FABP2 and myalgic encephalomeyelitis/chronic fatigue syndrome: ME/CFS patients had increased serum levels of FABP-2, a low molecular weight protein involved in the intracellular traffic of fatty acids, which comprises 4–6% of enterocyte cytosolic proteins, is undetectable or present in very low concentrations in the serum of healthy persons and is used as a marker of increased intestinal permeability [39].