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A strict 13-day crash diet — understand the claims and the reality
The Danish Diet — also known as the Copenhagen Diet or the 13-Day Diet — is a very strict, very low-calorie plan followed for exactly 13 days. It centres on black coffee, eggs, lean meat and small amounts of vegetables, with rigid daily menus and almost no room for substitution. Promoters claim that completing the 13 days can keep weight off for up to two years.
That two-year claim has no scientific basis. Like other crash diets, the Danish Diet works in the short term only because it creates a severe calorie deficit — often under 1,000 kcal per day. There is nothing magical about the specific foods, and there is no evidence that 13 days of restriction reprograms the metabolism for two years.
We include this guide for educational completeness, but the Danish Diet is firmly a fad diet. It is extreme, hard to follow, and not a sustainable or recommended way to lose weight.
Menus vary by source and become extremely repetitive over 13 days. Shown for educational purposes only.
No clinical research supports the Danish Diet's specific claims. The headline promise — two years of maintained weight loss from 13 days of dieting — is not backed by any study and contradicts everything known about how weight regulation works.
What it does do is impose a severe short-term deficit, which causes rapid scale weight loss. Much of that is water and glycogen, which return when carbohydrates and normal eating resume. Very low-calorie diets like this are also associated with muscle loss, fatigue, irritability and a high likelihood of rebound eating.
Lasting weight loss doesn't come from 13 extreme days — it comes from a moderate, sustainable deficit you can maintain for months. Prioritise protein, fill your plate with vegetables, walk daily, and aim for 0.3–0.7 kg of loss per week. Use our Calorie CalculatorCalorie Tracker for a realistic target and read How to Choose the Right Calorie Deficit to do it safely.
The Danish Diet, also called the Copenhagen Diet or 13-Day Diet, is a very strict, very low-calorie plan followed for exactly 13 days. It centres on black coffee, eggs, lean meat and small amounts of vegetables, with rigid rules and almost no flexibility. It claims long-lasting results, but there is no scientific evidence behind those claims.
This is a popular claim with no scientific support. No study has shown that 13 days of restriction produces 2 years of maintained weight loss. Any weight lost comes from a severe calorie deficit, and much of it is water that returns once normal eating resumes.
The Danish Diet provides very few calories — often under 1,000 per day — which is below the level most health authorities consider safe without medical supervision. It is nutritionally unbalanced and not recommended. It is unsuitable for people with diabetes, eating disorders, who are pregnant, or under 18.
Black coffee appears at most meals in the Danish Diet. Caffeine is a mild appetite suppressant and provides energy during severe restriction, but there is nothing special about coffee for fat loss. The heavy reliance on it reflects the diet's crash-diet design rather than any nutritional benefit.