Nutrigenomics
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Direct answer
One plate of dal-chawal does not behave identically in every genome. Nutrigenomics studies how nutrients alter gene expression — through transcription factors and epigenetic marks — while nutrigenetics asks how inherited variants alter the response to nutrients; medicine has used the second logic for decades, since a low-phenylalanine diet for phenylketonuria is nutrigenetics at work. Commoner variants modulate responses at population scale: MTHFR 677T raises homocysteine when folate is low, the lactase persistence variant decides who digests milk as an adult, and APOE ε4 sharpens lipid and Alzheimer risk. The honest position is that monogenic diet-gene interactions are clinically robust, whereas commercial DNA-based diets resting on many small-effect variants lack trial support. India engages the field through public health: FSSAI-mandated fortification of wheat flour and rice with iron, folic acid and vitamin B12.
What you must remember
- Working definitions: nutrigenomics = dietary compounds modifying gene expression (butyrate from fibre fermentation inhibits histone deacetylases); nutrigenetics = variants modifying nutrient response (lactase persistence, MTHFR).
- Classical diet-gene diseases: phenylketonuria (phenylalanine-restricted with tyrosine supplementation), galactosaemia, hereditary fructose intolerance, maple syrup urine disease — proof that genotype can dictate diet.
- Lactase persistence: the LCT promoter variant maintains enzyme beyond weaning in northern European lineages; adult-type hypolactasia is common among South Asians and is constantly mislabelled milk allergy — it is enzyme deficiency, not immune disease.
- MTHFR 677C>T: thermolabile variant, moderately raised homocysteine especially when folate is low; periconceptional folic acid (400 micrograms daily is the usual recommendation) reduces neural-tube risk regardless of genotype, so testing rarely changes management.
- APOE ε4: associates with higher low-density lipoprotein response to dietary fat and with Alzheimer risk — it should intensify lipid management, not prescribe a genotype-specific diet.
- Epigenetic nutrition: folate, B12, choline and methionine feed the one-carbon pool that methylates DNA; the Dutch Hunger Winter cohorts showed methylation marks persisting decades after fetal famine — the biology behind the Barker hypothesis taught with Indian low-birth-weight diabetes data.
- Population programmes: FSSAI's 2016 fortification standards (the +F mark) add iron, folic acid and B12 to atta, with rice fortification scaled through government safety-net schemes — public-health nutrigenomics in action.
- Scepticism where due: no trial has yet shown genome-based diets superior to standard counselling; say so plainly in a viva.
Worked example: counselling a vegetarian with high homocysteine
A 28-year-old lifelong vegetarian presents with a homocysteine of 21 micromoles per litre and a borderline-low vitamin B12 — the commonest panel in young Indian outpatients, since the diet lacks animal-source cobalamin while fortified flour keeps folate replete. Supplement B12 and the homocysteine falls; the nutrigenetic gloss, should his MTHFR genotype ever be tested, would only modulate the folate arm of the same pathway, not change the prescription. Contrast the metabolic clinic next door: a child with phenylketonuria whose blood phenylalanine is titrated against a prescribed amino acid mixture, tyrosine made essential by the block, and pregnancy planning stricter than any diet sheet. The two consultations mark the spectrum of the field — single-gene dietary prescription, robust and evidence-based; polygenic risk nudging, still promise.
How the exam frames it
"Give two nutrigenetic diseases" invites phenylketonuria and lactose intolerance; "which polymorphic enzyme affects folate metabolism" invites MTHFR; and the higher-scoring candidate distinguishes nutrigenomics from nutrigenetics in one sentence each. Indian-exam markers reward programme detail: the +F logo, the iron-folic acid-B12 triplet in fortified atta. The trap is overclaiming — "personalised genome diets are the future" earns less than "monogenic dietary therapy is standard of care; polygenic dietary advice is not".
Frequently asked questions
What is the difference between nutrigenomics and nutrigenetics?
Nutrigenomics asks how nutrients change gene expression; nutrigenetics asks how genetic variants change the response to nutrients.
Which population-level nutrigenomic intervention runs in India?
Fortification of wheat flour and rice with iron, folic acid and vitamin B12 under FSSAI standards, identified by the +F symbol.
Why is phenylketonuria called the model nutrigenetic disease?
Dietary phenylalanine restriction prescribed by genotype (phenylalanine hydroxylase deficiency) prevents intellectual disability — a gene-directed diet in daily clinical use.
Does MTHFR testing change folate recommendations?
Not currently — periconceptional folic acid is advised for all; the variant modestly raises homocysteine but does not dictate a different supplement.
Are DNA-based diets evidence-based?
No trial has shown them superior to standard dietary counselling; monogenic conditions remain the exception where genotype genuinely dictates diet.