The metabolic diet is one of the most searched diets in 2026. The promise sounds attractive: 13 days of strict eating and you lose between 7 and 9 kg, after which your metabolism has been “reset” and the weight stays off. But what’s behind these claims, what does the diet look like in practice, and what risks does it carry?

What the metabolic diet is

There are several variations under the same name, but the most widespread is a 13-day diet with severe caloric and carbohydrate restriction, originating from Denmark and sometimes attributed to the Danish State Hospital (an unconfirmed attribution).

Basic principles:

• Very low calories (800–1,000 kcal/day in some versions)
• Very low carbohydrates (especially sugar and refined products eliminated completely)
• High protein (eggs, lean meat, fish)
• Increased consumption of non-starchy vegetables (lettuce, tomatoes, cucumbers)
• Black coffee without sugar permitted (even recommended in some versions)
• Alcohol forbidden

In theory, carbohydrate restriction forces the body to burn fat (mild ketosis), while high protein protects muscle mass.

What science says about “metabolic reset”

The term “metabolic reset” is more marketing than science. Metabolism doesn’t “reset” in 13 days in the way many understand it. What actually happens:

What’s real: Severe restriction of carbohydrates and calories depletes glycogen (sugar reserves in muscles and liver), which causes rapid weight loss from water and glycogen — 1–3 kg in the first days, almost instantly. The rest of the loss comes from fat and, unfortunately, partly from muscle mass.

What’s not real: Metabolism doesn’t “forget” it was restricted. On the contrary — after a severe 13-day diet, the basal metabolic rate decreases (the body adapts to starvation), which means that after resuming normal eating, weight comes back quickly, often with extra.

This is the mechanism behind the yo-yo effect, well-documented in studies.

What the typical meal plan looks like

Versions circulate differently, but here’s an example of frequently seen structure:

Days 1–2: Black coffee for breakfast, boiled eggs + salad for lunch, grilled meat + salad for dinner.

Days 3–4: Coffee + dry cracker (sugar-free biscuit) in the morning, tomatoes + eggs for lunch, grilled fish + salad in the evening.

Days 5–7: Variations with chicken, lean beef, fish, eggs, non-starchy cooked vegetables (green beans, spinach, lettuce), oranges or grapefruit as the only permitted fruits.

Days 8–13: Similar menu, sometimes with introduction of additional foods — yogurt, low-fat cheese, carrots.

Quantities vary between versions. Some versions allow unlimited meat, others restrict it.

Realistic results

Some people do lose 5–8 kg in 13 days. But the composition of that loss matters:

• ~2–3 kg from water and glycogen (returns within 2–3 days after resuming carbs)
• ~2–3 kg from fat (real and permanent loss if you don’t return to excess)
• Sometimes 0.5–1 kg from muscle mass (undesirable)

Fat loss of 2–3 kg in 13 days is a realistic and good result. The problem is that many attribute all 7–8 kg to fat and are disappointed when kilograms return.

Important contraindications

The metabolic diet is not suitable for everyone and can be dangerous for:

• People with diabetes (large blood sugar fluctuations)
• People with kidney conditions (high protein stresses the kidneys)
• Pregnant or breastfeeding women
• Adolescents (increased nutritional needs during growth)
• People with eating disorders (severe restriction can worsen them)
• People with history of gout (high purine content from meat)

What makes it different from other rapid diets

Compared to diets like the cabbage soup diet or grapefruit diet, the metabolic diet has higher protein content, which partially limits muscle mass loss. That’s a real advantage over very restrictive diets based only on fruits or vegetables.

Compared to the keto diet, the metabolic diet is shorter and more calorically restrictive, but less strict about the type of fats consumed.

A more sustainable approach

If the goal is to lose weight for real and stay lean, 13 days of severe restriction doesn’t solve the long-term problem. Studies show that losing 0.5–1 kg per week through moderate caloric deficit (300–500 kcal/day) is easier to maintain and less metabolically damaging.

The metabolic diet can be a motivating starting point, if you’re aware that:

• Part of the loss is water
• After the 13 days, eating must be restructured, not resumed identically to before
• Without long-term changes, the weight comes back

Frequently asked questions

Can the metabolic diet be repeated after the 13 days?

Most versions recommend a break of at least 2 years before repeating. It’s not a firm medical restriction, but an acknowledgment that the diet is quite stressful for the body.

Can I exercise during the metabolic diet?

Light exercise is okay. Intense training is not recommended due to the reduced calories — the risk of hypoglycemia or exhaustion increases.

Why is black coffee permitted?

Coffee has a mild thermogenic effect (increases basal metabolic rate) and reduces appetite short-term. In strict low-calorie diets, these minor benefits matter more.

Do I lose the same weight whether I have a lot or a little to lose?

No. Those with a lot to lose lose faster at first. Those with little to lose lose more slowly and proportionally lose more muscle mass.

The metabolic diet works, but not for the reasons it claims. It’s a low-calorie, low-carb, high-protein diet — not a magic “reset.” If you do it, do it with realistic expectations and, necessarily, with attention to warning signs (persistent dizziness, extreme weakness, palpitations).

⚕️ The information in this article is for educational purposes and does not replace the advice of a doctor or nutritionist. Do not start a restrictive diet without first consulting a specialist, especially if you have chronic conditions.