In the early days of purified diet use, many research nutrition groups developed; each using their own favorite purified diet and usually using making them in house. For example, Vitamin A researchers developed separate and very distinct purified diet formulas from those studying Vitamin D or selenium or Vitamin E. Because of these differences, it became quite difficult to compare observations across these nutrient study disciplines, from lab group to lab group. Despite these differences, the formulas were generally well reported, allowing one group to know exactly what another group had fed their animals.
In the early 1970's, the American Institute of Nutrition (AIN) recognized that research nutritionists were traveling down these many separate tracks and also that other non-nutrition biologists were returning to the fold and using purified ingredient diets to study all aspects of health and disease. The AIN formed a committee and designed the AIN-76 rodent diet to 'guide' research and suggested that a simple purified ingredient diet be adopted for use as a 'standard' purified diet by all biologists. The AIN-76A rodent diet formula was the result.
In the AIN-76A rodent diet, the protein requirement is met by the milk protein casein, along with added methionine (to meet sulfur-containing amino acid requirements). Carbohydrates in this case are supplied by corn starch and sucrose, corn oil provides the fat and cellulose supplies the fiber. Vitamin and mineral mixes specific to rodents are added to ensure adequacy. Each nutrient is supplied by a separate, purified ingredient. (It is true that casein, for example contains trace levels of certain vitamins and will contain small amounts of some minerals. In general this only becomes of importance when the goal of the experiment is to induce a deficiency state in one of those vitamins or minerals. In those cases, one can use alcohol-extracted casein [to remove the trace amounts of fat and fat-soluble vitamins] or individual amino acids [the literal links in the protein chain] to lower the background levels of these nutrients).
In 1993 because of numerous nutritional and technical problems encountered with the diet during this period, AIN-76A was revised. Two new formulations were derived: AIN-93G for growth, pregnancy and lactation, and AIN-93M for adult maintenance. Some major differences in the new formulation of AIN-93G compared with AIN-76A are as follows: 7 g soybean oil/100 g diet was substituted for 5 g corn oil/100 g diet to increase the amount of linolenic acid; cornstarch was substituted for sucrose; the amount of phosphorus was reduced to help eliminate the problem of kidney calcification in female rats; L-cystine was substituted for DL-methionine as the amino acid supplement for casein, known to be deficient in the sulfur amino acids; manganese concentration was lowered to one-fifth the amount in the old diet; the amounts of vitamin E, vitamin K and vitamin B-12 were increased; and molybdenum, silicon, fluoride, nickel, boron, lithium and vanadium were added to the mineral mix. For the AIN-93M maintenance diet, the amount of fat was lowered to 40 g/kg diet from 70 g/kg diet, and the amount of casein to 140 g/kg from 200 g/kg in the AIN-93G diet. Because of a better balance of essential nutrients, the AIN-93 diets may prove to be a better choice than AIN-76A for long-term as well as short-term studies with laboratory rodents.(1)
1. Reeves PG, Nielsen FH, Fahey GC Jr. AIN-93 purified diets for laboratory rodents: final report of the American Institute of Nutrition ad hoc writing committee on the reformulation of the AIN-76A rodent diet. J Nutr. 1993 Nov;123(11):1939-51.