Military nutrition researchers have not taken this responsibility lightly. The history of American, Canadian, and British research on military rations is easily traced from the World War II era to the present. Rations have been studied in temperate, hot, cold, and high-altitude conditions. Experiments as early as the 1950s (Korean War era) were conducted by interdisciplinary teams of researchers who measured the spectrum of biochemical, physical, psychological, and social parameters (Johnson and Sauberlich, 1982). These investigators went to great effort to use state-of-the-art technologies in harsh field settings, just as investigators do now. Investigators then and now found it was possible to do extensive testing in the field, but difficult to hold extraneous variables constant. However, the vast majority of the studies were not designed to study the relationship of underconsumption to cognitive performance, per se, or the ability of military rations to sustain cognitive performance under stress.
For the purposes of this review, underconsumption was operationally defined as a loss of gross body weight due to restrained eating, loss of appetite, or exertion. In all cases energy expenditure exceeded energy intake (underconsumption: kcal intake/kcal expended < 1.00). Failing to consume sufficient calories to maintain body weight (while in the presence of ample food) should be an anomaly, since under normal circumstances it is unlikely to have survival value. The circumstances under which it reliably occurs are riveting. Underconsumption should be particularly rare when the individual faces novel and strenuous work. For this reason, the soldier's underconsumption in field settings is especially intriguing. Although the camouflage-colored, armor-like packaging and shelf-stable, ready-to-eat engineering of military rations can easily explain a few days of underconsumption, they cannot explain the consistent finding that soldiers steadily lose weight when eating military rations for periods of 10 to 45 days (Askew et al., 1986, 1987; Carter et al., 1992; Hirsch et al., 1985; Johnson and Sauberlich, 1982; King et al., 1992; Popper et al., 1987; Roberts et al., 1987; Thomas et al., 1995; USACDEC/USARIEM, 1986).
The boundary conditions of this phenomenon are as well established as its replicability. When soldiers were fed hot, cook-prepared, garrison-type meals in the field, they did not underconsume (Rose and Carlson, 1986), and when they were fed shelf-stable, ready-to-eat military field rations in a garrison-like environment, they did not underconsume (Hirsch and Kramer, 1993). Thus, the phenomenon of underconsumption is the result of an interaction between the field setting and the type of ration.