Scientists searched for methods to generate foods with qualities similar to those that animals receive in nature. Despite attempts to improve nutrients, animals wait for food to reach them; they don't hunt. In their original habitat, animals searched for their food source daily. In these confinement centers, animal trainers feed animals based on positive reinforcement, which devalues ​​their hunting skills (“Wild vs. Captivity”). Therefore, responding only to positive reinforcement causes animals to lose a large amount of daily exercise and increases stress. In addition, thanks to nutritionists and animal caretakers who studied and improved the meals, a standardization of the organization of these meals was created. The Institution of Association of Zoos and Aquariums, known as AZA, has put together guidelines that designate the Institution's orientations for the conservation of feeding programs. These feeding instructions include: preparing a nutritional diet that is consumed frequently, requiring a diet that represents the natural feeding cycle and an economical diet to feed ("AZA Nutrition"). AZA nutritional guidelines may be in place; however, the majority of zoos and aquariums do not take the extra step to change