Weight is more than a calorie calculation
ca. 17 Minuten
The key points
The energy balance holds. This article doesn’t question it, but looks at the factors that go into it.
That’s because energy needs aren’t a fixed number. According to IQWiG, resting energy expenditure accounts for about 70 percent of them on average and depends primarily on the proportion of muscle mass.
You’ll read a fact-check of three statements, the cited source in full, three evidence-based facts, a comparison of the calculation and test results, and why an abnormal result doesn’t explain someone’s weight.
What to expect in this article
1. Why the calculation holds
2. Fact-check: three statements
3. What varies in the calculation
4. The cited source
5. What follows from the quote and what doesn’t
6. Three evidence-based facts
7. The core idea in one sentence
8. Rare cases and why the word belongs here
9. Comparing the calculation and test results
10. What a result cannot explain
11. Who can benefit from testing
12. Which results a panel includes
13. Limitations: what these results leave unanswered
14. What matters about this topic
Frequently asked questions
Sources
Why the calculation holds
Let’s start with what this article does not do: it does not question the energy balance.
This isn’t a polite formality, but a distinction. Our magazine has a detailed article that works through the energy balance using sources from DGE, IQWiG, and WHO, and this article doesn’t contradict it.
What it does is look one level deeper. A calculation has inputs, and if one of them differs between two people, the same calculation produces different results.
This is exactly where blood test results come into play. They don’t change the calculation, but they can explain why one of its factors is different for someone.
A comparison makes this clear. Two people drive the same route in the same car and use different amounts of fuel. The physics are the same for both. What differs is the load, tire pressure, and driving style—and anyone who wants to understand the difference looks at those factors instead of questioning the physics.
The same applies to energy needs. The energy balance holds, and it’s still worth looking at the factors that go into it. That’s exactly what this article is about.
Fact-check: three statements
These three statements come up in almost every conversation about this topic.
Checked against the evidence
Common
“Everyone’s calorie requirements are roughly the same.”
Documented
IQWiG states that resting energy expenditure depends primarily on the proportion of body weight made up of muscle mass and accounts for about 70 percent of total calorie requirements on average (as of August 24, 2022).
Common
“If it doesn’t work, it must be the thyroid.”
Documented
IQWiG describes slight to moderate weight gain as a possible symptom of an underactive thyroid (as of 24.04.2024). It does not offer a general explanation for weight, and an underactive thyroid must be diagnosed by a medical professional.
Common
“Usually, a hormonal condition is behind it.”
Documented
IQWiG says the opposite: obesity is very rarely the result of a congenital or hormonal condition (as of 24.08.2022). The words “very rarely” appear explicitly.
What can vary in the calculation
The energy balance compares intake and expenditure. Neither side is constant.
Resting energy expenditure comes first on the expenditure side. IQWiG describes it as accounting for an average of about 70 percent of total calorie requirements, and identifies the proportion of muscle mass in body weight as the main influencing factor (as of 24.08.2022).
This already explains why two people with the same weight can burn different amounts of energy. It is not just weight, but its composition.
There is also a second factor that affects resting energy expenditure and can be measured. It is stated verbatim in the next chapter.
Why this is not an excuse
A misunderstanding regularly arises at this point, and we want to clear it up right away.
The fact that an input variable can change does not mean it can be arbitrary. Two people’s resting energy expenditure differs, but not by enough to invalidate the calculation.
The source itself explains what matters. It identifies the proportion of muscle mass in body weight as the main factor affecting resting energy expenditure (IQWiG, as of 24.08.2022) - something that can change over time and is not set in stone.
The purpose of this article is therefore not to offer reassurance. It is to help put an observation into context when it does not fit your own calculations, and to know where to take it.
The documented source
The sentence is short and describes a mechanism that is central to this topic.
Documented source
“When thyroid hormones are lacking, the metabolism slows down.”
Institute for Quality and Efficiency in Health Care
Underactive thyroid (hypothyroidism), as of 24.04.2024
The sentence describes a direction of effect, and one with a condition beforehand: when hormones are lacking. Without that condition, the second part does not apply.
The same source lists slight to moderate weight gain as a possible symptom of an underactive thyroid (as of 24.04.2024). This wording is also notably cautious: slight to moderate, and just one symptom among others.
What follows from the quote and what does not
The sentence means that the thyroid affects one of the inputs to the equation. That is a factual, documented statement.
It does not follow that a particular weight can be explained by the thyroid. The sentence describes a connection, not its extent, and the source explicitly describes the weight gain as mild to moderate.
Nor does it follow that someone should determine a value for themselves and draw conclusions from it. Identifying an underactive thyroid is a diagnosis, and diagnoses are made in a doctor’s office.
What follows is something more modest, but still useful: If someone observes over a longer period that something doesn’t fit their equation, this gives them reason to bring it up rather than blame it on a lack of discipline.
Three documented figures
Three figures from the sources reviewed. They provide context, not a diagnosis.
Documented figures
about 70%
of total calorie needs is accounted for by resting metabolic rate on average; it depends primarily on the proportion of muscle mass (IQWiG, as of August 24, 2022)
very rarely
according to IQWiG, obesity is the result of a congenital or hormonal disorder (as of August 24, 2022)
3 months
reflects the long-term blood sugar level over a period of time and therefore does not respond to a single week (MSD Manual, as of December 2025)
The middle figure is the most important one in this article. It prevents factual information from becoming a convenient explanation.
The core idea in one sentence
At this point, we can bring the topic together.
Blood test results don’t replace the equation. They can explain why one of its inputs differs for someone.
This sentence is deliberately cautious, and that caution is the point.
Anyone who uses blood test results to explain their weight is reading too much into them. Anyone who considers them irrelevant overlooks the fact that one of the inputs to the equation can in fact be influenced.
The rare cases and why that word belongs
There are conditions for which a link to weight has been described. IQWiG names them and precedes them with a word that must be quoted too.
The sentence reads: “Very rarely, obesity is the result of a congenital or hormonal disorder” (as of August 24, 2022). The same source gives Prader-Willi syndrome as an example, a genetic defect associated with insatiable hunger from childhood, as well as Cushing’s disease, a hormonal disorder in which the body produces too much cortisol.
The words “very rarely” are regularly omitted from informational texts, creating an impression that the source does not support. We’re leaving them in.
That does not diminish the importance of the information. For the few people affected, this finding matters—and it is made in a doctor’s office, not through a self-test.
The same source also describes how hormones can become imbalanced in obesity, for example because leptin no longer works as well in the body (as of 24.08.2022). Here too, the wording is cautious, and here too, it concerns an accompanying effect, not a cause.
The direction of this last point matters. The source says that hormones can become imbalanced when obesity is already present—not that an imbalance caused it. Reversing this direction turns an effect into a cause, which the statement does not support.
Calculation and values compared
The table compares which question the calculation answers and which a value answers. It provides context and does not make a diagnosis.
| Question | The energy balance | A lab value | Source |
|---|---|---|---|
| How is my weight changing? | Answers it through intake and expenditure | Does not answer that | IQWiG, Causes of obesity, as of 24.08.2022 |
| Why is my resting metabolic rate what it is? | Takes it as a given | Can contribute to one aspect, for example through thyroid values | IQWiG, Hypothyroidism, as of 24.04.2024 |
| Is there a medical condition? | Does not answer that | Does not answer that either; that is a medical diagnosis | A lab value is always just one component of an overall diagnosis (IQWiG, as of 02.04.2025) |
| How common is a hormonal cause? | Does not answer that | Does not answer that either | Obesity is very rarely the result of a congenital or hormonal disorder (IQWiG, as of 24.08.2022) |
The second row is the only one in which a lab value contributes anything, and even there it says “one aspect.”
The third row contains two noes and is still the most practically important. It says where the question belongs if someone wants to ask it seriously.
What stands out about the table overall is how few fields contain a clear yes. That’s not because we wanted to be cautious in our wording, but because that’s what the sources themselves say. Anyone looking for clear-cut links on this topic will find them more often in advice articles than in expert sources.
And one more observation: the energy balance and a lab value do not answer the same question in a single instance. They sit side by side, not in opposition—and that is exactly why comparing them in a table makes sense, rather than using it to judge.
What a value does not explain
A paragraph here to counter the obvious misinterpretation of this article.
If someone receives a test result after reading this and finds a value at the edge of the range, they haven’t found an explanation for their weight. They’ve found a number.
The IQWiG notes that an abnormal laboratory result alone cannot be used to conclude that someone has a disease, and that there are often harmless reasons for it (as of 02.04.2025). It also notes that a laboratory result must always be considered alongside other results, symptoms, and findings from other examinations.
These two sentences fill the gap this article would otherwise leave. A test result is one component, not an answer.
Anyone looking for an explanation can find one in a discussion that brings together medical history, observations, a physical examination, and, where appropriate, test results. That discussion takes place at a medical practice.
What a test result can do instead
After so many caveats, it’s fair to ask what a test result is actually good for. The answer is modest and practical.
It provides a documented baseline. If circumstances change and a second result is obtained months later, you can see a trend. That trend says more than any single result on its own.
It also provides a basis for discussion. If you go to a medical practice with a report that includes the date, unit, and laboratory, you can talk about figures rather than impressions. This doesn’t change the medical assessment, but it can make it easier.
The IQWiG sums up what a test can’t do in a sentence that could appear above all our articles: A single laboratory result is always just one component of an overall diagnosis (as of 02.04.2025).
Who may benefit from test results
This comparison concerns whether documented values could be helpful in your situation.
It may be useful for you if …
You want to bring dated figures to an appointment at a medical practice.
You want a documented baseline to see a trend later.
You understand that a test result adds to the picture but doesn’t replace it.
You also want to document other values that aren’t included in the health check.
Probably not, if …
You are hoping it will explain your weight. No test result can do that.
You want to change your diet based on the numbers. That’s something to discuss with someone who has the relevant expertise.
You have symptoms. In that case, you need evaluation at a medical practice.
You are already undergoing evaluation. In that case, the practice that started it should guide you.
Which values a panel includes
A capillary blood self-test does not provide a diagnosis, explain your weight, or replace medical evaluation. What it does provide is documented figures with a date.
Thyroid levels are particularly relevant to this topic because they relate to the aspect described in the quote. According to the product page, mybody®x’s (MYBODY Lab GmbH) Women’s Wellness Check includes TSH, fT3, and fT4, while the Men’s Wellness Check includes TSH.
Capillary blood test
Women’s Wellness Check | Women’s health test
Measures 18 values from the same sample, including TSH, fT3, fT4, cortisol, prolactin, SHBG, ferritin, vitamin B12, 25-OH vitamin D3, HbA1c and CRP. What the test does not do: It does not explain weight or provide a diagnosis. It does not measure resting metabolic rate, body composition or energy intake. It does not replace medical evaluation.
Lab analysis 3–5 business days after sample receipt
Product page statement, accessed 19.08.2026
Chapter at a glance
A panel documents values with dates, including thyroid values. It does not explain weight, measure resting metabolic rate or energy intake, or provide a diagnosis. Hypothyroidism is diagnosed in a medical practice.
Limitations: what the results leave unanswered
The first limitation is frequency. Obesity is very rarely the result of a congenital or hormonal disorder (IQWiG, as of 24.08.2022).
The second limitation is the extent. IQWiG describes mild to moderate weight gain as a possible symptom of hypothyroidism (as of 24.04.2024), and nothing more.
The third limitation is interpretation. An abnormal lab value alone does not point to a disease, and there are often harmless reasons for it (IQWiG, as of 02.04.2025).
The fourth limitation is the scope of measurement. A blood test measures neither resting metabolic rate nor body composition nor actual energy intake. All three matter more to the equation than any single value.
The fifth limitation is diagnosis. All the assessments in this article provide context and do not constitute a diagnosis. A diagnosis is made in a medical practice based on several factors.
What matters about this topic
If you take away just one thing from this article, let it be this: The equation holds, and its inputs vary from person to person.
According to IQWiG, resting metabolic rate accounts for about 70 percent of calorie requirements on average and depends primarily on the proportion of muscle mass (as of 24.08.2022). And when thyroid hormones are lacking, metabolism slows down (IQWiG, as of 24.04.2024).
At the same time, this statement protects the article from being misinterpreted: Obesity is very rarely the result of a congenital or hormonal condition (IQWiG, as of 24.08.2022). So if you notice something that doesn’t fit your calculation, discuss it with a medical professional, not on the basis of a lab report alone.
Frequently asked questions
So is the calorie calculation right or not?
It is correct, and this article does not dispute it. It shows that its inputs can vary from person to person. IQWiG notes that resting metabolic rate depends primarily on the proportion of muscle mass and accounts for about 70 percent of total calorie requirements on average (as of 24.08.2022).
Could my thyroid explain my weight?
IQWiG explains that metabolism slows when thyroid hormones are lacking and notes that mild to moderate weight gain can be a symptom of an underactive thyroid (as of 24.04.2024). A medical professional determines whether the thyroid is underactive. A single value cannot explain someone’s weight.
How often is a hormonal condition the cause?
IQWiG states: Obesity is very rarely the result of a congenital or hormonal condition (as of 24.08.2022). The same source cites Prader-Willi syndrome and Cushing’s syndrome as examples. The words “very rarely” are an important part of this statement.
Does a blood test measure my basal metabolic rate?
No. A blood test measures neither resting metabolic rate nor body composition nor actual energy intake. It provides concentrations of individual values at the time the sample is taken. For the calculation itself, the three factors mentioned are more important than any single lab value.
What should I do if my observation doesn’t match the calculation?
Discuss this observation with a medical professional, including the time period and as much specific information as possible. A documented finding can help prepare for this conversation, but does not replace it. IQWiG notes that a lab value must always be considered together with other values, symptoms, and findings from other examinations (as of 02.04.2025).
Next step
Numbers to discuss
The Women’s Wellness Check measures 18 values from capillary blood, including TSH, fT3 and fT4. It does not explain weight, measure resting metabolic rate, replace medical evaluation, or provide a diagnosis.
Go to the Women’s Wellness CheckRead more
You might also be interested in
The energy balance, calculated in detail.
The connection in detail.
Sources
- Institute for Quality and Efficiency in Health Care (IQWiG): Causes of obesity, as of 24.08.2022 – gesundheitsinformation.de
- IQWiG: Hypothyroidism, as of 24.04.2024 – gesundheitsinformation.de
- IQWiG: Understanding lab results correctly, as of 02.04.2025 – gesundheitsinformation.de
- MSD Manual, Professional Edition: Diabetes mellitus, Brutsaert EF (as of December 2025) – msdmanuals.com
The estimate that resting metabolism accounts for about 70 percent, the reference to muscle mass, the statement that congenital and hormonal causes are rare, the examples of Prader-Willi syndrome and Cushing’s disease, and the reference to leptin come from source [1]. The direct quote about a slowed metabolism and the estimate of slight to moderate weight gain come from [2]. The statement that this is one component of an overall diagnosis, the note that abnormal values can have harmless causes, and the statement that results should be considered together with symptoms and other findings come from [3]. The reference to a three-month period for long-term blood glucose comes from [4]. Information on price, values, sample type, and laboratory is from mybody®x product pages, accessed on 19.08.2026; processing times follow the central guideline for blood tests. All sources were accessed and reviewed on 19.08.2026.
mybody®x Editorial & Expert Team
Laboratory diagnostics Blood test interpretation Nutritional science Nutrigenetics
This article was created by the editorial and expert team at mybody®x. The team brings together laboratory diagnostics, nutritional science, and the interpretation of blood tests. You can find out who contributes on the authors page.
Published on 19.08.2026 · Last updated on 19.08.2026
The content is intended for general information and does not replace medical advice, diagnosis, or treatment. Reference ranges depend on the laboratory, method, and age; the information on your test report is always authoritative.
