Journal Name:
Am J Clin Nutr.

Article Title:
Polyunsaturated fatty-acids result in greater cholesterol-lowering and less triacylglycerol elevation than do monounsaturated fatty-acids in a dose-response comparison in a multiracial study-group.

Date Written:
1995

Volume:
62

Number:
2

Page:
392

Author(s):
Howard, B. V.; Hannah, J. S.; Heiser, C. C.; Jablonski, K. A.; Paidi, M. C.; Alarif, L.; Robbins, D.C.; Howard, W.J.

Article:
Epidemiological and experimental data have shown relationships between dietary saturated fatty acids (SFA), hypercholesterolemia, and the development of coronary heart disease (CHD). The National Cholesterol Education Program (NCEP) has recommended a reduction in dietary SFA and cholesterol intake. The efficacy of other types of fatty acids, specifically polyunsaturated (PUFA) and monounsaturated fatty acids (MUFA), on cholesterol concentrations has yet to be established. Recently, several studies have focused on cholesterol lowering by substitution of MUFA for SFA and show plasma cholesterol lowering to be equivalent with diets containing MUFA and PUFA. The objective of the present study was to compare the cholesterol-lowering effects of PUFA and MUFA in a reciprocal, dose-dependent fashion in the context of an NCEP Step 1 diet. All other variables known to substantially affect plasma cholesterol were held constant. The population studied was a group of 63 moderately hypercholesterolemic men and women. After a 6 week baseline diet containing 37% of energy from total fat and 15% from SFA, participants consumed four diets for 6 week each, in random order, containing 10% of energy as SFA; 3%, 6%, 10%, and 14% of energy as PUFA; and 17%, 14%, 10%, and 6% of energy as MUFA. All four test diets were formulated with commonly used foods and differed only in the content of oil blends. The oils were combinations of canola, coconut, corn, olive, and safflower and were supplemented with squalene to the amount found in olive oil so that each contained =4.5 mg squalene/g oil. Dietary cholesterol, fiber, plant sterol, and squalene contents were constant with all four diets.

The results showed a significant progressive decrease in total and low-density-lipoprotein cholesterol across the four diets, with the greatest decrease observed in the diet with the highest content of PUFA. Specifically, as the percent of energy from PUFA increased from 3% to 14% and the amount of MUFA decreased from 17% to 6%, there was a progressively larger decline in total and LDL cholesterol. A small decline in HDL cholesterol was observed on all four diets, with no significant differences between the four diets, although the sample size was not large enough to detect small differences in HDL. The authors postulated that the decline in HDL, which is unexplained metabolically, may be a result of the removal of SFA from the diet and occurs regardless of which unsaturated fatty acid is included. Also a trend between the four diets was noted in triacylglycerol increases, with the smallest occurring in the diets highest in PUFA. The magnitude of the cholesterol-lowering response was greater in those with higher baseline cholesterol and less in those who were more obese.

The magnitude of cholesterol lowering achieved with all four of the low-fat diets in this study was modest, ranging from 2% to 5% of the initial baseline concentrations. This study was designed to compare the influences of MUFA and PUFA, not to assess the cholesterol-lowering abilities of these types of fatty acids as pant of a total dietary plan. The difference in SFAs between baseline and the low-fat diets was only 5%, and cholesterol and fiber contents of the low-fat diets were held equivalent to those of baseline concentrations. Individuals with higher total cholesterol concentrations had the greater declines in cholesterol after all of the diets. The more obese individuals in the study cohort showed the least cholesterol lowering, and also the greatest tendency for elevation in triacylglycerol. Cholesterol lowering may be more difficult to achieve in obese patients.

In conclusion, in an NCEP Step 1 diet containing 30% total fatty acid and 10% SFA, the inclusion of higher proportions of PUFA resulted in a greater decrease in total cholesterol than did the inclusion of MUFA, and a lower response in triacylglycerol. Changes in HDL cholesterol were similar, regardless of which unsaturated fatty acid was used.

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