General Information
As a reference point, the AIN purified diets have in the range of 4-7% fat by weight, or about 10-18% of energy from fat. Adding fat (at the expense of carbohydrate) is done to increase the kcal density. Diets with higher fat levels will have a greater kcal density, since fat contains 9 kcal/g vs. 4 kcal/g for carbohydrate or protein. The AIN-93G diet contains approx. 3.8 kcal/g, while a typical diet with 45% kcal from fat has ~4.5 kcal/g and a diet with 60% of kcal from fat has ~5.0-5.5 kcal/g. In the formulation of a high fat diet, it is common to adjust other nutrients (vitamins, minerals, protein) relative to energy content.

A number of different fat sources can be used (solid fats, oils), and diets can be designed to target a specific fat level or fatty acid profile.

The amount and type of fat used can affect pellet quality. As the fat level increases, pellet quality (durability) is compromised. Some higher fat formulas are available only in non-pelleted form. Depending on the fat source used, the diet could be dense and crumbly, dough-like, or paste like.

Diets for Diet Induced Obesity (DIO)
Purified high fat diets used to induce obesity and obesity-related complications such as diabetes and metabolic syndrome typically have from 40-60% of energy derived from fat. The DIO flyer (same link as above) summarizes relevant diet details for seven different diets, and includes a table with information on the fatty acid profile of various fat sources used in purified diets.