I__. - International Military Testing Association

afterwards. The purpose of the current study was to determine whether such
nutrients/food ingredients as protein, carbohydrate, and caffeine would affect
performance not only on the MAST but also on several subtests (pattern
recognition, reaction time, symbolic reasoning, and hand-tapping) of the
Automated Portable Test System or APTS (Bittner et al, 1985) and visual-analogue
mood scales.
Previous research has demonstrated that protein can enhance performance
because it contains tyrosine, the amino acid precursor to norepinephrine, which
helps the body function in states of arousal or stress (Lieberman et al, 1984).. On
the other hand, carbohydrate leads to insulin release which helps clear the blood
of amino acids except tryptophan, resulting in greater passage of this serotonin
precursor into the brain. Serotonin can induce a drowsy quiescent state capable of
suppressing performance (Lieberman et al, 1982/83). Caffeine is a commonly
used performance enhancer demonstrated to increase alertness and vigilance
(Sawyer, Julia, and Turin, 1982). We particularly wanted to test whether caffeine
would interact with either protein or carbohydrate in affecting performance.
METHOD
The subjects were military and civilian employees, males only, at the US
Army Natick Research, Development & Engineering Center. All potential subjects
were screened for previous caffeine use. Only those who normally consumed
between 2 and 4 caffeinated beverages (coffee, tea, or soda) per day were
retained. The subjects then filled out a questionnaire regarding their typical
caffeine use, from which their total daily caffeine ingestion was estimated. The
subjects were then split into a protein-lunch group (16 subjects) and a
carbohydrate-lunch group (18 subjects) so that the average daily caffeine intake
was equivalent in both groups.
On the first day of testing, the subjects were trained in the use of the
automated MAST, the APTS (using the pattern recognition, reaction time, symbolic
reasoning, and hand-tapping subtests), and visual-analogue mood scales
(indicating on a IOO-mm line how relatively tense, hungry, dejected, tired, angry,
vigorous, and confused they felt). On the following two days of testing, all subjects
were fed the same standard, mixed-nutrient breakfast at 0730 hours, tested at 1000
hrs, fed the experimental lunch at 1130, given a math exercise immediately after,
then tested shortly after noon and finally at 1430. The timed math exercise (30
minutes maximum) was used because previous studies (Morse et al, 1989) found
that it served as an effective stressor to mobilize norepinephrine use. The protein
lunch group was served 5 g/kg turkey breast, while the carbohydrate lunch group
was provided with 5 g/kg sorbet. These two foods were chosen because previous
research had demonstrated them capable of having behavioral effects (Spring,
Lieberman, Swope, and Garfield, 1986). Subjects were instructed to eat as much
of their test meals as they could, but there was a wide variation in the proportion
281