Nutrigenomics and the future of dietetics.
Dietetics professionals will play a central role in disease management and prevention in the years ahead in ways never before possible. (6,7) Clinicians will possess knowledge and skills unique within health care. Those in the community health and public policy arenas will understand the molecular basis for ethnic differences in nutrient requirements and will be in a position to develop effective dietary approaches tailored to each ethnic group. Dietetics professionals in the food sciences will use nutrigenomics to identify and isolate the bioactive components in food and will develop health-promoting functional foods. The need for education of consumers and health care professionals will be extensive and ongoing. Clearly, nutrigenomics will have a significant impact on the field of dietetics.
The concept of nutrigenomics is not new. What is new is the appreciation of its integral role in health and disease. The biological world has long benefited from the practical applications of this concept. From primitive unicellular microorganisms to the most highly evolved mammals, genetic mechanisms exist that allow information from the environment surrounding a cell to be transmitted to the genetic material deep within that cell. In elaborate signalling cascades that impact gene expression, bioactive components from food serve to inform the organism about the nutritional sufficiency of its environment. These same bioactive dietary components supply an organism with essential nutrients that, because of genetic mutations, the organism cannot synthesise and depends upon the environment to supply. The evolutionary process itself has been significantly impacted by the 'goodness-of-fit' between the genetic make-up of an organism and the food present in its environment.
Contribution of the Human Genome Project
The Human Genome Project has been the impetus for the development of nutrigenomics as it is emerging today. (8) This ambitious project, which began in 1990, was initially conceived as a 15-year multinational effort to identify the sequence of three billion nucleotides that comprise human genetic material. The project has been highly successful, has grown significantly in scope and is ongoing. Today the human genome sequence is virtually complete, the genomes of numerous other organisms have been sequenced and the focus has shifted to determining the products of these sequences and their roles in the function of organisms.
One of the earliest practical applications derived from the Human Genome Project has been in the field of pharmacogenomics, the study of genetic influences on drug metabolism. (9) For any given pharmaceutical, there are individuals within a population who benefit from the drug's action, those who derive little benefit and those who experience harmful side-effects. The underlying basis for this heterogeneous response within a population is the genetic heterogeneity with respect to key drug-metabolising enzymes. Specific genetic variants of these enzymes have been associated with particular drug responses. Diagnostic tests are now available that allow clinicians to detect which genetic variants an individual carries and predict that individual's response to a particular drug. Pharmacogenomics points up the advisability of matching pharmaceutical therapy with the drug-metabolising capabilities of the individual, abilities that derive from the individual's genetic make-up.
In many respects, nutrigenomics parallels the development of pharmacogenomics. As with pharmaceuticals, a number of key enzymes and metabolic reactions are involved with the digestion, absorption and metabolism of food. Genetic variations in these key processes lead to a population's heterogeneous response to diets in general and specific food components in particular. The ability to match foods to the genetically determined capability of using that food for positive benefit is crucial to an individual's optimal health. (10,11)
However, nutrigenomics differs from pharmacogenomics in several important aspects. Many decades of pharmacological research have led to a strong foundation of scientific knowledge, which has given rise to the practical applications of pharmacogenomics. In contrast, nutrition research is in its infancy. Unlike drugs, food is a complex mixture of numerous components. Furthermore, an individual's genetic material has been interacting with food components for its entire lifetime, which may have lasting physiological consequences as compared with the limited drug-genome interactions. These important differences will likely slow the entry of nutrigenomics into wide-spread application compared with the rapid entry of pharmacogenomics.
Impact of nutrigenomics on dietetics
Nutrigenomics will ultimately impact all of dietetics. Research in the food and nutrition sciences is central to understanding underlying mechanisms that form the basis for practical applications. From food science research will come insight into which bioactive food components effect genetic changes and how. These components will be isolated and added to commonly eaten foods or made available as dietary supplements. Food scientists will be instrumental in developing new functional foods that contain bioactive dietary components known to promote health and reduce disease burden. From nutrition research will come strong associations between genes and diseases, which in turn will lead to diagnostic tests for the detection of particular genes. Nutrition research will further identify the influence of the environment on the outcome of those associations and be the source of targeted, effective therapeutic interventions. There will likely evolve a universal set of dietary recommendations that are based on genetic considerations, with dietary guidelines for specific populations reflecting the predominant genetic composition of that population.
Research into consumer acceptance and concerns is another important component of this emerging field. It is not enough to develop foods that promote health. In order for nutrigenomics to be maximally useful for health promotion purposes, foods must be tasty, eye-appealing and convenient. Further, consumers must come to view their genetic make-up as simply another piece of important health information, similar to height, weight and blood pressure. Additionally, the ethical, legal and social implications of nutrigenomics are critical issues to address.
The application of nutrigenomics will not wait until the research base has been built. Potential applications of food and nutrition research vary widely, from maximising the nutritional composition of foods, to guiding the dietary recommendations of populations and individuals, to designing nutritional interventions targeted to particular genetic constitutions. In the clinical realm, dietetics practitioners will have the opportunity to expand from nutrition counselling to genetic counselling to a combination of the two as diagnostic tests become available that pinpoint the genetic basis for a disorder and help determine the appropriate lifestyle interventions. Education and communication skills are integral to all of these anticipated applications.
Preparing for the nutrigenomics era
The scope of dietetics is expanding as its central role in health promotion and disease prevention becomes established. (6,7) Preparing for this expanding role is challenging, yet essential. The initial impact of nutrigenomics on dietetics will be felt increasingly over the next decade and then will escalate as the research foundation clarifies the interactions among genes, environment and bioactive food components and provides the basis for using these food components to effect desirable outcomes. A thorough understanding of food and nutrition at the mechanistic level will be required. Dietetics professionals must develop a solid base of knowledge from the core sciences: biology, chemistry, biochemistry, physiology, food science and nutrition, with genetic principles and technologies integrated throughout. Critical thinking skills are essential in an age of science-based practice. A lifelong approach to learning is necessary in order to stay abreast of dietetics as the pace of discovery escalates. Communication skills of all types will continue to be important regardless of practice focus. An understanding of the psychosocial dimension of human behaviour will be needed in many areas of dietetics. The dietetics professional of tomorrow is more likely to be an entrepreneur than has been true in the past and will benefit from attaining business development and management skills.
It is unlikely that all this knowledge and expertise can be acquired in the undergraduate years alone. Nutrigenomics provides an opportunity to reconsider the education and training of dietetics professionals. To develop the level of competency required, graduate level training is highly desirable if not essential. Furthermore, the undergraduate program will likely offer tracks that steer students into one of several possible practice directions and will focus on the academic preparation needed for successful practice. The master's level graduate program would then focus on the practical training needed for specialty certification along with any additional educational needs. Graduates will then function as entry-level practitioners, laboratory associates, educators and entrepreneurs. Doctoral level programs would include extensive practical experience and prepare students to conduct independent research, develop nutrition policy, or practise as relatively autonomous health care professionals specialising in nutrigenomics.
The dietetics professional as thought leader
A number of issues will emerge that will need to be addressed by thought leaders within the dietetics field. Among these issues are certainly the ethical, social and legal issues alluded to earlier. Thought leaders will also grapple with the best diet for the human genome. Given that human genes have changed little over the past 10 000 years since the agricultural revolution, (12) would that diet more resemble human's ancient diet rather than the highly processed diet of today? If the cultivation of grains occurred late in human development, is it sound from a genetic perspective for today's diet to be heavily grain-based? To what extent can the diet be a universal one fine-tuned for genetically distinct populations?
Issues relating to nutrient requirements, recommendations for nutrient intake, and how best to, and even whether to, fortify food with nutrients and other bioactive food components must be addressed. The amounts of each nutrient will vary based on the genetic variation of an individual, with some requiring far greater levels of particular nutrients than what is currently thought to be the normal range. How will the era of genomics impact the development of global dietary recommendations? The impact of food fortification on the human species from an evolutionary perspective will need to be debated. Will food fortification lead to selection for genotypes that would not normally survive and are ill-suited for today's environment? These and many other issues with far-reaching consequences will be debated.
Nutrigenomics will be a major force in dietetics. Dietetics professionals have an unprecedented opportunity to carve out unique, valuable niches within the research and application sectors of dietetics and to serve as thought leaders as nutrigenomics is integrated into health care, the food industry and public policy.
Ruth M. DeBusk
Geneticist and Clinical Dietitian, Tallahassee, Florida, USA
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