R M Dougherty

CONTROLLED, RANDOMISED TRIAL OF THE EFFECT OF DIETARY FAT ON BLOOD PRESSURE

57 couples living in two communities of North Karelia, aged 30-50 years, were randomly allocated to three groups. After a 2-week baseline period group I followed a diet low in fat (23% of energy) with a high polyunsaturated/saturated (P/S) ratio (1 . 0), group II reduced daily salt intake from 192 mmol to 77 mmol, and group III (control group) continued the usual diet. After the 6-week intervention period groups I and II reverted to their usual diets. In group I systolic blood pressure declined from 138 . 4 to 129 . 5 mm Hg and diastolic blood pressure from 88 . 9 to 81 . 3 mm Hg during the intervention period; the values rose during switch-back. The fall was greater among hypertensive than among normotensive subjects. In groups II and III the mean blood pressure changed very little during the study.

Effect of Diet on Serum Lipoproteins in a Population with a High Risk of Coronary Heart Disease

The population of North Karelia, a county in Finland, has a high rate of coronary heart disease. It also has a high prevalence of hypercholesterolemia, but whether this reflects a diet rich in animal fats or is a result of genetic factors is unclear. We studied the effect on serum lipoproteins of a low-fat diet with a high ratio of polyunsaturated to saturated fatty acids in 54 middle-aged volunteers in North Karelia. Total serum cholesterol decreased, from 263 +/- 8 mg per deciliter (mean +/- S.E.) to 201 +/- 5 mg in men (P less than 0.0001) and from 239 +/- 8 to 188 +/- 8 mg in women (P less than 0.0001), along with low-density-lipoprotein cholesterol and apoprotein B. High-density lipoprotein decreased from 54 +/- 2 mg per deciliter to 44 +/- 2 in men (P less than 0.0001) and from 56 +/- 3 to 47 +/- 2 mg in women (P less than 0.0001). A small but significant reduction occurred in serum apoprotein A-I, whereas apoprotein A-II increased slightly. The individual changes in low-density-lipoprotein cholesterol correlated with those in high-density-lipoprotein cholesterol. The changes in serum lipids and apoproteins were reversed when the participants returned to their original diets. Our results suggest that the hypercholesterolemia characteristic of this population is due at least in part to dietary factors.

Reduction in blood pressure associated with high polyunsaturated fat diets that reduce blood cholesterol in man

Abstract Ten male and 11 female subjects in the 40–60 age group were fed a 25% fat-calorie diet (Period I) with a P/S ratio of 1. The diet consisted of foods commonly eaten in the U.S.A. and was fed for 40 days, followed by a second 40-day feeding period of 35% fat calories (Period II) with a P/S ratio of 1. A significant decrease in systolic pressure for males and females was observed at the end of the 25% fat-calorie period. The lowered levels of systolic pressure were maintained throughout the 35% fat-calorie period. The diastolic pressure also decreased significantly during Period I; it showed a slight increase, however, during Period II. Plasma cholesterol was also significantly decreased during the first phase of the study and remained lowered during the second phase. Beta cholesterol response paralleled that of total cholesterol, while alpha cholesterol response paralleled that of percentage alpha lipoprotein lipid. Plasma lipoproteins reflected the changes in diet; percentage of pre-beta lipoprotein lipid rose during Period I, while percentage of alpha lipoprotein lipid fell. These results were reversed during Period II. No significant changes in percentage of beta lipoprotein lipid were observed. Blood urea nitrogen was significantly decreased during Period I, followed by a rise after Period II. Blood glucose tended to fall during Period II but rose above prestudy levels after the study. No significant changes were observed in body weights or plasma triglycerides. These results suggest that dietary fat may be one more important factor in elevated blood pressure in otherwise healthy subjects, and its influence should be investigated further in a larger controlled trial with both normo- and hypertensive subjects.

Concentration of dietary n-6 polyunsaturated fatty acids and the human immune status

We examined the effect of the dietary concentration of total fat and n-6 polyunsaturated fatty acids (PUFA) on the immune status of seven healthy women (age 30-65 years) who lived at our metabolic suite. During the first 20 days all subjects consumed a stabilization diet that contained 5.2 energy percent (en%) PUFA and 41.1 en% fat. For the next 40 days, three subjects consumed a diet with 3.2 en% PUFA and 26.1 en% fat, while the remaining four subjects consumed a diet with 9.1 en% PUFA and 31.1 en% fat. For the next 40 days, the diets of the two groups were crossed over. Blastogenesis of peripheral blood mononuclear cells cultured with phytohemagglutinin, concanavalin A, protein A, and pokeweed, and the serum concentrations of complement fractions C3 and C4 were significantly increased upon the feeding of both low fat (26.1 or 31.1 en%) diets compared to the values when the high fat (41.1 en%) diet was fed. None of the indices tested were different when the high PUFA (9.1 en%) and low PUFA (3.1 en%) diets were compared. Our results indicate that low fat diets improve some of the indices of human immune status and that a moderate increase in the level of n-6 PUFA in an otherwise low fat diet does not suppress the human immune system.

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.

Lack of effect on blood pressure by low fat diets with different fatty acid compositions

We compared the effects on blood pressure (BP) of three isocaloric diets with reduced total fat and saturated fatty acid (SAFA) contents but with different proportions of monounsaturated (MUFA) and polyunsaturated fatty acids (PUFA). Diet LF (low fat) provided 20 en% fat (7.9% SAFA, 7.8% MUFA, 3.0% PUFA); diet HP (high PUFA) 26 en% fat (7.5% SAFA, 8.2% MUFA, 8.1% PUFA), and diet HM (high MUFA) 26 en% fat (7.3% SAFA, 14.1% MUFA, 3.2% PUFA). The diets were consumed for 8 weeks (intervention) preceded by 2 weeks and followed by 8 weeks on a habitual diet (baseline/ switchback) with 33–34 en% fat (13–14% SAFA, 12% MUFA, 6% PUFA). Forty-five free-living couples were randomly allocated into the three diet groups, and 43 men and 44 women completed the study. BP was measured weekly with an automatic device. Compliance to diet was monitored by repeated food records, serum fatty acid compositions, and weekly visits to a nutritionist. Both systolic BP (SBP) and diastolic BP (DBP) remained unchanged throughout the study in all three groups. The weight-adjusted mean (s.e.m.) BP values showed changes in SBP of +1.7 (1.8), −0.4 (1.7), and +1.9 (1.9) mm Hg on the LF, HP, and HM diets, respectively (difference NS), and DBP of +0.1 (1.0), +0.6 (1.0), and −0.3 (1.0) mm Hg, respectively (difference NS) between the last 2 weeks of the baseline and intervention periods. The expected fatty acid intakes were achieved, and there were no between-group differences in change of body weight, intake of dietary fibre and potassium, and 24-h sodium excretion. A reduction in total fat and SAFA intake and changes in the proportions of dietary MUFA and PUFA did not affect the BP levels of this normotensive population with an adequate intake of PUFA at baseline.

The role of dietary polyunsaturated fatty acids and prostaglandins in reducing blood pressure and improving thrombogenic indices

Evidence linking dietary fats to blood pressure and thrombogenic indices is reviewed. Results of dietary studies performed at Beltsville, Maryland, have demonstrated that under controlled dietary conditions, i.e., when total fat intake is maintained at 25% fat calories with a P/S ratio of 1, at either a fixed or free-choice salt intake and where the body weight is maintained relatively constant, blood pressure can be lowered and platelet aggregation indices can be improved in men and women in the 40-60 age group. Results of a pilot epidemiologic study of farmers aged 40-45 in Finland and Italy generally confirm the experimental nutrition studies reported above. A possible explanation of these results based on the conversion of linoleic acid to prostaglandins as well as the physiological actions of prostaglandins is discussed.

Effects of reduced-fat diets with different fatty acid compositions on serum lipoprotein lipids and apolipoproteins.

OBJECTIVE To compare the effects on serum lipoproteins of three isocaloric diets with reduced total fat and saturated fatty acid (SFA) contents but with different proportions of monounsaturated (MUFA) and polyunsaturated fatty acids (PUFA). DESIGN A low-fat diet (LF) provided 20 en% fat, 7.9% SFA, 7.8% MUFA, 3.0% PUFA; a high-PUFA diet (HP) 26 en% fat, 7.5% SFA, 8.2% MUFA, 8.1% PUFA; and a high-MUFA diet (HM) 26 en% fat, 7.3% SFA, 14.1% MUFA, 3.2% PUFA. Diets were consumed for 8 weeks in a parallel design, after 2 weeks on a habitual diet with 33-34 en% fat, 13-14% SFA, 12% MUFA, 6% PUFA, and followed by an 8-week period on habitual diet. Compliance to diet was monitored by repeated food records and weekly visits to a nutritionist. SUBJECTS 45 free-living, middle-aged couples who were randomly allocated into the three diet groups; 43 men and 44 women completed the study. RESULTS During the diet periods, a small but significant reduction in body weight of 0.4-1.0 kg was observed in all groups. Similar and significant reductions of mean weight-adjusted serum total cholesterol (4-8%), low-density lipoprotein (LDL) cholesterol (7-11%), and high-density lipoprotein (HDL) cholesterol (8-11%) were observed during the diets. HDL2-cholesterol and apoprotein (apo) A-I levels were reduced whereas HDL3-cholesterol and apoA-II increased. ApoB was significantly decreased during the HM diet only. Serum triglycerides increased significantly during diets LF (25%, P < 0.01) and HP (19%, P < 0.05) but not during diet HM (5%, NS). CONCLUSIONS Reduction in the intake of total fat and saturated fatty acids reduced serum LDL-cholesterol and HDL2-cholesterol concentrations irrespective of the relative proportions of MUFA and PUFA in the diets. The results suggest that there might be some advantage in increasing the proportion of MUFA in low-fat diets, since the HM diet rich in MUFA reduced apoB and slightly attenuated the increase in serum triglycerides that is commonly associated with dietary fat reduction.

Dietary Polyunsaturated Fat and Hypertension

A significant reduction in blood pressure has been observed during low-fat high poly unsaturated fattyacids/saturated fattyacid--ratio diets in a series of studies conducted in the U.S. and Finland. The results suggest the active role of linoleic acid but the effects of decreased intake of saturated fats and the concomitant changes in the intake of other dietary components cannot be ruled out.