Fatty liver produced by dietary deficiencies: its pathogenesis and potentiation by ethanol

In a study of the pathogenesis of hepatic fat accumulation under experimental conditions mimicking chronic alcoholism, rats were fed a low-fat diet, deficient in amino acids and choline, containing either ethanol or isocaloric amounts of carbohydrate. Dietary deficiencies alone produced a moderately fatty liver after 24 days. The combination of ethanol and dietary deficiencies resulted in enhanced lipid accumulation, which was apparent after only 11 days. In an investigation of the origin of hepatic triglyceride fatty acids, the experiment was repeated after the adipose lipids had been marked by the feeding of oils containing characteristic fatty acids (linseed oil, containing linolenate, or coconut oil, containing laurate and myristate). In all animals, the fatty acid composition of the hepatic triglycerides differed markedly from that of adipose tissue; it had a larger percentage of endogenously synthesized fatty acids and a five times smaller percentage of the marker fatty acids. In addition, ethanol feeding resulted in a greater retention of the marker fatty acids in the adipose tissue. Thus, the deposition of hepatic triglycerides produced by the feeding of deficient diets is markedly potentiated by ethanol; the triglyceride fatty acids accumulated under these conditions appear to originate, for the most part, not from mobilization of depot fat, but from endogenous synthesis.     

Genesis of fatty liver and hyperlipemia in the fetal guinea pig.

10 to 20% of [1-14C] palmitate injected into pregnant guinea pigs was recovered in lipids of their fetuses. From these data and the rate of transport of palmitate in maternal blood, it appears that placental transport of free fatty acids can account for the accumulation of lipids in late gestational fetuses. About 80% of the labeled palmitate in the fetus appeared initially in lipids of the liver. 14C appeared in plasma triglyceride fatty acids after a few minutes and subsequently accumulated in lipids of white and brown adipose tissue, suggesting that much of the palmitate deposited in adipose tissue were derived from hepatogenous triglyceride fatty acids. By contrast, 14C was usually maximal in heart and carcass lipids before it appeared in plasma triglyceride fatty acids. Lipoprotein lipase activity in fetal adipose tissue was low, and activity of cofactor protein of lipoprotein lipase in fetal blood plasma was much lower than that observed in other mammalian species. On the basis of these and earlier observations, it is concluded that the accumulation of triglycerides in liver and blood plasma of fetal guinea pigs during late gestation is at least partly the result of the large uptake of maternally derived free fatty acids by the fetal liver accompanied by rapid synthesis and secretion of triglyceride-rich very low density lipoproteins into the blood. However, limited uptake of triglyceride fatty acids in adipose tissue may contribute to the fatty liver and hyperlipemia.     

Effect of ingestion of saline, glucose, and ethanol on mobilization and hepatic incorporation of epididymal pad palmitate-1-14C in rats

The effect of ingestion of saline, glucose, and ethanol (isocaloric with the glucose) on the mobilization of radiopalmitate from epididymal fat prelabeled in vivo and the incorporation of the mobilized label into liver lipids was investigated in rats. The mobilization of radiopalmitate from epididymal fat and the incorporation of the mobilized label into liver triglyceride were most markedly elevated by ingestion of ethanol. Increased mobilization and diversion of epididymal adipose tissue fatty acids to liver lipids of ethanol-treated rats were shown also by the close resemblance of the fatty acids of liver triglyceride to the fatty acids of epididymal fat. The amount of radiopalmitate mobilized by the saline-treated rats, comprising approximately a third of that mobilized by the ethanol-treated animals, was larger than the amount mobilized by the rats treated with glucose; most of it was oxidized rather than incorporated into the liver fats. In glucose-treated rats a larger fraction of radiopalmitate mobilized from one prelabeled epididymal pad was diverted to and incorporated into the lipids of the contralateral pad of the same animal. The specific activity of hepatic triglyceride of ethanol- and saline-treated rats was similar and significantly higher than that of animals treated with glucose. These data indicate that the ethanol-induced fatty liver can be attributed to an increased mobilization and incorporation of adipose tissue fatty acids into liver lipid and to an altered hepatic metabolism of fatty acids and triglyceride.     

Utilization of exogenous free fatty acids for the production of very low density lipoprotein triglyceride by livers of carbohydrate-fed rats

High carbohydrate diets enhance the hepatic output of very low density lipoprotein triglycerides. The fatty acids of these triglycerides could come from exogenous sources (i.e., diet or adipose tissue) or from de novo fatty acid synthesis in the liver. The role of exogenous free fatty acids was evaluated in rats fed Purina Chow or diets containing 10% fructose for up to 14 wk. In carbohydrate-fed rats, serum triglycerides were twice normal, and VLDL accounted for about 60% of the increases. Pre-beta-lipoprotein was increased and alpha- and beta-lipoprotein were decreased. Phospholipid and cholesterol levels were unchanged. Livers were perfused with glucose and free fatty acids. Perfusate free fatty acids rose from 180 to 1800 micro eq/liter as the infused acids increased from 0 to 992 micro eq/3 hr; simultaneously, net free fatty acid uptake rose from < 1 to 18 micro eq/g/hr and triglyceride output by the liver doubled. However, rates of secretion of triglyceride became constant, and triglyceride accumulated in liver at uptakes of free fatty acids > 13 micro eq/g/hr. More lauric and myristic acid appeared in the perfusate than was infused, suggesting the hepatic discharge of free fatty acids. Livers of fructose-fed rats secreted twice as much oleate-(14)C-labeled triglyceride as controls at all levels of free fatty acid uptake. The ratios of the specific activities of perfusate triglyceride to free oleate-(14)C were unaffected by diet and were about 0.6 and 1.0 at low and high triglyceride secretion rates, respectively. Thus, carbohydrate feeding did not result in altered uptakes of free fatty acids or preferential secretion of triglycerides containing endogenously synthesized fatty acid. Instead, the increased secretion of triglyceride was accomplished by enhanced formation of VLDL triglyceride from exogenous free fatty acids.     

Effects of prolonged ingestion of glucose or ethanol on tissue lipid composition and lipid biosynthesis in rat

The effects on lipid metabolism of long-term feeding of large amounts of ethanol or glucose differed from those that have been reported in short-term experiments. Three groups of male rats were investigated. The first was fed lab chow and 15% (v/v) ethanol ad lib.; the second was pair-fed with the first and given isocaloric amounts of glucose in lieu of ethanol; the third was fed lab chow and water ad lib. All three groups consumed nearly the same number of calories, and about 30% of the calories in the first group were derived from ethanol. Neither glucose nor ethanol added to a nutritionally adequate diet promoted the development of a fatty liver, although both stimulated acetate-(14)C utilization for hepatic lipid synthesis. In all three groups more than 80% of the label in hepatic lipid was found in fatty acids, and the distribution of label amongst the fatty acids of different chain lengths was virtually the same. Ethanol decreased while glucose increased the quantity of lipid in fat depots, and each altered the fatty acid composition of the lipids in adipose tissue, kidney, liver, and hepatic subcellular fractions in a different manner. The most striking of these changes was the relative increase in monounsaturated fatty acids and the decrease in essential fatty acids produced by glucose.     

The transfer of fatty acids across the sheep placenta

Maternal and fetal plasma concentrations of free fatty acids, triacylglycerols and phospholipids and the profile of their fatty acids were measured in three catheterized and unanaesthetized sheep. Fetal concentrations of all three lipid fractions were low and did not correlate with maternal concentrations. There were no measurable umbilical venous-arterial differences. Linoleic acid concentrations were low in both mother and fetus. The fatty acid composition of fetal adipose tissue, liver, lung and cerebellum of five animals was analysed. Again linoleic acid levels were very low, but phospholipids contained 2-8% arachidonic acid. [14C] linoleic acid and [3H] palmitic acid were infused intravenously into three ewes. Only trace amounts of labelled fatty acids were found in fetal plasma and these were confined to the free fatty acids. 14C-label was incorporated into fetal tissue lipids, but most of this probably was due to fetal lipid synthesis from [14C] acetate or other water-soluble products of maternal [14C] linoleic acid catabolism. It is concluded that only trace amounts of fatty acids cross the sheep placenta. They are derived mainly from the maternal plasma free fatty acids and might just be sufficient to be the source of the small amounts of essential fatty acids found in the lamb fetus, but are insignificant in terms of energy supply or lipid storage.     

Dietary mold oil rich in gamma linolenic acid increases insulin-dependent glucose utilization in isolated rat adipocytes

Effects of dietary fats differing in fatty acid composition on insulin-stimulated glucose metabolism in adipocytes isolated from rat white adipose tissue were compared. Rats were fed experimental diets containing various fats differing in fatty acid composition for 7 days. In the first experiment, rats were fed palm oil mainly consisting of palmitic (45.3%) and oleic acids (39.1%) or safflower oil rich in linoleic acid (71.6%). In the second trial, rats were fed palm oil, or a fat mixture rich in linoleic acid or mold oil rich in gamma-linolenic acid. Contents of fatty acids except for linoleic and gamma-linolenic acid were comparable between the fat mixture and mold oil. The former was devoid of gamma-linolenic acid and contained 42.0% linoleic acid, while the latter contained 25.9% gamma-linolenic and 15.7% linoleic acids. In the first experiment, the insulin-dependent increase in glucose oxidation and incorporation into lipids was higher in rats fed safflower oil compared to those fed palm oil. In the second experiment, the insulin-dependent increase in glucose oxidation and incorporation into lipids was higher in rats fed the fat mixture and mold oil than in those fed palm oil. However, the extent of the increase in these parameters was much greater in rats fed mold oil than in those fed the fat mixture. Therefore, dietary gamma-linolenic acid compared to linoleic acid increases glucose metabolism in response to insulin stimuli in isolated rat adipocytes.     

Essential fatty acids in tissue phospholipids and triglycerides of the zinc-deficient rat

This study addressed the possibility that zinc deficiency has different effects on the fatty acid composition of triglyceride compared to total phospholipid. Male weanling Sprague-Dawley rats were maintained for 6 weeks on a semisynthetic diet deficient in zinc (3 mg/kg zinc). Control rats (40 mg/kg zinc) were pair-fed. Lipid fractionation and fatty acid analysis were by thin-layer and gas chromatography, respectively. In zinc-deficient rats, the percentage of linoleic acid was increased or that of arachidonic acid was decreased in total phospholipids of plasma, liver, and testis, and in skin total lipids. Saturated and monounsaturated fatty acids were increased in the triglyceride of liver but decreased in the triglyceride of epididymal fat of zinc deficient rats. Essential fatty acids, as a proportion of total fatty acids, were decreased in triglyceride of liver but increased in triglyceride of epididymal fat of zinc-deficient rats. Our fatty acid data from tissue total phospholipids therefore support the concept that linoleic acid desaturation is impaired in zinc deficiency.     

Effect of fat free diet during the last week of pregnancy upon the linoleic and arachidonic acid content of fetal organ lipids and placenta lipids of the rat

Pregnant Wistar rats were fed a fatfree diet from day 16--22 of pregnancy. On day 22, the fatty acid components of cholesterol esters, triglycerides, free fatty acids and phospholipids of maternal (brain, muscle, serum, white adipose tissue, liver) and fetal (brain, carcass, serum, liver) tissues, including the placenta, were examined gaschromatographically for the participation of linoleic and arachidonic acid. In all fetal and maternal organs the linoleic acid levels in the fatty acid patterns were strongly reduced. The alterations nearly always involved all the lipid fractions of a tissue and were mostly equal within a tissue. The strongest decreases of linoleic acid occurred in the placenta, and the weakest, in the lipids of maternal muscle and maternal adipose tissue. The linoleic acid alterations were principally similar in fetal and the corresponding maternal tissues, while being less pronounced in case of maternal muscle. The participation of arachidonic acid in the fatty acid pattern is completely retained in the lipids of fetal organs, and is even enhanced in those of the placenta.     

Changes in the composition of fatty acids in blood plasma lipids and in various organs in traumatic shock

The composition of fatty acids of the total lipids of the myocardium, lungs, liver, intestine, adipose tissue, and blood plasma was studied during traumatic shock reproduced in dogs by crush of soft tissues of the hip. The formation of the shock process was accompanied by a rise in the percentage content of linoleic and arachidonic acids in the blood plasma and some organs; a close correlation existed between the linoleic acid content in the adipose tissue and the blood. Oleic acid deficiency was revealed in the lipids of the organs under study.     

Chronic Alcohol Exposure Disturbs Lipid Homeostasis at the Adipose Tissue-Liver Axis in Mice: Analysis of Triacylglycerols Using High-Resolution Mass Spectrometry in Combination with In Vivo Metabolite Deuterium Labeling

A method of employing high-resolution mass spectrometry in combination with in vivo metabolite deuterium labeling was developed in this study to investigate the effects of alcohol exposure on lipid homeostasis at the white adipose tissue (WAT)-liver axis in a mouse model of alcoholic fatty liver. In order to differentiate the liver lipids synthesized from the fatty acids that were transported back from adipose tissue and the lipids synthesized from other sources of fatty acids, a two-stage mouse feeding experiment was performed to incorporate deuterium into metabolites. Hepatic lipids extracted from mouse liver, epididymal white adipose tissue (eWAT) and subcutaneous white adipose tissue (sWAT) were analyzed. It was found that 13 and 10 triacylglycerols (TGs) incorporated with a certain number of deuterium were significantly increased in alcohol induced fatty liver at two and four weeks of alcohol feeding periods, respectively. The concentration changes of these TGs ranged from 1.7 to 6.3-fold increase. A total of 14 deuterated TGs were significantly decreased in both eWAT and sWAT at the two and four weeks and the fold-change ranged from 0.19 to 0.77. The increase of deuterium incorporated TGs in alcohol-induced fatty liver and their decrease in both eWAT and sWAT indicate that alcohol exposure induces hepatic influx of fatty acids which are released from WATs. The results of time course analysis further indicate a mechanistic link between adipose fat loss and hepatic fat gain in alcoholic fatty liver.     

Fatty acid synthesis in liver and adipose tissue of normal and genetically obese (ob/ob) mice during the 24-hour cycle.

1. The synthesis of long-chain fatty acids de novo was measured in the liver and in regions of adipose tissue in intact normal and genetically obses mice throughout the daily 24h cycle. 2. The total rate of synthesis, as measured by the rate of incorporation of 3H from 3H2O into fatty acid, was highest during the dark period, in liver and adipose tissue of lean or obese mice. 3. The rate of incorporation of 14C from [U-14C]glucose into fatty acid was also followed (in the same mice). The 14C/3H ratios were higher by a factor of 5-20 in parametrial and scapular fat than that in liver. This difference was less marked during the dark period (of maximum fatty acid synthesis). 4. In normal mice, the total rate of fatty acid synthesis in the liver was about twofold greater than that in all adipose tissue regions combined. 5. In obese mice, the rate of fatty acid synthesis was more rapid than in lean mice, in both liver and adipose tissue. Most of the extra lipogenesis occurred in adipose tissue. The extra hepatic fatty acids synthesized in obese mice were located in triglyceride rather than phospholipid. 6. In adipose tissue of normal mice, the rate of fatty acid synthesis was most rapid in the intra-abdominal areas and in brown fat. In obese mice, all regions exhibited rapid rates of fatty acid synthesis. 7. These results shed light on the relative significance of liver and adipose tissue (i.e. the adipose 'organ') in fatty acid synthesis in mice, on the mino importance of glucose in hepatic lipogenesis, and on the alterations in the rate of fatty acid synthesis in genetically obese mice.     

Regulation of lipid flux between liver and adipose tissue during transient hepatic steatosis in carnitine-depleted rats

Rats with carnitine deficiency due to trimethylhydrazinium propionate (mildronate) administered at 80 mg/100 g body weight per day for 10 days developed liver steatosis only upon fasting. This study aimed to determine whether the transient steatosis resulted from triglyceride accumulation due to the amount of fatty acids preserved through impaired fatty acid oxidation and/or from up-regulation of lipid exchange between liver and adipose tissue. In liver, mildronate decreased the carnitine content by approximately 13-fold and, in fasted rats, lowered the palmitate oxidation rate by 50% in the perfused organ, increased 9-fold the triglyceride content, and doubled the hepatic very low density lipoprotein secretion rate. Concomitantly, triglyceridemia was 13-fold greater than in controls. Hepatic carnitine palmitoyltransferase I activity and palmitate oxidation capacities measured in vitro were increased after treatment. Gene expression of hepatic proteins involved in fatty acid oxidation, triglyceride formation, and lipid uptake were all increased and were associated with increased hepatic free fatty acid content in treated rats. In periepididymal adipose tissue, mildronate markedly increased lipoprotein lipase and hormone-sensitive lipase activities in fed and fasted rats, respectively. On refeeding, carnitine-depleted rats exhibited a rapid decrease in blood triglycerides and free fatty acids, then after approximately 2 h, a marked drop of liver triglycerides and a progressive decrease in liver free fatty acids. Data show that up-regulation of liver activities, peripheral lipolysis, and lipoprotein lipase activity were likely essential factors for excess fat deposit and release alternately occurring in liver and adipose tissue of carnitine-depleted rats during the fed/fasted transition.     

Characterization and metabolism of ovine foetal lipids

1. Total phospholipid concentrations in liver, kidney and brain of the 140-day ovine foetus were only half of those in comparable maternal tissues. 2. Phosphatidylcholine was the predominant phospholipid in all foetal tissues examined. The most striking difference between foetal and maternal tissues in individual phospholipids was in the heart; foetal heart contained more ethanolamine plasmalogen than choline plasmalogen, whereas in adult tissue the concentration of these was reversed. Sphingomyelin content of foetal brain was only one-sixth of that of maternal brain tissue. 3. Oleic acid (18:1) was the predominant acid in the phospholipid extracted from foetal tissues, except in brain where palmitic acid (16:0) was slightly higher. In phospholipids from adult tissues there was a higher proportion of unsaturated fatty acids (linoleic acid, 18:2, and linolenic acid, 18:3) and a correspondingly lower proportion of oleic acid (18:1). The distribution of fatty acids in the neutral lipid fraction of foetal and maternal tissues was very similar; oleic acid (18:1) was generally the principal component. 4. (14)C derived from [U-(14)C]-glucose and [U-(14)C]fructose infused into the foetal circulation in utero was incorporated into the neutral lipids and phospholipids of heart, liver, kidney, brain and adipose tissue. 5. Phospholipid analysis revealed that the specific activity of phosphatidic acid was higher in liver than in other tissues. The specific activity of phosphatidylethanolamine was less than that of phosphatidylcholine in heart, but in other tissues they were about the same. The specific activities of phosphatidylinositol and phosphatidic acid in brain were very similar and were higher than the other components. The specific activity of phosphatidylserine was highest in liver and brown fat. 6. The pattern of incorporation of (14)C derived from [(14)C]glucose and [(14)C]fructose into foetal neutral lipids was similar. Diglyceride accounted for most of the radioactivity in brain, whereas triglyceride had more label in heart, liver, kidney and fat.     

Nutritional factors affecting quantity and quality of carcass fat in chickens.

Nonpathological fattening of a bird occurs when the amount of energy consumed exceeds its requirements for maintenance and growth. Dietary energy and protein levels, particularly the ratio of these two, are the main dietary factors affecting fatness. Consumption of diets low in protein results in excess energy intake and an increased hepatic lipogenesis. Excess protein has the opposite effect. It also increases the energy expenditure required to dispose of excess amino acids in the body. Severe deficiency of a specific amino acid does not increase fattening. The degree of fattening, particularly of the liver, induced by corticosterone injection is greater in birds fed diets containing a wide energy-to-protein ratio in comparison to a narrow ratio. The content of dietary fat per se does not affect carcass fat concentration although it alters the rate of liver fatty acid synthesis. The dietary fatty acid composition affects the composition of tissue fatty acids. Consumption of diets containing vegetable oils or high in protein increases the degree of unsaturation of tissue fat and thereby its susceptibility to oxidation. Dietary dl-alpha-tocopheryl acetate increases the stability of the lipids of adipose and muscle tissue of chicks with relatively saturated body fat, but the dietary effectiveness of this vitamin in improving the stability of tissues of birds having relatively unsaturated fat is limited.     

Influence of low ambient temperature and dietary lipids on adipose tissue and plasma fatty acid composition of the Japanese quail.

Japanese quail were maintained on synthetic diets containing 15% corn oil, 15% tallow, and zero fat, and were later exposed at 3.5 degrees C for 21 days. A distinct influence of dietary fat composition upon the adipose tissue triglyceride fatty acid composition was detected, but no change in fatty acid composition was produced with cold exposure. The fatty acid composition of adipose tissue from quail acclimatized to winter temperatures showed no trend towards a greater degree of unsaturation. There was no evidence of a gross selective mobilization of certain fatty acids from the depot lipids. Regional variation in the fatty acid composition of avian fats is discussed with respect to the level of food intake and body temperature.     

Activity and mRNA levels of enzymes involved in hepatic fatty acid synthesis and oxidation in mice fed conjugated linoleic acid

The effects of dietary conjugated linoleic acid (CLA) on the activity and mRNA levels of hepatic enzymes involved in fatty acid synthesis and oxidation were examined in mice. In the first experiment, male ICR and C57BL/6J mice were fed diets containing either a 1.5% fatty acid preparation rich in CLA or a preparation rich in linoleic acid. In the second experiment, male ICR mice were fed diets containing either 1.5% linoleic acid, palmitic acid or the CLA preparation. After 21 days, CLA relative to linoleic acid greatly decreased white adipose tissue mass but caused hepatomegaly accompanying an approximate 10-fold increase in the tissue triacylglycerol content irrespective of mouse strain. CLA compared to linoleic acid greatly increased the activity and mRNA levels of various lipogenic enzymes in both experiments. Moreover, CLA increased the mRNA expression of Delta6- and Delta5-desaturases, and sterol regulatory element binding protein-1 (SREBP-1). The mitochondrial and peroxisomal palmitoyl-CoA oxidation rate was about 2.5-fold higher in mice fed CLA than in those fed linoleic acid in both experiments. The increase was associated with the up-regulation of the activity and mRNA expression of various fatty acid oxidation enzymes. The palmitic acid diet compared to the linoleic acid diet was rather ineffective in modulating the hepatic lipid levels or activity and mRNA levels of enzymes in fatty acid metabolism. It is apparent that dietary CLA concomitantly increases the activity and mRNA levels of enzymes involved in fatty acid synthesis and oxidation, and desaturation of polyunsaturated fatty acid in the mouse liver. Both the activation of peroxisomal proliferator alpha and up-regulation of SREBP-1 may be responsible for this.     

Effect of dietary oils containing different amounts of precursor and derivative fatty acids on prostaglandin E2 synthesis in liver, kidney and lung of rats.

The availability of the fatty acids which are precursors of prostaglandins is affected by dietary intake. We have studied, in particular, the effects of dietary intake of lipids with different amounts of precursor and derivative fatty acids on the synthesis of prostaglandin E2 (PGE2) in rat liver, kidney and lung. Fifteen-month-old rats were fed for 3 months diets containing different amounts of oleic, linoleic, alpha linolenic, gamma linolenic and stearidonic acids. The fatty acid compositions of total phospholipids and prostaglandin E2 levels of liver, kidney and lung were investigated. In the organs studied, the intake of lipids at different amount of precursor/derivative fatty acids caused variations in the fatty acid composition of phospholipids. PGE2 showed different values which did not seem directly affected by tissue availability of arachidonate but by the effect of dietary lipids on the metabolic pool of polyunsaturated fatty acids (PUFAs).     

Distribution of radioactive glycerol and fatty acids among adipose tissue triglycerides after administration of glucose-U-14C

Adipose lipid obtained from fed rats 15 or 60 min after injection of radioactive glucose was separated into 10 triglyceride classes of differing fatty acid compositions. The distribution among these classes of total and radioactive triglyceride-glycerol was determined and found to be the same. Thus newly synthesized adipose triglycerides resemble in kind and proportion the triglycerides which exist in the tissue. This finding is in accord with the concept that the structures of adipose triglycerides are stable over long periods and that the turnover rate of the several triglyceride species are similar. After administration of radioactive glucose, the specific activity of saturated fatty acids was higher in the more saturated triglyceride species. These data indicate that newly formed saturated acids do not mix completely with all adipose tissue fatty acids available for esterification. Fatty acids derived from plasma triglyceride influenced the composition of newly synthesized adipose tissue triglyceride and thus constitute an important source of adipose tissue lipid.     

Ten generations of Drosophila melanogaster reared axenically on a fatty acid-free holidic diet

Wild-type Drosophila melanogaster were axenically raised on a completely synthetic fatty acid-free diet for at least ten consecutive generations, confirming that these insects do not require dietary polyunsaturated fatty acids. Capillary column gas-chromatographic analysis of lipids extracted from adults reared on yeast medium showed a peak which cochromatographed with linoleic acid, representing about 1.2% and 0.15% of all fatty acids in phospholipids and triacylglycerols, respectively. In flies reared on the synthetic diet for one generation or for five or more generations, the linoleic acid peak was still present but in about tenfold lower proportions of total fatty acids. This was true of both phospholipid and triglyceride fractions.