Human foods are comprised of over 25,000 different compounds, this warrants a new metabolome to be categorized: the food metabolome.  Understanding the human endogenous and a dietary food metabolism is useful in understanding what metabolites are essential and non-essential to the human. The “food metabolome” has been defined as the sum of all metabolites directly derived from the digestion of foods, their absorption in the gut, and biotransformation by the host tissues and the microbiota.  Others define the “food metabolome” simply as the whole set of food constituents in any foods.  The human food metabolism is defined more like the first definition.

It was through these early metabolome studies that scientists realized that the human metabolome was not as small or as simple as first imagined. In particular, noticeable differences in human metabolomes could be detected that appeared to depend strongly on diet, sex, health status, genetics, kinetics, physiology, and age—with diet being most important.  The human metabolome contains 50,000 different detectable compounds, while some plant species metabolomes contain up to 200,000 metabolites.

METABOLOMICS AND DISCOVERY OF NOVEL DIETARY BIOMARKERS

A nutritional biomarker can be any biological specimen that is an indicator of nutritional status with respect to intake or metabolism of dietary constituents. It can be a biochemical, functional or clinical index of status of an essential nutrient or other dietary constituent. – Google

To establish human food metabolomic profiles, biomarkers were identified from both literature and in lab studies using GC-MS, LC-MS, and NMR on biofluids (mostly urine and blood). Statistical analyses preformed with Matlab.

UTILITY OF FOOD METABOLIC PROFILES

• Finding diet-related diseases, understanding the relationships between diet and health, and understanding dietary means of combating disease
• Finding new bioactive food derived metabolites, non-endogenous
• Useful information in databases

The Human Metabolome Database (HMBD) is the largest metabolism / metabolite database:

• 2180 endogenous / synthesized metabolites mined from thousands of books, journals, and other online databases – as well as from own studies involving MS and NMR on urine, blood, and cerebrospinal fluids.  Studies done in their own lab involved perturbing pathways and using deduction to understand metabolites.
• 90 metadata fields for each metabolite member in the database.  This  includes  comprehensive compound description, names and synonyms, structural information, physico-chemical data, reference NMR and MS spectra, biofluid concentrations, disease associations, pathway information, enzyme data, gene sequence data, SNP and mutation data as well as extensive links to images, references and other public databases, etc.

  

• Search and Navigation Tools for browsing the database.  Browsing can occur at the levels of metabolites, diseases, pathways, biofluids, classes, proteins, and reactions. Searching can be accomplished through various input including: text, structure, sequence, MS data, GC data, and NMR data (input spectra or peak lists).  Site also includes its own local BLAST function.

These metabolites are further connected to some 115 non-redundant pathways, 2080 distinct enzymes, 110 000 SNPs as well as 862 metabolic diseases (genetic and acquired). More than 400 compounds are also linked to experimentally acquired ‘reference’ H and C NMR and MS/MS spectra. Concentration data (normal and abnormal values) for plasma, urine, CSF and/or other biofluids are also provided for a total of 883 compounds. The entire database, including text, sequence, structure and image data occupies nearly 18 GB of data—most of which can be freely downloaded.

To navigate NMBD, go to  http://www.hmdb.ca/ 

Metabolomics is the profiling of metabolites in a given biological environment.  Environmental resolutions range from the cell to tissue to organ to organism.  Much like transcriptomes and proteomes, the matabolome is a dynamic environment, where each profiling is a snapshot in time.  Current techniques do not allow complete profiling of an given metabolome, for each profile ideally will have every intermediate, hormone, signalling molecule, product, and secondary metabolite recorded with quantity.  Separation techniques include, gas chromotography, high performance liquid chromotography, and capillary electrophoresis.  Detection techniques include gas spectroscopy and nuclear magnetic resonance spectroscopy. Due to the unstable nature of some of these metabolites, it has been proven difficult to use these techniques to profile each metabolome in its entirety.

Application of having profiled metabolomes include:

• Toxicology
• Metabonomics – metabolomic profiling of diseased tissue
• Functional genomics – understanding phenotype response to genetic manipulation
• Nutrigenomics – understanding of ‘omics in regard to human nutrition
• Environmental metabolomics – understanding of metabolites in interaction with the environment

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