Report, Repeat and Revise
When choosing a control diet, one should ask three questions: Can I report it (can I tell others exactly what my animals were fed)? Can I repeat it (is there diet variability and will I be able to get the same results next year)? Can I revise it (as my hypotheses change, can I easily change the dietary components while keeping it otherwise matched to previous diets)? The answer should be “yes” to all three. Additionally the control diet formula should be matched to that of the experimental diet.
The goal of most laboratory animal studies is to study the effect of an intervention or treatment on phenotypic outcomes. Often this means that the experimental group of animals is fed a special diet. For example, this could be a high-fat diet, a diet lacking a nutrient or a diet with an added compound.
As scientists, we are all taught early in our careers how to minimize variability between experimental and control groups. We do this because reducing variability means that we will have greater power in our statistics to show phenotypic differences and ultimately be able to use fewer animals. In lab animal studies, we aim to reduce variability between groups by housing all of the animals in the same room, using the same number of animals per cage and using the same water, bedding, enrichment and diet. So, when experimental animals are fed a special diet, the control animals should be fed a diet matched in every way to the special diet, except of course for the dietary variable that the researcher is studying.