Too much protein: what it means for your kidneys and digestion
October 21, 2026approx. 14 minutesby mybody®x Editorial & Expert Team
In brief
In studies, an intake of at least 1.5 g per kg of body weight or at least 100 g per day is considered “high” in protein (Devries et al., 2018), but this is not a cutoff. No decline in kidney function was measured in healthy adults at this intake (Devries et al., 2018). Anyone with impaired kidney function should consult a doctor before adopting a high-protein diet (Ko et al., 2020).
The DGE (2017) gives a reference value of 0.8 g of protein per kg of body weight per day for adults aged 19 to under 65.
Undigested protein is fermented mainly in the lower part of the large intestine, and according to Windey et al. (2012), the connection between this and gut health has not been thoroughly researched.
According to MedlinePlus (2024), an elevated urea level, a kidney marker resulting from protein breakdown, can be caused by a high-protein diet as well as too little fluid, so it is not a measure of how much protein you eat.
In this article
How much protein is too much?
In research, an intake of at least 1.5 g of protein per kg of body weight or at least 100 g per day is considered “high” (Devries et al., 2018). This is a definition used in studies, not a cutoff.
Key takeaway
The DGE reference value (2017) describes the recommended intake for healthy people, while the study definition of “high” protein starts at 1.5 g per kg of body weight (Devries et al., 2018).
Anyone who eats quark every morning and drinks a protein shake after working out will eventually ask this question. The answer has two parts: a benchmark for what healthy people need, and a benchmark for what studies classify as high in protein. Both are useful, as long as you don’t confuse them. Protein and protein mean the same thing here.
What protein value is used as a reference?
The German Nutrition Society (DGE) gives a reference value of 0.8 g of protein per kg of body weight per day for adults aged 19 to under 65 (DGE, 2017). From age 65, the value is 1.0 g per kg, which the DGE (2017) explicitly describes as an estimate. In grams, this amounts to 57 g per day for men and 48 g for women aged 19 to under 65, according to the DGE (2017).
This reference value describes the recommended intake for healthy people. It is not a weight-loss target. For guidance on how to assess your own needs, see the article on daily protein requirements. Here, we’re looking at the other side: too much protein and its effects on the kidneys and gut. There’s also a dedicated article for women on women’s protein requirements.
When does research consider protein intake high?
A meta-analysis, or combined analysis of 28 studies, provides a clear definition (Devries et al., 2018). In that analysis, a diet was considered high in protein if it provided at least 1.5 g per kg of body weight or at least 100 g of protein per day (Devries et al., 2018). The box below shows all the criteria at a glance.
The researchers needed this threshold to compare groups. The comparison groups ate a normal or lower amount of protein, with at least 5% less energy from protein than the high-protein group (Devries et al., 2018). So the threshold separates study groups. It is not a judgment of what’s on your plate.
The key facts and figures
0,8 g
Protein per kg of body weight per day as the reference value for adults aged 19 to under 65; from age 65, 1.0 g per kg as an estimated value (DGE, 2017).
at least 1.5 g
Protein per kg of body weight per day was considered “high” in studies (Devries et al., 2018).
at least 20%
of energy from protein was another possible criterion (Devries et al., 2018).
at least 100 g
Daily protein intake was also enough to qualify as “high” (Devries et al., 2018).
Source: German Nutrition Society, 2017; Devries et al., 2018
Do athletes need more protein?
Not for recreational sports: According to the DGE (2017), adults who are active for 30 minutes at moderate intensity 4 to 5 times a week do not need to increase their protein intake.
It may seem logical that more exercise automatically means you need more protein. But the DGE explicitly draws the line at recreational sports and defines this precisely: 30 minutes of moderate-intensity physical activity 4 to 5 times a week (DGE, 2017). According to the DGE (2017), people who are active at this level do not need a higher intake than other adults.
You can mix and match your protein sources. Plant and animal proteins differ in their amino acid composition, but according to the DGE (2017), combining them strategically makes up for this—for example, by pairing grains with legumes.
The situation is different if you specifically want to build muscle. This question is addressed in the article on protein and muscle building. Here, we’re focusing on recreational sports, and the DGE’s (2017) answer for this group is clear.
Does too much protein harm the kidneys?
The analysis of 28 studies found no poorer kidney function in healthy adults on a high-protein diet (Devries et al., 2018). However, caution is warranted in people with impaired kidney function (Ko et al., 2020).
The concern has an understandable basis. The breakdown of protein produces urea, a waste product carried in the blood and excreted in urine through the kidneys (MedlinePlus, 2024). It is easy to conclude from this that high protein intake always harms the kidneys. But the analysis by Devries et al. (2018) did not find this to be the case for healthy kidneys.
What has research measured about high protein intake and healthy kidneys?
Devries and colleagues analyzed 28 studies with a total of 1,358 participants (Devries et al., 2018). They included only studies of adults without kidney disease that lasted longer than 4 days (Devries et al., 2018). Each compared a high-protein diet with normal or lower protein intake.
The researchers measured GFR, or glomerular filtration rate, a measure of kidney function. At the end of the studies, it was higher following a high-protein diet (Devries et al., 2018). However, when the researchers compared how GFR changed over the course of the studies, protein intake made no difference (Devries et al., 2018). Their conclusion is based on this comparison of changes.
Cited source
„Our analysis indicates that HP intakes do not adversely influence kidney function on GFR in healthy adults.“
Devries M. C. et al.
The Journal of Nutrition, 2018
In essence, according to Devries et al. (2018): A high-protein diet, abbreviated as “HP” in the original, does not impair kidney function in healthy adults, as measured by GFR.
This finding has clear limits. It applies to adults without kidney disease and uses GFR as the measure; the analysis did not examine long-term effects such as kidney failure (Devries et al., 2018). Because studies as short as five days were included, it tells us nothing about effects over decades (Devries et al., 2018). The article on kidney blood test results explains which values on your test report describe kidney function.
High protein intake with impaired kidney function: What applies?
Caution is warranted here: in people with impaired kidney function, a high-protein diet may further worsen kidney function (Ko et al., 2020). In that case, discuss such a diet with your doctor first.
The basis is a review article, meaning a summary of existing research with no original study (Ko et al., 2020). It starts from an observation: high-protein diets are popular for weight loss and among people with type 2 diabetes (Ko et al., 2020).
The finding is phrased cautiously. Based on the available evidence, kidney function may worsen in people with impaired kidney function, possibly even in people without impairment (Ko et al., 2020). The original uses the words “may” and “perhaps,” indicating a possibility and a degree of uncertainty.
The second part of the sentence is at odds with the analysis by Devries et al. (2018), which found no worsening of GFR in healthy people. Ko and colleagues themselves note conflicting results from earlier studies and say that long-term studies with large numbers of participants are needed (Ko et al., 2020). Taken together, Devries et al. (2018) and Ko et al. (2020) present this picture: no measured harm with healthy kidneys, but caution when kidney function is impaired.
When should you discuss a high-protein diet with your doctor?
If you have impaired kidney function or are at high risk of kidney disease. In this case, Ko et al. (2020) recommend considering a high-protein diet for weight loss or blood sugar control only with caution.
Two questions are enough for your appointment. Is a high-protein diet suitable for my current kidney test results? And when should the results be checked again if I change my diet? This gives the doctor what they need to assess the situation: your plan and your test results.
The table sets out both situations side by side, each with its source.
High protein and the kidneys compared
| Question | Healthy kidneys | Impaired kidney function or high risk |
|---|---|---|
| What the research shows | GFR did not worsen on a high-protein diet (Devries et al., 2018). | Worsening kidney function is possible (Ko et al., 2020). |
| Source type | Analysis of 28 studies with 1358 participants (Devries et al., 2018). | Review article with no original study (Ko et al., 2020). |
| What this means for you | No harm to GFR measured (Devries et al., 2018). | Discuss a high-protein diet with your doctor beforehand (Ko et al., 2020). |
Too much protein in the gut: What happens during digestion?
Undigested protein is fermented mainly in the lower large intestine when hardly any carbohydrates reach it (Windey et al., 2012). According to Windey et al. (2012), the implications for gut health have not been thoroughly researched.
Experts call this process protein fermentation: protein that has remained undigested up to that point is fermented in the lower part of the large intestine (Windey et al., 2012). One way to picture it is as the end of a conveyor belt. Whatever wasn’t processed at the earlier stations arrives at the end, where fermentation begins once carbohydrates become scarce.
This fermentation produces substances that may be harmful, such as ammonia and sulfur compounds (Windey et al., 2012). The word “may” matters here. The effects of these substances have been studied mainly in laboratory experiments (Windey et al., 2012).
The authors themselves draw a cautious conclusion: the relationship between protein fermentation and gut health has not been thoroughly researched (Windey et al., 2012). Therefore, this study does not support a statement such as “a lot of protein harms the gut.” But it does not support the opposite, either.
Chapter at a glance
Undigested protein is fermented mainly in the lower large intestine when hardly any carbohydrates reach it (Windey et al., 2012). This may produce harmful substances such as ammonia and sulfur compounds (Windey et al., 2012). Their effects have been studied mainly in the laboratory (Windey et al., 2012). According to Windey et al. (2012), the relationship between protein fermentation and gut health has not been thoroughly researched.
Which blood tests show how the body processes protein?
Urea is produced when protein breaks down and can increase with a high-protein diet (MedlinePlus, 2024). But like creatinine, it is a kidney marker, not a measure of how much protein you eat.
What does urea tell us about the amount of protein?
Not much on its own. Urea is a waste product from protein breakdown that the kidneys excrete in urine (MedlinePlus, 2024). That is why it is classified as a kidney marker on lab results.
According to MedlinePlus (2024), a higher urea level can be related to a high-protein diet, among other things, as well as too little fluid in the body. Conversely, a lower level can be related to too little protein in the diet, but also to liver disease (MedlinePlus, 2024).
In general, a high urea level is considered a sign that the kidneys are not working well (MedlinePlus, 2024). However, according to MedlinePlus (2024), an abnormal result does not always mean there is a condition that needs treatment. As for whether someone is eating too much protein, the urea level reflects several factors, so it alone cannot show whether someone is eating too much protein.
Is creatinine a protein level?
No. Creatinine is a normal waste product that forms when you use your muscles and some muscle tissue breaks down (MedlinePlus, 2023). Meat can temporarily raise the level (MedlinePlus, 2023).
According to MedlinePlus (2023), a high creatinine level does not always mean there is a kidney problem. MedlinePlus (2023) lists the following as some possible other causes:
- too little fluid in the body
- muscle diseases and injuries
- intensive training
- a meat-rich diet
Creatine sounds similar, but it refers to something else. Whether creatine changes kidney values is covered in a separate article on creatine and kidney values.
What does an amino acid test tell you about protein, and what doesn't it tell you?
An amino acid test measures the building blocks of protein in your blood, showing your current status. It does not show how much protein you eat.
Amino acids are the building blocks that make up protein. The PerformanceCheck | The Amino Acid Test by mybody®x (MYBODY Lab GmbH) measures 22 amino acid-related values from capillary blood, including the nine essential amino acids. You collect the blood yourself at home with a finger prick while fasting. Amino acid levels fluctuate significantly depending on your last meal; follow the fasting instructions in the guide, or the test will measure your breakfast.
Send the sample back in the enclosed return mailer, and you'll receive the report as a PDF in the customer portal. It cannot show whether you eat too much protein. Urea and creatinine are not among the values measured.
What the amino acid test cannot do: It cannot tell you how much protein to eat, and it won't make any muscle bigger. An abnormal result does not automatically mean illness. The findings serve as a guide and help you prepare for a doctor's appointment; they are not a substitute for medical evaluation.
From the mybody®x range · blood test
PerformanceCheck | Amino Acid Test
Measures 22 amino acid-related values from capillary blood, including the nine essential amino acids. You collect the sample yourself at home while fasting. It does not measure urea or creatinine, and it does not show how much protein you eat.
Lab analysis 3–5 business days after sample receipt
Limits: What is not conclusively known about too much protein?
The sources state their own limitations. Knowing them helps you weigh the results appropriately.
For the reference value for people aged 65 and over, the DGE (2017) gives estimates because the protein requirement of older adults cannot be determined with the desired accuracy.
The analysis of healthy kidneys identifies an unclear risk of selection bias as its main limitation (Devries et al., 2018). It measures GFR and includes studies as short as five days, so it cannot support conclusions about long-term effects (Devries et al., 2018).
The paper on impaired kidney function summarizes existing research and uses cautious terms such as “may” and “perhaps” (Ko et al., 2020). This is not a definitive finding, but it is a reason for caution.
The substances produced by protein fermentation have mainly been studied in the laboratory (Windey et al., 2012). Elevated urea levels can have several possible causes (MedlinePlus, 2024), as can elevated creatinine levels (MedlinePlus, 2023). And the PerformanceCheck shows amino acids in your blood at the time of sampling, not the amount of protein you consumed.
Too much protein: What matters in the end for you?
The threshold used in the studies (Devries et al., 2018) is not a limit; it separates study groups. No harm to GFR was measured with a high-protein diet in healthy adults (Devries et al., 2018), but people with impaired kidney function should discuss such a diet with a doctor first (Ko et al., 2020). What happens in the gut to undigested protein has been described, but according to Windey et al. (2012), its effects on gut health have not been thoroughly studied. Urea and creatinine are kidney markers, but they do not indicate how much protein was on your plate.
Frequently asked questions
Is 100 g of protein a day too much?
In studies, 100 g of protein a day is already considered “a lot” (Devries et al., 2018). This is not a limit, but a definition researchers use to compare groups. In an analysis of 28 studies involving healthy adults, the change in GFR with a high-protein diet did not differ from that with normal or lower intake (Devries et al., 2018). However, for people with impaired kidney function or a high risk of kidney disease, Ko et al. (2020) advise caution; in that case, the question should be discussed with a doctor.
Do older people need more protein?
The DGE (2017) gives 1.0 g of protein per kg of body weight per day for people aged 65 and over, and 0.8 g per kg for adults aged 19 to under 65. The value for older adults is explicitly an estimate. The DGE (2017) explains: “the protein requirement for older adults cannot be determined with the desired accuracy, so no recommended intake can be derived.” The higher value is therefore a cautious guideline, not an exact recommendation derived from the evidence.
Is plant protein just as good?
Not inherently, but the difference can be offset. According to the DGE (2017), plant and animal proteins differ in their amino acid composition. The DGE (2017) writes: “However, this can be offset by deliberately combining different foods, such as grains with legumes.” According to the DGE (2017), those who eat a plant-based diet can offset the difference through their food choices.
Why should you avoid eating meat before a creatinine test?
Because meat can temporarily raise creatinine levels (MedlinePlus, 2023). You may therefore be asked not to eat meat for 24 hours before the test (MedlinePlus, 2023). According to MedlinePlus (2023), creatinine is produced when you use your muscles and some muscle tissue breaks down. According to MedlinePlus (2023), a high level does not always mean there is a kidney problem. Follow your clinic's instructions so your result can be interpreted more accurately.
Does urea rise when you eat a lot of protein?
That may be the case: MedlinePlus (2024) lists a high-protein diet as one possible reason for a higher urea level. Another reason in the same list is not having enough fluid in the body (MedlinePlus, 2024). According to MedlinePlus (2024), urea is produced when protein is broken down and is excreted through the kidneys, which is why it appears among the kidney values on test results. According to MedlinePlus (2024), an abnormal result does not always mean an illness that needs treatment, and it does not tell you on its own how much protein you eat.
Next step
Measure amino acids in fasting blood
The PerformanceCheck measures 22 amino acid-related values from a fasting capillary blood sample. It does not tell you how much protein you should eat.
Take the amino acid test What kidney values in blood tests show How to interpret urea and creatinine in your test resultsRead more
Sources
- German Nutrition Society (DGE): Reference Values for Nutrient Intake, Protein (2017 edition) – dge.de
- Devries M. C. et al., The Journal of Nutrition (2018); Ko G. J. et al., Journal of the American Society of Nephrology (2020) – europepmc.org (Devries) · europepmc.org (Ko)
- Windey K. et al., Molecular Nutrition & Food Research (2012) – europepmc.org
- MedlinePlus (U.S. National Library of Medicine): BUN (2024 edition) and Creatinine Test (2023 edition) – medlineplus.gov (BUN) · medlineplus.gov (creatinine)
The reference values and information on recreational sports are based on [1]. The statements on healthy kidneys and impaired kidney function are based on [2]. Protein fermentation in the large intestine is described in [3]. Urea and creatinine are explained in [4]. The information on the PerformanceCheck | Amino acid tests correspond to the mybody®x product range. Information current as of: 20.10.2026.
mybody®x Editorial and Specialist Team
Nutrition Kidney values
This article was prepared by the mybody®x editorial and specialist team and checked against the cited sources. Learn more about the team on the authors page.
Published on 21.10.2026 · Last updated on 21.10.2026
The content is for general information and is not a substitute for medical advice, diagnosis, or treatment. Reference ranges depend on the laboratory, method, and age - the information on your test results is always authoritative.
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