We have previously shown that acute sleep curtailment induces insulin resistance, both in healthy individuals as well as in patients with type 1 diabetes, suggesting a causal role for sleep disturbances in pathogenesis of insulin resistance, independent of endogenous insulin production. However, the underlying mechanisms remain unclear. This study aimed to explore the metabolic pathways affected by sleep loss using targeted metabolomics in human fasting plasma samples. Healthy individuals (n = 9) and patients with type 1 diabetes (n = 7) were studied after a single night of short sleep (4 h) versus normal sleep (8 h) in a cross-over design. Strikingly, one night of short sleep specifically increased the plasma levels of acylcarnitines, essential intermediates in mitochondrial fatty acid oxidation (FAO). Specifically, short sleep increased plasma levels of tetradecenoyl-l-carnitine (C14:1) (+32%, p = 2.67*10(-4)), octadecanoyl-l-carnitine (C18:1) (+22%, p = 1.92*10(-4)) and octadecadienyl-l-carnitine (C18:2) (+27%, p = 1.32*10(-4)). Since increased plasma acylcarnitine levels could be a sign of disturbed FAO, it is possible that sleep curtailment acutely induces inefficient mitochondrial function. Our observations provide a basis for further research into the role of acylcarnitines as a potential mechanistic pathway by which sleep deprivation - even short term - causes adverse metabolic effects, such as insulin resistance.