What Is Nutrigenomics? How Your Genes Affect Diet

What does nutrigenomics actually study?

Nutrigenomics looks at the two-way relationship between genes and food. Your genes affect how you digest, absorb and use nutrients, and the food you eat can in turn influence how some genes are switched on or off.

In practice, most consumer interest is in one question: should people with different genes eat differently? For a few traits, the answer is clearly yes. For most, the genetic effect is small compared with the overall quality of your diet.

Where is the evidence strongest?

Lactose and the LCT gene

This is the clearest example of genes shaping diet. Babies make an enzyme called lactase to digest the sugar in milk. In most people, lactase production falls after infancy.

According to MedlinePlus Genetics, around 65% of people worldwide have a reduced ability to digest lactose after infancy. Whether you keep making lactase into adulthood depends largely on variants in a genetic switch that controls the LCT gene, and one copy of the "persistence" version is enough.

The pattern varies hugely by ancestry:

• Only about 5% of people of Northern European descent lose the ability to digest lactose
• Among people of East Asian descent, 70 to 100% do
• It is also very common in people of West African, Arab, Jewish, Greek and Italian descent

A genetic result here can explain symptoms you have already noticed. It does not mean you must avoid dairy, as many people tolerate small amounts, and how you feel after eating is still the best guide.

Caffeine and the CYP1A2 gene

Your liver breaks down caffeine mainly using an enzyme made by the CYP1A2 gene. Common variants make some people slower metabolisers, so caffeine stays in their system for longer.

A well-known study in Costa Rica compared 2,014 people who had a heart attack with 2,014 people who had not. Among slow metabolisers, drinking 2 to 3 cups of coffee a day was linked to 36% higher odds of a heart attack, rising to 64% higher at 4 or more cups. Among fast metabolisers, there was no increase in risk.

This was an observational study, so it shows a link rather than proof of cause. Still, it is one of the better examples of a genotype changing how a common food or drink may affect health.

Where is the evidence more nuanced?

MTHFR and folate

MTHFR is one of the most talked-about nutrition genes online, and also one of the most misunderstood. It makes an enzyme involved in processing folate, a B vitamin.

A common variant called C677T is very widespread. The US Centers for Disease Control and Prevention (CDC) says more people in the US carry one or two copies than do not. Crucially, the CDC states that people with an MTHFR variant can process all types of folate, including folic acid, and that people with two copies have blood folate levels only slightly lower on average.

So the advice does not change. Anyone who could become pregnant is advised to take 400 micrograms of folic acid a day, whatever their MTHFR result. The American College of Medical Genetics and Genomics has also advised that MTHFR testing should not be part of routine checks for blood clotting risk, because of its limited clinical usefulness.

If you see claims that an MTHFR result means you need special, expensive forms of folate, treat them with caution and speak to a healthcare professional.

Do DNA-based diets work better than standard advice?

This is where honesty matters most. Two large trials have tested the idea directly.

The Food4Me trial

Food4Me was a randomised trial across seven European countries, with 1,269 adults completing six months. People who received personalised nutrition advice made healthier changes than those given standard advice, eating less red meat, salt and saturated fat.

But adding genetic information on top of advice based on their current diet did not make the advice more effective. Personalisation helped. The DNA part, on its own, did not add measurable benefit in this trial.

The DIETFITS trial

DIETFITS randomly assigned 609 adults to a healthy low-fat or a healthy low-carbohydrate diet for a year. Both groups lost a similar amount of weight, and a genetic pattern thought to predict which diet would suit people better made no significant difference.

What this means

The current evidence suggests:

• A small number of gene and diet links are strong and practical, such as lactose and caffeine
• Many others are real but small, and explain only a little of how people differ
• Matching a whole diet plan to your genes has not yet been shown to beat good, personalised advice based on how you actually eat

That does not make genetic insight pointless. It means it works best as one layer of information, alongside your habits, your symptoms and markers like blood tests or your gut microbiome.

→ Genetic Risk vs Destiny: Are Your Genes Your Fate?

How should you use nutrition genetics?

Used well, nutrigenomics can help you understand why certain foods or drinks affect you differently from friends and family. A few practical principles help:

• Use strong findings, like lactase persistence, to explain what you already notice
• Treat small-effect findings as nudges, not rules
• Keep the basics first: plenty of fibre, vegetables, whole grains and minimally processed food suit almost everyone
• Talk to a GP, dietitian or genetic counsellor before making big changes, especially in pregnancy or if you take medication

→ What Can a DNA Test Reveal About Your Health?

What can you do next?

If you are curious how your genes shape the way you handle foods like dairy and caffeine, a whole genome test can show your nutrition-related variants alongside the rest of your genetic health picture, with expert support to put it in context.

→ Explore the Comprehensive Genetic Test
→ How Does Genetic Testing Work?
→ Genetic Risk vs Destiny: Are Your Genes Your Fate?