Diet- Induced Disease Models

Simple Idea

The idea behind open source diets is simple: each nutrient is supplied by a separate, purified
ingredient. In the strictest sense of the terms, purified and semipurified diets differ in the types
ingredients used, though today the terms are generally used to mean the same thing. Purified
ingredient diets are generally ‘open' formulas, meaning that they are published and available to
the scientific community.

History

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 (PDF 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).

It is because these ingredients are refined materials, each containing one nutrient, (as opposed to the less refined chow ingredients) that allowed research nutritionists to define the nutritional requirements of animals, by selectively removing one nutrient at a time from the diet. This also means that the possible modifications one can make to a purified ingredient open source diet are virtually limitless. This is also what continues to make OpenSource Diets powerful research tools and why so many scientists have turned to them in recent years.

Report, Repeat and Revise

First, open source diets are simple to report . For example, a paper may state that “rats were fed the AIN-76A diet for the entire study”. The list of ingredients and their quantities can be easily and precisely described. Hence, researchers world wide will be able to duplicate the diet should they want to, or compare it to the diet they are using. And, since there is very little variation between batches of purified ingredients, the AIN-76A diet made today will be the same as the AIN-76A diet made a year from now. This repeatability of OpenSource diets over time provides advantages over chows, either when using a special formulation (such as one low in thiamin for example) or when using the diet for maintenance during a toxicological study, when variation in data over time may make interpreting the toxicity of the compound difficult.

It is in diet modifications where OpenSource diets most clearly illustrate their advantage over chow diets. For example, diets with high levels of sucrose (and no corn starch) have been formulated and used to study the development of insulin resistance. The fat source can be changed from coconut oil, to olive oil to safflower oil, to study the effects of changing the fat type from primarily saturated, to monounsaturated to polyunsaturated fatty acids, respectively. As mentioned earlier, individual or multiple vitamins and minerals can be removed to study their deficiencies and to define requirements. OpenSource Diets are simple to revise.