Two people with similar lifestyles and environmental exposures can have very different health outcomes. Two people of the same age eat a diet low in fruits and vegetables and high in sodium, carbs and saturated fat. One develops hypertension, hypercholesterolemia, and eventually atherosclerosis, while the other lives a long life without such chronic disease. And I’m sure you have many personal examples of this kind in your circle of friends & social acquaintances.
Today we are able to answer this medical paradox thanks to incredible advances in the fields of genetics, genomics & nutrigenetics: our health is partly determined by small genetic variations in our inherited DNA. Contrary to what the American constitution would have you believe, not all men are created equal! Or at least not from a genetic point of view.
One of the things that nutrigenetics demonstrates beyond any doubt is that genetics plays a critical role in determining how a person responds to dietary intake. Thus, in an ideal healthcare system with a focus on preventative medicine, people should be able to receive personalised nutrition recommendations based on their genetic makeup.
Nutrigenetics is the study of the relationships among genes, diet, and health outcomes. The medical research in this field investigates the link between genotype and specific nutrient needs, as well as the relationship between genotype and specific chronic diseases. Nutrigenomics, a related but distinct field, is the study of how genes and nutrients interact at the molecular level.
Nutrigenetics is an exciting field of medical research, and the foundation of personalised nutrition. Clearly, population-based dietary recommendations are helpful, but they aren’t adequate for all individuals since people respond differently to diets.
With nutrigenetics, the focus is on the individual and his/her genetic make-up. Once someone is genotyped for specific genetic variations, he or she is made aware of their risk for nutrient deficiencies and chronic disease, and consequently given strategies to dramatically reduce their risk.
Interestingly, genetic variation among individuals is minimal. Most people are approximately 99% genetically identical, with little variation in the roughly 3 billion base pairs that comprise the human genome. However, this approximately 1% genetic variation leads to a wide variability of health outcomes, depending on dietary intake and other environmental exposures.
For instance, if a gene is important for metabolism and if the individual has a genetic variation in that gene (also referred to as a single nucleotide polymorphism or SNP), he may develop a a metabolic inefficiency and put on weight more easily, or become tired more easily. In such a case, more nutrient precursors will be needed to make the desired product – usually an enzyme. If the gene with the functional SNP encodes for a hormone, the hormone may not work as well.
Estimates show more than 10 million SNPs in the human genome exist; each individual has his or her own number and pattern of SNPs. Think of SNPs as misspellings, if genes provide incorrect information, this will be read and interpreted in an incorrect way and will result in incorrect products (enzymes, hormones etc).
Individual genetic variability affects a person’s nutritional status in many ways. For example, a person’s genetic sequence affects his or her nutrient requirements, energy utilisation, appetite and taste, and risk of chronic disease in response to diet. Research is under way to determine how specific SNPs, or genetic variations, affect each of these aspects of nutrition.
Personalised Nutrition & Nutrient Requirements Based on Genotype
Although nutrient requirements vary from person to person, the Recommended Dietary Allowance (RDAs) appears to meet the needs of most people but only at the level of “getting by”: the RDAs are aimed at avoiding the development of severe nutrient deficiency such as scurvy, they are not aimed at people thriving or optimum health.
To make you better understand what these requirements mean, imagine you’re going on a trip called LIFE. The RDAs are the equivalent of the smallest budget possible that will prevent you from being homeless or starving: you’ll sleep in cheap hostels and do a lot of couch surfing, your diet will be poor and monotonous, you’ll have a lot of colds and infections, bad skin, poor energy, headaches, etc . Now imagine having a higher budget – you’ll be able to afford decent accommodation, yummy food and generally have a very good time!
Nutrigenetics can help with identifying which specific nutrients you need to replenish on, or what food item you need to avoid, in order to thrive as an individual. At the moment, the evidence on genotype and nutrient needs exists for several micronutrients, including vitamin C, choline, and folate.
Vitamin C, Glutathione & Risk of Chronic Disease
Vitamin C is an essential nutrient that’s necessary for the synthesis of collagen and the inhibition of oxidative damage, which is characteristic of long-term diabetes complications, heart disease, cancer etc. While vitamin C deficiency is relatively rare in developed countries around the world, the inverse relationship between vitamin C status and chronic disease makes it one of the most important nutrients to obtain. A recent study investigated whether genetic variations in the gene that codes for the enzyme glutathione S-transferase—which helps maintain the antioxidant capacity of vitamin C—had any effect on serum vitamin C status. Interestingly, individuals with at least one of two specific genetic polymorphisms within the glutathione S-transferase gene had an increased risk of serum vitamin C deficiency if they didn’t meet the RDA for vitamin C. This study shows how critical it is for people with this genetic polymorphism to supplement with vitamin C regularly in order to maintain serum levels associated with normal physiologic function and prevent scurvy.
Choline, PEMT & Liver Function
Choline is an essential nutrient that maintains cell membranes and sources of methyl groups (which are single carbons with three hydrogen atoms attached to them). A constant source of methyl groups is important for multiple biochemical reactions, including the synthesis of amino acids and neurotransmitters. Although choline is classified as an essential nutrient, some women can synthesise choline endogenously thanks to the enzyme phosphatidylethanolamine Nmethyltransferase (PEMT). PEMT makes phosphatidylcholine in response to oestrogen, thus decreasing the need for dietary choline, since phosphatidylcholine can be converted to choline.
A recent study demonstrated that a common SNP in the gene that codes for the PEMT enzyme increases the risk of liver or muscle dysfunction in people who are choline deficient. About one-half of women have the SNP that prevents the PEMT gene from responding to oestrogen, thus increasing their dietary choline requirements. In this study, 80% of premenopausal women on a low-choline diet who had both copies of the SNP developed liver or muscle dysfunction compared with 43% of women with one copy of the SNP and 13% of those without the SNP. Thanks to genetic testing, those who have the PEMT SNP will be advised to consume higher intake of dietary choline to avoid liver or muscle dysfunction.
Postmenopausal women are at increased risk of choline deficiency as PEMT is regulated by oestrogen. So not only do these women have greater choline requirements, they’re more likely to suffer health effects if they have the PEMT SNPs compared with women who aren’t postmenopausal.
Folate, MTHFR and Risk of Cardiovascular Disease
Folate is an essential nutrient that is necessary for the synthesis and repair of DNA. A strong association between folate status and the incidence of neural tube defects in newborns became apparent in the 1980s.While the underlying link between folate status and neural tube defects is still unclear, research has shown that individuals with a specific SNP in the enzyme methylenetetrahydrofolate reductase (MTHFR)—necessary for the production of 5- methyltetrahydrofolate, which converts homocysteine to methionine—may have a higher folate requirement than those who don’t have the genetic variation. These findings were based on reduced serum folate levels in response to the same dose of folic acid supplementation.
The studies on vitamin C, choline, and folate clearly indicate that genetic variations affect an individual’s nutrient requirements. Your nutritionist won’t know if you require a higher nutrient intake or supplementation unless you undergo genetic testing.
Genetic Testing & Personalised Nutrition as the Foundation of Preventative Medicine
Recent studies indicate that genetics affects whether a person will develop a chronic disease in response to diet and lifestyle. Fortunately, research also shows that people who are genetically predisposed to chronic disease won’t necessarily develop the condition if they follow a specific preventive diet. In an age of personalised nutrition, individuals who are genetically predisposed to chronic disease will be advised to adhere to a preventive diet, since they’d be more likely to develop the disease.
At the moment, personalised nutrition based on genetic composition is mostly available privately, and individuals seeking personalised nutrition beyond what their primary care provider offers can contact companies that offer genetic testing or speak to their nutritionist for advice.
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