Impairments in mobility are only one of the health problems faced by persons living with spinal cord injury (SCI). Neurological deficits also change unconscious bodily functions, such as the processing of food. Specifically, our laboratory has documented exaggerated fat in the blood following a meal, a phenomenon known as postprandial lipemia (PPL). The purpose of this study was to use a novel in vivo technique to determine the mechanisms of PPL in persons with SCI. One person without injury, one with paraplegia, and one with tetraplegia were recruited based on their exceptional fitness. For the experiment, participants consumed a balanced liquid meal (50%:35%:15% carb:fat:protein). The amount of fat free mass (FFM) in their bodies was used to determine the calories in their meal (20 kcal·kgFFM-1). Mixed into the meal was a “stable isotope tracer” (5 mg·kgFFM-1 [U-13C]palmitate) that allows for determination of exogenous (from the meal) or endogenous (from stores in the body) fat metabolism. Specifically, this technique determines the source of the fats that are either used as metabolic energy or that remain in the circulation, thus contributing to PPL. Samples were obtained before feeding and at 7 time points up to ~6.5 hrs following the meal. Results: Use of endogenous fat was lower in the paraplegic (2.33 g·hr-1) and tetraplegic (2.21 g·hr-1) compared to the person without injury (4.13 g·hr-1). Lower rates of fat use corresponded with lower blood epinephrine levels in paraplegia and tetraplegia (0-4.98 nmol·hr·L-1) compared to the person without injury (85.23 nmol·hr·L-1). The persons with paraplegia did not show evidence of PPL, but the person with tetraplegia exhibited exaggerated PPL due to a 422 and 214 % greater peak concentration of exogenous and endogenous fat, respectively. Conclusion: Endogenous fat use is impaired in persons with SCI and is associated with low levels of circulating epinephrine. These findings suggest that hormonal deficiency contributes to dysregulation of fat metabolism in SCI. Blunted fat use occurred despite “normal” blood fat concentrations in the person with paraplegia. This unique finding suggests that fat leaving the blood is not fully metabolized but instead stored, possibly contributing obesity in SCI.

Additional author(s): Armando J. Mendez, Mark S. Nash, Kevin A. Jacobs