Methods of determining contributions to metabolic pathways

A method of determining a contribution of a first pathway and a contribution of a second pathway, which is different from the first pathway, to biosynthesis of a lipid class in an individual, wherein the lipid class, which comprises a marker composition, is produced from a first precursor by the first pathway and from a second precursor by the second pathway, wherein the first precursor is different from the second precursor, comprising

• determining P1, wherein P1 is a level of a marker composition and, wherein the first precursor is transformed to said lipid class via the first pathway,
• determining P2, wherein P2 is a level of said marker composition, wherein said second precursor is transformed to the lipid class via the second pathway, wherein the first precursor is different from the second precursor and wherein the first pathway is different from the second pathway,
• determining TL, wherein TL is a level of the marker composition in the lipid class,
• and then calculating the contribution of the first pathway as (TL−P2)/(P1−P2) and the contribution of the second pathway as (TL−P1)/(P2−P1), thereby determining the contribution of the first pathway and the contribution of the second pathway to the biosynthesis of the lipid class.