Nutrigenetics explained: what the evidence shows and where the limitations lie

2. April 2025 ca. 19 Minuten

What to expect in this article

1. Nutrigenetics and nutrigenomics: the difference
2. How professional societies assess the field
3. Why making this connection is so difficult
4. Six cases where genetics plays a role
5. Lactose intolerance as a textbook example
6. Celiac disease: predisposition and diagnosis in numbers
7. Why a predisposition is not a prediction
8. Three claims about genetic tests fact-checked
9. What the Genetic Diagnostics Act regulates
10. What a test can do in this context
11. Limitations: what this article doesn’t answer
12. What remains of nutrigenetics
Frequently asked questions
Sources

Nutrigenetics and nutrigenomics: the difference

Two terms sit side by side but describe opposite perspectives. Nutrigenetics asks how a person’s genetic information influences the effects of a food in the body. Nutrigenomics, conversely, asks how food components affect genetic material and how it is read.

The Bundesgesundheitsblatt offers a definition of the second field: Nutrigenomics is a branch of research that examines the interaction between nutrition and the genome.

The scale of the genome

To indicate the scope of what we’re discussing here, the MSD Manual gives a figure: humans have around 20,000 to 25,000 genes. We found no reliable figure for the number of base pairs in the sources we reviewed, so we don’t give one.

This number alone says little about how informative a test is. What matters is how many of these genes are involved in a particular trait and how much each one contributes. The next chapter’s assessment hinges on exactly that.

How professional societies assess the field

In 2023, the North Rhine-Westphalia Consumer Advice Center compiled the assessments of several professional associations. It includes the statement by a working group of the German Nutrition Society verbatim.

We quote this statement even though mybody®x itself offers DNA tests for nutrition. What this means for our own offering is set out in Chapter 10, and it does have implications.

What other professional associations say

The same special reprint reports the position of the German Society of Human Genetics, according to which the potential risks of misinterpretation or overinterpretation are considered substantially greater than the advertised benefits. Regarding microbiome analysis from a stool sample, it cites the German Society for Gastroenterology, which advises against it because a single undefined sample is not scientifically informative enough.

In 2013, the German Ethics Council commented on lifestyle genetic tests, describing their scientific basis as scant, for example because it rests on a few small studies. The same statement says that the significance of the data obtained and their relevance to people’s lifestyle choices remain unclear.

Why drawing conclusions is so difficult

The professional associations’ criticism is not directed at the existence of genetic differences. It is directed at the conclusion that these differences warrant a recommendation for action. One figure makes the problem clear.

The special reprint by the North Rhine-Westphalia Consumer Advice Center lists 941 known genetic loci for obesity and 240 identified loci for type 2 diabetes. So hundreds of sites in the genome contribute to the same trait, each with only a small effect.

What follows from this

A test that reads just a few of these sites captures a fraction of the picture. Deriving a dietary recommendation from this fraction assumes that the part captured makes the difference.

This is precisely the evidence that professional associations say is missing. The special reprint states the methodological core: There is insufficient evidence from randomized controlled trials on the effectiveness of including genetic tests in nutritional counseling.

The key concept is effectiveness. The question is not whether a test reads variants correctly, but whether people ultimately eat more healthily or become healthier with this additional information.

Six cases where genetics delivers

Between the general reservation and actual practice lies a series of cases in which a single gene really does make the difference. The table brings them together.

The last two rows are the most honest in the table. Percentage figures are circulating for both cases, but we could not find them in the institutional sources we reviewed.

Lactose intolerance as a textbook example

No case shows the link between genetic information and nutrition as clearly as lactose intolerance. The IQWiG describes it as usually hereditary and refers to an inherited or primary form.

Lactose intolerance in numbers

Source: Institute for Quality and Efficiency in Health Care (IQWiG), Lactose intolerance; Verbraucherzentrale NRW, Personalized nutrition (2023)

Why the difference between regions is so large

The range from 5 to over 90 percent is among the largest differences that can be given for any dietary trait. It shows how strongly a single gene can act when it really is the deciding factor.

At the same time, it illustrates a pitfall. If you conclude from this case that dietary recommendations can generally be justified genetically, you are applying an exception to the rule. For most traits, the picture is more like obesity, with 941 gene loci.

What makes the case so unusual

Three conditions come together in lactose intolerance, and all three are rare. A single gene is decisive, the condition is clearly noticeable, and the resulting course of action is clear.

Most questions about nutrition lack at least one of these conditions. When hundreds of gene locations are involved, when the condition develops gradually, or when the findings do not point to a clear course of action, a test result loses its practical value.

It is also worth noting that lactose intolerance is usually diagnosed in medical practice without genetic testing. A breath test or a tolerance test shows the condition directly, while a genetic test shows the predisposition.

Celiac disease: predisposition and disease in figures

Celiac disease is the clearest example of the difference between predisposition and disease. IQWiG cites three figures that belong together.

In Germany, slightly more than 30 out of 100 people carry the genetic predisposition, specifically the HLA gene types DQ2 or DQ8. Around 1 to 2 percent of people in Europe have a confirmed diagnosis of celiac disease. And only around 2 to 3 out of 100 people with this predisposition actually develop celiac disease.

What a genetic test can do here

These three figures point to a clear division of roles. People who do not carry the predisposition are extremely unlikely to develop celiac disease, so the test can largely rule it out. Those who do carry it, however, learn little, because 97 to 98 out of 100 carriers remain healthy.

A test with this structure is useful for ruling out the condition, but not for predicting it. This matters for relatives: according to the same text, around 10 to 15 out of 100 first-degree relatives of someone with celiac disease are also affected.

Why the process still goes through a medical practice

Even when used appropriately, genetic testing is not the starting point for diagnosing celiac disease. Diagnosis is based on antibodies in the blood and, in many cases, a tissue sample from the small intestine.

The order is important. People who are already eating gluten-free may get inaccurate antibody test results because without the trigger, there is no reaction. Changing your diet before diagnostic testing can therefore make it harder to determine what is going on.

In this process, the genetic test plays a secondary role as a tool for ruling out the condition. It does not replace diagnostic testing, nor does it come before it.

Why a predisposition is not a prediction

What became apparent with celiac disease applies more broadly. The technical term for this is incomplete penetrance: a variant is present, but it does not lead to the condition in all carriers.

The figures come from the MSD Manual and refer to homozygous carriers of the C282Y variant in the HFE gene, which causes over 80 percent of hemochromatosis cases. With a prevalence of 1 in 200 among people of Northern European ancestry, the variant is by no means rare.

What this test result means

A finding that identifies a variant describes a possibility, not a condition. Other factors lie between genetic predisposition and its expression, and a genetic test does not capture them.

This is precisely where the concern of the German Society for Human Genetics comes in: it considers the risks of misinterpretation or overinterpretation greater than the advertised benefit. A result without context can easily be read as a diagnosis, but it is not one.

Three Claims About Genetic Tests: A Fact Check

Three claims commonly appear in advertising for DNA nutrition tests. We check them against the sources cited in this article.

The three assessments come from three different professional associations and point in the same direction. That is what an article on this topic must report, even when it comes from a provider.

What the Genetic Diagnostics Act Covers

Germany has a separate law governing genetic testing. Two sections are key to this topic.

Section 7 establishes the physician requirement: Genetic testing for medical purposes may only be performed by physicians, and predictive testing only by specialists in human genetics or appropriately qualified physicians. Section 9 governs counseling: Before consent is given, people must be informed about the nature, significance, and scope of the test, and given adequate time to consider it.

The Unresolved Distinction

The precise boundary between a medical purpose and a purely lifestyle purpose has not been conclusively clarified by law. A legal opinion from 2024 takes a broad interpretation under which tests related to health, such as those for food intolerances, are also subject to the physician requirement.

We acknowledge this uncertainty rather than glossing over it. Since February 1, 2012, genetic counseling in connection with genetic testing may also only be provided by specially qualified physicians.

Why the law is so strict

There is a reason for this strictness that goes beyond data protection. A genetic finding affects not only the person tested but, to some extent, their relatives too, because they may carry the same predispositions.

There is also the fact that it cannot be reversed. A blood value can be measured again six months later and may have changed. A genetic variant remains, and the information about it cannot be taken back.

That is precisely the aim of the duty to provide information under Section 9, with its adequate reflection period. It is intended to ensure that before taking the test, someone knows what they will no longer be able not to know afterward.

For consumer tests without medical supervision, this leaves an unresolved issue. Consumer advice centers sum up the practical consequence in one sentence: Without context, the results could unsettle and overwhelm you.

What a test can do within this framework

After nine chapters with clear reservations, the question remains: what does a DNA test for nutrition actually provide? The honest answer is narrower than the advertising for this product category usually suggests.

It reads genetic variants and describes predispositions. It does not provide a diagnosis, predict disease, or offer dietary recommendations with proven effectiveness. The cited DGE working group rejects precisely this last point, and the same applies to our tests.

mybody®x works with a certified specialist laboratory in Germany, processes data in compliance with the GDPR, and has been active since 2016, with direct-to-consumer sales since 2022.

Limitations: what this article does not answer

We did not find a Germany-specific percentage for lactose intolerance. The stated 5 to 15 percent refers to people in Europe, and we report it as given there.

None of our preferred sources provides a figure for the number of base pairs in the human genome. That is why the commonly cited figure of three billion does not appear in this text.

We found no reliable percentages in our preferred institutional sources for alcohol breakdown via ALDH2 or caffeine breakdown via CYP1A2. Both associations have been described, but we still do not quantify them.

Finally, a boundary concerning this article itself. This article does not assess whether a DNA nutrition test is useful. It reports what professional associations say about it and leaves the decision to the reader. If you suspect an intolerance or illness, the next step is medical testing.

What remains of nutrigenetics

If you take one distinction away from this article, let it be the difference between ruling something out and predicting it. That determines what a genetic finding is worth to you.

Celiac disease illustrates both points in the same figures. Those who do not carry the predisposition can practically rule out the disease. Those who do carry it belong to a group in which 97 to 98 out of 100 people remain healthy. The same test is informative in one case and almost meaningless in the other.

It began with the question of how much nutrigenetics determines our lives. The most reliable answer is: very clearly in a few areas, and so little in most areas that no recommendation can be derived from it.

Frequently asked questions

Sources

1. North Rhine-Westphalia Consumer Advice Center: Personalized nutrition – Can a genetic test and stool sample lead to success? Reprint from Knack•Punkt, issue 1/23, as of 2023 – verbraucherzentrale.nrw
2. Institute for Quality and Efficiency in Health Care (IQWiG): Celiac disease (gluten intolerance) and lactose intolerance – gesundheitsinformation.de
3. MSD Manual: Introduction to genetics, phenylketonuria, and hereditary hemochromatosis – msdmanuals.com
4. Federal Ministry of Justice: Genetic Diagnostics Act (GenDG), 2009, as amended – gesetze-im-internet.de

The verbatim quotation from the DGE working group, the note about the lack of evidence from randomized controlled trials, the 941 and 240 genetic loci, the positions stated by the German Society of Human Genetics and the German Society for Gastroenterology, and the sentence about the lack of classification are from source [1]. The figures on lactose intolerance, HLA genotypes DQ2 and DQ8, the prevalence of celiac disease, and the proportion of affected first-degree relatives are from [2]. The figure of 20,000 to 25,000 genes, the information on phenylketonuria, and all figures on hemochromatosis are from [3]. The physician-reservation and the duty to provide information are from [4]. Additional citations: the definition of nutrigenomics from the German Federal Health Gazette (2006); the assessment of lifestyle genetic tests from an opinion by the German Ethics Council (2013); the information on genetic counseling since February 1, 2012, from an overview by the Berlin Medical Association; the legal assessment of the broad interpretation of the physician-reservation from a publication by the Data Protection Expertise Network (2024). Information on price, scope, sample type, and laboratory comes from the mybody®x product page, accessed on August 11, 2026. All sources were accessed and reviewed on August 11, 2026.