Page 80 - Small Animal Clinical Nutrition 5th Edition

80 Small Animal Clinical Nutrition

Box 5-7. Adequate vs. Optimal Nutrient Intake.*
VetBooks.ir NUTRITIONAL ESSENTIALITY of selenium) with reduced risks of chronic diseases.

In these cases, nutrient effects do not appear to have the speci-
Nutritional essentiality describes those factors in the external ficity connoted by the nutritional essentiality paradigm. For exam-
chemical environments of organisms specifically required for nor- ple, the complementary natures of the antioxidant functions of vita-
mal physiologic functions. At least 40 such factors (e.g., vitamins, min E, vitamin C and selenium suggest that any one “spares” the
minerals, amino acids, fatty acids, water) are generally considered need for the others in protecting against lipid peroxidation. Thus,
to be nutritionally essential. Foods are considered nutritionally the antioxidant nutrients appear to be risk modifiers of disease
“adequate” if they contain amounts of each of these essential nutri- rather than primary agents in their etiologies.
ents that meet or exceed known needs.
The science of nutrition has functioned for a century under the ARE NON-NUTRIENTS REQUIRED?
nutritional essentiality paradigm that holds nutrients are essential
to prevent ill health in very specific ways. Specific prevention of The nutritional essentiality paradigm relates only to nutrients (i.e.,
nutrient deficiency diseases has been used to define nutrient dietary factors that are absorbed and function in normal host
essentiality and establish dietary recommendations. Indeed, unless metabolism). Yet, it has become evident that some such non-nutri-
a clinical disease has been related specifically to the deprivation of ents (e.g., fiber) can positively affect health through functions that
a certain nutrient, then that nutrient has not been considered are technically external to the body. Several positive physiologic
“essential.” responses have been associated with the consumption of isolated
Investigators have been able to estimate nutrient requirements fiber fractions or fiber-containing foods. Epidemiology has revealed
quantitatively based on the specific deficiency disease connotation of associations of fiber-rich diets with reduced risks of cancer, coro-
the nutritional essentiality paradigm. The term “required” is general- nary heart disease, diabetes mellitus, diverticulosis, hypertension
ly used in reference to the lowest intake that prevents disease. Such and gallstone formation in people. Yet, under the nutritional essen-
minimum requirements, while seemingly physiologically relevant, are tiality paradigm, these effects are not easily described.
difficult to define or measure with any reasonable precision due to
inter-individual variation, which is also difficult to estimate. NEW PARADIGM
Reference levels of intake (“adequate levels”) are set to exceed A new paradigm for nutrition is emerging out of the limitations of
such minimums, and thus to have acceptably low risk of deficien- the essentiality paradigm. It takes an individualized view of organ-
cy. Because risk is the probability of events occurring within popu- isms. It recognizes both endogenous and exogenous conditions as
lations, allowances relate to populations with their characteristic determinants of the dietary needs for definable health outcomes.
food habits and inherent inter-individual variations in minimum These outcomes are not necessarily specifically associated with
requirements. Thus, the recommended dietary allowances (RDAs) single nutrients. It recognizes these factors as nutrients if their
and the reference (recommended) dietary intakes (RDIs) are implic- activities benefit the metabolism and/or gastrointestinal function of
itly intended to relate to the United States population (human) just the host. It recognizes various outcomes as appropriate for various
as the Association of American Feed Control Officials (AAFCO) Dog individuals, both within a species/population, as well as between
Food and Cat Food Nutrient Profiles relate to pet populations.
species.
Freedom from overt physiologic dysfunction and reduced risk of
CONDITIONALLY ESSENTIAL?
chronic diseases have become important outcomes in human and
The nutritional essentiality paradigm does not pertain to cases in pet nutrition. Nutritional needs will be based on individual genetic
which nutrient needs of an individual or minority subgroup differ and metabolic characteristics to the end that foods can be pre-
markedly from those of the general population. Under certain condi- scribed on an individual basis.
tions, a dietary source of a “nonessential” nutrient can be needed to Its having become rather elastic in its application indicates that
prevent physiologic dysfunction. For example, glutamine can reduce the nutritional essentiality paradigm has been outgrown: Nutrients
nitrogen loss and infection rate of bone marrow transplant patients. have come to be described as being required/essential for particu-
Carnitine can improve weight gain and nitrogen balance of parenter- lar functions. Some are called dispensable/indispensable under
ally fed infants, and helps maintain lean muscle mass in animals certain conditions. Several are recognized as beneficial at levels
undergoing weight loss. The nutritional roles of these nutrients are greater than may be required.
simply not addressed by the nutritional essentiality paradigm. Outgrowth of the old paradigm is occurring at an increasing pace
with the development of the modern field of molecular biology. It is
NONSPECIFIC EFFECTS? now clear that some nutrients function as gene regulators and that
genetic bases can predispose to disease. The time is quickly
The specific deficiency disease connotation of the nutritional essen- approaching when it will be possible to identify disease predisposi-
tiality paradigm has become a growing problem in dealing with tion, metabolic characteristics and specific dietary needs individu-
issues of diet and health.This is because the paradigm does not per- ally. Then, the population-based paradigm will be defunct and a
tain to functions of nutrients that are either nonspecific or nontradi- new way of thinking about dietary needs will emerge.
tional (i.e., outside the known functions of nutrients). Such functions
have been suggested by recent epidemiology, which has produced
evidence linking the consumption of several nutrients (e.g., high *Excerpted from an article originally published by PetFood Industry
intakes of vitamin A-containing foods, relatively high intakes or high in July/August 1998, pages 31-43.
plasma levels of vitamin E and supranutritional dietary supplements