Effects of food restriction in military training on T-lymphocyte responses

In a stress model which included food restriction, we examined the effects of physically rigorous military training and increased caloric intake on T-lymphocyte responses and lymphocyte subsets. T-lymphocyte proliferation and release of soluble receptor for interleukin-2 (sIL-2R) in vitro were measured in two separate training classes of male U.S. Army ranger course (RC) trainees at the start and during the RC. Trainees in group 1 (n = 55) and 2 (n = 50), respectively, had mean (+/- SD) energy intakes of 11.8 +/- 7.0 and 13.6 +/- 6.7 MJ/d, averaged total daily energy expenditures of 16.7 and 17.6 MJ/d, and experienced body weight losses of 15.6% and 12.6%. Both groups showed decreased T-lymphocyte responses in vitro: proliferation to phytohemagglutinin (PHA) and tetanus toroid (TT), and released sIL-2R to PHA. Group 2 with an intended 15% increase in energy during the RC over group 1 showed 22% and 26% less severe suppressions of T-lymphocyte proliferation and released sIL-2R, respectively, in vitro. Group 2 also showed that short-term (9 days) removal of the food restriction stressor allowed for corrected body weight, total lymphocyte and T-lymphocyte subset counts but not suppressed T-lymphocyte responses in vitro. These results demonstrate that soldiers in physically rigorous military training are at risk of suppressed T-lymphocyte immunocompetence, and this is greater if they also experience inadequate energy intake.