Plasma lipid and lipoprotein concentrations of men consuming a low-fat, high-fiber diet.

This study assessed the influence of a low-fat, high-fiber diet on blood lipid concentrations of 42 men with desirable or moderately elevated cholesterol concentrations. A low-fat diet (19% fat, 4% saturated fatty acids, 4.6 g fiber/MJ) was compared with a high-fat diet (41% fat, 15% saturated fatty acids, 2.0 g fiber/MJ) and with subjects' self-selected diets. Substituting the low-fat for the high-fat diet decreased total, low-density-lipoprotein, and high-density-lipoprotein cholesterol by 17-20%. Lipid changes between 6 and 10 wk were minor. A reduction in plasma cholesterol of greater than 0.52 mmol/L was achieved with the low-fat diet in 59% of men changing from their self-selected diets and in 79% changing from the high-fat diet. Percent reduction was independent of subjects' cholesterol classification. Results indicate that significant reductions in plasma cholesterol can be achieved by the majority of men committing to a low-fat, high-fiber diet.     

Lack of effect on blood pressure by polyunsaturated and monounsaturated fat diets.

We carried out a blind highly controlled study to investigate the effects of a sunflower-oil-rich diet and a rapeseed-oil-rich diet on the blood pressure of normotensive subjects. Twenty-nine men and 30 women, average age 30 years (range 18-65) were first fed a baseline diet high in saturated fatty acids (19 E% (percentage of total energy), total fat 36 E%) for 2 weeks. According to the crossover design 30 subjects then received a sunflower oil diet high in polyunsaturated fatty acids (13 E%, total fat 38 E%) followed by a low erucic acid rapeseed oil diet high in monounsaturated fatty acids (16 E%, total fat 38 E%) for 3.5 weeks each. The other 29 subjects had the same diets in reverse order. At the end of the saturated fat period systolic blood pressure was 122.6 +/- 11.5(mean +/- SD) mmHg and diastolic blood pressure 75.4 +/- 7.5 mmHg; during the sunflower oil diet the figures were 119.6 +/- 10.3 and 73.9 +/- 7.4 mmHg, and during the rapeseed oil diet 120.1 +/- 11.2 and 72.6 +/- 6.4 mmHg, respectively. There was a significant difference in diastolic blood pressure only between the two oil diets (P less than 0.01). At the end of a 4 weeks' recovery period the systolic and diastolic blood pressures of the subjects were even lower (118.6 +/- 10.6 and 72.3 +/- 8.3 mmHg, respectively) than during the study. These results suggest that the dietary changes had only minor effects - if any at all - on blood pressure in healthy normotensive subjects.     

Dietary fat and menstrual-cycle effects on the erythrocyte ghost insulin receptor in premenopausal women

The effect of high- and low-fat diets with different levels of fatty acid unsaturation on insulin receptors of erythrocyte ghosts was studied during different phases of the menstrual cycle in 31 healthy premenopausal women. Subjects were divided into two groups and consumed controlled diets containing 39% fat with a ratio of polyunsaturated to saturated fatty acids (P:S) of either 0.30 or 1.00 for four menstrual cycles. They were switched to 19% fat at the same P:S for another four cycles. Fasting blood samples were collected during the follicular and luteal phases. Insulin receptors were measured from right-side-out ghosts. Insulin binding was significantly lower due to fewer receptors when subjects were fed the low-fat, high-carbohydrate diet compared with the high-fat, low-carbohydrate diet. There was no significant effect of level of unsaturation or time of menstrual cycle on insulin binding. Thus, insulin receptors on erythrocytes respond to dietary lipids.     

Flow-mediated vasodilation is not impaired when HDL-cholesterol is lowered by substituting carbohydrates for monounsaturated fat

Low-fat diets, in which carbohydrates replace some of the fat, decrease serum cholesterol. This decrease is due to decreases in LDL-cholesterol but in part to possibly harmful decreases in HDL-cholesterol. High-oil diets, in which oils rich in monounsaturated fat replace some of the saturated fat, decrease serum cholesterol mainly through LDL-cholesterol. We used these two diets to investigate whether a change in HDL-cholesterol would change flow-mediated vasodilation, a marker of endothelial function. We fed thirty-two healthy volunteers two controlled diets in a weeks' randomised cross-over design to eliminate variation in changes due to differences between subjects. The low-fat diet contained 59.7 % energy (en%) as carbohydrates and 25.7 en% as fat (7.8 en% as monounsaturates); the oil-rich diet contained 37.8 en% as carbohydrates and 44.4 en% as fat (19.3 en% as monounsaturates). Average (sd) serum HDL-cholesterol after the low-fat diet was 0.21 (sd 0.12) mmol/l (8.1 mg/dl) lower than after the oil-rich diet. Serum triacylglycerols were 0.22 (sd 0.28) mmol/l (19.5 mg/dl) higher after the low-fat diet than after the oil-rich diet. Serum LDL and homocysteine concentrations remained stable. Flow-mediated vasodilation was 4.8 (SD 2.9) after the low-fat diet and 4.1 (SD 2.7) after the oil-rich diet (difference 0.7 %; 95 % CI -0.6, 1.9). Thus, although the low-fat diet produced a lower HDL-cholesterol than the high-oil diet, flow-mediated vasodilation, an early marker of cardiovascular disease, was not impaired.     

Snack chips fried in corn oil alleviate cardiovascular disease risk factors when substituted for low-fat or high-fat snacks

BACKGROUND: The perception that all high-fat snacks are unhealthy may be wrong. OBJECTIVE: We aimed to assess whether replacing low-fat and high-fat snacks with snacks rich in polyunsaturated fatty acids (PUFAs) and low in saturated and trans fatty acids would improve cardiovascular health. DESIGN: Thirty-three adults participated in a randomized crossover trial of 3 controlled feeding phases of 25 d each in which a different type of snack was provided: low-fat (30.8% of energy from fat, 5.2% of energy from PUFAs), high-PUFA (36.3% of energy from fat, 9.7% of energy from PUFAs), or high-fat (37.9% of energy from fat, 5.8% of energy from PUFAs) snack. RESULTS: Each diet reduced LDL- and total cholesterol concentrations, but reductions were greater with the low-fat and the high-PUFA diets than with the high-fat diet: LDL cholesterol (11.8% and 12.5% compared with 8.8%, respectively; P = 0.03 and 0.01), total cholesterol (10.5% and 10.7% compared with 7.9%, respectively; P = 0.03 and 0.02). The high-PUFA diet tended to reduce triacylglycerol concentrations (9.4%; P = 0.06), and this change was greater than that with the low-fat (P = 0.028) and high-fat (P = 0.0008) diets. CONCLUSIONS: These data show that snack type affects cardiovascular health. Consuming snack chips rich in PUFA and low in saturated or trans fatty acids instead of high-saturated fatty acid and trans fatty acid or low-fat snacks leads to improvements in lipid profiles concordant with reductions in cardiovascular disease risk.     

A high-fat meal increases cardiovascular reactivity to psychological stress in healthy young adults

The consumption of high levels of saturated fat over the course of several weeks may lead to exaggerated cardiovascular reactivity. The consumption of a single high-fat meal has been associated with a transient impairment of vascular function. In a randomized, repeated measures, crossover study we tested whether the consumption of a single high-fat meal by healthy, normotensive participants would affect cardiovascular reactivity when compared with an isocaloric, low-fat meal. Thirty healthy participants ate a high-fat (42 g) and a low-fat (1 g) meal on 2 separate occasions, and their cardiovascular response to 2 standard laboratory stressors was measured. Systolic blood pressure, diastolic blood pressure, and total peripheral resistance were greater in participants following the consumption of the high-fat meal relative to the low-fat meal. The findings of the present study are consistent with the hypothesis that even a single high-fat meal may be associated with heightened cardiovascular reactivity to stress and offer insight into the pathways through which a high-fat diet may affect cardiovascular function.     

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.     

Comparison of Effects of Long-Term Low-Fat vs High-Fat Diets on Blood Lipid Levels in Overweight or Obese Patients: A Systematic Review and Meta-Analysis

Dietary fat plays an important role in the primary prevention of cardiovascular disease, but long-term (≥12 months) effects of different percentages of fat in the diet on blood lipid levels remain to be established. Our systematic review and meta-analysis focused on randomized controlled trials assessing the long-term effects of low-fat diets compared with diets with high amounts of fat on blood lipid levels. Relevant randomized controlled trials were identified searching MEDLINE, EMBASE, and the Cochrane Trial Register until March 2013. Thirty-two studies were included in the meta-analysis. Decreases in total cholesterol (weighted mean difference –4.55 mg/dL [–0.12 mmol/L], 95% CI –8.03 to –1.07; P=0.01) and low-density lipoprotein (LDL) cholesterol (weighted mean difference –3.11 mg/dL [–0.08 mmol/L], 95% CI –4.51 to –1.71; P<0.0001) were significantly more pronounced following low-fat diets, whereas rise in high-density lipoprotein (HDL) cholesterol (weighted mean difference 2.35 mg/dL [0.06 mmol/L], 95% CI 1.29 to 3.42; P<0.0001) and reduction in triglyceride levels (weighted mean difference –8.38 mg/dL [–0.095 mmol/L], 95% CI –13.50 to –3.25; P=0.001) were more distinct in the high-fat diet groups. Including only hypocaloric diets, the effects of low-fat vs high-fat diets on total cholesterol and LDL cholesterol levels were abolished. Meta-regression revealed that lower total cholesterol level was associated with lower intakes of saturated fat and higher intakes of polyunsaturated fat, and increases in HDL cholesterol levels were related to higher amounts of total fat largely derived from monounsaturated fat (of either plant or animal origin) in high-fat diets (composition of which was ～17% of total energy content in the form of monounsaturated fatty acids, ～8% of total energy content in the form of polyunsaturated fatty acids), whereas increases in triglyceride levels were associated with higher intakes of carbohydrates. In addition, lower LDL cholesterol level was marginally associated with lower saturated fat intake. The results of our meta-analysis do not allow for an unequivocal recommendation of either low-fat or high-fat diets in the primary prevention of cardiovascular disease.     

Studies of women eating diets with different fatty acid composition. II. Urinary eicosanoids and sodium,and blood pressure.

Dietary fatty acid composition is known to affect various aspects of eicosanoid metabolism. This research was conducted to evaluate effects of a diet similar to the US average consumption in 1974 (40 en% fat, polyunsaturated to saturated fatty acid ratio, P/S = 0.3) or a diet modified to contain 30 en% fat, P/S = 1.0, on eicosanoid metabolism in young women. Following a period on self-selected diets, women in Nebraska and Iowa were fed the diets for 28-day periods in a crossover design. Urinary eicosanoids, sodium (Na) excretion, and blood pressure were determined. Diet effects were confounded by carryover effects. For urinary eicosanoids the sequence of higher saturated fat (SFA) followed by lower SFA resulted in significantly greater excretion, whereas the reverse order of diets did not cause significant changes. Diastolic blood pressure was not affected by diet, but systolic pressure was lower with the modified diet in the lower to higher-SFA sequence. The change from self-selected to experimental diets does not seem to account for the carryover effects. The interpretation is that linoleate is depleted from tissues more slowly than it is repleted. Effects upon Na excretion were related to SFA more than to linoleate in the diet.     

Studies of women eating diets with different fatty acid composition. II. Urinary eicosanoids and sodium, and blood pressure

Dietary fatty acid composition is known to affect various aspects of eicosanoid metabolism. This research was conducted to evaluate effects of a diet similar to the US average consumption in 1974 (40 en% fat, polyunsaturated to saturated fatty acid ratio, P/S = 0.3) or a diet modified to contain 30 en% fat, P/S = 1.0, on eicosanoid metabolism in young women. Following a period on self-selected diets, women in Nebraska and Iowa were fed the diets for 28-day periods in a crossover design. Urinary eicosanoids, sodium (Na) excretion, and blood pressure were determined. Diet effects were confounded by carryover effects. For urinary eicosanoids the sequence of higher saturated fat (SFA) followed by lower SFA resulted in significantly greater excretion, whereas the reverse order of diets did not cause significant changes. Diastolic blood pressure was not affected by diet, but systolic pressure was lower with the modified diet in the lower to higher-SFA sequence. The change from self-selected to experimental diets does not seem to account for the carryover effects. The interpretation is that linoleate is depleted from tissues more slowly than it is repleted. Effects upon Na excretion were related to SFA more than to linoleate in the diet.     

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.     

Dietary Fats and Blood Pressure: A Critical Review of the Evidence

Comparisons of blood pressure patterns among populations suggest that low-fat diets or consumption of unsaturated fatty acids decrease blood pressure. However, in most single populations dietary fatty acids and total fat, as determined by diet history, are not significantly correlated with blood pressure. Dietary fatty acids, quantitated by levels in adipose tissue or plasma lipoproteins, had no consistent association with blood pressure. Dietary fatty acids and total fat were not predictive of the development of hypertension over four years in a large cohort of nurses in the United States. Although several dietary trials lacking randomized controls suggested effects of dietary fats on blood pressure, 11 of 12 controlled trials showed no significant effects. All seven double-blind trials, and the two trials of longest duration (one and five years), showed no effect of either varying the content of total fat or of exchanging polyunsaturated for saturated fatty acids. In summary, there is little convincing evidence that the amount or type of dietary fat, varied within customary dietary patterns, affects blood pressure levels in persons with normal or mildly elevated blood pressure.     

Effect of synthetic triglycerides of myristic, palmitic, and stearic acid on serum lipoprotein metabolism.

OBJECTIVES: To determine relative effects of diets high in synthetic sources of myristic (14:0), palmitic (16:0) or stearic (18:0) acid on concentrations and metabolism of serum lipoproteins. DESIGN: Eighteen healthy women participated in a three-way cross-over study for five week periods separated by seven week washout periods, diets were assigned in random order. SUBJECTS: Premenopausal women, not on medication, were from three races (Caucasian, African-American, Asian) and four apolipoprotein E phenotype groups (3/3, 3/2, 4/3, and 4/2). INTERVENTION: During the first week the subjects consumed a baseline diet providing 11 energy (en)% saturated fat, 10en% polyunsaturated fat and 14en% monounsaturated fat. Followed by test diets with 19en% saturated fat (including 14en% test saturated fatty acid), 3en% polyunsaturated fat, and 14en% monounsaturated fat for four weeks. Synthetic fats (trimyristin, tripalmitin, and tristearin) were used in blends with natural fats and oils. RESULTS: Mean concentrations of serum total, esterified and LDL cholesterol were significantly lower after 18:0 than after 16:0 (n = 16-18, P < 0.01 for treatment effect). Myristic acid (14:0) had an intermediate effect. Receptor-mediated degradation of 125I-LDL in mononuclear cells obtained from the subjects was lower after 16:0 than after 14:0 and 18:0 (n = 16-18, P=0.05 for treatment effect). Differences in the digestibilities of the fats were not a major factor in the results. Strong cholesterolemic responses to the 16:0 diet were partly explained by apoE phenotype. CONCLUSIONS: As noted previously, stearic acid was neutral compared to 14:0 and 16:0. In contrast to studies involving natural fats, 14:0, fed as a synthetic triglyceride, was less cholesterolemic than 16:0 in a majority of subjects. ApoE phenotype influenced the cholesterolemic response particularly when diets high in 16:0 were eaten.     

Dietary fat and cecal microbial activity in the rat

Weanling rats were fed low-fat (1% w/w safflower oil) or high-fat (1% w/w safflower oil plus 35% w/w beef fat or cocoa butter) diets for 30 days, and the activities of five cecal microbial enzymes were determined. When compared with the low-fat diet, beef fat significantly increased total cecal beta-glucuronidase activity, but cocoa butter, with a similar fatty acid composition, did not. Both high-fat diets significantly decreased total cecal azoreductase, beta-glucosidase, and nitrate reductase activities, but neither significantly affected urease activity. When expressed as specific activities (per 10(11) bacteria), cocoa butter decreased azoreductase, and beef fat caused increases of beta-glucuronidase and urease. Beef fat, but not cocoa butter, significantly reduced cecal bacterial numbers when compared to the low-fat diet. Both high-fat diets led to equivalent reductions in the proportion of aerobic bacteria.     

Dietary fat, insulin sensitivity and the metabolic syndrome

Insulin resistance is the pathogenetic link underlying the different metabolic abnormalities clustering in the metabolic syndrome. It can be induced by different environmental factors, including dietary habits. Consumption of energy-dense/high fat diets is strongly and positively associated with overweight that, in turn, deteriorates insulin sensitivity, particularly when the excess of body fat is located in abdominal region. Nevertheless the link between fat intake and overweight is not limited to the high-energy content of fatty foods; the ability to oxidize dietary fat is impaired in some individuals genetically predisposed to obesity. Insulin sensitivity is also affected by the quality of dietary fat, independently of its effects on body weight. Epidemiological evidence and intervention studies clearly show that in humans saturated fat significantly worsen insulin-resistance, while monounsaturated and polyunsaturated fatty acids improve it through modifications in the composition of cell membranes which reflect at least in part dietary fat composition. A recent multicenter study (KANWU) has shown that shifting from a diet rich in saturated fatty acids to one rich in monounsaturated fat improves insulin sensitivity in healthy people while a moderate alpha-3 fatty acids supplementation does not affect insulin sensitivity. There are also other features of the metabolic syndrome that are influenced by different types of fat, particularly blood pressure and plasma lipid levels. Most studies show that alpha-3 fatty acids reduce blood pressure in hypertensive but not in normotensive subjects while shifting from saturated to monounsaturated fat intake reduces diastolic blood pressure. In relation to lipid abnormalities alpha-3 fatty acids reduce plasma triglyceride levels but in parallel, increase LDL cholesterol. Substitution of unsaturated fat for saturated fat not only reduces LDL cholesterol but contributes also to reduce plasma triglycerides in insulin resistant individuals. In conclusion, there is evidence available in humans indicating that dietary fat quality influences insulin sensitivity and associated metabolic abnormalities. Therefore, prevention of the metabolic syndrome has to be targeted: (1) to correct overweight by reducing the energy density of the habitual diet (i.e., fat intake) and (2) to improve insulin sensitivity and associated metabolic abnormalities through a reduction of dietary saturated fat, partially replaced, when appropriate, by monounsaturated and polyunsaturated fats.     

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.     

Dietary fat and blood pressure: an intervention study on the effects of a low-fat diet with two levels of polyunsaturated fat

The role of dietary fat in human blood pressure control was studied among 84 middle-aged subjects (mainly couples) in two semirural communities in North Karelia, Finland. The families were randomly allocated into two groups that, after a baseline period of 2 weeks, changed their diet for a 12-week intervention period so that the proportion of energy derived from fats was similarly reduced in both groups, from 38 to 24%, but the polyunsaturated/saturated fatty acid (P/S) ratio was increased--from 0.2 to 0.9 in group I and to 0.4 in group II. After the intervention period, both groups switched back to their usual diet for a period of 5 weeks. During the intervention period, total serum cholesterol was reduced by 16% in group I and 14% in group II. Mean body weight and urinary sodium, potassium, calcium, and magnesium excretion changes were small or nonexistent. Mean systolic blood pressure decreased 4 mm Hg in group I (P less than 0.01) and 3 mm Hg in group II (P less than 0.01), and mean diastolic blood pressure decreased 5 mm Hg (P less than 0.001) and 4 mm Hg (P less than 0.01), respectively. The reductions were reversed during the switch-back period (P less than 0.01). These results confirm previous findings of the blood-pressure-reducing effect of a low-fat/high-P/S diet. Although a number of possible confounding factors can be ruled out, the dietary constituent accounting for the blood pressure change cannot be ascertained definitely. The results showed no significant further blood pressure reduction with more than a moderately increased P/S ratio when the saturated fat intake was markedly reduced.     

Essential fatty acids and prostaglandins

The World Health Organization's recommendation for dietary intake of essential fatty acids is 3% of energy (en%) of linoleate. Evidence from rat studies suggests that more than 3 en% is desirable for the regulation of eicosanoid metabolism. With such a low level of available linoleate, humans tend to synthesize more prostanoids than they do with 6% or more energy from linoleate. High rates of prostanoid synthesis probably are deleterious, so that the lower rate commensurate with 6-12 en% of linoleate probably is desirable. The amount of linoleate needed for normal function is influenced by the dietary content of other fatty acids, particularly saturated fats and those of the n-3 family. Vitamin E is necessary for normal metabolism of polyunsaturated fatty acids. In a diet providing sufficient available total energy with 30% as fat, the lower range of linoleate (6-8 en%) probably is sufficient if the saturated fatty acid content is 10% or less. With a greater proportion of saturated fatty acids, more linoleate is needed to maintain a polyunsaturated to saturated fatty acid ratio of 0.7 to 1.0. Some n-3 fatty acids probably are required, and more than a minimal amount may be beneficial. Current recommendations are for 0.5-1.0 en% in a diet containing 5-6 en% of linoleate.     

Influence of Dietary Fats Upon Systolic Blood Pressure in the Rat

Studies were performed to determine whether feeding diets with differing fatty acid content and composition had an influence on systolic blood pressure in the rat. Weanling male rats were fed standard laboratory chow (2.9% fat in total), or synthetic diets (10% fat in total) containing fish oil, butter, coconut oil or corn oil, for 5 weeks. Coconut oil and butter diets were rich in saturated fatty acids, whilst fish oil and corn oil were rich in the n-3 and n-6 unsaturated fatty acids respectively. Systolic blood pressure was measured using an indirect tail-cuff method at the end of the feeding period, and compared to a group of weanling rats.

Feeding the different diets did not alter the growth of the rats, so all animals were of similar weights at the time of blood pressure determination. Control (chow fed) animals, at nine weeks of age, had higher systolic blood pressures than the weanling, baseline control group. Fish oil fed rats had similar pressures to the chow fed rats. Corn oil fed rats had significantly lower systolic pressures than the controls. The rats fed the diets rich in saturated fatty acids (butter and coconut oil) had significantly higher blood pressures than all other groups. Systolic blood pressure was found to be significantly related to the dietary intakes of saturated and unsaturated fatty acids. The dietary intake of linoleic acid was significantly higher in corn oil fed rats than in other groups. Systolic blood pressure was inversely related to linoleic acid intake. Feeding a diet rich in saturated fatty acids significantly increases blood pressure in the rat. A high intake of n-6 fatty acids, and in particular linoleic acid, appears to have a hypotensive effect. Prenatal exposure of the rats to a maternal low protein diet, abolished the hypertensive effects of the coconut oil diet and the hypotensive effect of the corn oil diet upon young adult females. The intrauterine environment may, therefore, be an important determinant of the effects of these fatty acids on blood pressure in later life.     

Effects of alterations in fatty acid intake on the blood pressure of adolescents: the Exeter-Andover Project.

To judge the effect on blood pressure, the ratio of polyunsaturated to saturated fatty acids (P:S) of foods served to students at two boarding high schools was modified alternately at each school for one school year. The average P:S of the diet of males increased from 0.53 to 0.93 during the intervention whereas among females it increased from 0.64 to 0.98. Comparison of repeated systolic and diastolic blood pressure measurements near the end of the school year did not demonstrate a beneficial effect of the dietary fat changes on the blood pressure of these normotensive adolescents. Compared with the blood pressure patterns during control years, the dietary intervention resulted in slightly higher systolic (+0.88 mm Hg; 95% CI -0.66, +2.42) and diastolic (+1.23 mm Hg; 95% CI = +0.04, +2.42) blood pressure readings among males. Among females the intervention resulted in slightly lower systolic (-0.54 mm Hg; 95% CI = -1.95, +0.88) and diastolic (-0.80 mm Hg (95% CI -2.18, +0.58) blood pressure readings.