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This Special Issue summarizes the results of several studies aimed at providing information on a series of questions related to the adequate protein and energy intakes that allow adequate growth and function in children and work performance and productivity in adults. The effect of different sources of protein on nitrogen balance and the requirements of essential amino acids in young children were also explored in fully recovered, previously malnourished children housed in the Metabolic Ward of the Biomedical Division of INCAP. The following are the main results of these investigations: Animal experiments and studies in children recovering from protein-energy malnutrition (PEM) strongly suggest that even when requirements of all nutrients are satisfied, inactivity reduces the rate of linear growth and physical activity improves it as well as lean body mass repletion. The effects of different energy intakes on nitrogen balance demonstrated how energy intake modifies the need to ingest different amounts of protein to satisfy protein requirements. Insensible nitrogen losses in preschool children and their relation to protein intake was demonstrated. The quality of even "good protein sources" modifies the amount needed to satisfy nitrogen requirements, and corn and bean-based diets can satisfy protein needs for health and even growth of young children. Essential amino acid requirements of 2-year-old children was assessed by diverse measurements of nitrogen metabolism and amino acid levels in blood, and were found lower than those recommended by FAO-WHO. In rural adult populations the relationship between energy and protein intake, productivity and body composition, and the impact of environmental hygiene on nitrogen balance was demonstrated and measured.

Anemia is highly prevalent, especially in poorly nourished populations living in unsanitary conditions. Studies of the Central American population showed that iron was the predominant deficient hematopoietic micronutrient and that correction of nutrient deficiencies led to hematological normality as defined by WHO. The bioavailability of diverse iron compounds added to the mostly vegetable diets of such populations showed the superior absorption of chelated iron (NaFeEDTA) and its strong effectiveness in correcting iron deficiency when added to sugar. The consequences on development and mental behavioral functions as well as on work capacity of iron deficiency and anemia in infants, children and adults, and the positive effects of their correction was demonstrated. In protein-energy malnourished (PEM) children, the deficit in active tissue mass (basal oxygen consumption) and in total hemoglobin content were closely related. This relationship persisted as the rates of active tissue mass repletion was modified by levels of protein intake. This demonstrated the strong adaptive nature of hemoglobin content in response to oxygen needs in PEM and during recovery. Gastrointestinal functions in PEM and in populations demonstrated the bacterial invasion of the upper GI tract and how this resulted in secondary bile acids that are toxic to the intestinal mucosal cells impairing their absorptive functions. Environmental hygiene in populations reversed gut bacterial migration and improved GI function.

This article summarizes thirty years of intensive clinical metabolic and therapeutic studies of the consequences of severe protein deficiency relative to calories, which results in kwashiorkor, and of a balanced deficiency of protein and calories that results in marasmus. Evidence is provided that these are two different metabolic diseases, but kwashiorkor is usually superimposed on some degree of chronic marasmus and hence most cases studied were marasmic kwashiorkor. The value of the creatinine/height index to indicate the degree of lean body cell mass with any disease is demonstrated.

The aim of this study was to determine whether women with low iron stores (plasma ferritin

Background: Lime-treated corn gruel (atole) is a common weaning food in iron-deficient populations, especially in Mexico and Central America, and is a potential vehicle for fortification with iron., Objective: The objective of this study was to screen promising iron compounds for use in the fortification of atole, using in vitro enzymatic digestion-dialysis techniques, while also considering their response to known iron absorption enhancers and inhibitors., Methods: Atole, unaltered or preincubated with phytase, was fortified with iron (10 mg/L) from ferrous sulfate, ferrous bisglycinate, or ferrous fumarate, or with ferric chloride, ferric ammonium citrate, or ferric sodium ethylenediaminetetraacetic acid (NaFeEDTA), and submitted to in vitro digestion. Dialysis of calcium, copper, iron, phosphorus, and zinc (analyzed by inductively coupled plasma atomic emission spectrometry) was measured when atole was fortified with iron compounds alone or together with ascorbic acid or disodium ethylenediaminetetraacetic acid (Na2EDTA)., Results: Iron dialyzability was higher with NaFeEDTA (p < .05) than with all other iron compounds, which did not differ among themselves in iron dialyzability. Addition of ascorbic acid had no significant effect on iron dialysis, whereas Na2EDTA enhanced iron dialyzability by 7 to 10 times in unaltered atole and 15 to 20 times in phytase-preincubated atole (p < .05). Addition of Na2EDTA always increased intrinsic zinc dialyzability, and most of the time this increase was significant. Phytase pretreatment generally increased mineral dialysis., Conclusions: Adding EDTA (either as NaFeEDTA or as Na2EDTA) to atole can increase the dialyzability of ferrous and ferric iron compounds and enhance the dialyzability of intrinsic zinc without any negative effects on calcium, phosphorus, or copper dialysis.

Tracer methodology using radioisotopes in human nutrition and metabolism research has been very productive but its use has been the object of unjustified limitations because of modeling decisions without adequate consideration of new data. These limitations have encumbered research studies in the metabolism of micro- and macronutrients particularly where nutritional deficiencies are prevalent. Even though stable isotope methodologies in human research are very useful in specific applications they are expensive and are often fraught with serious pitfalls, when compared to studies for the same purposes using radioisotopes. We have been developing safe radioisotopic methods to study the absorption and metabolism of micronutrients, especially iron and zinc, that can be applied to populations in the developing world. These and other applications of radioisotopes should allow scientists to conduct research diminishing the dependence on stable isotopes and on facilities and laboratories existing only in selected sites in the industrial world, and thus should enhance productive local and collaborative research. All radioisotopic research must be subjected to strict safety criteria, based on scientific evidence of risk, but should not be hampered by exaggerated fears of unfounded risk. Examples on the use of radio and stable isotopes to study iron and zinc absorptions are given including the radiation exposure and risk calculations.