The trend in the media, on web sites, and other sources of information on the topic of human nutrition to identify particular foods as "good" or "bad" is confusing at best. Unfortunately, that trend appears to have become common in discussion of pet nutrition as well. Much opinion can be found to either praise or malign a particular food or food ingredient. Depending on the source or the findings of a particular study, some substances are both "good" and "bad." Most often, the positive or negative effect of a food on health is related to dose. However, that factor is often lost in discussion of the effects of an ingredient on health.

Occasionally, petfood consumer advocates will decide to attack the safety or value of a petfood ingredient based on little pertinent data but much speculation and innuendo. This occurred with the antioxidant preservative ethoxyquin in the early 1990's. A web site seemingly devoted to the total removal of menadione (a synthetic source of vitamin K activity) from petfoods has many companies nervous. However, it appears that it is the petfood companies themselves that often drives the consumer's concerns regarding petfood ingredient safety. Eager to distinguish themselves from competitors, it is the marketing strategy of some companies to disparage the safety and wholesomeness of other products on the market. Even without accompanying explanations, simple statements of "no this!" or "that-free!" leads the consumer to question why a perfectly legitimate ingredient with a long history of safe use is in the other product, and to fret over what harmful effects that may have on their pets. At the same time, companies may laud the inclusion of ingredients for which there are no appreciable data or experience to show safety as used. In fact, many times the ingredient isn't even approved for use in animal feeds or petfoods.

While "good" or "bad" doesn't appear appropriate to describe most legitimate ingredients, some sure are "ugly." For example, "meat by-products" connote all sorts of unappealing perceptions, while it includes many parts that humans do eat themselves (e.g., livers, but also intestinal casings, thymus, kidneys, brains and blood). Other components of meat by-products may include things humans do not eat, such as spleens, udders and bone. While unappetizing to most people, they still can be legitimate sources of nutrition, and if processed correctly, consumed safely by pets.

Under the law, all ingredients in petfoods must be either GRAS (generally recognized as safe) substances, approved food additives, or otherwise sanctioned for its intended use in animal feed.

Food additives may be "direct" or "indirect" food additives. Examples of the former include preservatives and other substances intended for technical effects on the food, but may also include nutrients such as selenium. For regulatory purposes, irradiation of food or feed is considered a direct food additive. Indirect food additives include packaging and other food contact materials, food equipment lubricants, and other substances that may become a component of the final product. A food additive must be approved by FDA prior to use in petfood. Extensive data must be submitted to characterize the nature or the substance, to document methods of manufacturing, and to demonstrate both utility and safety. Aspects of safety reviewed include acute and chronic toxicity, carcinogenicity, teratogenicity and mutagenicity. Limits or restrictions on levels in products, types of products, intended species, etc., are spelled out in the resulting regulation.

GRAS substances include a codified list of ingredients in the FDA regulations, primarily of ingredients found to be of common use in foods or feeds prior to the change of laws in 1958 that established the food additive approval process. This includes many spices and other flavoring agents, nutrients, and other substances intended for technical effects on the food (e.g., preservatives, anticaking agents, emulsifiers, gums). The regulations note that not all ingredients that would be GRAS can be codified, though. Substances commonly thought of a "food" (e.g., salt, vinegar) or has a long history (i.e., pre-1958) of safe use in diets of animals are most often considered GRAS. Thus, many of the ingredients listed in AAFCO that may stem back to as far as 1909 may in fact be GRAS, but simply are not formally codified as such.