Proteomics of blood cells and biofluids is emerging as a valuable tool to assess the effects of nutritional or clinical interventions on health and disease. This study aimed to 1) assess the amount and variability of proteins available from platelets, PBMC, plasma, urine and saliva from 10 healthy volunteers for proteomics analysis, and 2) whether protein yield is affected by prolonged fasting. Volunteers provided a blood, a saliva and a morning urine sample once a week for four weeks on different days after an overnight fast. Volunteers were fasted for a further 24 hours after the fourth sampling day before providing their final blood, saliva and morning urine sample. Each 10 mL of whole blood provided 400-1500 µg protein from platelets after isolation and washing, and 100-600 µg protein from PBMC using the OptiPrep™ method. 30 mL plasma provided 350-650 mg protein depleted of albumin and IgG. A spot sample of morning urine provided 2-16 mg protein per mL, and a spot sample of whole saliva provided 70-950 mg protein per mL. None of these protein yields were influenced by the degree of fasting (i.e. overnight or a 36-hour fasting challenge), age or body mass index. In contrast to the yield from plasma, platelets and PBMC, the protein yield of urine and saliva was highly variable within and between subjects. Certain disease conditions may cause higher or lower PBMC counts and thus protein levels, or increased urinary protein levels.