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.
DIO Series Control Diets
Recently we have added three new control diet formulas for use with our DIO series diets in addition to D12450B.
D12450B D12450H D12450J D12450K
35% Sucrose D12451 Match/ 17% Sucrose D12492 Match/ 7% Sucrose No Sucrose
You may want to consider one of these other formulas depending on your research model. Contact one of our nutrition scientists for more information. See references below.
The Importance of a Proper Control 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.
While this concept is embraced by some researchers (1), it is surprising how often researchers do not use a matched control diet. One unfortunately common example is the use of a low-fat grain-based (GB) diet as the ‘control’ for a high-fat purified ingredient diet. Purified ingredient diets and GB diets should never be compared against each other since there are far too many differences between these diet types to make comparisons meaningful. If, for instance, a researcher finds that dozens of genes in a microarray are differentially expressed on a high-fat purified ingredient diet compared to a low-fat GB diet, it is tempting to conclude that gene expression was altered due to the differences in fat levels between the diets. However, just about everything else in the diets was different too, including the protein source, type and amount of dietary fiber and levels of minerals and vitamins, to name a few. Equally important (and often something not known by researchers) is the fact that GB diets contain many plant-derived chemical entities that are absent from purified ingredient diets. Examples include phytoestrogens and heavy metals, both of which can have real and measurable effects on the animal’s phenotype.
One reason sometimes given for the use of GB diets as ‘controls’ for purified ingredient diets is cost. There is no doubt that purified ingredient diets cost more than GB diets; this is mainly due to the inherent costs of the raw materials. So to use a properly matched purified ingredient diet does add costs to the study. But how much money is actually saved if the use of a GB diet brings into question the conclusions made from the data?
In dietary studies, without the use of a properly matched, purposely designed control diet, it is simply not possible to know how to interpret the data at the end of the experiment. Unfortunately, this can lead to erroneous conclusions and, ironically, the need to spend more money (and time) repeating the study.