weight cycling, were discussed and appear to be insignificant. In this section, several major health implications of chronic restrictive dieting are described.

Energy Deficit and Cognitive Function

Military readiness may be affected by chronic energy deficit. The original studies of semi-starvation by Keys et al. (1950) demonstrated that long-term food restriction is associated with reduced heart rate, lethargy, depression, and irritability. While the subjects in these studies complained of changes in intellectual functions such as concentration, judgment, and memory, the testing protocol used in these studies did not demonstrate a serious impairment. More recent research has focused on the impact of chronic dieting on cognitive functions.

Chronic dieting may have a negative impact on cognitive functions, such as attention, vigilance, and reaction time, that may be important in a military setting. For example, evidence suggests that restrained eating (that is, conscious control of eating in relation to concerns about weight) may result in preoccupation with food and eating, binge eating once food is available, and increased emotional responsiveness (Polivy, 1996). Chronic dieters may be more distractible than nondieters and are less able to concentrate on rote tasks in the face of noise or other environmental distractions (Polivy, 1996); they may also display poorer vigilance, poorer immediate memory, and have slower reaction times (Green and Rogers, 1995; Green et al., 1994; Kretsch et al., 1997). Short-term dieting has been reported to decrease plasma tryptophan and brain serotonin function (as indicated by an increase in tryptophan-stimulated prolactin secretion) and to increase irritability and sleep disturbance in women (Anderson et al., 1990; Goodwin et al., 1987a, b).

Studies on the psychological effects of chronic dieting have produced mixed results. For example, some studies have reported depression, anxiety, decreased self-esteem, and other negative psychological outcomes among dieters (Brownell and Rodin, 1994; French and Jeffery, 1994; Polivy, 1996). However, other studies have reported positive psychological findings, such as improved mood and decreased depression (French and Jeffery, 1994). The positive findings may be associated with use of behavior therapy when dieting, which may counteract some of the negative psychological impacts of chronic dieting (French and Jeffery, 1994). As mentioned previously, dieting behavior may also be a risk factor for the development of eating disorders, but its causal strength is unclear (French and Jeffery, 1994).

Female Athlete Triad

Chronic restrictive dieting and high levels of exercise have been associated with amenorrhea and a related increase in the risk of osteoporosis and stress fracture of the lower extremities and pelvis in a syndrome known as the female athlete triad (ACSM, 1997; Bennell et al., 1995).

A considerable amount of research has been devoted to pinpointing the nutritional factor(s) responsible for, as well as the mechanisms involved in, female athlete triad. In a review that focused on women who participate in competitive athletics, the frequency of stress fractures was reported to be four times higher in women who report irregular menses than in eumenorrheic

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