Effects of diets varying in fat and P/S ratio on blood pressure and blood lipids in adult men

Nonpharmacologic measures have been increasingly applied to the management of patients with essential hypertension. Published findings concerning dietary factors and blood pressure are reviewed. Specifically, the impact of manipulations of dietary sodium, potassium, magnesium, calcium and dietary fat on blood pressure is considered. The data support a beneficial role for calcium supplementation and sodium restriction, a lesser role for potassium supplementation and a decrease in total and saturated fat intake in at least some hypertensive persons. At this time, no dietary alteration can be recommended for broad application to the population as a whole.

Serum lipids and their acyl group profiles from a group of hypertensive patients with elevated systolic and diastolic pressure were compared with normotensive subjects of matched age, body weight and dietary habits. The level of serum triacylglycerols was elevated in the hypertensive subjects, but the cholesterol level remained normal. The acyl groups of serum triacylglycerols and cholesterylesters from hypertensive subjects indicated a higher proportion of the saturated fatty acids (16:0 and 18:0) and a lower proportion of linoleic acid (18:2) as compared to normal controls. There was no obvious change in the level and acyl group composition of serum phosphatidylcholine between the two groups. Since the hypertensive and normotensive subjects indicated similar dietary habits, the resulting differences in serum lipids reflected an abnormality in the lipolytic process in the hypertensive subjects.

In normal, hypertensive and hyperlipemic subjects, diets supplemented wiht linoleic acid (LA) or α-linolenic acid (LNA) resulted in an increase of the corresponding fatty acids in serum lipids. However, their C₂O-derivatives, the prostaglandin precursors arachidonic acid (AA) and eicosapentaenoic acid (EPA), respectively, were not or only slightly augmented. On the other hand, an EPA-rich diet produced a marked increased of this fatty acid, especially in cholesterol esters. After this diet the decreases of blood pressure and serum lipids were more pronounced when compared with LA- and LNA-rich diets containing a 20-fold higher dose of the polyunsaturated fatty acids. The slow formation of AA and EPA from LA and LNA seems to be a characteristic finding in humans, being different from preferred laboratory animals, for instance, rats. This observation was independent of the presence of risk factors, like arterial hypertension or hyperlipoproteinemia (HLP).

Thirty men, 34 to 61 years old, were fed four diets as follows: diet I — 43% of calories from fat (%FC) with a polyunsaturated to saturated fatty acid (P/S) ratio of 0.3; diet II −25% FC, P/S 0.3; diet III — 43% FC, P/S 1.0; diet IV — 25% FC, P/S 1.0 to study the effects of level and type of fat and of fiber intake on the excretion of selected fatty acids, including linoleic acid (LOA). Each of the four diets was fed for two 6-week periods (after 7-day pre-study and 21-day stabilization periods), with a random switchover at the end of the first 6-week period. Diets, urine, and feces were analyzed during the last 7 days of each period. Of the saturated fatty acids, stearic acid had the lowest apparent digestibility in all diets. The digestibility of oleic acid was high and was similar for all diet groups despite differences in intakes. LOA exeretion was slightly higher (0.81 and 0.86 g/day) with diets III and IV, in which men ate 44 and 24 g of LOA/day, than with diets I and II (0.46 and 0.56 g/day) in which men had 20 and 12 g LOA/day, respectively. Those amounts of LOA excreted represented, however, only a small protion of that eaten. LOA was slightly less digestible in diets II and IV (95.5% and 96.5%), in which the men ate more fiber (11.4 g/day), than in diets I and III (97.7% and 98.2%) in which the men ate less fiber. LOA digestibility was reduced by decreasing fat content of the diet in both high and low P/S diets. Whether those small differences are of physiological importance remains to be seen. Otherwise, this finding emphasizes the need for more research to investigate whether greater absolute amounts of LOA are required when low-fat diets are fed.

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 < 0.01) and 3 mm Hg in group II (P < 0.01), and mean diastolic blood pressure decreased 5 mm Hg (P < 0.001) and 4 mm Hg (P < 0.01), respectively. The reductions were reversed during the switch-back period (P < 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.