Stearic acid absorption and its metabolizable energy value are minimally lower than those of other fatty acids in healthy men fed mixed diets

Compared with other saturated fatty acids, stearic acid appears to have different metabolic effects with respect to its impact on risk for cardiovascular disease. These differences may in part reflect biologically important differences in absorption. This study was designed to compare the absorption and the metabolizable energy value of stearic acid with other fatty acids from mixed diets fed to healthy humans. Healthy men (n = 11) were fed four diets with multiple fat sources that contained approximately 15% of energy (en%) from protein, 46 en% from carbohydrate and 39 en% from fat with 8 en% substitution across diets of the following: trans monoenes, oleic acid, saturated fatty acids (lauric + myristic + palmitic) or stearic acid fed as triacylglycerides. Fats were incorporated into mixed diets comprised of foods typically consumed in the United States. After a 14-d adaptation period, volunteers collected all feces for 7 d. Across diets, absorption of stearic acid (94.1 +/- 0.2%) was lower (P < 0.0002) than that of palmitic acid (97.3 +/- 0.2%) and higher than generally reported. Absorption of lauric, myristic, oleic, linoleic and trans 18:1 monoenes did not differ from each other (>99%) but was higher than that of stearic and palmitic acids (P < 0.001). Metabolizable energy values were similar for all fatty acids. Although absorption of palmitic and stearic acids was affected by diet treatment, the magnitudes of the differences were small and do not appear to be biologically important, at least in terms of lipoprotein metabolism. On the basis of these results, reduced stearic acid absorption does not appear to be responsible for the differences in plasma lipoprotein responses to stearic acid relative to other saturated or unsaturated fatty acids.     

Effect of diets rich in oleic acid, stearic acid and linoleic acid on postprandial haemostatic factors in young healthy men

The aim of the present study was to investigate the effects of stearic acid-, oleic acid- and linoleic acid-rich meals on postprandial haemostasis in young healthy volunteers whose background diets had been controlled for 14 d in a residential study. Six healthy male volunteers were assigned randomly to consume diets rich in stearic acid, oleic acid or linoleic acid for 14 d. On day 15, plasma lipids and haematological variables were measured in the fasted state, and 3 and 7 h (factor VII and prothrombin activation peptide fragments, 1 and 2 only) after consumption of a test meal. Test meals provided 40 % of the subjects' daily energy requirement, with 41 % of the energy provided as fat, 17 % energy as protein and 42 % energy as carbohydrate. The mean fat content of the meal was 45 (sd 5) g. Significant alterations from fasted values were observed for activated factor VII after 7 h), factor VII antigen after 7 h), prothrombin activation peptide fragments 1 and 2 after 7 h) and plasminogen activator inhibitor type 1 activity after 3 h) after consumption of each of the three meals. No significant differences were observed in haemostatic values (factor VII coagulant activity, factor VII antigen, tissue plasminogen activator activity prothrombin activation peptide fragment and plasminogen activator inhibitor type-1) with regard to diet except for activated factor VII at 3 h; values were higher after the oleic acid- and linoleic acid-rich meals than after the stearic acid-rich meal After consumption of each of the three meals, chylomicrons contained proportionately more palmitic acid than the lipids ingested. The present study shows that there are demonstrable changes in postprandial haemostasis when young healthy volunteers with controlled dietary backgrounds are challenged with a physiological fat load. These changes are independent of the fatty acid composition of the test meals.     

Whole body oxidation of dietary fatty acids: implications for energy utilization

Whole body oxidation of dietary stearic, oleic, and linoleic acid was measured in males consuming a test diet of normal foods at a level commensurate with energy requirements for 16 days. Labeled stearic, oleic or linoleic acid was consumed with the breakfast meal on either day 8, 11, or 14. Breath samples were analyzed for total CO2 content and 13CO2 abundance. Breath enrichment of 13CO2 after ingestion of labeled substrate was calculated over background 13C abundance with diet only and expressed as fraction of substrate dose absorbed. Fecal excretion of labeled and diet fatty acids was determined for pooled stool collections. Stearic, oleic, and linoleic acids were separated from fecal fat extracts and combusted to determine 13CO2 enrichment over background. Both dietary and labeled stearic acid were less well absorbed than either oleic or linoleic acids. At hours 7-9 after ingestion of the labeled breakfast, significant differences in percent of absorbed dose excreted in breath were observed between all three fatty acids. Significant differences were observed in apparent amounts of labeled oleate, linoleate, and stearate oxidized after 3 to 9 h. This difference in fatty acid oxidation challenges the assumption that dietary fat is oxidized at a rate independent of its long chain fatty acid composition.     

Small differences in the effects of stearic acid, oleic acid, and linoleic acid on the serum lipoprotein profile of humans

BACKGROUND: Studies have suggested that oleic and stearic acids, as well as oleic and linoleic acids, have comparable effects on the serum lipoprotein profile. If so, then substituting these three 18-carbon fatty acids for each other would result in similar effects on the serum lipoprotein profile. OBJECTIVE: The aim of this study was to compare simultaneously the effects of stearic, oleic, and linoleic acids on the serum lipoprotein profile of healthy subjects. DESIGN: Forty-five subjects (27 women and 18 men) consumed in random order 3 experimental diets, each for 5 wk. The diets provided 38% of energy from fat, of which 60% was supplied by the experimental fats. The dietary compositions of the diets were the same, except for 7% of energy, which was provided by stearic, oleic, or linoleic acid. At the end of each intervention period, serum lipid and lipoprotein concentrations were measured. In addition, LDL, HDL, and VLDL particle sizes and particle concentrations of lipoprotein subclasses were analyzed by nuclear magnetic resonance spectroscopy. RESULTS: No significant diet-induced changes in serum lipids and lipoproteins were found. Mean (+/-SD) serum LDL-cholesterol concentrations were 3.79 +/- 0.91, 3.71 +/- 0.79, and 3.65 +/- 0.91 mmol/L with the high-stearic acid, high-oleic acid, and high-linoleic acid diets, respectively (P = 0.137 for diet effects). Mean (+/-SD) HDL-cholesterol concentrations were 1.45 +/- 0.43, 1.46 +/- 0.45, and 1.46 +/- 0.44 mmol/L (P = 0.866). LDL, HDL, and VLDL particle sizes and lipoprotein subclass distributions also did not differ significantly between the 3 diets. CONCLUSIONS: With realistic intakes of stearic, oleic, and linoleic acids, differences between their effects on the serum lipoprotein profile are small.     

Modification of plasma and hepatic lipids of guinea pigs by feeding high oleic acid pork compared with regular pork.

Meat from such monogastric animals as swine can be modified to substitute monounsaturated fatty acids for saturated fatty acids. Because monounsaturated fatty acids have a beneficial effect on serum lipids as compared with saturated fatty acids, the objective of this study was to assess the effect of modified pork as compared with regular pork on serum and hepatic lipids. Guinea pigs were fed diets containing pork from control diet-fed hogs or from hogs fed a diet containing high oleic acid sunflower oil. The pork provided almost all of the fat in the diets at the level of 4 and 15 g/100 g diet, 10 or 34% energy. The high oleic pork muscle and fat contained 26 and 46% less palmitic and stearic acids (the primary saturated fatty acids), respectively, and 31 and 29% more oleic acid (the primary monounsaturated fatty acid) than the regular pork muscle and fat, respectively. Cholesterol concentration of diets ranged from 0.06 to 0.08% of the diet. Although total serum cholesterol, HDL cholesterol and triglyceride concentrations did not differ due to type of pork, results indicated that serum LDL cholesterol was lower (15%) and hepatic cholesterol was greater (15%) in the high oleic pork, 15% fat group as compared with the control pork 15% fat group. Also, serum LDL cholesterol concentration was higher in the groups fed 15% fat compared with those fed 4% fat. In this study pork modified to have more oleic acid and less saturated fatty acids had a positive effect on tissue lipids when fed to animals.     

Stearic, oleic, and linoleic acids have comparable effects on markers of thrombotic tendency in healthy human subjects

Because human studies concerning the effects of stearic acid on thrombotic tendency are inconsistent, we compared the effects of stearic acid with those of its unsaturated derivatives, oleic acid and linoleic acid. In this randomized, crossover study, 45 subjects (27 women and 18 men) consumed, in random order, 3 experimental diets, each for 5 wk. Diets contained approximately 38% of energy as fat. Dietary compositions were the same except for 7% of energy from stearic, oleic, or linoleic acids. At the end of each period, ex vivo and in vitro platelet aggregation, and variables of coagulation, fibrinolysis, and hematology were evaluated. In men, ex vivo platelet aggregation time as measured by filtragometry (P = 0.036 for diet effects) was favorably prolonged during consumption of the linoleic acid diet compared with the stearic acid diet (P = 0.040), but there was no difference with consumption of the oleic acid diet (P = 0.198). In vitro platelet aggregation induced by collagen and ADP, and variables of coagulation (factor VII amidolytic activity and concentrations of fibrinogen and prothrombin fragment 1 and 2) and fibrinolysis [plasminogen activator inhibitor (PAI) activity and concentrations of tissue plasminogen activator (tPA)/PAI-1 complexes] did not differ among the 3 diets. The mean platelet volume of the subjects decreased during consumption of the stearic acid diet by 0.32 fL compared with the oleic acid diet (P < 0.001) and by 0.35 fL compared with the linoleic acid diet (P < 0.001). In conclusion, our results do not suggest that stearic acid is highly thrombogenic compared with oleic and linoleic acids.     

A stearic acid-rich diet improves thrombogenic and atherogenic risk factor profiles in healthy males

OBJECTIVE: To determine whether healthy males who consumed increased amounts of dietary stearic acid compared with increased dietary palmitic acid exhibited any changes in their platelet aggregability, platelet fatty acid profiles, platelet morphology, or haemostatic factors. DESIGN: A randomized cross-over dietary intervention. Subjects and interventions: Thirteen free-living healthy males consumed two experimental diets for 4 weeks with a 7 week washout between the two dietary periods. The diets consisted of approximately 30% of energy as fat (66% of which was the treatment fat) providing approximately 6.6% of energy as stearic acid (diet S) or approximately 7.8% of energy as palmitic acid (diet P). On days 0 and 28 of each dietary period, blood samples were collected and anthropometric and physiological measurements were recorded. RESULTS: Stearic acid was increased significantly in platelet phospholipids on diet S (by 22%), while on diet P palmitic acid levels in platelet phospholipids also increased significantly (8%). Mean platelet volume, coagulation factor FVII activity and plasma lipid concentrations were significantly decreased on diet S, while platelet aggregation was significantly increased on diet P. CONCLUSION: Results from this study indicate that stearic acid (19g/day) in the diet has beneficial effects on thrombogenic and atherogenic risk factors in males. The food industry might wish to consider the enrichment of foods with stearic acid in place of palmitic acid and trans fatty acids.     

The effects of varying dietary fat on the nutrient intake in male and female runners

OBJECTIVE: The present study examined the effects of varying dietary fat levels on nutrients in female and male endurance runners. METHODS: Three diets (low, medium and high fat) were designed for each subject using their food preferences and three-day food records. Each diet was eaten for 28 to 31 days. The diets were self-selected from seven-day sample menus. Twelve male and 13 female runners between 18 and 55 years of age who averaged 42 miles/week participated in the study. Daily food intakes, activity records and weekly palatability/hunger scales were completed. RESULTS: Dietary fat intakes, as a percent of total energy intake (%E), averaged 17%E, 31%E, and 44%E on the low, medium and high fat diets, respectively. Energy consumption was less than their estimated energy expenditure (EEE) on all diets. On the low fat diet, the female runners were consuming approximately 60% of their EEE. As dietary fat increased, the difference between calorie intake and estimated energy expenditure became less and the subjects were less hungry on the two higher fat diets. For all subjects, as energy intakes increased, so did carbohydrate intake. Therefore, carbohydrate intake was not different on the two lower fat diets. Irrespective of gender, calcium and zinc intakes, which were below 1989 RDAs, increased with increasing fat intakes, between the low and medium fat diets. Zinc intake was also higher on the highest fat diet. Essential fatty acid intakes for females on the low fat diet were less than 2.5%E. Half of the female runners ate less than the RDA of calcium and zinc on the low fat diet and Fe on the medium fat diet. CONCLUSION: This study suggests that endurance runners may not be consuming enough calories on a low fat diet and that increasing dietary fat increased energy consumption. On the low fat diet, essential fatty acids and some minerals (especially zinc) may be too low. A low fat diet could compromise health and performance.     

Palmitic and stearic acids similarly affect plasma lipoprotein metabolism in cynomolgus monkeys fed diets with adequate levels of linoleic acid

This study was designed to evaluate whether the exchange of specific saturated fatty acids [SFA; palmitic acid (16:0) for stearic acid (18:0)] would differentially affect plasma lipids and lipoproteins, when diets contained the currently recommended levels of total SFA, monounsaturated fatty acids and polyunsaturated fatty acids (PUFA). Ten male cynomolgus monkeys were fed one of two purified diets (using a cross-over design) enriched either in 16:0 (palmitic acid diet) or 18:0 (stearic acid diet). Both diets provided 30% of energy as fat (SFA/monounsaturated fatty acid/PUFA: 1/1/1). The palmitic acid and stearic acid diets were based on palm oil or cocoa butter (59% and 50% of the total fat, respectively). By adding different amounts of sunflower, safflower and olive oils, an effective exchange of 16:0 for 18:0 of approximately 5% of energy was achieved with all other fatty acids being held constant. Monkeys were rotated through two 10-wk feeding periods, during which time plasma lipids and in vivo lipoprotein metabolism (following the simultaneous injection of (131)I-LDL and (125)I- HDL were evaluated). Plasma triacyglycerol (0.40 +/- 0.03 vs. 0.37 +/- 0.03 mmol/L), plasma total cholesterol (3.59 +/- 0.18 vs. 3.39 +/- 0.23 mmol/L), HDL cholesterol (1.60 +/- 0.16 vs 1.53 +/- 0.16 mmol/L) and non-HDL cholesterol (2.02 +/- 0.26 vs. 1.86 +/- 0.23 mmol/L) concentrations did not differ when monkeys consumed the palmitic acid and stearic acid diets, respectively. Plasma lipoprotein compositional analyses revealed a higher cholesteryl ester content in the VLDL fraction isolated after consumption of the stearic acid diet (P < 0.10), as well as a larger VLDL particle diameter (16.3 +/- 1.7 nm vs. 13.8 +/- 3.6 nm; P < 0.05). Kinetic analyses revealed no significant differences in LDL or HDL transport parameters. These data suggest that when incorporated into diets following current guidelines, containing adequate PUFA, an exchange of 16:0 for 18:0, representing approximately 11 g/(d.10.46 mJ) [ approximately 11 g/(d.2500 kcal)] does not affect the plasma lipid profile and has minor effects on lipoprotein composition. Whether a similar effect would occur in humans under comparable dietary conditions remains to be established.     

The effect of six different C18 fatty acids on body fat and energy metabolism in mice

We studied the effects of five high-fat semi-purified diets varying at a 4% (w/w) level in either stearic, oleic, linoleic, alpha-linolenic, or gamma-linolenic acid on body fat and energy metabolism in BALB/c mice. A diet containing caprylic, capric, lauric, and myristic acid was used as a reference diet and a diet with 4% conjugated linoleic acid (CLA) was used as a positive control as it is known to effectively lower body fat in mice. The diets were fed for 35 d. Body fat was significantly lower in the CLA group than in the other groups but was not significantly different among the non-CLA groups. Among the non-CLA groups, the linoleic acid group tended to have the highest and the alpha-linolenic acid group the lowest proportion of body fat. In energy-balance studies, the percentage of energy intake that was stored in the body was significantly lower in the CLA group compared with the other dietary groups. The percentage of energy intake eliminated in excreta was highest in the stearic acid group followed by the gamma-linolenic acid group. These results were reflected in apparent fat digestibility, which was lowest in the stearic acid group. The percentage of energy intake expended as heat was highest in the CLA-fed mice. The results of the present study suggest that body fat and energy accretion in mice fed diets containing different C18 fatty acids is by far the lowest with CLA and that linoleic acid produced the highest fat intake and energy accretion.     

Total fat intake modifies plasma fatty acid composition in humans

Plasma fatty acid composition reflects dietary fatty acids. Whether the total fat content of the diet alters the fatty acid composition of plasma phospholipid, cholesteryl ester, triacylglycerol and free fatty acids is unknown. To evaluate the effects of low versus high fat diets on plasma fatty acids, a 12-wk, randomized, crossover, controlled feeding trial was conducted in healthy men and women with isoenergic low fat (20% energy) and high fat (45% energy) diets containing constant proportions of fatty acids. Ten subjects consumed one experimental diet for 28 d, their usual diet for 4 wk and the alternate experimental diet for 28 d. Endpoint measures of plasma fatty acids were determined at the end of each experimental period. The effects of the two diets were compared within subjects by analysis of variance. Plasma fatty acids (%) varied in response to total dietary fat with significantly greater total polyunsaturated fat, (n-6) and 18:2(n-6) levels in phospholipids and cholesteryl esters after high fat dietary consumption. The low fat diet was associated with significantly greater total (n-3) fatty acids, 20:5(n-3) and 22:6(n-3) levels in plasma phospholipid fatty acids and cholesteryl esters. Consumption of a low fat diet alters fatty acid patterns in a manner similar to that observed with feeding of (n-3) long-chain fatty acids. This change is likely related to decreased competition for the enzymes of elongation and desaturation, with reduced total intake of 18:2(n-6) favoring elongation and desaturation of available (n-3) fatty acids.     

Short-term diets enriched in stearic or palmitic acids do not alter plasma lipids,platelet aggregation or platelet activation status

OBJECTIVE: To determine whether healthy males who consumed increased amounts of dietary stearic acid compared with increased dietary palmitic acid through the consumption of commercially available foods, exhibited any changes in plasma lipids, platelet aggregation or platelet activation status. DESIGN: A randomised cross-over dietary intervention. SUBJECTS AND INTERVENTIONS: Nine free-living healthy males consumed two experimental diets (stearic acid enriched, diet S, and palmitic acid enriched, diet P) for 3 weeks in a randomised cross-over design separated by a 3 week washout phase. The diets consisted of approximately 30% of energy as fat (30% of which was derived from the treatment diets) providing approximately 13 g/day as stearic acid and 17 g/day as palmitic acid on diet S and approximately 7 g/day as stearic acid and 22 g/day as palmitic acid on diet P. The dietary ratio of stearic to palmitic acids was 0.76 on diet S compared with 0.31 on diet P. Blood samples were collected on days 0 and 21 of each dietary period. RESULTS: LDL cholesterol levels and platelet aggregation response to the agonist ADP were significantly decreased (P<0.025) in subjects on diet S compared with day 0. Apart from that, there were no significant changes in plasma lipids, platelet aggregation, mean platelet volume and platelet reactivity between diets. There were no significant changes in stearic or palmitic acid levels in plasma phospholipid or triacylglycerol. There was a significant difference in palmitic acid levels in platelet phospholipids between the two diets. CONCLUSIONS: Use of commonly available foods led to a 27% increase in stearic acid (diet S) and a 19% increase in palmitic acid (diet P), on diets S and P respectively, and no significant differences between the two diets in plasma lipoprotein concentrations, platelet aggregation or platelet activation status.     

Effect of low carbohydrate diets during pregnancy on embryogenesis and fetal growth and development in rats

Effects in pregnant rats of feeding diets specifically deficient in carbohydrate were studied. The dietary nonprotein energy source was lipid, provided as intact fat (soybean oil) or a fatty acid mixture (edible oleic acid) or a combination of these. These diets provided 9.5% casein protein, which was shown to be minimally adequate in both the lipid-based experimental diets and the high carbohydrate control diet. The diets were fed from mating through d 21 of pregnancy, and pups were delivered by cesarean section. The soybean oil-based zero-carbohydrate diet supported embryogenesis and produced at term normal numbers of normal appearing pups of body weight lower than that of pups from the high carbohydrate control diet. In contrast, the oleic acid-based zero-carbohydrate diet failed to maintain pregnancy, indicating a requirement for carbohydrate or intact fat or both. To maintain pregnancy to term required both 5-10% intact fat and 4% carbohydrate as glucose or its equivalent amount of glycerol from lipid. From feeding graded levels of glucose in fatty acid based diets containing 5-10% intact fat as soybean oil, the carbohydrate requirement was found to be 6-8% glucose to sustain maternal food intake and weight gain and to produce normal fetal weight at term, and 12% glucose to provide approximately half the fetal liver glycogen levels in controls fed a high carbohydrate diet. These experiments have produced the first evidence of the quantitative requirement for carbohydrate for embryogenesis and fetal growth and development in the pregnant rat dam.     

Influence of short-term dietary measures on dioxin concentrations in human milk.

Breast-feeding may expose infants to high levels of toxic chlorinated dioxins. To diminish intake of these lipophilic compounds by the baby, two diets were tested for their ability to reduce concentrations of dioxins in human milk. The diets were a low-fat/high- carbohydrate/low-dioxin diet. (about 20% of energy intake derived from fat) and a high fat /low-carbohydrate/low-dioxin diet. These diets were tested in 16 and 18 breast-feeding women, respectively. The test diets were followed for 5 consecutive days in the fourth week after delivery. Milk was sampled before and at the end of the dietary regimen, and dioxin concentrations and fatty acid concentrations were determined. Despite significant influences of these diets on the fatty acid profiles, no significant influence on the dioxin concentrations in breast milk could be found. We conclude that short-term dietary measures will not reduce dioxin concentration in human milk.     

Fatty acid composition of skeletal muscle reflects dietary fat composition in humans

BACKGROUND: It is still unknown whether the fatty acid composition of human skeletal muscle lipids is directly influenced by the fat composition of the diet. OBJECTIVE: We investigated whether the fatty acid composition of the diet is reflected in the fatty acid profile of skeletal muscle phospholipids and triacylglycerols. DESIGN: Thirty-two healthy adults (25 men and 7 women) included in a larger controlled, multicenter dietary study were randomly assigned to diets containing a high proportion of either saturated fatty acids (SFAs) [total fat, 36% of energy; SFAs, 18% of energy; monounsaturated fatty acids (MUFAs), 10% of energy] or MUFAs (total fat, 35% of energy; SFAs, 9% of energy; MUFAs, 19% of energy) for 3 mo. Within each diet group, there was a second random assignment to supplementation with fish oil capsules [containing 3.6 g n-3 fatty acids/d; 2.4 g eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3)] or placebo. A muscle biopsy sample was taken from the vastus lateralis muscle after the diet period. Parallel analyses of diet and supplementation effects were performed. RESULTS: The proportions of myristic (14:0), pentadecanoic (15:0), heptadecanoic (17:0), and palmitoleic (16:1n-7) acids in the skeletal muscle phospholipids were higher and the proportion of oleic acid (18:1n-9) was lower in the SFA group than in the MUFA group. The proportion of total n-3 fatty acids in the muscle phospholipids was approximately 2.5 times higher, with a 5 times higher proportion of eicosapentaenoic acid (20:5n-3), in subjects supplemented with n-3 fatty acids than in those given placebo. Similar differences were observed in the skeletal muscle triacylglycerols. CONCLUSION: The fatty acid composition of skeletal muscle lipids reflects the fatty acid composition of the diet in healthy men and women.     

Beef tallow increases the potency of conjugated linoleic acid in the reduction of mouse mammary tumor metastasis

Animal studies consistently show that dietary conjugated linoleic acid (CLA) reduces mammary tumorigenesis including metastasis. Relatively low concentrations of CLA are required for those effects, and a threshold level exists above which there is no added reduction. We reasoned that the concentration of CLA required to effectively alter mammary tumor metastasis may be dependent on the type of dietary fat because select fatty acids can enhance or suppress normal or malignant cell growth and metastasis. For this study, the diets (a total of 12 different groups) differed in fatty acid composition but not in energy from fat (40%). In experiments involving spontaneous metastasis, mice were fed for 11 wk; in experiments in which mice were injected i.v. with tumor cells, they were fed for 7 wk. Mice were then assessed for the effect of CLA concentration on mammary tumorigenesis. Mammary tumor growth was not altered, but metastasis was significantly decreased when beef tallow (BT) replaced half of a defined vegetable fat blend (VFB). That blend reflects the typical fat content of a Western diet. In addition, that same VFB:BT diet lowered the concentration of CLA required to significantly decrease mammary tumor metastasis from 0.1% of the diet to 0.05%. A diet in which corn oil replaced half of the VFB did not lower the threshold from 0.1 to 0.05%. In vitro, the main fatty acid in vegetable oil, linoleic acid, reduced the efficacy of CLA toxicity on mammary tumor cells in culture. Alternatively, fatty acids normally found in BT, such as oleic, stearic, and palmitic acids, either did not change or enhanced the cytolytic effects of CLA isomers on mouse mammary tumor cells in culture. These data provide evidence that dietary BT, itself with negligible levels of CLA, may increase the efficacy of dietary CLA in reducing mammary tumorigenesis.     

Effect on blood pressure of two diets differing in total fat but not in saturated and polyunsaturated fatty acids in healthy volunteers

The effects of a low-fat, carbohydrate-rich and a high-fat, olive-oil-rich diet on blood pressure were studied under strict dietary control. Forty-seven healthy normotensive men and women were fed a diet high in saturated fatty acids (20 en%) and total fat (38 en%) for 17 d. Twenty-four subjects then received a low-fat, carbohydrate-rich diet (total fat 22 en%) and the other 23 a high-fat, olive-oil-rich diet (oleic acid 24 en%, total fat 41 en%) for 36 d. Both test diets had the same level of saturated fatty acids (7-10 en%) and linoleic acid (4 en%). Systolic blood pressure fell by 2.3 and diastolic by 4.7 mm Hg in the carbohydrate group and by 2.7 and 4.4 mm Hg in the olive-oil group, respectively (differences between diets groups not significant). These results suggest that a high-fat diet rich in monounsaturated fatty acids has no deleterious effect on blood pressure in healthy normotensive subjects in comparison with a low-fat, carbohydrate-rich diet.     

Effect of isoenergetic low- and high-carbohydrate diets on substrate kinetics and oxidation in healthy men

The effect of diet composition on post-absorptive (15 h fast) fatty acid and glucose metabolism was investigated in five healthy men after 2 weeks on a low-carbohydrate (Low-CHO) diet (30 % energy intake from carbohydrates, 55 % from fat, 15 % from protein) and after 2 weeks on a high-carbohydrate (High-CHO) diet (energy intake 75, 10 and 15 % from carbohydrates, fat and protein respectively). The diets were isoenergetic and comprised real foods. Stable-isotope tracer methodology and indirect calorimetry were employed to measure glucose and fatty acid kinetics and oxidation. The relative contribution of carbohydrate to the total energy expenditure was significantly higher after the High-CHO diet. After the High-CHO diet, total and plasma fatty oxidation (2.4 (SE 0.7) and 2.1 (SE 0.4) micromol/kg per min respectively) were significantly lower than after the Low-CHO diet (4.8 (SE 0.5) and 4.6 (SE 0.8) micromol/kg per min for total and plasma fatty oxidation respectively). The rate of appearance (Ra) of non-esterified fatty acids (NEFA) in plasma and the arterial NEFA concentration were both significantly lower following the High-CHO than the Low-CHO diet. However, even after the High-CHO diet, NEFA Ra was threefold higher than plasma fatty acid oxidation. Thus, the decrease in fatty acid oxidation after consumption of a high-carbohydrate diet for 2 weeks in healthy men is unlikely to result from decreased fatty acid delivery to the tissues. Glucose Ra and arterial plasma glucose concentration were similar after the two diets. After the High-CHO diet, arterial lactate concentration was higher and total carbohydrate oxidation rate well exceeded glucose Ra in plasma. Therefore, alterations in intracellular mechanisms may limit fatty acid oxidation after high-carbohydrate diets.     

Effects of dietary trans fatty acids on blood pressure in normotensive subjects.

Consumption of essential fatty acids of the (n-6) series may affect blood pressure in man. Trans fatty acids in the diet interfere with the metabolism of essential fatty acids in rats. We therefore measured the effect of dietary trans fatty acids on blood pressure in 25 men and 34 women. Each subject consumed, in random order, three mixed natural diets, each for three weeks. The composition of the three diets was similar, except for 10.4 per cent of energy, which was provided by either oleic acid, trans fatty acids, or saturated fatty acids. The intake from polyunsaturated fatty acids was 3.4 per cent on the saturated-fat diet and 4.6 per cent on the other two diets. On the oleic-acid diet systolic blood pressure was 113 +/- 12.8 mmHg and diastolic blood pressure 66 +/- 8.3 mmHg, on the trans-fatty-acid diet 112 +/- 12.2 mmHg and 67 +/- 8.1 mmHg, and on the saturated-fat diet 112 +/- 12.6 mmHg and 67 +/- 8.1 mmHg. No significant differences were observed in blood pressure levels between the three diets. We conclude that neither trans nor saturated fatty acids influence blood pressure levels in normotensive subjects relative to oleic acid.     

Effect of individual dietary fatty acids on postprandial activation of blood coagulation factor VII and fibrinolysis in healthy young men

BACKGROUND: Hypertriglyceridemia may represent a procoagulant state involving disturbances to the hemostatic system. Plasminogen activator inhibitor type 1 (PAI-1) is increased in the presence of hypertriglyceridemia. Free fatty acids (FFAs) in plasma may promote factor VII (FVII) activation. OBJECTIVE: We tested the hypothesis that FVII activation would be less after consumption of saturated fatty acids than after other fatty acids. DESIGN: The effects of 6 matching dietary test fats, rich in stearic (S), palmitic (P), palmitic + myristic (M), oleic (O), trans 18:1 (T), and linoleic (L) acid, respectively, on the postprandial lipid and hemostatic profile (after 2, 4, 6, and 8 h) were investigated in 16 young men. High-fat meals (1 g fat/kg body wt; 43% from the test fatty acid) were served in the morning on 6 separate days. RESULTS: All fats increased FVII activation. The S fat resulted in a lower increase in activated FVII (FVIIa) than did the T fat and in a lower FVII coagulant activity (FVII:c) than did the O fat (P < 0.02, diet x time interaction). When the data were pooled, the saturated (S, P, and M) test fats resulted in a smaller postprandial increase in FVIIa (P = 0.036, diet effect), a smaller increase in FVII:c (P < 0.001, diet x time interaction), a greater rise in tissue plasminogen activator concentrations (P = 0.028, diet effect), and a tendency to a greater postprandial decline in PAI-1 (P = 0.06, diet effect) compared with the unsaturated test fats (O, T, and L). The increase in FVIIa was not significantly associated with the level of lipemia, plasma FFAs, or plasma lipoprotein lipase activity. CONCLUSION: Our results indicate a lesser increase in FVIIa after the consumption of saturated fats, especially the S fat, than after unsaturated test fats.