Nutrigenomics and Personalized Nutrition: Science and Concept

Martin Kussmann; Laurent B. Fay

Disclosures

Personalized Medicine. 2008;5(5):447-455. 

In This Article

Nutritional Needs Vary With Life Stage, Lifestyle & Situation

Life Stage

The nutritional requirements of humans depend on an individual's stage in life. Early in life, growth and development are primary biological objectives and change rapidly, as do the related dietary needs and responses.[24] Puberty and the transition to reproductive fertility cause a significant change in hormonal status, with physiological and metabolic consequences, many of which alter dietary needs and responses.[25] The reproductive cycle itself (estrus, pregnancy, lactation and involution) represents all distinct physiological states for which varying nutritional implications apply beyond classical guidelines.[26,27]

Thanks to modern disease prevention and therapy, human life expectancy has increased dramatically. One result of this success has been the emergence of 'elderly' as a sustained and distinct life stage. With greater numbers of elderly humans, their unique physiological, metabolic and even microbial states are being recognized, and so are their unique nutritional needs.[28,29] Disease, injury or pathology affects virtually every individual at some point in life. Clinical nutrition addresses the unique metabolic demands of disease states, and nutritional solutions are being designed to accelerate recovery and minimize long-term consequences from these periods.

Environment

The term 'environment' encompasses, in this context, all exogenous inputs to a phenotype, such as acute and chronic, random and volitional, as well as chemical, physical and behavioral impacts. The nature of these inputs can be attributed to their source (e.g., solar UV irradiation) or to their effects (e.g., vitamin D formation).[30] These inputs can be either random and unavoidable (e.g., urban pollution) or volitional (e.g., smoking). They may also be generalized to a larger population (e.g., exposure to fluoridated drinking water) or may be unique to specific individuals (e.g., chronic consumption of sweetened beverages).[31]

Lifestyle

A critical aspect affecting an individual's environment and nutritional phenotype is the available food choices. While many consumers have access to increasingly diverse diets throughout the year, for others, choice does not necessarily afford diversity.[32] One of the luxuries of modern humans is the freedom to pursue preferred lifestyles. Faced with a highly diverse food supply, consumers can take advantage of a wide variety of dietary intakes of micro- and macro-nutrients and caloric contents. These intakes may come in diverse forms that may range from a single large meal per day to a dozen snack-like eating occasions.

Environment × genotype = imprinting

Environment at one stage in life can exert persistent effects on the nutritional phenotype later in life. These environmental impacts can manifest as imprinting, programming, memorization or colonization. As mentioned in the previous section, the explicit covalent modifications of DNA that persist through cell divisions are increasingly well described in the field of epigenetics.[33]

In addition, the development of olfactory preferences persists through much of an individual's life, guiding their lifelong food choices.[34] Our sense of taste provides the final analysis of food prior to ingestion and uptake: once in the mouth, the gustatory sense tells us to spit or to swallow. We are attracted or repelled by visual and olfactory signals of food. In addition, olfactory and gustatory inputs are integrated with visual, visceral, mechanical and even auditory stimuli in the brain to generate complex flavor profiles. Each profile is classified with hedonic values of liking or disliking. This integration of sensory inputs into long-term food preferences is the major basis of an individual's food choice. As food choice determines the quality of diets, the quality of diets and their consequences for health are linked to the processes of taste. Taste and health are therefore tightly coupled.

Finally, an environmental factor that exerts persistent effects on nutritional phenotype is the composition and genetic diversity of the various microorganisms living in each individual's intestine, that is, the gut microbiota. Indeed, the basal metabolic state and indigenous bacteria play a crucial role in an individual's health. All mammals have symbiotic relationships with their gut microbiome, which consists of a diverse and metabolically active consortium of species exhibiting a spatially heterogeneous micro-ecology.[35] Evidence suggests that gut microbial metabolism and species variation within the microbiome of the mammal is of considerable importance in determining calorific bioavailability to the host.[36]

Imprinting during prenatal development has been shown to cause methylation differences across entire regions of a fetal genome and can result from various nutrient imbalances and deficiencies of the mother.[37] As technologies for measuring epigenetic DNA modifications have emerged, studies in animal models exposed to various nutrients and environmental and lifestyle factors have shown the influence of these environmental parameters on the DNA methylation state.[38] Such studies suggest that these nutritional factors are also relevant to humans, and similar persistent effects through epigenetic changes in the human genome could be predicted.

The remodeling of cells and tissues as a form of imprinting has been well documented, although not yet fully understood. Adipocyte hyperplasia early in development is proposed as one of the factors that could account for the high predisposition to adult obesity in children who are overweight.[39] These animal studies have documented that specific dietary factors early in life – of animals at least – stimulate or inhibit the proliferation of adipocytes. This effect, in itself, could account for a persistent and altered response to diets later in life. For example, the dietary factors omega-6 and -3 polyunsaturated fatty acid are apparently effective at altering cellular development within the range of normal human diets. Moreover, muscle mass is also responsive to the combination of conditioning and protein content of the diet.[40] The persistence of muscle mass, its influence on whole-body energy metabolism, its metabolic contributions post-training, and a larger store of amino acids as muscle proteins are expected to alter an individual's reaction to environmental conditions such as diet.[41]

The imprinting of sensory preference is perhaps the least understood but most influential in the conditioning of modern humans to their habitual diets. Humans apparently do not rely on nutrient cues to guide their food choices; instead, they rely on a system of acquired food preferences. The remarkable property of olfactory preference is the process by which liking and disliking of particular flavors are acquired as a series of contextual memories early in life.[42] This system of acquired flavor preferences underlies much of the cultural variation in foods and cuisines around the world. This also means that flavor preferences for foods with poor nutrient quality, if acquired early in life, may guide a person's life-long habit of poor food choices, partly due to the fact that the sensations will continue to be positively perceived. These olfactory-based food preference patterns can be developed very early in life; for example, the flavor preferences of lambs for grazing is acquired from maternal feeding patterns established prior to weaning.[43]

A final means by which early dietary exposure can program a person's response to later diet is the influence on an individual's gut microbiome. Such dietary influences can be achieved both through direct inoculation of particular microorganisms present in foods[44] or via the selective manipulation of subsets of microorganisms by food components that can only be fermented/utilized by certain bacterial populations.[45] Until recently, the role of an individual's microflora was considered to be relatively minor in terms of their overall health. Stimulated by the astonishing discoveries by Gordon et al. on the influence of specific bacteria on energy metabolism and predisposition to obesity,[36,46] the microflora is being increasingly viewed as a pivotal factor in human metabolism, immunity, sensation, disease resistance, inflammation and comfort.

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