Metabolic profiling of meat and fish and their impact on human metabolism

Licentiate thesis, 2016

High intake of meat is frequently associated with increased risk of disease, while the opposite is true for fish; yet few studies have compared meat and fish in terms of both its composition of low-molecular weight (LMW) molecules and its effects on metabolite concentrations in humans. The work presented in this thesis aimed to use metabolomics to get a holistic overview of compositional differences between fish and meat, and the effects of dietary fish or meat intake on human metabolism. To investigate the metabolite composition of meat and fish, fillets of beef, pork, chicken, cod, salmon and herring (fresh and pickled), n=6 per fish or meat type, were minced, mixed and samples of both raw and baked minced fillet taken. The metabolite profile of the samples was measured using gas chromatography-mass spectrometry (GC-MS) based- metabolomics. Metabolite profiles of fish and meat were compared, as well as the individual fish and meat types. To investigate the effects on plasma metabolite profile of replacing chicken and pork with herring, GC-MS-metabolomics analysis of plasma samples from of a randomized crossover trial with eleven healthy obese men and women (age 24–70 years) was conducted. Subjects were randomly assigned to four weeks of herring diet or a reference diet of chicken and lean pork, five meals per week, followed by a washout and the other intervention arm. The composition experiments revealed that the LMW composition (amino-acids, other nitrogen-containing compounds, lipids, organic acids/alcohols and sugars) of meat and fish differed less than expected, while there was wide variation within the measured meat and fish samples. Eating herring instead of chicken and lean pork led to several metabolite changes in the tricarboxylic acid cycle and urea cycle, as well as differences for several metabolites including methyl-histidine, a potential biomarker of meat intake. These results support the idea that it is not sufficient to broadly compare ‘meat’ and ‘fish’ in nutrition studies due to wide variation in metabolite composition, and that replacing lean pork and chicken with herring may have profound consequences on energy and amino acid metabolism.