What genetics contributes to personalised nutrition, and where it fits alongside other biological data.
Genetics is one of several biological layers that determine individual nutritional response, and it is the most stable of them. Your genetic variants are fixed at conception and do not change throughout your lifetime. This gives genetic data a different character from blood biomarker results, microbiome composition, or current nutritional status: it provides a permanent biological reference point rather than a snapshot of current state.
Understanding what role genetics plays in personalised nutrition, and what it does not determine, helps you use genetic information appropriately as part of a broader nutritional picture.
Specific genetic variants affect how efficiently the body absorbs particular nutrients through the gut wall. TMPRSS6 variants affect hepcidin-regulated iron absorption. TRPM6 and TRPM7 variants affect magnesium transport into cells. These absorption efficiency differences mean that the same dietary intake produces different levels of the absorbed nutrient in circulation depending on genotype.
Many dietary nutrients require conversion by the body before they can be used. Folate must be converted to 5-methyltetrahydrofolate (5-MTHF) by the MTHFR enzyme. ALA omega-3 must be converted to EPA and DHA by FADS1/2 enzymes. Beta-carotene must be converted to vitamin A by BCO1. Genetic variants in the genes encoding these enzymes reduce conversion efficiency, meaning more of the dietary precursor is required to achieve the same functional outcome.
CYP1A2 variants affect how quickly caffeine is metabolised. Other CYP enzyme variants affect the metabolism of certain vitamins and dietary compounds. These speed differences have practical implications for dietary choices, supplement timing, and the health effects of specific dietary habits.
VDR variants affect how effectively vitamin D binds to its receptor in cells, and therefore how well cells respond to circulating vitamin D. This is one reason why blood vitamin D levels do not tell the complete story of functional vitamin D status — the cellular response to those levels also varies by genotype.
Genetics describes tendencies, not certainties. The most significant MTHFR variant reduces folate conversion efficiency but does not guarantee folate deficiency. Whether folate deficiency actually develops depends on dietary intake, gut health, lifestyle factors, and other modulators. Genetics sets the biological terrain; diet and lifestyle determine what happens on that terrain.
Genetics also does not explain all individual variation in nutritional response. The PREDICT study found that gut microbiome composition explains more of the variation in postprandial glucose response between individuals than genetics does. Complex dietary outcomes are shaped by the interaction of genetic factors, microbiome composition, current nutritional status, and lifestyle, not by genetics alone.
The most informative use of genetic nutritional data is when it is integrated with blood testing and dietary tracking. Blood testing tells you your current nutritional status. Genetic analysis tells you why your status tends to be what it is. Dietary tracking tells you whether your eating patterns are providing what your genetics suggests you need in greater-than-average amounts.
These three layers are complementary. A low ferritin result on a blood test combined with TMPRSS6 variants that reduce iron absorption tells you both what your current status is and why your body struggles to maintain iron stores. The combination determines what practical response is most likely to be effective, and whether simply increasing dietary iron is likely to be sufficient or whether additional strategies are needed.
For well-established gene-nutrient relationships, the genetic evidence is robust. MTHFR and folate, VDR and vitamin D, CYP1A2 and caffeine, FADS1/2 and omega-3. These are well-replicated in peer-reviewed literature with clear mechanistic explanations.
For more complex dietary outcomes, the genetic contribution is real but smaller and less individually predictive. The optimal macronutrient ratio for any specific person is shaped by hundreds of genetic variants interacting with each other and with environmental factors. No current genetic test can predict this with high accuracy. Honest personalised nutrition is transparent about where the genetic evidence is strong and where it is still developing.
