Acylcarnitine concentrations increase in response to an extended energy deficit, but return to baseline concentrations following a 2-week recovery in male US Army Rangers.

Energy deficit often occurs during military training and operations due to prolonged and strenuous physical exertion and limited access to food. During energy deficit, the body predominately relies on fat stores. This results in greater circulating acylcarnitine species as acyl groups are moved into the mitochondria for β-oxidation. Carnitine and acylcarnitine species have not been assessed during prolonged energy deficit and following a recovery period in healthy males undergoing strenuous military training. The objective of this study was to determine longitudinal changes in plasma carnitine and aclycarnitines following a prolonged and severe energy deficit and short-term recovery. This secondary analysis examined plasma carnitine and acylcarnitine concentrations before (PRE) and after (POST) 61-day U.S. Army Ranger training and following 2 weeks of recovery (REC). During training, participants (n = 22; mean ± standard deviation: 23.2 ± 2.8 years; 81.7 ± 9.3 kg; 16.5 ± 6.8% body fat) consumed ∼2200 kcal/day and were in an ∼1000 kcal/day energy deficit. Carnitine and acylcarnitine (C2-C22) concentrations were measured by tandem mass spectrometry. At POST, participants had increased concentrations of total short-chain acylcarnitines and 10 of 58 acylcarnitine species (C2, C5, C8-dicarboxylic acid (DC), C16:1, C16:1-hydroxyl group (OH), C18:1-OH, C18:1-DC, C18:2-OH, C20:2-OH, C22:3; P ≤ 0.05) compared to PRE. These acylcarnitine species returned to PRE concentrations following REC (P > 0.05). Greater bodyweight loss was associated with greater increases in short-chain acylcarnitine (r = -0.68; P = 0.0006), medium-chain acylcarnitine (r = -0.61; P = 0.0035), and long-chain acylcarnitine (ρ = -0.65; P = 0.0013) concentrations. Severe energy deficit incurred during strenuous military training increased 10 acylcarnitine species. However, 2 weeks of recovery was sufficient for acylcarnitine concentrations to return to baseline concentrations.