation and desaturation of 18:2 c,t isomers in lactating and neonatal rats

The previous studies showed that dietary 18:2 c,t isomers could be chain-elongated and desaturated to produce unusual 20:4 isomers. The present study was undertaken to determine the minimal amount of 18:2n-6 required to suppress the chain elongation and desaturation of 18:2 c,t isomers in the lactating and neonatal rats when animals were fed 15% partially hydrogenated canola oil diet containing 1.72% energy as 18:2 c,t isomers and varying amounts of free 18:2n-6. These diets induced marginal essential fatty acid (EFA) deficiency states (0.56% energy 18:2n-6) to EFA adequacy (2.56% energy 18:2n-6). After feeding for 50 d, the female animals were mated with males by overnight pairing. After conception, the lactating rats were killed, together with one pup from each dam, at term and day 26 of lactation. Two unusual 20:4 isomers in both maternal and neonatal liver phospholipids were identified as 20:4delta5c,8c,11c,14t and 20:4delta5c,8c,11c,15t, which were derived from 18:2delta9c,12t and 18:2delta9c,13t, respectively. The results showed that 18:2n-6 at about 2.0% of total energy in maternal diet was required to block the production of 20:4delta5c,8c,11c,14t and 20:4delta5c,8c,11c,15t in the maternal liver, whereas 18:2n-6 at about 2.5% of total energy in maternal diet was required to suppress production of these unusual 20:4 isomers in the neonatal liver.

Factor VIIa response to a fat-rich meal does not depend on fatty acid composition: a randomized controlled trial

A fat-rich meal increases activated factor VII (FVIIa), but it is not clear whether this increase depends on the fatty acid composition of the meal. Therefore, we studied the FVIIa response to fat-rich meals with different fatty acid composition in a randomized controlled crossover trial and investigated whether this response is mediated by an increase in serum triglycerides. Elderly women (> 60 years, n=91) received on separate days four different fat-rich breakfasts (50 energy percent [en%] of fat) and a control breakfast (1.5 en% fat; crossover). The fat-rich breakfasts differed in fatty acid composition: one rich in palmitic acid (21.7 g), one in stearic acid (18.6 g), and the other two in linoleic and linolenic acid-one with a ratio 3:1 (12.5/3.9 g) and the other with a ratio of 15:1 (18.8/1.2 g). At 8 AM before the breakfast (fasting) and at 1 and 3 PM, blood samples were taken, in which FVIIa and serum triglycerides were measured. FVIIa response to the fat-rich meals ranged from 11.6 mU/mL (95% confidence interval: 8.3,14.9) on the stearic meal to 15.9 mU/mL (12.0,19.8) on the linoleic/linolenic 15:1 meal at 1 PM and from 14.9 mU/mL (10.6,19.2) to 21.1 mU/mL (16.6,25.6) for the same meals at 3 PM. The responses did not differ between the fat-rich meals. After the control breakfast, FVIIa decreased, with 6.3 mU/mL (3.9,8.7) at 1 PM and 8.7 mU/mL (6.3,11.1) at 3 PM. The triglyceride response was lower after both linoleic/linolenic rich breakfasts compared with the palmitic and stearic breakfast (P<.05) and was not associated with the FVIIa response at any of the blood sampling occasions. The results of this study show that the response of FVIIa to a fat-rich meal is independent of its fatty acid composition and is not mediated by serum triglycerides.

Pathophysiologic studies of experimental chronic pancreatitis in rats induced by injection of zein-oleic acid-linoleic acid solution into the pancreatic duct

An experimental model of chronic pancreatitis was induced by a retrograde injection of a viscous solution consisting of zein-oleic acid-linoleic acid (0.05 ml/100 g body weight) into the rat pancreatic duct. Histologic and biochemical changes were investigated over a period of 6 months after induction of this model. The treated rats gained weight, but pancreatic weight decreased with time. Histologically, the widening of acinar lumen and cellular vacuolization occurred within 24 h at the parenchyma neighboring the small ducts filled with the injected solution. Degenerative parenchyma, interstitial edema, and inflammatory cell infiltration were pronounced 1 week later. Thereafter, duct-like tubular complex formation progressed, and the exocrine tissue exhibited marked atrophy of the gland with irregular fibrosis and fat replacement over a period of 6 months. Pancreatic contents of protein, amylase, DNA, and RNA markedly decreased, as did pancreatic weight, whereas hydroxyproline content increased. Oral administration of camostat did not affect pancreatic weight and contents of enzyme in this model. Urinary para-aminobenzoic acid (PABA) excretion in the BT-PABA test decreased to 54% at 6 weeks and 22% at 6 months. Although three quarters of pancreatic immunoreactive insulin (IRI) content was lost after 6 months, overt diabetes did not occur. The results suggest that an obstructive mechanism in the small ducts plays an important role in the genesis and development of chronic pancreatitis.

Increased arachidonic acid induced platelet chemiluminescence indicates cyclooxygenase overactivity in schizophrenic subjects

Platelets were found to emit a burst of chemiluminescence during incubation with arachidonic or linoleic acid. This chemiluminescence response may indicate activation of the enzyme prostaglandin synthase in the arachidonate-induced platelet chemiluminescence as it is inhibited by aspirin. Stimulation of platelets with arachidonic acid and linoleic acid induced a concentration dependent chemiluminescence response. Platelets from drug naive schizophrenic subjects showed significantly increased arachidonic acid metabolism compared to control subjects. No significant difference was observed between schizophrenic and control subjects in the chemiluminescence response to linoleic acid. In schizophrenic subjects treated with neuroleptic drugs the overactive arachidonic acid response was normalized. Linoleic acid chemiluminescence response was unaffected by neuroleptic treatment. Hyperactive cyclooxygenase activity may reflect a similar condition in the brain and implicates prostaglandin pathway abnormalities in the pathogenesis of schizophrenia.

A diet rich in walnuts favourably influences plasma fatty acid profile in moderately hyperlipidaemic subjects

OBJECTIVE

To compare two low fat diets one rich in walnuts on parameters of lipid metabolism in a group of hyperlipidaemic subjects.

DESIGN

A randomised cross over study.

SETTING

Department of Human Nutrition, University of Otago, Dunedin, New Zealand

SUBJECTS

Twenty one men with mean (s.d.) levels of total and LDL cholesterol of 6.58 (0.60) and 4.63 (0.58) respectively.

INTERVENTIONS

For two periods of four weeks subjects were asked to consume two low fat diets (fat 30% total energy), one containing, on average, 78 g/d walnuts. Walnuts obtained through Lincoln University and the Walnut Growers Group (South Canterbury).

RESULTS

Participants reported a higher total fat intake on the walnut diet (38% compared with 30% on the low fat diet P < 0.01) The most consistent change in fatty acid profile of triacylglycerol, phospholipid and cholesterol ester on the walnut diet was a significant (P < 0.01) increase in linoleic acid. Triacylglycerol linolenate also increased significantly (P < 0.01). Total and LDL cholesterol were lower on both experimental diets than at baseline, 0.25 mmol/l and 0.36 mmol/l respectively on the walnut diet and 0.13 mmol/l and 0.20 mmol/l respectively on the low fat diet. High density lipoprotein cholesterol was higher on both the walnut and low fat diets when compared to baseline (0.15 mmol/l and 0.12 mmol/l, respectively). When comparing the walnut and low fat diets only apo B was significantly lower (P < 0.05) on the walnut diet.

CONCLUSIONS

Despite an unintended increase in the total fat intake on the walnut diet, fatty acid profile of the major lipid fractions showed changes which might be expected to reduce risk of cardiovascular disease. The reduction of apolipoprotein B suggests a reduction in lipoprotein mediated risk, the relatively low myristic acid content of both diets perhaps explaining the absence of more extensive differences in lipoprotein levels on the two diets.

Effect of a high linoleic acid diet on delta 9-desaturase activity, lipogenesis and lipid composition of pig subcutaneous adipose tissue

The effects of three diets were compared: a high linoleic acid diet (diet M containing 4% maize oil), diet T containing 4% beef tallow, and C, a conventional control diet, on delta 9-desaturase activity and lipogenesis in pig subcutaneous adipose tissue. Diet M increased lipogenesis (estimated from the activities of acetyl-CoA-carboxylase, malic enzyme and glucose-6-phosphate dehydrogenase), and decreased delta 9-desaturase activity, in comparison to the other diets. Linoleic acid content was higher in the pigs fed diet M than in the other pigs (amounting to 26% of total tissue fatty acids versus 15%, respectively). The lower monounsaturated fatty acid content in adipose tissue of pigs fed diet M compared to pigs fed other diets could be associated with the lower delta 9-desaturase activity and the lower oleic acid content of diet M. The present study suggests that delta 9-desaturase could be involved in the regulation of monounsaturated fatty acid content and hence in the quality of pig adipose tissue.

Effects of chain length and unsaturation of fatty acid mixtures infused into the abomasum of lactating dairy cows

Six cows were utilized in a 6 x 6 Latin square design with 21-d periods to determine effects of the postruminal profile of fatty acids on dry matter (DM) intake, milk yield and composition, nutrient digestibilities, and plasma metabolites. Treatments were abomasal infusions of 1) control [168 g/d of meat solubles (carrier for fatty acids) plus 10.6 g/d of Tween 80 (emulsifier)], 2) control plus 450 g/d of mostly saturated fatty acids, 3) control plus 450 g/d of palm oil fatty acids low in linoleic acid, 4) control plus 450 g/d of palm oil fatty acids, 5) control plus 450 g/d of soybean oil fatty acids, and 6) control plus 450 g/d of soybean oil fatty acids high in palmitic acid. Treatments 2, 3, 4, and 6 contained similar ratios of C16 to C18 fatty acids. Infusion of soybean oil fatty acids or soybean oil fatty acids high in palmitic acid decreased intakes of DM, organic matter, crude protein, acid detergent fiber, neutral detergent fiber, gross energy, and total fatty acids and tended to decrease yields of milk and fat-corrected milk compared with the infusion of mostly saturated fatty acids. Infusion of palm oil fatty acids low in linoleic acid or palm oil fatty acids decreased milk fat percentage compared with other treatments. Ruminal characteristics and apparent digestibilities of DM, organic matter, crude protein, acid detergent fiber, neutral detergent fiber, energy, total fatty acids, and total C18 fatty acids were not different. Infusion of fatty acids increased concentrations of cholesterol in plasma. The amount of unsaturated fatty acids passing into the small intestine may influence responses of dairy cows to supplemental fat.

Possible mechanisms for the differential effects of high linoleate safflower oil and high alpha-linolenate perilla oil diets on platelet-activating factor production by rat polymorphonuclear leukocytes

As compared with high dietary linoleate safflower oil, high dietary alpha-linolenate perilla oil decreased platelet-activating factor (PAF) production by nearly half in calcium ionophore (CaI)-stimulated rat polymorphonuclear leukocytes (PMN). In the CaI-stimulated PMN from the perilla oil group, the accumulated amount of arachidonate (AA) plus eicosapentaenoate (EPA) was 30% less and that of lyso-PAF was 50% less, indicating that the decreased availability of lyso-PAF is a factor contributing to the relatively low PAF production. Consistently, eicosatetraynoic acid (ETYA), a dual inhibitor of cyclooxygenase and lipoxygenase, increased free fatty acids (FFA) and decreased PAF production possibly by decreasing the availability of lyso-PAF. Although, leukotrienes (LTs) have been proposed to stimulate PAF production synergistically, a potent LTB4 receptor antagonist, ONO-4057, decreased the formation of free fatty acids and LTB4, but stimulated PAF production somewhat, indicating that LTB4 may not stimulate PAF production in PMN. Lysophospholipid-induced transacylase (CoA-independent transacylase) activity in PMN homogenates was 25-30% lower in the perilla oil group but no significant differences were observed in the lyso-PAF acetyltransferase and PAF acetylhydrolase activities between the two dietary groups. Thus, decreased transacylase activity is another factor associated with the relatively low PAF production in the perilla oil group.

Cholesteryl ester transfer protein gene polymorphism is a determinant of HDL cholesterol and of the lipoprotein response to a lipid-lowering diet in type 1 diabetes

The TaqIB cholesteryl ester transfer protein (CETP) gene polymorphism (B1B2) is a determinant of HDL cholesterol in nondiabetic populations. Remarkably, this gene effect appears to be modified by environmental factors. We evaluated the effect of this polymorphism on HDL cholesterol levels and on the lipoprotein response to a linoleic acid-enriched, low-cholesterol diet in patients with type 1 diabetes. In 44 consecutive type 1 diabetic patients (35 men), CETP polymorphism, apolipoprotein (apo) E genotype, serum lipoproteins, serum CETP activity (measured with an exogenous substrate assay, n = 30), clinical variables, and a diet history were documented. The 1-year response to diet was assessed in 14 type 1 diabetic patients, including 6 B1B1 and 6 B1B2 individuals. HDL cholesterol was higher in 10 B2B2 than in 14 B1B1 homozygotes (1.63 +/- 0.38 vs. 1.24 +/- 0.23 mmol/l, P < 0.01). HDL cholesterol, adjusted for triglycerides and smoking, was 0.19 mmol/l higher for each B2 allele present. CETP activity levels were not significantly different between CETP genotypes. Multiple regression analysis showed that VLDL + LDL cholesterol was associated with dietary polyunsaturated:saturated fatty acids ratio (P < 0.02) and total fat intake (P < 0.05) in the B1B1 homozygotes only and tended to be related to the presence of the apo E4 allele (P < 0.10). In response to diet, VLDL + LDL cholesterol fell (P < 0.05) and HDL cholesterol remained unchanged in 6 B1B1 homozygotes. In contrast, VLDL + LDL cholesterol was unaltered and HDL cholesterol decreased (P < 0.05) in 6 B1B2 heterozygotes (P < 0.05 for difference in change in VLDL + LDL/HDL cholesterol ratio). This difference in response was unrelated to the apo E genotype. Thus, the TaqIB CETP gene polymorphism is a strong determinant of HDL cholesterol in type 1 diabetes. This gene effect is unlikely to be explained by a major influence on the serum level of CETP activity, as an indirect measure of CETP mass. Our preliminary data suggest that this polymorphism may be a marker of the lipoprotein response to dietary intervention.

Morphological and biochemical status of the mammary gland as influenced by conjugated linoleic acid: implication for a reduction in mammary cancer risk

Previous research showed that treatment with conjugated linoleic acid (CLA) during the period of active mammary gland morphogenesis was sufficient to confer a lasting protection against subsequent mammary tumorigenesis induced by methylnitrosourea. The present study was designed to characterize certain morphological and biochemical changes of the mammary gland that might potentially render it less susceptible to cancer induction. Female Sprague Dawley rats were fed a 1% CLA diet from weaning until about 50 days of age. The mammary gland parameters under investigation included (a) the deposition of neutral lipid, (b) the identification and quantification of CLA and its metabolites, (c) the density of the epithelium, and (d) the proliferative activity of various structural components. Our results showed that CLA treatment did not affect total fat deposition in the mammary tissue nor the extent of epithelial invasion into the surrounding fat pad but was able to cause a 20% reduction in the density of the ductal-lobular tree as determined by digitized image analysis of the whole mounts. This was accompanied by a suppression of bromodeoxyuridine labeling in the terminal end buds and lobuloalveolar buds. The recovery of desaturation and elongation products of CLA in the mammary gland confirmed our prior suggestion that the metabolism of CLA might be critical to risk modulation. The significance of the above findings was investigated in a mammary carcinogenesis bioassay with the use of the dimethylbenz[a]anthracene model. When CLA was started at weaning and continued for 6 months until the end of the experiment, this schedule of supplementation produced essentially the same magnitude of mammary tumor inhibition in the dimethylbenz[a]anthracene model as that produced by 1 month of CLA feeding from weaning. The observation is consistent with the hypothesis that exposure to CLA during the time of mammary gland maturation may modify the developmental potential of a subset of target cells that are normally susceptible to carcinogen-induced transformation.

The intake of polyunsaturated fatty acids by cats is reflected in their adipose tissue

To find out whether the composition of the subcutaneous adipose tissue of cats reflects the intake of polyunsaturated fatty acids, we performed a feeding trial. Six groups of kittens were fed on diets with variable combinations of corn, linseed, and fish oil. After 5 months, biopsies of subcutaneous adipose tissue were analysed for their contents of linoleic, alpha-linolenic, eicosapentaenoic, and docosahexaenoic acid. The observed strong correlations between dietary and fat tissue polyunsaturated fatty acids indicate that the fatty acid composition of adipose tissue may be used as an index of the fatty acid composition of the diet. Thus, in epidemiological studies on the possible relationship between dietary fat type and feline disease the fatty acid composition of adipose tissue might be a useful measure.

Dietary management of cardiovascular diseases

Since cholesterol was discovered in atherosclerotic plaques and was able, when given in diet, to induce the same type of lesions in animals, the aim of previous dietary changes was to reduce serum cholesterol as much as possible. For this purpose, the intake of saturated fats was decreased and replaced by linoleic acid, the main fatty acid lowering cholesterol. Nevertheless, this type of diet in primary or secondary prevention did not succeed in reducing satisfactorily cardiovascular and total mortality unless the intake of fish (DART and Hjermann trials) i.e. of n-3 fatty acids, was increased. On the other hand, the diet with the greatest life expectancy in the western world is that of Crete, largely vegetarian with a high intake of alpha-linolenic acid. Such a diet, compared to the usual prudent diet in 600 patients after a first myocardial infarction, reduced within a few months all cause mortality and cardiovascular events by more than 70%. Thus a highly palatable diet adapted from Crete seems to be much more efficient to prevent recurrences and death after a first myocardial infarction than the hypocholesterolemic diet presently advised.

Modulation of adjuvant-induced arthritis by dietary arachidonic acid in essential fatty acid-deficient rats

Controlled feeding of linoleic acid (LA) or arachidonic acid (AA) to essential fatty acid-deficient (EFAD) rats was used to define the relationship between dietary AA and the inflammatory response evoked during adjuvant-induced arthritis. Based on energy percentage, EFAD rats were fed AA at the human daily equivalent (1x; 5.5 mg/day) or 10 times that amount (10x; 55 mg/day) or, alternatively 0.5x of LA (273 mg/day). Feeding of 0.5x LA restored the plasma level of AA to that in chow-fed controls. In contrast, feeding of 1x AA only partially restored the plasma level of AA; 10x AA was required to fully replete AA. In parallel to the degree of repletion of AA in plasma, there were accompanying decreases in the levels of palmitoleic acid, oleic acid, and Mead acid. Compared to rats fed the standard laboratory chow diet (Control), edema in the primary hind footpads was decreased by 87% in EFAD, 71% in EFAD + 1x AA, 45% in EFAD + 10x AA, and 30% in EFAD + 0.5x LA. The decrease in edema in the footpads of EFAD rats was nearly identical to the decrease in edema in the footpads of Control rats dosed with indomethacin. Hind footpad edema correlated with the final AA plasma level and eicosanoid levels extracted from hind footpad tissue, but not with neutrophil infiltration. The data showed that 0.5x LA and 10x AA, but not 1x AA, could quickly replete AA, accompanied by the synthesis of AA-derived eicosanoids and restoration of edema. These results suggest that in humans consumption of the average daily amount of AA without concurrent ingestion of LA would not alleviate an EFAD state.

Essential fatty acid preparation improves biochemical and cognitive functions in experimental allergic encephalomyelitis rats

This study examined the possible effects of a novel mixture of fatty acids, SR-3 (a specific ratio of alpha-linolenic acids), on brain biochemistry and on learning deficits induced by injection of an agent that induces experimental allergic encephalomyelitis. Treatment with SR-3 caused a decrease in myelin and changes in the fatty acid profile of brain synaptosomes, and a learning deficit. Eighteen days of treatment with SR-3 reversed the biochemical and learning deficit significantly, but did not restore them to normal levels. We propose that, most probably, the main action of SR-3 is the modulation of the cholesterol level, which in turn causes the modulation of the fatty acid profile and enhances learning by allowing improved neuronal communication.