A nutritional balance study involves the measurement of the intake of a specific nutrient as well as the elimination of that nutrient in urine, feces, sweat, etc. If intake is greater than loss of a particular nutrient the individual is said to be in "positive balance." If intake is less than loss, an individual is said to be in "negative balance" for the nutrient of interest.
A balance study is useful for determining the amount of a nutrient that will prevent deficiency; however, it provides little information regarding the amount of a nutrient required for chronic disease prevention or optimum health.
The fraction of an administered compound that reaches the blood distribution network (heart, blood, and blood vessels) and is transported to site of action (target tissue).