Key Points
Metabolic syndrome (MetS) is among the most common cause of increased cardiovascular disease (CVD) risk in otherwise healthy populations. This group has shown that an energy-restricted diet enriched with α-linolenic acid (ALA) from canola oil had greater efficacy in lowering risk factors in MetS than an energy-restricted diet enriched with olive oil. Moderate doses of ALA (3.4 and 6 g/d) for 3 to 6 wk led to a significant increase of ALA in isolated low-density lipoprotein (LDL) particles and erythrocytes and increased EPA concentrations due to increased conversion from ALA. In the present study, this group examined the effects of an energy-restricted diet enriched with ALA on fatty acid composition of serum phospholipids in patients with MetS. The ALA dose of 3.4 g/d used represented approximately twice the mean daily habitual intake of the patients. The findings showed that serum phospholipid ALA did not increase after 26wk of a hypoenergetic diet and did not increase EPA concentrations in serum phospholipids. These results were unexpected, given the numerous previous reports in humans that consumption of high-ALA diets for several weeks to months increased ALA and/or EPA in plasma/serum phospholipids, lipoproteins, erythrocytes, leukocytes, and platelets.
The present data suggest that the efficiency of conversion of ALA to EPA not only depends on nutritional and physiological factors (e.g., doses of ALA and LA, age, and sex), but also on energy intake (hypo- versus isoenergetic). A long-term (6 mo) catabolic state may significantly decrease the availability of ALA for conversion to long chain n-3 PUFAs by increasing the relative partitioning of ALA into the β-oxidation pathway.
ABSTRACT
OBJECTIVES: Plant-derived α-linolenic acid (ALA) may exert cardioprotective effects. Dietary ALA can undergo desaturation and elongation to form long-chain ω-3 polyunsaturated fatty acids, but the extent to which this occurs in humans is unclear. The aim of the study was to examine the effects of an energy-restricted diet enriched with ALA on fatty acid composition of serum phospholipids in patients with metabolic syndrome. METHODS: The present analysis compared the effects of a hypoenergetic diet high in ALA (3.4 g/d) with a control diet low in ALA (0.9 g/d) on fatty acid composition of serum phospholipids in 81 overweight or obese patients with features of metabolic syndrome. RESULTS: After a 26-wk intervention, concentration of ALA in serum phospholipids remained constant in both diet groups. The control group had a significant decrease in serum phospholipid eicosapentaenoic acid concentration, although no significant intergroup difference was observed. Serum phospholipid docosahexaenoic acid concentration significantly decreased to a similar extent with both interventions. Additionally, both interventions significantly decreased serum phospholipid concentrations of palmitic acid, stearic acid, total saturated fatty acids, linoleic acid, total ω-6 and ω-3 polyunsaturated fatty acids, with no effect of diet group on these changes. Compared with the ALA diet, the control diet led to a significant increase in serum phospholipid oleic acid concentration. CONCLUSION: Daily intake of 3.4 g of ALA during a 26-wk energy-restricted diet did not lead to an enrichment of serum phospholipids with ALA and did not increase eicosapentaenoic acid due to conversion. Additionally, dietary ALA was unable to compensate for a decrease in serum phospholipid docosahexaenoic acid.
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