Greater dietary fat oxidation in obese compared with lean men: an adaptive mechanism to prevent liver fat accumulation?
Liver fat represents a balance between input, secretion, and oxidation of fatty acids. As humans spend the majority of a 24-h period in a postprandial state, dietary fatty acids make an important contribution to liver fat metabolism. We compared hepatic fatty acid partitioning in healthy lean (n = 9) and abdominally obese (n = 10) males over 24 h. Volunteers received three mixed meals adjusted for basal metabolic rate. U-13C-labeled fatty acids were incorporated into the meals, and [2H2]palmitate was infused intravenously to distinguish between sources of fatty acids incorporated into VLDL-TG. Immunoaffinity chromatography was used to isolate VLDL-TG of hepatic origin. Liver and whole body fatty acid oxidation was assessed by isotopic enrichment of 3-hydoxybutyrate and breath CO2. We found a similar contribution of dietary fatty acids to VLDL-TG in the two groups over 24 h. The contribution of fatty acids from splanchnic sources was higher (P < 0.05) in the abdominally obese group. Ketogenesis occurred to a significantly greater extent in abdominally obese compared with lean males, largely due to lessened downregulation of postprandial ketogenesis (P < 0.001). The appearance of 13C in breath CO2 was also greater (P < 0.001) in abdominally obese compared with lean men. Hepatic elongation and desaturation of palmitic acid were higher (P < 0.05) in abdominally obese than in lean males. Oxidation of dietary fatty acids and hepatic desaturation and elongation of palmitic acid occurred to a greater extent in abdominally obese men. These alterations may represent further pathways for redirection of fatty acids into export from the liver or oxidation to prevent liver fat accumulation.
Hodson
Leanne
L
Oxford Centre for Diabetes, Endocrinology and Metabolism, Nuffield Department of Clinical Medicine, University of Oxford, United Kingdom. leanne.hodson@oxlip.ox.ac.uk
McQuaid
Siobhán E
SE
Humphreys
Sandy M
SM
Milne
Ross
R
Fielding
Barbara A
BA
Frayn
Keith N
KN
Karpe
Fredrik
F
D020155:3-Hydroxybutyric Acid / Q000097:blood / Q000378:metabolism; D000328:Adult; D000410:Alanine Transaminase / Q000097:blood / Q000378:metabolism; D001055:Apolipoproteins B / Q000097:blood / Q000378:metabolism; D019540:Area Under Curve; D002097:C-Reactive Protein / Q000032:analysis / Q000378:metabolism; D004041:Dietary Fats / Q000378:metabolism*; D005230:Fatty Acids, Nonesterified / Q000097:blood / Q000378:metabolism*; D005234:Fatty Liver / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000097:blood / Q000378:metabolism; D008074:Lipoproteins / Q000097:blood / Q000378:metabolism; D008079:Lipoproteins, VLDL / Q000097:blood / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000378:metabolism*; D019518:Postprandial Period; D014280:Triglycerides / Q000097:blood / Q000378:metabolism*; D055815:Young Adult; D005723:gamma-Glutamyltransferase / Q000097:blood / Q000378:metabolism
D001055:Apolipoproteins B; D004041:Dietary Fats; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D008074:Lipoproteins; D008079:Lipoproteins, VLDL; D014280:Triglycerides; C030087:lipoprotein triglyceride; D002097:C-Reactive Protein; D005723:gamma-Glutamyltransferase; D000410:Alanine Transaminase; D020155:3-Hydroxybutyric Acid