Carbohydrates, tryptophan, and behavior: A methodological review.

In this methodological review, we examine the behavioral effects of carbohydrates and tryptophan and conclude that high-carbohydrate foods do not provoke hyperactivity, contrary to popular beliefs. Unbalanced carbohydrate meals, however, often induce fatigue and can impair performance among both children and adults. Although tryptophan hastens sleep onset, dulls pain sensitivity, and may reduce aggressiveness, it is unclear whether similar effects can be obtained through carbohydrate ingestion. We provide support for the hypothesis that carbohydrates and tryptophan function similarly and like drugs that modify brain biochemistry and accompanying mood and behavior. We also examine implications for clinical populations who selectively crave carbohydrates. Despite professional skepticism, both anecdotal and empirical evidence continue to suggest that foods affect behavior. The empirical literature has now grown sufficiently to evaluate the validity of beliefs about one nutrient category, carbohydrates. Claims about the psychological effects of carbohydrates, especially sugar, are multiple. They range from the assumption that sugar enhances activity and aggression, to the premise that sugar has an energizing effect on behavior, to the assertion that sugar induces an anxious or depressed mood. Scientific evaluation and dissemination of accurate information about diet-behavior relations may lead to beneficial applications. They may also help to dispel folk wisdoms that can justify ineffective or even harmful health practices. Recent clinical research suggests that certain population subgroups selectively crave carbohydrates, usually as snack foods. Examples include some proportion of individuals with obesity (Hopkinson & Bland, 1982; Wurtmanetal., 1985), postpartum depression (Dalton, 1980), seasonal affective disorder (Rosenthai et al., 1984) and nicotine withdrawal (Grunberg, 1982). It is possible that these individuals are unwittingly practicing selfmedication, using carbohydrates to induce desired effects on mood and behavior. To evaluate this possibility, one must define the effects of carbohydrates on mood and behavior. To provide a rationale and interpretive framework for the empirical literature, we first examine possible mechanisms to explain the acute behavioral effects of carbohydrates. In the second section, we review findings from empirical studies of children, in which hyperactivity and associated performance impairments have been the most studied dependent variables. In the third section, we focus on studies of adults, including the effects of carbohydrate or tryptophan on mood, performance, pain, and sleep. We evaluate results with reference to methodological factors that could contribute to discrepant conclusions. These factors include research design, sample characteristics,