Dietary & Drug Studies
Dietary studies are conducted to answer questions people have about themselves and animals, such as “What foods are best to eat?” Since the beginning of the 20th century, scientists have been attempting to answer such questions using animals in dietary studies. It is important to use animals in dietary studies, for only in living systems can the complex interactions that occur among nutrients and digestive fluids be observed. There are some cases, for example, in which the need for one nutrient decreases when the concentration of another increases. There are also cases in which the damaging effects of poisons, such as mercury, can be reduced by the addition to the diet of certain nutrients, such as selenium. Chemical methods have not yet been developed that give scientists the same information attained by bioassays, or tests in living systems.
If an animal is to be used to study a particular nutrient, it must require that nutrient. Rats are able to synthesize their own vitamin C, and therefore do not require it in their diet. Consequently, for dietary studies of vitamin C, species such as guinea pigs and nonhuman primates must be used because they require vitamin C in their diets.
In new drug studies, a bioassay provides a means of determining the activity of a substance in a living animal. If pairs of animals are given substances that are identical except for a known different ingredient, then any difference observed might be attributable to that ingredient. In this way, a synthetic hormone might be compared with a naturally occurring hormone to see if they both have the same effect in test animals. Bioassays must also be used to test for substances for which no in vitro test is known.