Why "Turning Genes On or Off" Is Often an Oversimplification

The claim

Supplements, diets, devices and tests are sometimes marketed as "turning on good genes" or "turning off bad genes." The wording borrows from real science, so it sounds credible. This page explains what scientists mean by gene expression, why an on/off picture is a simplification, and how to read such claims. It is information only and not medical advice.

What scientists mean by gene expression

NHGRI defines gene expression as the process by which the information in a gene is turned into a function, mostly through making RNA molecules. It says expression can be thought of as an "on/off switch" for when and where products are made and also as a "volume control" for how much. [1] It adds that expression is carefully regulated and changes substantially under different conditions and cell types. [1]

So the switch image is a teaching shortcut. In reality genes are adjusted continuously, in different amounts in different cells, all the time. The Genotype-Tissue Expression project analyzed RNA sequencing data from 1,641 samples across 43 tissues from 175 individuals and cataloged thousands of tissue-specific and shared regulatory variants. [2] A gene that is active in one tissue may be quiet in another.

Epigenetics adds a layer, not a switch you can flip

NHGRI describes epigenetic changes as chemical modifications that change the degree to which genes are turned on and off. [3] MedlinePlus Genetics says patterns of epigenetic modification vary among individuals, between tissues within a person, and even between cells within a tissue. [4] It also says environmental influences, such as diet and exposure to pollutants, can affect the epigenome. [4]

That is not a recipe. A study of people whose mothers were exposed to famine in the Dutch Hunger Winter found that, six decades later, they had less DNA methylation of the imprinted IGF2 gene than their unexposed same-sex siblings. [5] That is an association measured in a specific historic event. It does not show that a food, supplement or habit can switch a chosen gene on or off in a helpful way. For definitions, see epigenetics explained and genes, variants and gene expression.

Why it is an oversimplification

• Many genes, many cells. Expression differs between tissues, so a change measured in one tissue, such as blood, cannot be assumed to apply to another. [2]
• Direction is not good or bad. More or less expression of a gene is not automatically better. The process is carefully regulated. [1]
• A change is not a health outcome. Showing that a product changed expression of some genes in cells or animals is a mechanism or biomarker finding. It does not show that people feel or live better. See mechanism vs demonstrated benefit and claim check: changes gene expression means treats disease.
• Association is not cause. Epigenome-wide studies, which link epigenetic marks to traits, suffer from multiple problems in design and execution that severely limit their interpretability. [6]
• Passing changes to children is uncertain. An influential review concluded that the environment can certainly influence gene expression, but transgenerational consequences are another matter, and how much occurs in humans remains unclear. [7]

How to evaluate a gene-expression claim

1. Which study type: cells, animals or people?
2. Which genes, in which tissue, and by how much?
3. Was a clinical outcome measured, or only expression?
4. Was it compared with a placebo or control group?
5. Is the product the same as the one tested?

If answers are missing, treat it as a marketing claim. Proper evidence for "turning genes on or off" to treat or prevent disease with a consumer wellness product was not found in the sources checked for this page (NHGRI, MedlinePlus Genetics and the reviews cited here). Gene-specific records are in the Research Library.