Consumer DNA tests have made words like "genomics" and "nutrigenomics" familiar, and many now promise diet advice based on your genes. So how much can your DNA really tell you about what to eat, and how much can what you eat change what your genes do? Here's a plain-English guide, including what the research does and doesn't support yet.
What is genomics?
Genetics is the study of individual genes and how traits are passed down. Genomics is the study of all of a person's genes together, including how they interact with each other and with the environment. That matters because most common conditions, such as heart disease, diabetes and many cancers, come from a mix of many genes and lifestyle rather than a single gene. According to the National Human Genome Research Institute, genomic factors play a role in nine of the ten leading causes of death in the US.
The field took off after the Human Genome Project, completed in April 2003, produced the first sequence of the human genome.
How do DNA and genes work?
DNA
DNA (deoxyribonucleic acid) carries the instructions that build and run nearly every living thing. It's written in four chemical "letters": adenine (A), thymine (T), cytosine (C) and guanine (G). On the double helix, A always pairs with T and C with G, and the order of the letters spells out the instructions, much like letters spell out words. A copy of your genome sits in almost every cell, packed into 23 pairs of chromosomes.
Genes and proteins
A gene is a stretch of DNA with the instructions for making a specific protein. To use those instructions, the cell copies the gene into messenger RNA (mRNA). The mRNA travels out of the nucleus to a ribosome, a molecular machine that reads it and links amino acids together in the right order to build the protein. Proteins then form your tissues and organs, carry signals between cells and drive chemical reactions.
What are gene variants and SNPs?
A gene variant is a change in the DNA sequence. Inherited variants are passed from parent to child and are present in virtually every cell for life. Acquired variants happen later, in certain cells only, from things like environmental exposures or errors when cells divide, and they can't be passed on.
Some variants are common enough to count as normal human variation, behind traits like eye color and blood type. The most common type is the single nucleotide polymorphism, or SNP: a one-letter difference. Each of us has roughly 4 to 5 million SNPs, and most have no effect on health at all. A small number influence things like how we respond to certain foods or medicines, or our risk of some conditions.
What is nutrigenomics?
Nutrigenomics, or nutritional genomics, studies the two-way relationship between diet and genes: how nutrients and food compounds influence which genes are switched on and off and how the body handles metabolism, and how your genetic variants shape your response to food. The long-term goal is evidence-based, personalized dietary advice. It also helps explain why two people can respond so differently to the same diet.
A well-known example is MTHFR, a gene for an enzyme that processes folate. A common variant, often called C677T, makes the enzyme less stable. About 10 to 15% of North American white people and about 25% of Hispanic people carry it on both copies of the gene, and they tend to have higher blood levels of homocysteine. That's a reason to make sure you get enough folate from leafy greens, beans and fortified foods. It is not, on its own, a diagnosis: most people with the variant are healthy.
Can a DNA test tell you what to eat?
Not yet with much precision. In the Food4Me trial, a large European randomized study, personalized nutrition advice improved people's diets more than standard advice did, but adding genetic information to the advice did not make it any more effective. Personal responses are real, though: in a study of 800 people, blood sugar responses to identical meals varied widely from person to person, and an algorithm using blood tests, habits, activity and gut microbiome could predict each person's response well, without needing their DNA.
So treat a consumer DNA report as a conversation starter, not a meal plan. Results can't diagnose anything, and a single gene rarely tells the whole story. If a result worries you, talk to your doctor or a genetic counselor before changing your diet or starting high-dose supplements.
What can you do with this today?
Whatever your genes say, the basics that support healthy gene expression and metabolism are the same for nearly everyone: a varied, mostly plant-based diet with plenty of fiber, regular movement, good sleep and stress management. For more, read about why eating a variety of protein sources matters, what antioxidants do and our guide to three keys to a healthy microbiome.
