Genomics is an exceedingly complex topic, in part because there are approximately 30,000 genes and 8 million to 10 million single-nucleotide polymorphisms (SNPs). Few intervention studies, however, have truly tested the importance of SNPs to gene expression. Most of the evidence about the effects of diet as an environmental stimulus on gene expression comes from observational studies of differences in the patterns of deoxyribonucleic acid (DNA) methylation in response to folate intake. Issa et al. (2001), for example, showed a 300-fold variation in the methylation pattern among individuals.
An individual’s response to dietary interventions will depend in part on his or her genetic background (nutrigenetic effects), the cumulative effects of food components on genetic expression profiles (nutritional transcriptomic and nutritional epigenomic effects), the occurrence and activities of proteins (nutritional proteomic effects), and the dose and temporal changes in cellular low-molecular-weight compounds (metabolomic effects).
The examination of epidemiological data from studies on the relationships of food or food components to health outcomes reveals much variability in outcomes both among studies and within single studies. Examples include studies that have addressed the influence of soy on the