Richa Prakash, Central University of Punjab
Introduction
With the development in science and technology, we got a basic idea of the nutritional needs of human beings leading to the minimization of malnutrition and health conditions resulting from nutritional deficiency. This led to an approach known as “one-size-fits-all”, and also platforms like MyPlate and Food Guide Pyramid, developed by the US Department of Agriculture. But, worldwide genomic studies have shown population-based variation in common SNPs (Single Nucleotide Polymorphisms) leading to differential expression of certain genes involved in the metabolism of some common micro and macronutrients consumed in our diets. So, different people may have different metabolic reactions to the same food putting a one-size-fits-all approach in question, paving a path for a new concept known as precision or personalized nutrition or nutrigenetics. This approach aims to provide a customized dietary plan based on the genetic makeup of the individuals just like pharmacogenomics, the interaction between our genetic makeup and drugs. This concept is growing fast with several companies offering dietary recommendations based on the genomic constitution of the individuals but we need further research in this field to understand the advantages and limitations of this concept.
Genetic makeup and variability
Genes make up <1% of the human genome containing more than 300 billion base pairs of DNA. A single gene can be transcribed into multiple transcripts containing only certain specific exons (the coding region of the gene) that can be translated into isoforms of proteins. Instead of looking very different from each other, two individuals are <1% different at their genomic levels. The most widely used method of studying genetic variation is studying single base pair differences known as SNPs. Genome-wide Genetic Association Studies, popularly known as GWAS works on the hypothesis of common disease common variant (CD-CV), meaning common disease-causing alleles will lead to many common human diseases. It is designed to study a specific trait by taking into consideration cases and controls of hundred thousand to million SNPs of all the individuals under study. The GWAS catalog includes more than 188,000 such studies of SNPs and traits. Some examples of personalized nutrition-related studies are metabolism of micro and macronutrients, fasting blood glucose, metabolism of cholesterol, obesity, levels of vitamin D, etc. But the GWAS related to personalized nutrition have been done only in people with European ancestry and these won’t be valid for other populations. Also, GWAS results should not be considered confirmed, these give us only a preliminary insight that needs to be confirmed with further studies.
Gene-diet interaction anatomy
Different components of our diet can be affected by genetic variations leading to harmful interaction between genes and diet. The gene-diet interaction can be affected by various factors including environmental, genetic, and biological factors. The interaction can be initiated by a change in the exposure pattern of an important nutrient for the human body. This exposure is not advantageous if the intake of the particular nutrient is changed in a genetically different population and there is no clinical trial to study the effect of this change across the populations. An example can be an increased fatty acid exposure recommended by American health agencies in 1961 to lower the levels of serum cholesterol and LDLs (Low-Density Lipoproteins). Food companies followed the recommendation and stated using poly-unsaturated fatty acids (PUFAs) in place of saturated fatty acids leading to increased inflammation and diseases related to inflammation. The next component that can lead to harmful gene-diet interaction is when some people or ethnic/racial groups in a population have genetic variants for the metabolism of a particular nutrient leading to a differential gene expression as compared to other individuals of the population. The third factor can be epigenetic changes affecting the metabolism of an important dietary nutrient. Literature studies have shown that these epigenetic changes/alterations can result from dietary exposures.
Personalized nutrition (Precision diet) examples
The first example is the interaction between caffeine sensitivity and the CYP1A2 (Cytochrome P450 1A2) gene responsible for about 95% metabolism of caffeine. About 13 SNPs have been identified on this gene and one of them is rs762551 causing an A to C substitution leading to reduced methylxanthine (the enzyme that metabolizes caffeine in the liver) activity. This results in caffeine hypersensitivity. A personalized diet or nutrigenetics can help people to identify the chances of alcohol dependence and can guide them with drinking behavior. Two enzymes are involved in ethanol metabolism, namely alcohol dehydrogenase and aldehyde dehydrogenase. The alcohol dehydrogenase 1B catalyzes the first step of ethanol metabolism and thousands of polymorphisms have been identified in this gene. The most clinically significant SNPs are rs2066702 and rs1229984 which leads to increased alcohol metabolism, less consumption, and a very low risk of alcohol dependence.
Direct-to-consumer genetic testing (DTC-GT) is a process of providing direct genetic testing to people without any health professional. Companies using DTC-GT providing precision dietary advice have increased. They provide the risk of disorders caused by a single gene change, not a clinical diagnosis. But, these results can be misleading to people with non-European ancestry as the GWAS catalog has studied from people with European ancestry. Another ethical consideration is the misinterpretation of DTC-GT recommendations.
Conclusion
Nutrigenetics is an emerging field and lots of developments are needed to pave the path to tailor dietary plans based on the genetic makeup of the individual leading to a healthy society. Genomics along with metabolomics and epigenomics will play a critical role in nutrigenetics. We can be hopeful for a future in which we can eat for our genes.
Also read: Red Meat: Caution and Control for Colorectal Cancer
References
- Mullins, V. A., Bresette, W., Johnstone, L., Hallmark, B., & Chilton, F. H. (2020). Genomics in Personalized Nutrition: Can You “Eat for Your Genes”?. Nutrients, 12(10), 3118. https://doi.org/10.3390/nu12103118
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