dietetics
(dī‵ĕ-tĕt'ĭks 
)
[Gr. diaitetikos ]
The science of applying nutritional data to the regulation of the diet of healthy and sick individuals. Some fundamental principles and facts of this science are summarized here.
Conservation of Energy: To produce metabolic balance, the number of calories consumed must equal the energy required for basic metabolic needs plus additional energy output resulting from muscular work and added heat losses. Thus a person whose basal rate is 1000 kcal per 24 hr may do work and lose heat during the day, adding about 1500 kcal to the energy output; he or she must, therefore, obtain 2500 kcal per day.
One g of fat yields approx. 9 kcal. One g of carbohydrate or protein yields about 4 kcal.
Note: To convert kilocalories to kilojoules, multiply them by 4.1855.
Conservation of Matter: Everything that leaves the body, whether exhaled as carbon dioxide and water or excreted as urea and minerals, must be replaced by food. Thus, a person excreting 10 g of nitrogen daily must receive the same in his or her diet, for the element can be neither created nor destroyed. This metabolic balance may be monitored by careful chemical analysis of all that is eaten and excreted.