Hidden in the photograph: The myth of complete metabolic coverage possible in metabolomics investigations.

Since the late 1970s, many 'omics-style investigations have advanced our understanding of systems at all levels, from community level, through organismal, to individual cellular processes. Beginning with genomics and progressing through transcriptomics, proteomics and finally to metabolomics, the scope of interest shifts significantly from what is genetically possible to what is currently expressed, produced and measurable in a system. While the ideal goal of any 'omics investigation is to fully describe a system, loss of information occurs at each decision-making juncture. These losses are often not considered in the experimental planning stage but, when combined, they drastically affect the power of an investigation and the conclusions that can be drawn from it. Herein we discuss through the analogy of photography many of the decision-making junctures of metabolomics investigations and the resultant losses of information occurring at each.