A single-subject design was used to investigate the impact of a dietary change on the emotional state of four individuals selected by means of the Behavioral Index of Metabolic Imbalance and a subsequent interview. The dietary change for three subjects consisted of a high protein-low carbohydrate diet void of sucrose and caffeine, whereas only caffeine and sucrose were eliminated for the fourth subject. The dependent variable used with the first subject was a self-report of symptoms experienced, whereas the Minnesota Multiphasic Personality Inventory (MMPI) and the Profile of Mood State (POMS) were used with the other subjects. Results revealed that subjects reported many symptoms and/or presented a distressed profile during baseline assessment. However, following a 2-week dietary change symptoms declined, and the MMPI or POMS profiles reflected a more stable and less distressed individual. Overall, the results suggest that a dietary change can remediate the emotional distress exhibited by some individuals.

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A series of two studies was conducted to develop and cross-validate a psychometric instrument capable of identifying individuals experiencing a dietary induced mood disturbance. The first study focused on the development of the Christensen Dietary Distress Inventory (CDDI) by identifying the items which would differentiate dietary responders from nonresponders. Dietary responders were identified as those individuals whose mood disturbance improved following a dietary intervention and deteriorated following either a return to their typical diet or following a challenge of refined sucrose or caffeine as opposed to placebo or aspartame. The results revealed that 34 CDDI items differentiated dietary responders from the nonresponders. The test-retest reliability of this scale was .87. The second study cross-validated the CDDI. Using an A-B single-subject design and double-blind challenges, seven of 23 research participants were identified as definite dietary responders, nine as definite dietary nonresponders, and seven as probable dietary responders. The dietary responders' and nonresponders' CDDI scores were significantly different and a point-biseral of .48 existed between the subjects' CDDI score and their group categorization. Such data indicate that the CDDI is a valid psychometric instrument. Inspection of the sensitivity and specificity indices indicates that a cutoff score of 13 results in the selection of the most true positives with the least number of false positives.

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The impact of expectancy on the experience of caffeine-related symptoms was investigated by randomly assigning subjects to an expectancy or nonexpectancy instructional condition. Subjects were administered the State-Trait Anxiety Inventory and a Symptom Questionnaire prior to and 45 minutes after receiving their designated instructional set and ingesting a cellulose-filled gelatin capsule which ostensibly was filled with caffeine. Results revealed that a significant expectancy effect existed on five Symptom Questionnaire items.