These are the genetic variants analyzed by a metabolic test

What to expect in this article

1. Which genes influence weight loss?
2. What an SNP is and why it matters
3. How many gene loci research has found
4. The numbers at a glance
5. FTO: the best-studied gene locus
6. Why many small effects still explain something
7. Which topics an analysis covers
8. How many variants a metabolic test reads
9. Three analysis areas compared
10. Two statements about genes and weight fact-checked
11. Limitations: what the numbers do not show
12. What the scale means for you
Frequently asked questions
Sources

Which genes affect weight loss?

Very many, and each contributes only a little. In Nature Reviews Genetics, Loos and Yeo count more than 1,100 independent gene loci associated with obesity-related traits (2021). The best-studied one among them is called FTO and accounts for around one kilogram when converted for a height of 1.70 meters.

This answers the question of whether there is one decisive gene: no. What exists is a large number of small contributions that add up to a hereditary component.

DNA analysis is intended for nutritional and lifestyle counseling. It is not a diagnostic procedure, does not predict illness, and does not replace a medical examination or consultation. Genetic variants describe probabilities in population groups, not fixed outcomes for individuals.

What an SNP is and why it matters

The genetic code consists of around three billion building blocks. At most positions, all people carry the same building block; at several million positions, there are differences. Such a position is called an SNP, pronounced “snip.”

An SNP is therefore not a disease or a defect, but a variant that is common in the population. Some of these variants are associated with measurable differences; many are not associated with anything.

A metabolic test reads exactly these kinds of positions. At mybody®x (MYBODY Lab GmbH), this means more than 700,000 positions are tested, and a smaller selection of them is included in the analysis.

The difference between a gene and a locus

Studies rarely speak of genes; instead, they refer to loci. A locus is a section of the genetic material where an association has been found, without this establishing which gene there is responsible.

This distinction explains an imprecision that runs through many informational texts. Anyone who speaks of 1,100 genes is saying more than the studies support. The studies refer to positions where something was found.

Why there are two variants at one position

Every person carries two copies of their genetic material, one from their mother and one from their father. At each position, there are therefore two variants, technically called alleles, which may be the same or different.

That is why effect sizes in the scientific literature are always reported per allele. Anyone carrying both copies of a variant has the effect added together; anyone carrying neither does not have it.

For reading a report, this is the most important information to know in advance. A report that mentions a predisposition means a combination of these variants, not a yes-or-no statement.

How many loci research has identified

The review by Loos and Yeo summarizes the state of this field. One sentence quantifies how many genome-wide association studies have been conducted and what they have found.

In English, this sentence means: Nearly 60 genome-wide association studies have identified more than 1,100 independent loci associated with a range of obesity traits. GWAS stands for genome-wide association study, an investigation that scans the entire genetic material for statistical associations.

What such a study does and does not do

A genome-wide association study compares very large numbers of people and looks for positions in the genetic material where carriers of a trait differ from non-carriers. It finds associations, not causes.

This difference is why the scientific literature is cautious. An association may mean that a locus has an effect, or that it lies near something that does. Both look the same statistically.

This also explains why the number of loci identified has increased over the years. The genetic material has not changed; the number of people studied has. Larger samples make smaller effects visible.

For interpreting a report, this means that the list of analyzed positions is a snapshot, not a final tally. Your result remains the same; only the knowledge about it continues to grow.

What obesity traits mean in these studies

In the scientific literature, the collective term refers to several measures, including body mass index, waist circumference, and the waist-to-hip ratio. These measures describe different aspects and are not fully correlated.

That is why the figure of more than 1,100 gene loci is a total across different traits, not a list for just one. Anyone reading it as a figure for body weight is interpreting it too narrowly.

The figures at a glance

The following three figures come from the same review and describe the same state of research. They are the robust figures on which this article is based.

The state of research in numbers

Source: Loos RJF and Yeo GSH, Nature Reviews Genetics, 2021

Why the middle figure is the most interesting

According to the same paper, the largest single study of body mass index included almost 800,000 people. This figure explains why so many gene loci could be identified at all: the larger the sample, the smaller the effects that become statistically visible.

The converse is the actual finding. If 800,000 people are needed to detect an effect, that effect is not perceptible in an individual person.

FTO: the most thoroughly studied gene locus

FTO is the gene locus that has been studied for the longest and most thoroughly in this field. It was discovered early and has a comparatively large effect among the known variants.

Loos and Yeo quantify this effect at 0.35 kilograms per square meter per allele, equivalent to around one kilogram at a height of 1.70 meters (2021). An allele is one of two versions that a person can carry at this position.

One kilogram is measurable and real. It is also the amount that a week of restless sleep, moving house, or a stressful month can shift. Anyone who turns this value into an explanation for twenty kilograms has lost sight of the scale.

What lies at the lower end

The same review reports effects as low as 0.04 kilograms per square meter per allele for the largest study of body mass index, which corresponds to about 120 grams at a height of 1.70 meters (2021).

The full range in this overview runs from 120 grams to one kilogram. Anyone reading a summary should keep this range in mind when it refers to a predisposition.

Why FTO is still so well known

The gene locus was discovered early and has since been studied most thoroughly. Prominence in research comes from a head start, not from effect size, and that head start has carried over into popular advice literature.

There is also a linguistic coincidence. The abbreviation is often associated with the English word for fat mass, which reinforces the impression of a switch. It is not a switch.

Loos and Yeo also point out that the precise mechanisms of action have not yet been fully clarified (2021). The best-known genetic locus in this field is therefore also one for which an important question remains open.

Why Many Small Effects Still Explain Something

A common fallacy is made at this point. If each individual variant explains only one kilogram or less, the argument goes, then genetics are meaningless when it comes to body weight.

That is not true. What matters is nevertheless different from what advertising claims: The hereditary component arises from the sum of many small contributions, not from a switch that can simply be flipped.

Two conclusions follow for a test. It can describe the direction of individual predispositions, for example regarding satiety or carbohydrate metabolism. It cannot combine them into a total that produces a prediction.

A professional assessment by Prof. Dr. Christina Holzapfel, reproduced on the DGE blog, takes the same view: The approximately 1,000 genetic loci identified to date each have only a small effect on body weight (2025). This is the assessment of one individual expert and not an institutional position.

Which Topic Areas an Analysis Covers

A metabolic test sorts the evaluated items by topic, because a list of SNP designations would be unreadable to anyone. These topics are the actual content of a report.

Recurring areas include fat burning, carbohydrate metabolism, satiety, and the body's response to exercise. Each area summarizes several individual findings.

The direction in which it is read is important. A range describes a predisposition, not a behavior. A predisposition is not a fixed determination, and a good report states this wherever someone might otherwise read one into it.

How to Interpret a Range Meaningfully

A finding about satiety does not say how much you eat. It describes how strong the signal that ends a meal is, and from this follows a question, not an instruction.

The question is: At what point during your meal is the portion decided? Anyone who knows that their satiety signal is weaker is more likely to decide beforehand rather than while eating—and that is precisely a practical change.

Anyone who knows that their sense of satiety is genetically less pronounced can finally understand why portion control requires more effort from them than from others. They can deliberately choose strategies that address this specific issue instead of blaming themselves for a lack of discipline.

How many variants a metabolism test reads

mybody®x's entry-level test analyzes over 80 genetic variants from a saliva sample. These produce 24 analysis reports in 5 chapters spanning around 140 pages.

DNA analysis from saliva

WeightLoss | SLIM DNA test

Over 80 genetic variants from a saliva sample, analyzed in 24 reports across 5 chapters spanning around 140 pages. What the test does not do: It does not state an effect size in kilograms for your personal variants, provide a diagnosis, predict weight-loss success, or replace a medical examination.

Price €169.00 As of 12 August 2026; subject to change

Sample type Saliva

Processing time Kit shipping 1–3 business days
Laboratory analysis 15–25 business days after sample receipt

Laboratory ISO-certified laboratory analysis
Information from the product page, accessed 12 August 2026

About WeightLoss SLIM

How these findings can be translated into diet and training is described in the overview article on genes and weight loss in practice. This article stays with the foundation: which positions are analyzed and how large the effects are.

Three analysis areas compared

The areas of a report differ in how well they are supported by evidence and what can be derived from them. The table compares three of them according to the same four criteria.

The third line is the most honest. For two of the three areas, we found no reliable individual figure in the sources reviewed, and so there is none there either. An estimated figure would be the worse error.

Two statements about genes and weight fact-checked

The following two sentences appear in many texts on this subject, one as an advertising claim and one as a rebuttal. Both can be tested against the same figures.

Checked against the evidence

The second point needs a qualification so that it does not become a promise of an effect. The fact that the sum matters does not mean that a test could calculate it and turn it into a forecast. The evidence does not support that calculation.

Limitations: what the figures do not show

An effect size does not yield a personal prediction. The figures from Loos and Yeo come from population studies, and effect sizes from such studies describe averages across very large numbers of people.

A correlation does not establish causation either. A genome-wide association study identifies locations where carriers of a trait differ, but it does not explain why.

There is also a gap in interpretation. According to the expert assessment reported in the DGE blog, the function of many gene loci examined in such tests is not fully clear (2025). This concerns interpretation, not measurement.

After all, no analysis captures everything that affects weight alongside genetics. Sleep, stress, medication, illnesses, and living conditions all play a role, and none of these factors is present in a saliva sample.

This list reads like an argument against the analysis. It is an argument against expecting that averages from more than 800,000 people could yield a statement about you.

What the scale of the effect means for you

If you take away just one action from this article, let it be this: Compare every statement about genes and weight that you encounter with the figure of one kilogram. That is the strongest known individual effect.

The reason is unremarkable. This one number exposes every exaggeration in this product category, and it costs nothing but the willingness to remember it. Anyone who promises more has gone beyond the evidence.

It all began with the question of which genes influence weight loss. The most honest answer is: more than a thousand, each with such a small effect that the question was wrongly framed.

Frequently asked questions

Sources

1. Loos RJF, Yeo GSH: The genetics of obesity: from discovery to biology. Nature Reviews Genetics, 2021 – pmc.ncbi.nlm.nih.gov
2. German Nutrition Society: Personalized nutrition – how does it work? Interview with Prof. Dr. Christina Holzapfel, DGE Blog, 2025 – dge.de

The verbatim quotation concerning the number of studies and genetic loci, the effect sizes of 0.35 and 0.04 kilograms per square meter per allele, the conversion for a height of 1.70 meters, the reference to the largest individual study with nearly 800,000 participants, and the classification of FTO come from source [1]. The quotation appears in the original English, with its meaning in German reproduced in the paragraph below. The assessments of the small effect of individual loci and the fact that the function of many genetic loci has not been fully clarified come from [2]; there, they are attributed to a named individual and do not represent an institutional position of the DGE. Information on price, scope, procedure, sample type, and laboratory comes from mybody®x, accessed on 08/12/2026; processing times follow the central specifications for DNA tests. For the areas of carbohydrate processing and response to exercise, no reliable individual figures were found in the reviewed source material; the corresponding table cells therefore remain explicitly blank rather than estimated. All sources were accessed and reviewed on 08/12/2026.

mybody®x Editorial & Expert Team

Nutrigenetics Nutritional science Laboratory diagnostics Blood test interpretation

This article was created by the mybody®x editorial and expert team. The team combines nutrigenetics, nutritional science, and laboratory diagnostics. Contributors are listed on the authors page.

Published on 12/08/2026 · Last updated on 12/08/2026

DNA analysis is intended for nutritional and lifestyle counseling. It is not a diagnostic procedure, does not predict illness, and does not replace a medical examination or consultation. Genetic variants describe probabilities in population groups, not fixed outcomes for individuals.