Saliva and urine are other matrices used in metabolomics studies, since the collection of the samples is simple, safe, non-invasive, and does not require assistance of any trained personnel. A recent study performed on saliva samples collected from volunteers demonstrated the possibility of simultaneous extraction of around 400 metabolites with a wide range of polarity (e.g., amino acids, carboxylic acids, eicosanoids, fatty acids, and glycerophospholipids; log P in the range −3.5÷10) using DI-SPME in combination with an RPLC- MS method [43]. The results also demonstrated the ability of detected peaks to differentiate clearly male and female individuals as well as changes in saliva metabolome induced by 7 days of diet.