Abstract
Reproductive functions are regulated by the sophisticated coordination between the neuronal and endocrine systems and are sustained by a proper nutritional environment. Female reproductive function is vulnerable to effects from dietary restrictions, suggesting a transient adaptation that prioritizes individual survival over reproduction until a possible future opportunity for satiation. This adaptation could also partially explain the existence of amenorrhea in women with anorexia nervosa. Because amino acid nutritional conditions other than caloric restriction uniquely alters amino acid metabolism and affect the hormonal levels of organisms, we hypothesized that the supply of essential amino acids in the diet plays a pivotal role in the maintenance of the female reproductive system. To test this hypothesis, we examined ovulatory cyclicity in female rats under diets that were deficient in threonine, lysine, tryptophan, methionine or valine. Ovulatory cyclicity was monitored by daily cytological evaluations of vaginal smears. After continuous feeding of the deficient diet, a persistent diestrus or anovulatory state was induced most quickly by the valine-deficient diet and most slowly by the lysine-deficient diet. A decline in the systemic insulin-like growth factor 1 level was associated with a dietary amino acid deficiency. Furthermore, a paired group of rats that were fed an isocaloric diet with balanced amino acids maintained normal estrous cyclicity. These disturbances of the estrous cycle by amino acid deficiency were quickly reversed by the consumption of a normal diet. The continuous anovulatory state in this study is not attributable to a decrease in caloric intake but to an imbalance in the dietary amino acid composition. With a shortage of well-balanced amino acid sources, reproduction becomes risky for both the mother and the fetus. It could be viewed as an adaptation to the diet, diverting resources away from reproduction and reallocating them to survival until well-balanced amino acid sources are found.
Highlights
Understanding gender-specific nutritional requirements is an important goal of modern health care research, for women whose nutritional requirements change during different reproductive stages, including pregnancy, lactation, menstruation and menopause
A significant repression of food intake was observed after the onset of all of the essential amino acid-deficient diets
This study found that consumption of a Val, Met, Trp, Thr or Lys-deficient diet promptly induced a persistent diestrus state in female Wistar-Imamichi rats
Summary
Understanding gender-specific nutritional requirements is an important goal of modern health care research, for women whose nutritional requirements change during different reproductive stages, including pregnancy, lactation, menstruation and menopause. In rodents, caloric restriction inhibits the reproductive cycle in females but does not adversely affect male fertility [3,4,5]. Anorexia nervosa of sufficient severity induces amenorrhea in women [6,7], whereas no observable reproductive dysfunction is found in men with this eating disorder behavior. Serotonergic vulnerability caused by nutritional insufficiency varies by gender and female reproductive stage [8]. Pre-menopausal women were found to be more resistant than men to obesity-related atherosclerotic heart disease [9], and the influence of energy intake on disease susceptibility may be different between females and males
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