Journal Name:
J. Nutr.
Article Title:
Decreasing Linoleic Acid with Constant a-Linolenic Acid in Dietary Fats Increases (n-3) Eicosapentaenoic Acid in Plasma Phospholipids in Healthy Men
Date Written:
2007
Volume:
137
Number:
0
Page:
945
Author(s):
Liou, Y.A.; King, D.J.; Zibrik, D.; Innis, S.M.
Article:
High linoleic acid (LA) intakes have been suggested to reduce a-linolenic acid [ALA, 18:3(n-3)] metabolism to eicosapentaenoic acid [EPA, 20:5(n-3)] and docosahexaenoic acid [DHA, 22:6(n-3)], and favor high arachidonic acid [ARA, 20:4(n-6)].
A randomized cross-over study with men (n = 22) was conducted to compare the effect of replacing vegetable oils high in LA with oils low in LA in foods, while maintaining constant ALA, for 4 week each, on plasma (n-3) fatty acids.
Non vegetable sources of fat, except fish and sea foods, were unrestricted. Plasma phospholipid fatty acids at wk 0, 2, 4, 6, and 8, and triglycerides, cholesterol, serum C reactive protein (CRP), and IL-6, and platelet aggregation at wk 0, 4, and 8. LA and ALA intakes resulted in diets with LA:ALA ratios of 4:1 and 10:1 during the low and high LA diets, respectively. The plasma phospholipid LA was higher and EPA was lower during the high than during the low LA diet period, but DHA declined over the 8-wk period. The plasma phospholipid ARA:EPA ratios were 20.7 and 12.9 after 4 wk consuming the high or low LA diets, respectively; LA was inversely associated with EPA but positively associated with ARA:EPA. LA intake did not influence ALA, ARA, DPA, DHA, or total, LDL or HDL cholesterol, CRP or IL-6, or platelet aggregation. In conclusion, high LA intakes decrease plasma phospholipid EPA and increase the ARA:EPA ratio, but do not favor higher AA.
Dietary intakes of LA have increased over the last century from 0.3% of energy in the early 1900s and now contributes 85–90% of total polyunsaturated fatty acids and 5–7% of dietary energy in the U.S., Canada, and many westernized nations due largely to an increased consumption of LA-rich vegetable oils. The favorable effects of (n-3) fatty acids in reducing the risk of CVD, possibly involving multiple mechanisms including eicosanoid metabolism, inflammatory mediators, platelet aggregability, hemostatic and myocardial function, and plasma lipids, are well known. *The objective of this study was to determine whether replacing vegetable oils and fats in bakery and snack foods, margarines, and cooking and salad oils with oils low in LA, compared with oils high in LA, increases (n-3) fatty acids and lowers (n-6) fatty acids in plasma lipids of adult men. To address this objective, foods using high or low LA oils to provide 55% of total dietary fat intakes, and a total dietary intake of 3.8 or 10.5% energy from LA, with a constant intake of 1% energy ALA, were fed to 22 healthy young male subjects. The design was a randomized cross-over study with men.
Non vegetable sources of fat, except fish and sea foods, were unrestricted. Plasma phospholipid fatty acids at wk 0, 2, 4, 6, and 8, and triglycerides, cholesterol, serum C reactive protein (CRP), and IL-6, and platelet aggregation at wk 0, 4, and 8. LA and ALA intakes resulted in diets with LA:ALA ratios of 4:1 and 10:1 during the low and high LA diets, respectively.
The plasma phospholipid LA was higher and EPA was lower during the high than during the low LA diet period, but DHA declined over the 8-wk period. The plasma phospholipid ARA:EPA ratios were 20.7 and 12.9 after 4 wk consuming the high or low LA diets, respectively; LA was inversely associated with EPA but positively associated with ARA:EPA. LA intake did not influence ALA, ARA, DPA, DHA, or total, LDL or HDL cholesterol, CRP or IL-6, or platelet aggregation. In conclusion, high LA intakes decrease plasma phospholipid EPA and increase the ARA:EPA ratio, but do not favor higher AA.
The data from this study demonstrated that changing the fats and oils in the diets of adult men to achieve an intake of 3.8% energy from LA while maintaining an intake of 1% energy from ALA results in higher EPA and higher EPA:ARA ratio in plasma phospholipids than a LA intake of 10.5% energy.
An intake of 1% energy from ALA is about double the current mean ALA intake in North America. The results provide a clear demonstration that lowering dietary LA intake increases EPA in plasma phospholipids. The results also show that although an intake of 10.5% energy from LA with a LA:ALA ratio of 10:1 resulted in lower plasma phospholipid levels of EPA, it did not favor higher levels of ARA compared with an intake of 3.8% energy from LA with a LA:ALA ratio of 4:1.
The current ratio of (n-6):(n-3) fatty acids in many western diets is in excess of 10:1, and a ratio of 4:1 or lower has been suggested as optimal for human health. The results of this study are consistent with the hypothesis that high dietary LA inhibits the desaturation of ALA. A strong inverse association between the plasma phospholipid LA and EPA that predicted that for every 10% increase in LA, EPA decreased by 0.64 g/100 g fatty acids. The association between LA and EPA showed no evidence of a plateau at lower levels of LA intake, which suggests that additional lowering of LA would result in further increases in the plasma phospholipid EPA. Of note, 1% dietary energy from ALA in an LA:ALA ratio of 4:1 does not maintain a plasma phospholipid level of DHA as high as that achieved by a mixed diet that includes fish.
Changes in serum CRP, IL-6, or platelet aggregation were not attributable to changes in dietary LA or the LA:ALA ratio, although the subjects in our study were not at risk for disease, and values for these measures were within normal ranges. *In summary, this study indicates that a diet with 1% energy from ALA and a LA:ALA ratio of 4:1 results in higher plasma phospholipid EPA and a 40% lower ARA:EPA ratio than a diet containing a LA:ALA ratio of 10:1, with no change in the plasma phospholipid the level of ARA. A notable difference between diets high in ALA with a low LA:ALA ratio and diets high in EPA and DHA is that, whereas dietary EPA and DHA reduce blood lipid ARA, no such effect occurred in our study, which involved relatively simple changes in LA intake.
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