The ability of the body to deposit material in the tissues in times of plenty and to mobilize it when need arises can readily be demonstrated. Thus the areolar connective tissue is a reservoir for excess energy in the form of fat, the muscle and liver contain protein that is available in an emergency, and now even the skeleton is looked on as a labile structure as far as the give and take of mineral salts is concerned. It is not surprising, then, that metabolic balance studies tend to show differences in the retention of biochemically important substances depending on the relative adequacy of the intake of these substances before the period of observation. In general, a more or less prolonged suboptimal consumption of a dietary essential is likely to be followed by an increased retention when the supply is abundant. This phenomenon has been shown for nitrogen, vitamin A,
METABOLISM IN PREGNANCY. JAMA. 1937;108(22):1892. doi:10.1001/jama.1937.02780220050012
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