Conversion of α-linolenic acid in humans is influenced by the absolute amounts of α-linolenic acid and linoleic acid in the diet and not by their ratio

• Published in: The American journal of clinical nutrition Vol. 84; no. 1; pp. 44 - 53
• Main Authors: Goyens, Petra LL, Spilker, Mary E, Zock, Peter L, Katan, Martijn B, Mensink, Ronald P
• Format: Journal Article
• Language: English
• Published: Bethesda, MD American Society for Nutrition 01.07.2006; American Society for Clinical Nutrition; American Society for Clinical Nutrition, Inc
• Subjects: adults; alpha-Linolenic Acid - administration & dosage; alpha-Linolenic Acid - blood; alpha-Linolenic Acid - metabolism; Biological and medical sciences; blood chemistry; blood lipids; Breath Tests; Carbon Isotopes; Diet; dietary fat; docosahexaenoic acid; docosapentaenoic acid; docosenoic acids; Dose-Response Relationship, Drug; Double-Blind Method; eicosapentaenoic acid; Fatty acids; Fatty Acids, Unsaturated - analysis; Fatty Acids, Unsaturated - blood; Fatty Acids, Unsaturated - metabolism; Feeding. Feeding behavior; Female; Fundamental and applied biological sciences. Psychology; Humans; linoleic acid; Linoleic Acid - administration & dosage; Linoleic Acid - blood; Linoleic Acid - metabolism; linolenic acid; lipid metabolism; lipid peroxidation; lipids; Male; men; Metabolism; Middle Aged; oxidation; Oxidation-Reduction; phospholipids; Phospholipids - analysis; Phospholipids - blood; Phospholipids - metabolism; plasma; polyunsaturated fatty-acids; tissues; Vertebrates: anatomy and physiology, studies on body, several organs or systems; women; Human; stable isotopes; Linolenic acid; Ratio of α-linolenic to linoleic acid; Diet; Oxidation; Ratio; Isotopes; humans; Feeding; Linoleic acid; conversion
• ISSN: 0002-9165; 1938-3207
• DOI: 10.1093/ajcn/84.1.44

BACKGROUND: Human in vivo data on dietary determinants of α-linolenic acid (ALA; 18:3n-3) metabolism are scarce. OBJECTIVE: We examined whether intakes of ALA or linoleic acid (LA; 18:2n-6) or their ratio influences ALA metabolism. DESIGN: During 4 wk, 29 subjects received a control diet (7% of energy from LA, 0.4% of energy from ALA, ALA-to-LA ratio = 1:19). For the next 6 wk, a control diet, a low-LA diet (3% of energy from LA, 0.4% of energy from ALA, ratio = 1:7), or a high-ALA diet (7% of energy from LA, 1.1% of energy from ALA, ratio = 1:7) was consumed. Ten days before the end of each dietary period, [U-¹³C]ALA was administered orally for 9 d. ALA oxidation was determined from breath. Conversion was estimated by using compartmental modeling of [¹³C]- and [¹²C]n-3 fatty acid concentrations in fasting plasma phospholipids. RESULTS: Compared with the control group, ALA incorporation into phospholipids increased by 3.6% in the low-LA group (P = 0.012) and decreased by 8.0% in the high-ALA group (P < 0.001). In absolute amounts, it increased by 34.3 mg (P = 0.020) in the low-LA group but hardly changed in the high-ALA group. Nearly all ALA from the plasma phospholipid pool was converted into eicosapentaenoic acid. Conversion of eicosapentaenoic acid into docosapentaenoic acid and docosahexaenoic acid hardly changed in the 3 groups and was <0.1% of dietary ALA. In absolute amounts, it was unchanged in the low-LA group, but increased from 0.7 to 1.9 mg (P = 0.001) in the high-ALA group. ALA oxidation was unchanged by the dietary interventions. CONCLUSION: The amounts of ALA and LA in the diet, but not their ratio, determine ALA conversion.