The choice between cereal based or semi-pure diets.
Custom diets are formulated to set nutritional specifications from a range of raw materials. But the choice of raw materials is important.
For cereal based diets the list of ingredients includes grains and grain byproducts, other plant materials, meat, fish, vegetable oils, minerals such as limestone or dolomite and many other “natural” materials. In addition to the well defined nutritional composition “natural” raw materials contain compounds that are physiologically and / or pharmacologically active.
For pure or semi-pure diets we formulate the diet from highly refined raw materials. This results in a more fully characterised diet, theoretically reproducible anywhere.
A recent publication by Nielsen 2018 describes some of these differences https://doi.org/10.1093/jn/nxy121
For more detail go here