Abstract
There is a debate about the optimal dietary ratio of the parent n6 fatty acid linoleic acid (LA) and n3 fatty acid alpha-linolenic acid (ALA) to promote an efficient conversion of ALA to EPA and DHA, which have implications for human health. The aim of the present study was to compare the effects of a low-LA/high-ALA (loLA/hiALA) diet with a high-LA/low-ALA (hiLA/loALA) diet on fatty acid concentrations in red blood cells (RBCs). Fifteen omnivore healthy men (mean age 26.1 ± 4.5 years) with a low initial EPA/DHA status (sum (∑) EPA + DHA% of total fatty acids in RBC at baseline: 4.03 ± 0.17) received both diets for two weeks with a nine-week wash-out phase in between. Fatty acid intake of the subjects was tightly controlled. Concentrations [μg mL-1] and relative amounts [% of total fatty acids] of fatty acids in RBCs were analyzed at baseline (day 0), day 7 and 14 by means of GC-FID. The dietary LA/ALA ratios were 0.56 ± 0.27 : 1 and 25.6 ± 2.41 : 1 and led to significantly different changes of ALA, LA, EPA and ∑EPA + DHA concentrations in RBCs. In the course of the loLA/hiALA diet ALA and EPA concentrations and relative amounts of ∑EPA + DHA increased, whereas LA concentrations decreased. The DHA concentration was unaffected. The hiLA/loALA diet led to slightly decreased EPA concentrations, while all other fatty acid concentrations remained constant. Compared to our previous study, where we simply increased the ALA intake, our results show that ALA supplementation combined with a reduced LA intake (loLA/hiALA diet) more efficiently enhanced EPA blood concentrations. The absence of changes in the PUFA pattern in consequence of a LA/ALA ratio of 25.6 ± 2.41 : 1 suggests that the high LA/ALA ratio of the Western diet already leads to a saturation and a further increase of the ratio does not affect the PUFA pattern.
Highlights
The long chain (LC) omega-3 (n3) polyunsaturated fatty acids (PUFAs) eicosapentaenoic acid (EPA, C20:5n3) and docosahexaenoic acid (DHA, C22:6n3) are known for their beneficial health effects mainly with regard to cardiovascular[1,2,3,4,5] and cognitive health.[6,7,8] Dietary sources of EPA and DHA are limited and in the Western diet intake of these fatty acids is far below the recommendations
The examination of the dietary records combined with analysis of fatty acids in the lunch meal showed that the linoleic acid (LA) intake was 7.30 ± 0.37 g d−1 (2.78 en%) during loLA/hiALA diet and 18.2 ± 0.54 g d−1 (6.95 en%) during hiLA/loALA diet, while the alpha-linolenic acid (ALA) intake was 13.1 ± 0.22 g d−1 (4.98 en%) during loLA/hiALA diet and 0.71 ± 0.09 g d−1 (0.27 en%) during hiLA/loALA diet
Our finding that EPA concentrations in red blood cells (RBCs) significantly increased by 35.0 ± 13% after 7 days and by 57.6 ± 18% after 14 days following the loLA/hiALA diet is a likely result of an increasing conversion of ALA to EPA, since no EPA was ingested via the background diet
Summary
The long chain (LC) omega-3 (n3) polyunsaturated fatty acids (PUFAs) eicosapentaenoic acid (EPA, C20:5n3) and docosahexaenoic acid (DHA, C22:6n3) are known for their beneficial health effects mainly with regard to cardiovascular[1,2,3,4,5] and cognitive health.[6,7,8] Dietary sources of EPA and DHA are limited and in the Western diet intake of these fatty acids is far below the recommendations. The essential n3 precursor fatty acid alpha-linolenic acid (ALA, C18:3n3) is present in high amounts in some plant oils, C18:2n6) due to competition for the same desaturation and elongation enzymes[12,13] and for incorporation into cell membranes.[14] The intake of LA has increased substantially in Western diets during the last century.[15,16] the dietary ratio of the n6 fatty acid LA to the n3 fatty acid ALA is about 10–20:1 The biological efficacy of n3 PUFAs is improved and at the same time production of n6 derived pro-inflammatory mediators is decreased.[20]
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