Updated: October 2026
In short: The ketogenic diet keeps carbohydrates extremely low so that the body produces ketones. In studies lasting 12 months and longer, people lost on average about 0.9 kg more with it than with a low-fat diet, with slightly higher LDL cholesterol. The consumer advice centre (Verbraucherzentrale) considers the diet highly questionable. It isn't suitable for everyone, so medical advice beforehand makes sense.
Keto has been an evergreen for years: lots of fat, hardly any carbohydrates, fast results on the scales. The interest is huge, and so are the questions. What's allowed, what does it really do, what's behind the keto flu, and who is the ketogenic diet unsuitable for? We checked studies and consumer information and put them honestly in context, without promises.
What is the ketogenic diet?
With the ketogenic diet (keto diet), carbohydrate intake is cut so far that the body increasingly breaks down fat and produces ketone bodies from it. This state is called ketosis. The Verbraucherzentrale describes keto diets as eating patterns in which carbohydrates are almost entirely given up: only about 5 percent of energy comes from carbohydrates, which at 2,000 kcal is around 25 grams per day. In one meta-analysis, a very low-carbohydrate ketogenic diet was defined as a maximum of 50 g of carbohydrates per day.
The ketogenic diet was originally developed for neurological conditions.
What can you eat on the keto diet?
From the carbohydrate limit follows what is the focus in practice and what has hardly any room. We found no binding official food list in the sources checked. The table shows common practice.
| Usually the focus | Usually strongly limited |
|---|---|
| Meat, fish, eggs | Bread, pasta, rice |
| Cheese and high-fat dairy | Potatoes, legumes |
| Oils, butter, nuts, seeds | Sugar, sweets, juices |
| Low-carbohydrate vegetables | Most kinds of fruit |
Note the contrast with the DGE recommendations: the DGE advises wholegrain, legumes at least once a week and a maximum of 300 g of meat per week. These key points don't fit classic keto eating. You can find many recipes and plans online; we can't assess them individually.
Does the keto diet help with weight loss?
Often in the short term, with a small edge in the long term. A meta-analysis of 13 studies with 1,415 participants and a duration of at least 12 months found: on a very low-carbohydrate ketogenic diet, body weight was on average 0.91 kg lower than on a low-fat diet. Triglycerides and diastolic blood pressure fell, HDL rose, but LDL cholesterol also rose, by 0.12 mmol/l.
For low-carb diets in general, the Verbraucherzentrale cites weight losses of 5 to 10 percent in 12 months, similar to low-fat diets. At the start, though, you mainly lose 2 to 3 kilograms of water first. So the quick numbers at the beginning aren't only fat. Whether you can stick with keto plays a part in the end.
What is the keto flu and what symptoms are there?
"Keto flu" is what people affected call complaints during the transition phase. A recent overview lists as the most common side effects temporary keto flu symptoms such as tiredness, headaches and nausea, as well as digestive complaints, increased urination and low blood sugar. The Verbraucherzentrale lists headaches, weakness and dizziness.
How long these symptoms last, we can't say for sure from the sources checked. If you feel unwell on a lasting basis, better to stop and get medical advice.
How risky is the ketogenic diet?
The Verbraucherzentrale writes that doctors and researchers consider ketogenic diets highly questionable, because a very high fat share brings no advantage over moderate low carb. A higher intake of purines can also raise uric acid levels and increase the risk of gout and kidney stones.
In the meta-analysis, LDL cholesterol rose slightly. How keto affects you over years can't be answered conclusively from the sources we checked. The studies in the meta-analysis lasted at least 12 months; there is no blanket answer to "How long can you do keto?"
Who is the ketogenic diet not suitable for?
A 2026 overview lists rare metabolic diseases as absolute contraindications. Particular caution applies with, among others, acute pancreatitis, advanced liver or kidney disease, familial hypercholesterolaemia, diabetes with certain medication (such as SGLT2 inhibitors, metformin, insulin, GLP-1 receptor agonists), high blood pressure treated with medication, gallbladder conditions, pregnancy and breastfeeding, being underweight and intensive exercise. Interactions with medication are also possible.
If you have pre-existing conditions or take medication, be sure to talk to your doctor first. With an eating disorder, a strict diet is not suitable.
What does a day on a ketogenic diet look like?
An example for orientation, not a plan and not a recommendation. You have to check amounts and carbohydrate content yourself so you stay under your limit. Also drink enough: the DGE gives around 1.5 litres a day, ideally water or calorie-free drinks.
| Meal | Idea |
|---|---|
| Breakfast | Scrambled eggs with spinach and cheese |
| Lunch | Salad with fish, olive oil and nuts |
| Evening | Roasted vegetables with chicken and herb quark |
| Snack | Nuts or a piece of cheese |
What should you bear in mind if you want to try keto anyway?
Talk to your doctor first, especially if you have pre-existing conditions or take medication. Plan a clear time period and a way back to a balanced diet, because according to the Verbraucherzentrale, a yo-yo effect is almost guaranteed with diets that don't change eating behaviour. Watch for warning signs such as persistent weakness, dizziness or severe headaches, and stop if in doubt.
If you don't know where to start, the Meal Plan for Weight Loss helps as a balanced alternative.
Keto, low carb or intermittent fasting: what suits you?
All paths lead through an energy deficit. If you're looking for a less strict option, moderate low carb or a balanced diet with a deficit is the better-tolerated starting point. The Verbraucherzentrale sees no advantage of keto over moderate low carb.
| Approach | Briefly put |
|---|---|
| Keto | Very strict, side effects and contraindications possible |
| Moderate low carb | Similar results to low-fat diets after 12 months |
| Balanced with a deficit | Recommendation of the DGE and NHS, 0.5 to 1 kg per week |
On fasting and ketosis, also read Intermittent Fasting and Ketosis. Basics on carbohydrates: Carbohydrates: Good or Bad? and Low Carb vs. High Carb.
Pairs well with frank.
If you're looking for relaxed meals rather than a strict diet: our Soup Cleanse combines organic soups, organic Ginger Shots and juices for 1 to 7 days. The Soup Cleanse is not a ketogenic diet and not a weight-loss product.
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- Carbohydrates: Good or Bad? The Key Differences
- High Energy Levels, please! Low Carb vs. High Carb Diet
- Basic Rules for Losing Weight
Frequently asked questions about the ketogenic diet
What is the keto diet?
An eating pattern with extremely few carbohydrates (by one meta-analysis's definition a maximum of 50 g per day) and lots of fat, so that the body produces ketones.
What can you eat on the keto diet?
In practice mainly meat, fish, eggs, cheese, oils, nuts and low-carbohydrate vegetables. Bread, pasta, rice, sugar and most kinds of fruit are strongly limited. We found no official list.
How fast do you lose weight on keto?
Quickly at the start, but according to the Verbraucherzentrale the first 2 to 3 kg are mostly water. After 12 months, the advantage over a low-fat diet was around 0.9 kg in one meta-analysis.
What is the keto flu?
Temporary complaints at the start such as tiredness, headaches and nausea. How long they last, we can't say for sure from the sources checked.
Who is keto not suitable for?
Among others, with certain metabolic diseases, advanced liver or kidney disease, pregnancy and breastfeeding, being underweight and when taking certain medication. Talk to your doctor first.
Note: This article is for general information and does not replace medical or therapeutic advice. If you have symptoms or pre-existing conditions, are pregnant or take medication, please speak to your doctor first.
