Keto diet: what it involves and who it is not suitable for
The essentials at a glance
A ketogenic diet reduces carbohydrates to about five percent of energy intake, or roughly 25 grams per day. The consumer advice center considers it highly questionable and sees no advantage over a moderately low-carbohydrate diet. The DGE recommends that more than 50 percent of energy in a balanced mixed diet come from carbohydrates.
This article explains what happens in the body during keto and sets out what two independent institutions say about it. Both belong together: The mechanism is undisputed, but the assessment is not. Where the reviewed sources are silent, that is also stated here.
You will first learn what a ketogenic diet technically means. This is followed by the assessments of the institutions, the groups for whom it is not suitable, the figures on weight loss, an overview of permitted and eliminated foods, and a detailed section on how to tell that it is not right for you.
What to expect in this article
1. What a ketogenic diet actually is
2. What the institutions say about it
3. Who should not follow keto
4. How many carbohydrates are normal
5. What really happens when you lose weight
6. What is allowed, reduced, and eliminated
7. What a keto day actually looks like
8. How to tell that it is not right for you
9. Three statements that persist
10. How to find out what suits your body
11. Limits: what a DNA test cannot do
12. What you can change starting tomorrow
Frequently asked questions
Sources
What a ketogenic diet actually is
A ketogenic diet is first and foremost a calculation. Carbohydrates are reduced to the point where the body no longer meets most of its energy needs from them. The consumer advice center puts this at about five percent of energy intake—roughly 25 grams of carbohydrates per day for 2,000 kilocalories (2022).
For comparison: A medium-sized banana contains roughly that amount. So does a slice of bread. This is not about eating less sugar, but about a different way of constructing the plate.
Key message
The difference between a ketogenic diet and a moderately low-carbohydrate diet is not a matter of degree but a leap: 25 versus up to 140 grams of carbohydrates per day.
What the name means
The term comes from ketone bodies. When the body has very few carbohydrates available for an extended period, it produces substitute fuels from fat that the brain can use. This state gives the dietary pattern its name.
The mechanism itself is undisputed. What is disputed is whether it makes sense to induce it permanently. This is exactly where advertising claims and institutional assessments diverge.
For sports, the DGE describes a ketogenic composition consisting of 75 to 85 percent of energy from fat, 15 to 25 percent from protein, and under 50 grams of carbohydrates per day (DGE, Position Paper on Fats in Sports Nutrition, 2019). This makes the scale tangible: fat provides four-fifths of the energy.
Where the boundary to low carb lies
The two terms are often mentioned together but mean different things. The consumer advice center describes a moderately low-carbohydrate diet as one in which up to 35 percent of energy—or no more than 140 grams per day—comes from carbohydrates (2022).
The entire difference in this article lies between 25 and 140 grams. Anyone who says low carb but means keto is confusing an adjustment with a complete overhaul.
What the institutions say about it
Few dietary approaches show such a wide gap between public enthusiasm and institutional assessment. The clearest statement comes from the consumer advice centers.
Documented source
“Doctors and researchers consider ketogenic diets, in which you virtually give up carbohydrates completely, to be highly concerning.”
Consumer advice center
High-fat and high-protein diets, as of 02/10/2022
The sentence reflects the assessment of experts and appears on a page the consumer advice center attributes to itself. It addresses its readers formally, which is why the quote uses “Sie” instead of “du.”
The same source gives the reason. Compared with a moderately low-carbohydrate diet, a ketogenic diet offers no advantage; instead, side effects such as headaches, weakness, and dizziness are possible (consumer advice center, 2022). The effort is therefore greater, but the benefit is not.
What the DGE says—and what it does not
Accuracy is essential here because guidebooks often claim more than is supported by evidence. The German Nutrition Society has not published an independent position statement on the ketogenic diet as a weight-loss method that could be found in this research.
What it does have is a guideline: A balanced mixed diet should contain limited amounts of fat and more than 50 percent of energy intake in the form of carbohydrates (DGE, Reference Values for Carbohydrates). A ketogenic diet contains around five percent. The difference speaks for itself, but it is an inference, not a prohibition.
Anyone who reads somewhere that the DGE advises against keto should therefore check what this is based on. The well-founded rejection comes from the consumer advice center, not the DGE.
Who should not follow a keto diet
This chapter appears deliberately near the beginning. A text that puts the exclusion criteria at the end fails to reach precisely the reader they are intended for.
Have it medically evaluated first or avoid it altogether
Diabetes
The consumer advice center expressly advises against trying low-carbohydrate diets without first consulting a general practitioner or diabetes specialist (2022)
Elevated uric acid levels or a history of gout
The Verbraucherzentrale cites an increased risk of gout attacks and kidney stones (2022)
Kidney disease
for the same reason, and because the proportion of protein inevitably increases with keto
Pregnancy and breastfeeding
a dietary pattern that eliminates entire food groups is the wrong approach here
History of an eating disorder
strict prohibition lists and constant counting are not a harmless method with this history
Regular medication use
such a far-reaching change should be discussed with a doctor, not attempted as a self-experiment
The first two points are stated verbatim by the Verbraucherzentrale. The remaining four are interpretations and have no source citation because the sources reviewed do not support them. This is explicitly indicated and has not been embellished with an invented source.
Why caution is especially important with diabetes
A dietary pattern that reduces carbohydrates by four-fifths intervenes precisely where diabetes treatment is adjusted. Anyone taking medication whose dosage is tailored to a particular carbohydrate intake also changes the effect of that medication by changing their meal plan.
That is why the Verbraucherzentrale's warning is stated so clearly. The issue is not whether a low-carbohydrate diet is generally an option for people with diabetes, but that changing the diet does not happen without affecting the practical treatment that manages the condition.
What is eliminated in a vegetarian diet
For vegetarians and vegans, an additional problem arises, as shown in the overview in Chapter 6. Legumes are listed there under “eliminated,” and they are also the most important plant-based source of protein.
Anyone who wants to achieve a higher protein intake without meat or legumes has only eggs, dairy products, and nuts to choose from. That is a very narrow basis for a sustainable diet.
How many carbohydrates are normal
Three figures put the entire discussion into perspective. They come from two different sources and describe the same value: the proportion of carbohydrates in energy intake.
Proportion of carbohydrates in energy intake
over 50%
DGE guideline for a balanced mixed diet
up to 35%
moderately low-carb, no more than 140 g per day
around 5%
ketogenic, about 25 g per day at 2,000 kcal
Sources: German Nutrition Society, carbohydrate reference values; Verbraucherzentrale, 2022
What happens when carbohydrates are eliminated
The DGE describes the consequence plainly: Reducing the proportion of carbohydrates in the diet inevitably leads to an increase in the proportion of fat and/or protein (DGE, position paper 2011).
This is the core point that gets lost in advertising copy. Eliminating carbohydrates means adding something else. With a ketogenic diet, that something is primarily fat, and in an amount that is unusual in everyday life.
What really happens when you lose weight
The rapid initial success is real and is regularly misinterpreted. The Verbraucherzentrale notes that with low-carbohydrate diets, people often lose weight quickly at first, but initially this is mainly a loss of two to three kilograms of water (2022).
Losing two to three kilograms in the first week feels like proof. It is not. That is why ketogenic eating feels more effective in the first few days than any other dietary change.
Over twelve months, weight loss from low-carb diets is usually between five and ten percent of initial body weight, according to the same source (2022). IQWiG gives three to eight kilograms over six to twelve months for weight-loss programs in general, with an average of five to six (2022).
Why the diet type makes little difference
This is the most robust statement in this entire article, and it comes from IQWiG. An analysis of studies comparing different weight-loss programs found that it makes little difference whether one eats a diet that is higher in fat or lower in carbohydrates (IQWiG, 2022).
When the direction of the change matters little, something else matters: whether it can be maintained. The same source notes that many diets fail in the long term or even create a yo-yo effect, in which weight is higher for some time after the diet than before (IQWiG, 2022).
What the yo-yo effect has to do with the method
IQWiG notes that many diets fail in the long term or even create a yo-yo effect, in which weight is higher for some time after the diet than before (2022). The sentence says nothing about keto in particular, but it describes the pattern that results when a change cannot be maintained permanently.
The narrower the framework, the greater the leap when reintroducing foods. At 25 grams of carbohydrates a day, there is no half portion of bread, only before and after. This is not a matter of character, but a feature of the concept.
What is allowed, what is reduced, what is eliminated
The following overview assigns common food groups to the three levels resulting from the limit of around 25 grams of carbohydrates per day. It is a classification by carbohydrate content, not a recommendation.
| Food group | Level | Note |
|---|---|---|
| Meat, fish, eggs | Allowed | Virtually carbohydrate-free and therefore the foundation of every ketogenic plan |
| Oils, butter, cream | Allowed | The fat content inevitably rises when carbohydrates are eliminated (DGE, 2011) |
| Leafy greens, cabbage, zucchini | Allowed | The only vegetable group that fits into the daily budget in any significant amount |
| Cheese and quark | Allowed | Aged cheese contains hardly any carbohydrates, while fresh cheese products contain somewhat more |
| Nuts and seeds | reduced | Highly variable depending on the type. With a daily budget of 25 g, even a handful counts |
| Milk and yogurt | reduced | Milk sugar is a carbohydrate. A large glass uses up a noticeable portion of the budget |
| Berries | reduced | The only fruit group that is generally still included in small amounts |
| Bread, pasta, rice, potatoes | eliminated | A single slice of bread is already within the range of the daily budget |
| Legumes | eliminated | This removes the most important source of protein from a vegetarian diet |
| Fruit other than berries | eliminated | A medium-sized banana is roughly equivalent to the entire daily budget |
| Sugar and sweets | eliminated | The only item on the list that the DGE also believes should be limited in a balanced diet |
What stands out in this overview is that the “eliminated” column consists almost entirely of plant-based foods. Grains, legumes, and fruit are precisely the groups that should make up the largest share of a balanced mixed diet.
This explains the consumer advice center’s assessment better than any list of side effects. A diet that eliminates three of the five basic food groups is not fine-tuning.
What a keto day actually looks like
Two examples, calculated against a budget of around 25 grams of carbohydrates. They show how restrictive this framework is in everyday life.
A day that works
In the morning, scrambled eggs with butter and spinach. At lunch, pan-fried salmon with zucchini and olive oil. In the evening, salad with aged cheese, nuts, and an oil-and-vinegar dressing. In between, water, coffee without milk, and unsweetened tea.
This day contains no bread, no side dish, and no fruit except perhaps a small portion of berries. It can be put together, and for many people it is appealing during the first week.
A day that falls apart
The same day with a glass of milk in your coffee, an apple in the afternoon, and a slice of bread with dinner. Each of these three small items is inconspicuous on its own; together, they clearly exceed the budget.
This is precisely the practical difference from a moderately low-carbohydrate diet. At 140 grams a day, an apple and a slice of bread are included. At 25 grams, they mean giving up.
What most often gets in the way in everyday life
Three situations regularly cause the framework to collapse. The cafeteria that serves a side with every dish. The restaurant visit where the low-carbohydrate option is a special order. And the household where meals are cooked for several people, only one of whom eats keto.
In all three cases, the diet itself is not the problem, but the environment. Anyone who knows this in advance plans differently or chooses a more flexible framework. Those who realize it along the way consider themselves undisciplined.
How to tell that it’s not right for you
This section is the reason this article exists. It is more detailed than the rest because ketogenic diets are abandoned more often than they are maintained, and because giving up is rarely a matter of willpower.
The consumer advice center lists headaches, feelings of weakness, and dizziness as possible side effects (2022). If they occur and persist for days, this is not a sign of adaptation but something to take seriously.
Fictional scenario for illustration
Example: Sandra, 41
Sandra switches to a ketogenic diet on a Monday. In the first week, the scale shows two and a half kilograms less, and she is convinced that she has finally found the right approach. In the third week, headaches appear, which she attributes to too little sleep. In the fifth week, she eats bread for the first time in a month because a birthday is coming up. After that, getting back on track is difficult because the approach does not allow for half measures. After eight weeks, she weighs as much as before and considers herself undisciplined. In reality, she tried a dietary approach whose suitability for everyday life the consumer advice center explicitly questions.
Four signs suggest that this dietary approach does not fit your life. First: You regularly eat out or in a cafeteria. Second: You cook for a family that eats normally. Third: You do endurance sports and notice a drop in performance. Fourth: After two weeks, you think about food more than before, not less.
None of these points is a medical criterion. All four determine whether a dietary change lasts six months. And according to the IQWiG evaluation, that is precisely what matters, because the direction of the dietary change itself has little influence on the outcome.
The difference between dietary change and deprivation
A dietary change that works in everyday life changes the composition of your meals. One experienced as deprivation changes your relationship with food. The difference rarely shows up in the first week and almost always by the sixth.
A useful test is to ask what happens when you are invited somewhere. If you can follow the dietary approach there without explanation, it works. If it requires an announcement to the hosts, avoiding certain foods, or making up for it the next day, it becomes an exception in everyday life.
This is not an argument against consistency. It is an argument for choosing a framework that makes consistency possible in the first place. With 140 grams of carbohydrates, dinner with friends is built in; with 25 grams, it is a breach.
When you should stop and seek medical advice
The consumer advice center lists headaches, feelings of weakness, and dizziness as possible side effects. If they persist for several days or worsen, they should be medically evaluated rather than simply endured.
The same applies to newly occurring joint pain, because the same source cites an increased risk of gout attacks. It also applies to discomfort when urinating or pain in the flank, as these may indicate kidney stones, whose risk is likewise mentioned there.
None of these symptoms is proof. All are reasons to stop and ask someone who can examine you. If you notice warning signs, do not change your diet—make an appointment.
Three statements that persist
Common versus evidence-based
Common
“Keto works better than other diets.”
Evidence-based
A review of studies found that it makes little difference whether someone follows a low-fat or low-carbohydrate diet (IQWiG, 2022). Compared with a moderately low-carbohydrate diet, the Verbraucherzentrale finds no advantage (2022).
Common
“The first kilos prove that it works.”
Evidence-based
At the beginning, low-carbohydrate diets initially cause you to lose mainly two to three kilograms of water (Verbraucherzentrale, 2022).
Common
“Keto is simply low carb, but more strict.”
Evidence-based
A moderately low-carbohydrate diet means up to 35 percent of energy or no more than 140 grams per day, while a ketogenic diet means about 5 percent or around 25 grams (Verbraucherzentrale, 2022). That is a factor of five.
How to find out what suits your body
If the direction of the dietary change makes little difference, the question of what suits you personally becomes more important than the question of which method to use. A DNA test from mybody®x (MYBODY Lab GmbH) provides indications, but it comes with a clear limitation.
DNA test from saliva
DNA Metabolism Analysis | including 28-day plan & recipe book
According to the product page, it provides insights into genetic factors and helps identify foods that fit your everyday life. Important for this topic: The product page makes no statement about ketogenic diets. So the test does not tell you whether keto is right for you, nor does it provide a diagnosis.
Laboratory analysis 15–25 working days after sample receipt
Product page information, accessed on 28 August 2026
The test includes the MY FOODBOOK with 60 recipe ideas tailored to your individual results. It exemplifies how results can become concrete meals instead of another list of prohibitions.
Chapter at a glance
According to the IQWiG review, it makes little difference to weight-loss success whether someone follows a low-fat or low-carbohydrate diet (2022). This shifts the decisive question from the method to whether it can be maintained. A DNA test can provide indications of your individual predisposition, but it cannot determine whether a ketogenic diet is suitable for you.
Limitations: what a DNA test cannot do
A DNA test describes a predisposition, not a predetermined outcome. It does not diagnose anything or predict weight-loss success. As for the ketogenic diet specifically: The product page does not cover this topic, and this article does not claim anything that is not stated there.
This article also has a substantive limitation. The sources reviewed address the ketogenic diet as a weight-loss method and its side effects. They do not address its use in medical contexts where it is administered under medical supervision. That is a different field and does not belong in a nutrition article.
A third limitation concerns the overview in Chapter 6. It classifies food groups according to their carbohydrate content. The number of grams in a specific product is shown on its packaging, not in this table.
What this article deliberately does not do
It does not cite studies showing a particular benefit of a ketogenic diet. Not because none exist, but because the editorially approved sources contain no assessment of them. For a guide, a study without an expert institution putting it into context is the weakest possible foundation.
It also does not specify target ketone levels or methods for measuring them. The sources reviewed do not address this, and this article does not include a figure without a verifiable source.
What follows from this is not a recommendation against a ketogenic diet. It is the finding that the reliable evidence is more cautious than the public enthusiasm, and that everyone should know about this gap before making the change.
What you can change starting tomorrow
If you take away just one action from this article, let it be this: Before you reduce carbohydrates to 25 grams, try 140. That is the level the Verbraucherzentrale describes as moderately low-carb, and it sees no disadvantage compared with keto.
The reason is practical. At 140 grams, bread, fruit, and a side dish remain part of the menu. This makes it possible for a dietary change to get you through a birthday, a business trip, and an evening with the family—and according to the IQWiG evaluation, that matters more than the approach itself.
If you nevertheless decide to follow such a restrictive approach, take two precautions. First, work through the exclusion criteria in Chapter 3 honestly, and if you have diabetes, gout, or kidney disease, consult your doctor beforehand. Second, set a date in advance to assess whether it is still working for you. Without that date, a trial turns into a state that no one evaluates anymore.
It all began with the question of what lies behind the keto diet. The honest answer is: a plausible mechanism and an assessment that is far more cautious than its reputation. Both belong in the same answer.
Frequently asked questions
How many carbohydrates are allowed on a ketogenic diet?
Around five percent of energy intake, which amounts to approximately 25 grams per day at 2,000 kilocalories (consumer advice centre, 2022). By comparison, a moderately carbohydrate-reduced diet contains up to 35 percent, or no more than 140 grams, per day, while the German Nutrition Society recommends that more than 50 percent of the energy in a balanced mixed diet come from carbohydrates. This means that the difference between ketogenic and moderately carbohydrate-reduced diets is roughly a factor of five.
Do you lose weight faster with keto than with other diets?
In the first few days, the scale often shows a significantly lower number, but this initially consists mainly of two to three kilograms of water (consumer advice centre, 2022). Over twelve months, weight loss with low-carb diets is usually between five and ten percent of the initial body weight. An IQWiG review of studies also found that it makes little difference whether one eats a diet lower in fat or carbohydrates (2022).
Who is a ketogenic diet not suitable for?
The consumer advice centre expressly advises people with diabetes not to try carbohydrate-reduced diets without first consulting their general practitioner or diabetes clinic (2022). The same source cites an increased risk of gout attacks and kidney stones. In the case of kidney disease, during pregnancy and breastfeeding, with a history of an eating disorder, or when taking medication regularly, such a dietary change should be discussed with a doctor.
What side effects are possible?
The consumer advice centre lists headaches, weakness, and dizziness as possible side effects of ketogenic diets and notes that the risk of gout attacks and kidney stones increases (2022). IQWiG generally notes that such diets can be unbalanced and may have side effects (2022). If symptoms persist for days, this is not a sign that you are getting used to them.
Does a DNA test tell me whether keto is right for me?
No. The DNA Metabolism Analysis product page makes no statement about a ketogenic diet. It describes insights into genetic foundations and indications of which foods fit into your daily routine. A DNA test does not provide a diagnosis or predict weight-loss success. Anyone who wants to know whether a particular dietary approach is suitable for them should review the exclusion criteria in Chapter 3 and, if in doubt, seek medical advice.
Next step
A starting point instead of a method
If the direction of the change makes little difference, it is more worthwhile to look at your own predisposition than to try the next diet. The DNA Metabolism Analysis provides helpful indications. It does not replace medical advice and does not assess any individual dietary approach.
View DNA Metabolism Analysis Protein-rich foodsRead more
You might also be interested in this
Because the proportion of protein inevitably increases on a ketogenic diet, it is worth looking at the figures behind it.
The effects of eliminating entire food groups first become apparent in the nutrients found in grains and legumes.
Sources
- Consumer Advice Centre: High-fat and high-protein diets (as of 10.02.2022) – verbraucherzentrale.de
- Institute for Quality and Efficiency in Health Care (IQWiG): Weight-loss programs and medications (as of 2022) – gesundheitsinformation.de
- German Nutrition Society (DGE): Reference values for carbohydrate intake – dge.de
- German Nutrition Society (DGE): Reference values for energy intake from carbohydrates and fat, position paper (2011) – dge.de
The verbatim quotation assessing ketogenic diets, the information on carbohydrate amounts in ketogenic and moderately low-carbohydrate diets, the side effects, the note for people with diabetes, and the figures on water and weight loss are taken from source [1]. The study analysis comparing low-fat and low-carbohydrate diets, the information on the yo-yo effect, and the weight figures for weight-loss programs are taken from [2]. The guideline value of more than 50 percent of energy intake from carbohydrates comes from [3], as does the statement that the proportion of fat and protein must inevitably increase from [4]. The information on the composition of a ketogenic diet in sports comes from the position paper “Fats in Sports Nutrition” by the German Nutrition Society, published in Ernährungs Umschau international 9/2019; under the rule for institutional sources attributed in running text, it is not included in the numbered list. Information on price, sample type, scope, and included components comes from the mybody®x product page, accessed on 28.08.2026; processing times follow the central guideline for DNA tests. All sources were accessed and checked on 28.08.2026.
mybody®x Editorial & Expert Team
Nutritional science Nutrigenetics Laboratory diagnostics Blood analysis interpretation
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 06.10.2025 · Last updated on 28.08.2026
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 laboratory report is always authoritative.
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