Edward Fern

The Nutrient Balance Concept: A New Quality Metric for Composite Meals and Diets

Background Combinations of foods that provide suitable levels of nutrients and energy are required for optimum health. Currently, however, it is difficult to define numerically what are ‘suitable levels’. Objective To develop new metrics based on energy considerations—the Nutrient Balance Concept (NBC)—for assessing overall nutrition quality when combining foods and meals. Method The NBC was developed using the USDA Food Composition Database (Release 27) and illustrated with their MyPlate 7-day sample menus for a 2000 calorie food pattern. The NBC concept is centered on three specific metrics for a given food, meal or diet—a Qualifying Index (QI), a Disqualifying Index (DI) and a Nutrient Balance (NB). The QI and DI were determined, respectively, from the content of 27 essential nutrients and 6 nutrients associated with negative health outcomes. The third metric, the Nutrient Balance (NB), was derived from the Qualifying Index (QI) and provided key information on the relative content of qualifying nutrients in the food. Because the Qualifying and Disqualifying Indices (QI and DI) were standardized to energy content, both become constants for a given food/meal/diet and a particular consumer age group, making it possible to develop algorithms for predicting nutrition quality when combining different foods. Results Combining different foods into composite meals and daily diets led to improved nutrition quality as seen by QI values closer to unity (indicating nutrient density was better equilibrated with energy density), DI values below 1.0 (denoting an acceptable level of consumption of disqualifying nutrients) and increased NB values (signifying complementarity of foods and better provision of qualifying nutrients). Conclusion The Nutrient Balance Concept (NBC) represents a new approach to nutrient profiling and the first step in the progression from the nutrient evaluation of individual foods to that of multiple foods in the context of meals and total diets.

Protein turnover, nitrogen balance and rehabilitation.

Not many studies have been done on protein turnover during recovery from malnutrition. Some relevant information can, however, be obtained from measurements on normal growing animals, since rehabilitation and normal growth have in common a rapid rate of net protein synthesis. The key question is the extent to which net gain in protein results from an increase in synthesis or a decrease in breakdown or both. Different studies have used different methods, and all methods for measuring protein turnover have some disadvantages and sources of error. It is important to bear this in mind in evaluating the results. Consequently, part of this paper will be devoted to questions of methodology. Whole body protein turnover has been measured in children recovering from severe malnutrition. During the phase of rapid catch-up growth the rate of protein synthesis is increased. As might be expected, it increases linearly with the rate of weight gain. At the same time there is a smaller increase in the rate of protein breakdown. The resultant of these two processes is that, over and above the basal rate of protein synthesis, 1.4 grams of protein have to be synthesized for 1 gram to be laid down. Very similar results have been obtained in rapidly growing young pigs. Experimental studies on muscle growth in general confirm the conclusion that, at least in muscle, rapid growth is associated with rapid rates of protein breakdown as well as of synthesis. This has been shown in muscles of young growing rats, as well as in muscles in which hypertrophy has been induced by stretch or other stimuli. In contrast, the evidence suggests that rapid growth involves a fall in the rate of protein degradation. The magnitude of the nitrogen balance under any conditions is determined by the difference between synthesis and breakdown. In the absence of any storage of amino acids, this must be the same as the difference between intake and excretion (S - B = I - E). A question of great interest is whether, at a given intake, the extent of N balance is determined primarily by regulation of synthesis and breakdown or by regulation of amino acid oxidation. Clearly, a reduction in amino acid degradation is equivalent to an increase in amino acid intake. An interesting subject for future research is the extent to which the amino acid degrading enzymes adapt to the requirements imposed by growth and rehabilitation.