Your neighbour drinks three coffees a day and sleeps like a baby; you, a single espresso at 4 pm keeps you awake until midnight. Your sister eats pasta without gaining a gram; you, a plate of spaghetti sends your blood sugar soaring. This variability is neither chance nor willpower: a documented share of it falls to nutrigenomics, the science of how our genetic variants modulate the response to food. It is the field that fascinates the public most, and the one where commercial promises run furthest ahead of the evidence.
What a SNP is: inter-individual variability
The human genome contains roughly 3 billion base pairs. Two people share 99.9% of that sequence; the remaining 0.1% makes the difference. A single nucleotide polymorphism (SNP) is a letter that differs at a precise position: at one spot in a gene, you carry an A, your neighbour a G. Most SNPs have no effect; some change an enzyme’s speed, a receptor’s sensitivity, a protein’s expression.
These small variations are why the same plate produces different blood sugars, blood lipids and satiety from one person to the next. Nutrigenomics documents these differences; the commercial promise (a DNA test that tells you your ideal diet) is largely ahead of the science.
FTO, APOE, MTHFR: the most studied genes
Three genes dominate the popular nutrigenomics literature, and each illustrates a different limit.
| Gene | What the variant does | What it changes | What it does not change | |
|---|---|---|---|---|
| FTO | Satiety and adiposity | Variant associated with +1 to 3 kg on average | Lower sensitivity to satiety | Exercise cancels out nearly all the effect |
| APOE | Lipid transport | APOE4 raises LDL and cardiovascular risk | Stronger response to saturated fats | Lifestyle remains decisive (the MIND diet protects carriers too) |
| MTHFR | Methylation, folate | C677T reduces enzyme activity by 30-70% | Increased need for active folate (methylfolate) | Predicts no disease on its own |
Documented variants, real effect, and what the SNP does not determine
FTO is the most publicised obesity gene: carriers of the risk variant weigh on average 1 to 3 kg more, through a duller sense of satiety. Yet the effect almost entirely disappears in physically active carriers: the gene loads the gun, lifestyle pulls the trigger.
APOE codes the protein that transports lipids; the E4 allele raises LDL cholesterol and cardiovascular (and Alzheimer’s) risk. It makes the response to saturated fat more pronounced, but does not change the fundamentals: the Mediterranean diet remains protective in E4 carriers.
MTHFR is the most useful example: the C677T variant reduces the activity of the enzyme that converts folate into its active form. In homozygotes (5 to 15% of the population depending on the group), the need for active folate rises and homocysteine may climb. This is the SNP where dietary adjustment (methylated folate, or more green vegetables) has a measurable effect.
What DNA tests can say, and cannot
Consumer tests (23andMe and the like) read several hundred thousand SNPs and derive reports from them: “you metabolise caffeine slowly”, “you carry an increased risk of weight gain on saturated fat”. Some of these reports rest on solid associations (CYP1A2 and caffeine, MTHFR and folate); others extrapolate weak associations into overly confident advice.
What a test can honestly deliver: an indication of sensitivity (to caffeine, salt, saturated fats), an alert worth monitoring (homozygous MTHFR, APOE4), a motivation to act on the terrain. What it cannot: draw your ideal diet, predict your exact response to a food, replace clinical follow-up. The glycaemic response to a potato depends as much on the microbiome, last night’s sleep and the previous meal as on genotype.
The TCM reading: constitution facing genotype
Nutrigenomics has a surprising ancestor: constitutional typology. TCM never waited for sequencing to assert that two patients do not eat alike: the Jing received from the parents sets a starting capital, and the four Korean Sasang constitutions (Tae-Yang, Tae-Eum, So-Yang, So-Eum) describe four terrains that respond differently to the same foods. The So-Eum (digestively cold, fine-boned) does not digest like the Tae-Eum (robust, prone to overload): the same cold soup that suits one congests the other.
The correspondence is not an equivalence: the TCM constitution is a phenotypic whole (morphology, temperament, digestive terrain), not a genotype. But both traditions share the same conviction: the average recommendation serves the average, not the individual. This is exactly what nutrigenomics is rediscovering with letters in place of constitutions.
The plate does not wait for the genotype
The practical lesson of nutrigenomics cuts both ways: yes, your genes modulate your response to food; no, they do not exempt you from the fundamentals. No SNP turns an ultra-processed diet into a good choice, and none forbids green vegetables. Real variability plays out in adjustments (caffeine tolerance, folate needs, response to saturated fats), not in the broad directions. The vitamin and mineral guide and the glycaemic index remain the same for everyone; what changes is the individual dose.
Frequently asked questions about nutrigenomics
Should I have a DNA test to choose my diet?
No, not as a first step. The foundational recommendations (vegetables, fibre, adequate protein, limiting ultra-processed foods) hold for every genotype. A test can be useful for specific points: caffeine sensitivity (CYP1A2), folate needs (MTHFR), response to saturated fats (APOE4). It does not write a diet.
Does the MTHFR variant oblige me to take supplements?
In C677T homozygotes, the need for active folate (5-MTHF) is increased and homocysteine may rise, which often justifies a higher intake of methylated folate or supplementation. In heterozygotes the effect is moderate and a folate-rich diet (green vegetables, pulses) often suffices. The decision is made with a doctor, guided by a homocysteine measurement.
Does APOE4 really change anything on the plate?
It strengthens the case for measures already recommended: limiting saturated fats, generous soluble fibre and omega-3, a Mediterranean or MIND-style diet. The protective effect of these diets is documented in E4 carriers as well; they stand to gain even more. The genotype does not change the direction; it changes the urgency.
Does my genotype explain why I gain weight more than others?
Partly, but less than people think. Variants like FTO add on average 1 to 3 kg of susceptibility, not 15. The rest lies with environment (diet, activity, sleep, stress), the microbiome and insulin resistance. The gene makes the terrain more sensitive; it does not write it alone.
Your genes are a terrain, not a programme
Nutrigenomics is the modern answer to a question TCM has always asked: why do two bodies not respond alike to the same plate? The answer has changed tools (the SNP replaces the constitution) but not substance: real variability exists, it justifies adjustments, it does not abolish the fundamentals. Inherited Jing sets the capital; diet decides its upkeep. A DNA test can fine-tune a few settings; the daily plate remains the main lever.
In the Yin Shi app, the food sheets give the thermal nature and tropism of each product: sardine and spinach tick the boxes of terrain to nourish, fast sugars those of terrain to spare, whatever the genotype.
Further reading: the glycaemic index and the sweet flavour, insulin resistance as Spleen deficiency, the Korean Sasang constitutions, the microbiome as Spleen Dampness, and the vitamin and mineral guide.
To go further
Yin Shi ecosystem resources directly related to this article.