Training in an energy deficit is reflected in several values
The key points
Taking in less energy than you expend over an extended period changes more than just your weight. Several laboratory values may shift as well.
The MSD Manual uses a specific term for this: fasting and starvation are among the states in which thyroid values may be abnormal without a thyroid disease being present.
You will read three evidence-based points, which values may be affected, the quoted source in full, three fact-checked statements, and when physical signals should be addressed by a medical practice.
What to expect in this article
1. What is meant by training in an energy deficit
2. Three evidence-based points
3. Why several values may shift at the same time
4. Which values may be affected
5. Abnormal does not mean diseased
6. The documented source
7. What this quote means in practice
8. The key point in one sentence
9. When physical signals should be addressed by a medical practice
10. Three fact-checked statements
11. What these values can and cannot tell us here
12. Who may benefit from testing
13. What an amino acid profile shows in this context
14. Limitations: what values do not reveal in an energy deficit
15. What matters about this topic
Frequently asked questions
Sources
What is meant by training in an energy deficit
This refers to a situation in which someone takes in less energy over an extended period than they expend while continuing to train.
This article does not assess this situation or encourage anyone to pursue it. Nor does it provide figures for a deficit, a target weight, or a body-fat percentage. Such details belong in a discussion with a medical practice or a qualified nutrition professional who knows the person.
What it does is provide factual information: If the body lacks energy over an extended period, this may be reflected in several laboratory values. Anyone who receives test results during this phase should know this so as not to misinterpret them.
To put energy needs into perspective: IQWiG notes that resting energy expenditure depends primarily on the proportion of muscle mass relative to body weight and accounts for an average of about 70 percent of total calorie needs (as of August 24, 2022).
Three evidence-based points
Three pieces of information from the reviewed sources. They provide context and are not a diagnosis.
Evidence-based information
About 70%
On average, resting energy expenditure accounts for this share of total calorie needs; it depends primarily on the proportion of muscle mass (IQWiG, as of August 24, 2022)
0.8 g/kg
The DGE recommends 0.8 g/kg of body weight per day as the protein intake for adults under 65; from age 65, the recommendation is 1.0 g/kg (as of 2025)
No reason
According to the DGE, there is no physiological reason in athletes’ everyday diets to supplement protein intake with supplements (2020)
The first statement explains why a deficit affects the body more than just the number on the scale. Most of the body's needs arise at rest, for processes that have to continue regardless.
Why several values shift simultaneously
The body does not treat an energy deficit as an isolated problem. It responds with adaptations that affect various systems.
That is why it is typical for several values to change simultaneously rather than just one during such a phase. And that is precisely what makes interpreting a report considerably more difficult.
Because when someone sees a report with three abnormal lines, they think of three problems. But it is also possible that they share a common cause.
Which of these two interpretations applies cannot be determined from a laboratory report alone. IQWiG states that a lab value must always be considered together with other values, symptoms, and findings from other examinations (as of April 2, 2025).
Which values may be affected
The table summarizes what the reviewed sources say about individual values in this context. It provides context and does not constitute a diagnosis.
| Value group | What the sources say | What this does not imply | Source |
|---|---|---|---|
| Thyroid values | Fasting and starvation are among the conditions in which serum thyroid hormone levels may be low even though no thyroid disorder is present | That a thyroid disorder is present. According to the source, those affected are actually euthyroid | MSD Manual, Boucai, as of February 2024 |
| Amino acids | The body cannot produce nine of the twenty amino acids itself; they must be obtained through food | That a single value reflects intake. Several steps lie between the plate and the blood value | MSD Manual, Bhupathiraju and Hu, as of November 2025 |
| Albumin | Measuring plasma albumin provides information about the severity of protein-energy malnutrition | That every abnormality leads to treatment. The source states that such results rarely affect treatment | MSD Manual, Bhupathiraju and Hu, as of December 2025 |
| All other values | None of the sources reviewed explicitly mentions additional values in connection with training while in a deficit | That no others would be affected. It only means that we have no source for them | Sources reviewed on August 19, 2026 |
The last line is important to us. Long lists of values with specific percentages circulate online on this topic, and we do not reproduce them because we cannot find them in the sources we reviewed.
The third line contains a qualification that is rarely quoted. Regarding abnormal blood values in malnutrition, the MSD Manual explicitly states that these results rarely affect treatment (as of December 2025).
Abnormal does not mean diseased
The biggest misconception about a test result in this phase concerns the meaning of an abnormal value.
A value outside the reference range is interpreted as an indication of disease. In the context of energy deficiency, it may instead be an adaptation: a response by the body to the situation it is in.
This is not downplaying the issue. An adaptation can certainly be a reason to change something. But it is different from a disease of the organ whose value is abnormal.
For the thyroid, the MSD Manual has a specific name for precisely this constellation, and the corresponding chapter provides the quotation for the next section.
The documented source
The sentence explicitly lists fasting and starvation alongside illnesses without turning them into illnesses.
Documented source
“Patients with various acute or chronic nonthyroidal illnesses may have abnormal thyroid function test results. These include fasting, starvation …”
MSD Manual, Professional Edition
Euthyroid Sick Syndrome, Laura Boucai, last reviewed February 2024
The chapter title is already half the explanation. The same chapter describes the condition as one in which serum levels of thyroid hormones are low even though those affected do not have thyroid disease (Boucai, last reviewed February 2024).
That is precisely the value of the quotation for this article. It shows that the specialist literature recognizes a case in which an abnormal value means something different from what it appears to indicate.
What this quotation means in practice
For someone who receives a test result during a period of low energy, the quotation has three practical implications.
First, information about your own situation belongs in the conversation in which the test result is discussed. Anyone who has been training with low energy for months should mention it, because it changes how an abnormal value is interpreted.
Second, a single abnormal value during this phase is not yet a reason to take a preparation or change a training program. What follows is determined by a medical practice based on several factors.
Third, a later comparison value is especially informative here. If a value changes again under altered conditions, that says more than any single measurement.
The core in one sentence
At this point, the topic can be brought together.
A test result from a period of low energy also describes that period. Anyone who fails to take that into account misreads it.
The sentence applies in both directions. It warns against mistaking an adaptation for a disease, and equally against dismissing a disease as merely an adaptation.
No one decides which of the two possibilities applies at the kitchen table. Distinguishing between them is precisely the job of a medical practice.
When physical signals belong in a medical practice
This section is the most important part of the article, and it is not about lab values.
Anyone who trains with too little energy over an extended period may notice physical changes before any value has been measured. These include persistent exhaustion, a drop in performance despite maintaining the same training, frequent infections, sleep problems, constantly feeling cold, or an absent or irregular menstrual cycle.
Such signals are a reason to visit a medical practice, regardless of whether a finding is available. They are not a sign of a lack of discipline, but feedback from the body.
One more thing belongs here: If thoughts about food, weight, or training take up a lot of space, become distressing, or are difficult to control, that is also a good reason to talk to someone about it. A medical practice is one possible first point of contact, as is a counseling service.
A blood test is not the first step in either case and does not replace it. At most, it may play a role later if someone with relevant expertise decides it would be helpful.
Three statements fact-checked
These three statements are widespread in training circles.
Checked against the evidence
Widespread belief
“A low thyroid value during a calorie deficit means that the thyroid is diseased.”
Evidence-based
The MSD Manual describes a condition in which serum levels are low even though there is no thyroid disease, and explicitly lists fasting and starvation as triggers (Boucai, as of February 2024).
Widespread belief
“You need supplements when in a calorie deficit, otherwise you lose muscle.”
Evidence-based
The DGE states that, in the everyday diets of athletes, there is no physiological reason to supplement protein intake with supplements, and that a balanced diet is generally superior to supplements (2020).
Widespread belief
“Basal metabolic rate is roughly the same for everyone.”
Evidence-based
The IQWiG notes that resting energy expenditure depends primarily on the proportion of muscle mass relative to body weight and accounts on average for around 70 percent of total calorie needs (as of August 24, 2022).
What measurements can and cannot tell you here
A finding from such a phase has limited but real value.
It documents a baseline with a date. If circumstances change later and a second finding is recorded, a direction can be identified—and directions say more than individual points.
It brings numbers into a conversation. Anyone visiting a medical practice because they have noticed something has a better basis with a documented finding than with a memory.
What it does not do: It does not say whether a deficiency is too severe. It does not say whether training should be adjusted. And it does not replace a conversation in which someone asks about symptoms and conducts an examination.
Who may benefit from a measurement
The comparison relates to whether a measurement would contribute anything in your situation.
It may be useful for you if …
You want a documented baseline to compare with later.
You want to bring dated numbers to a conversation at a medical practice.
You know that an abnormal value during this phase may also be an adaptation, and interpret it accordingly.
You record the conditions of the sample so that a later comparison will be meaningful.
Probably not if …
You notice physical signals. In that case, a medical practice is the first step, not a test.
Thoughts about food, weight, or training are causing you distress. In that case, what you need is a conversation, not numbers.
You hope it will confirm that everything is fine. No test result can provide that.
You are already undergoing evaluation. In that case, the medical practice that began it is in charge.
What an amino acid profile provides in this regard
A capillary blood self-test does not provide a diagnosis, replace medical evaluation, or answer whether a deficit is appropriate. What it provides is documented numbers with a date.
The PerformanceCheck from mybody®x (MYBODY Lab GmbH) measures 22 values, including the nine essential amino acids. According to the MSD Manual, dietary intake is their only source because the body cannot produce them itself.
Capillary blood test
PerformanceCheck | Amino acid test
Measures 22 values from the same sample: nine essential amino acids, ten non-essential amino acids, plus taurine, ornithine, and citrulline. What the test does not do: It does not assess a deficit or training plans, and it does not include thyroid values, albumin, or a complete blood count. It does not provide a diagnosis or replace medical evaluation. The fasting requirement in the instructions must be followed.
Laboratory analysis 3–5 business days after receipt of the sample
Information from the product page, accessed 19 August 2026
Chapter at a glance
An amino acid profile documents 22 values with a date. It does not assess a deficit, include thyroid values, or replace medical evaluation. If you experience physical signals or distressing thoughts about food and weight, a conversation is the first step—not a test.
Boundaries: what values in a deficit leave unanswered
The first boundary is interpretation. An abnormal value during this phase may be an adaptation rather than an illness. A medical practice determines which of the two it is.
The second boundary is our sources. In this article, we deliberately do not provide percentages for individual values in a deficit because we could not find them in the sources we reviewed.
The third boundary is consequence. Regarding abnormal blood values in malnutrition, the MSD Manual notes that these results rarely affect treatment (as of December 2025).
The fourth boundary is sequence. Physical signals and distressing thoughts about food or weight belong in a conversation—and that conversation should come before any test.
The fifth limitation is diagnosis. All the explanations in this article provide context and do not constitute a diagnosis. A laboratory value must always be considered together with other values, symptoms, and findings from other examinations (IQWiG, as of April 2, 2025).
What matters about this topic
If you take away just one thing from this article, let it be this: A test result from a period of low energy intake also describes that period.
The MSD Manual explicitly lists fasting and starvation among the conditions in which thyroid values can be abnormal even though no thyroid disease is present (Boucai, as of February 2024). Anyone who overlooks this information may draw the wrong conclusion from a test result.
And the point that takes precedence over everything else: If your body is sending signals or thoughts about food, weight, or training are troubling you, having a conversation is the first step. A blood test is not.
Frequently asked questions
Does a calorie deficit change my thyroid values?
The MSD Manual describes a condition in which serum thyroid hormone levels are low even though no thyroid disease is present, and explicitly lists fasting and starvation among its triggers (Boucai, as of February 2024). A doctor can clarify what this means in an individual case.
Which values change during a calorie deficit, and by how much?
We do not provide specific percentages because we did not find them in the sources we reviewed. The statements about thyroid values and plasma albumin are supported; according to the MSD Manual, plasma albumin indicates the severity of protein-energy malnutrition (as of December 2025). We deliberately do not reproduce lists of percentages from the internet.
When is a calorie deficit too large?
This article deliberately does not answer this question with figures. It depends on the individual, training volume, medical history, and goals, and should be discussed with a doctor or a qualified nutrition professional. Physical symptoms such as persistent exhaustion, declining performance, frequent infections, or menstrual-cycle changes are reasons to seek this advice.
Do I need protein supplements while in a calorie deficit?
The DGE states in its position paper that, in the everyday diets of athletes, there is no physiological reason to supplement protein intake, and that a balanced diet is generally superior to supplements (2020). As a reference value, the DGE gives 0.8 g of protein per kilogram of body weight per day for adults under 65 (as of 2025).
Should I get tested at all during this phase?
If you notice physical symptoms, seeing a doctor is the first step—not getting tested. If, on the other hand, you want a documented baseline for later comparison, a measurement may be useful—provided you record the testing conditions so that a comparison is meaningful.
Next step
Documenting a baseline with a date
The PerformanceCheck measures 22 values from capillary blood. It does not assess a deficiency, include thyroid values, replace medical evaluation, or provide a diagnosis. If you are experiencing physical symptoms, talking to a healthcare professional is the first step.
Go to the PerformanceCheckRead more
You might also be interested in
How an amino acid profile is structured.
The timelines behind it.
Sources
- MSD Manual, Professional Edition: Euthyroid sick syndrome, Boucai L (last reviewed February 2024) – msdmanuals.com
- MSD Manual, Professional Edition: Protein-energy undernutrition (PEU), Bhupathiraju SN, Hu F (as of December 2025) – msdmanuals.com
- MSD Manual, Professional Edition: Nutrient overview, Bhupathiraju SN, Hu F (as of November 2025) – msdmanuals.com
- Institute for Quality and Efficiency in Health Care (IQWiG): Causes of obesity, as of 24.08.2022 – gesundheitsinformation.de
- IQWiG: Understanding laboratory values correctly, as of 02.04.2025 – gesundheitsinformation.de
- German Nutrition Society (DGE): Position paper on protein intake in sports, press release 13/2020 – dge.de
- DGE: Selected questions and answers about protein and essential amino acids, as of 2025 – dge.de
The verbatim quotation about fasting and starvation, as well as the description of the condition with low serum levels in the absence of thyroid disease, come from source [1]. The information about plasma albumin and the note that such results rarely affect treatment come from [2]. The information about the nine essential amino acids comes from [3]. The figure of approximately 70 percent for resting energy expenditure and the note about muscle mass come from [4]. The statement about considering the results together with symptoms and other findings comes from [5]. The quotation about the lack of a physiological reason for supplements comes from [6]. The reference values of 0.8 and 1.0 g of protein per kilogram of body weight come from [7]. Information about price, values, sample type, and laboratory comes from the mybody®x product page, accessed on 19.08.2026; processing times follow the central specification for blood tests. All sources were accessed and reviewed on 19.08.2026.
mybody®x Editorial & Expert Team
Laboratory diagnostics Blood analysis interpretation Nutritional science Nutrigenetics
This article was created by the mybody®x editorial and expert team. The team combines laboratory diagnostics, nutritional science, and the interpretation of blood analyses. Those who contribute to it are listed 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 report is always authoritative.
Share now:
What Your Skin Reveals About Your Blood Values
Which DNA test is right for me? Five analyses, one way to choose