title: Effects of beef- and fish-based diets on the kinetics of n-3 fatty acid metabolism in human subjects.
abstract: BACKGROUND
  The quantity and type of dietary polyunsaturated fatty acids (PUFAs) can alter essential fatty acid metabolism in humans. Diets rich in 20- and 22-carbon PUFAs may inhibit desaturase expression or activity and decrease the synthesis of long-chain unsaturated fatty acids.
  
  
  OBJECTIVE
  It was theorized that the fat content of a fish-based diet would inhibit the kinetics of the in vivo metabolism of n-3 fatty acids compared with a beef-based diet.
  
  
  METHODS
  A compartmental model was used to determine the coefficients of the kinetic rate constants from the plasma concentration time curves of pentadeuterated (d(5)) 18:3n-3, 20:5n-3, 22:5n-3, and 22:6n-3 of 10 subjects who subsisted on 3 diets with different long-chain PUFA contents. For 3 wk, subjects reported their food intake from their usual diets and then consumed a beef-based diet for 3 wk and then a fish-based diet for an additional 3 wk. Subjects consumed 1 g d(5)-18:3n-3 ethyl ester at weeks 3, 6, and 9. Blood was drawn over 168 h and the plasma analyzed for fatty acids. The coefficients of the kinetic constants of n-3 fatty acid metabolism and the percentage utilization of the substrates were determined.
  
  
  RESULTS
  Across all diets, < 1% of plasma 18:3n-3 was utilized for long-chain PUFA synthesis. There was a 70% reduction in the value of the rate constant coefficient that regulated transfer of the isotope from the 22:5n-3 compartment to 22:6n-3 when the fish-based diet was compared with the beef-based diet. The turnover rate of plasma d(5)-22:6n-3 also decreased.
  
  
  CONCLUSIONS
  The primary effect of a fish-based diet on the kinetics of n-3 metabolism involves processes that inhibit the synthesis of 22:6n-3 from 22:5n-3. These processes may involve a system of feedback control mechanisms responsive to the plasma concentration of 22:6n-3.
authors.affiliation: Food Composition Laboratory, Beltsville Human Nutrition Research Center, US Department of Agriculture, Beltsville, MD, USA. bpawl@mail.nih.gov
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Pawlosky
authors.forename: Joseph R
authors.initials: JR
authors.lastname: Hibbeln
authors.forename: Yuhong
authors.initials: Y
authors.lastname: Lin
authors.forename: Susan
authors.initials: S
authors.lastname: Goodson
authors.forename: Patti
authors.initials: P
authors.lastname: Riggs
authors.forename: Nancy
authors.initials: N
authors.lastname: Sebring
authors.forename: Gerald L
authors.initials: GL
authors.lastname: Brown
authors.forename: Norman
authors.initials: N
authors.lastname: Salem
mesh_terms: D000328:Adult; D000818:Animals; D002417:Cattle; D003903:Deuterium; D044943:Fatty Acid Desaturases / Q000378:metabolism*; D015525:Fatty Acids, Omega-3 / Q000008:administration & dosage / Q000493:pharmacokinetics*; D043371:Fatty Acids, Omega-6; D005231:Fatty Acids, Unsaturated / Q000008:administration & dosage / Q000096:biosynthesis* / Q000097:blood / Q000493:pharmacokinetics; D005247:Feeding Behavior; D005260:Female; D005399:Fishes; D005504:Food Analysis; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D008297:Male; D008460:Meat; D008954:Models, Biological; D017747:Seafood; D017962:alpha-Linolenic Acid / Q000378:metabolism*
chemical_list: D015525:Fatty Acids, Omega-3; D043371:Fatty Acids, Omega-6; D005231:Fatty Acids, Unsaturated; D017962:alpha-Linolenic Acid; D003903:Deuterium; D044943:Fatty Acid Desaturases