Fasting-Mimicking Diet (FMD)

What FMD Is

A 5-day eating plan with set calorie and macronutrient targets, followed by a return to normal eating. As described in published research, it involves approximately:

• Day 1: about 1,100 calories (roughly 10% protein, 55% fat, 35% carbohydrate)
• Days 2-5: about 700-800 calories (roughly 9% protein, 44% fat, 47% carbohydrate)
• Mostly plant-based foods such as vegetable soups, olives, nuts, and crackers or bars
• Low protein and low sugar
• Added vitamins and minerals

Unlike intermittent fasting schedules such as 16:8, FMD is not done continuously. It is a short, occasional period of very low intake.

How It Is Thought to Work

The idea is to reduce calories, protein, and sugar enough to trigger some of the body's responses to fasting, while providing enough food to make five days more manageable than a water fast. Proposed effects include:

• Lower levels of IGF-1, a growth-related hormone influenced by protein and calorie intake
• Mild ketosis as the body uses more fat for fuel
• Lower glucose and insulin levels
• Changes in cellular processes such as autophagy, shown mainly in animal studies

Much of the mechanistic work comes from studies in mice and cells. How closely FMD reproduces the effects of a water fast in people has not been fully established.

What the Evidence Shows

FMD has been studied more than many named fasting plans, but the human evidence is still limited in size and length. The best-known human trial is a randomized study of about 100 generally healthy adults who completed three monthly 5-day cycles: Fasting-mimicking diet and markers/risk factors for aging, diabetes, cancer, and cardiovascular disease. Science Translational Medicine (2017). Participants in the FMD group had modest reductions in body weight, body fat, and IGF-1, and, in those with higher starting levels, in blood pressure, fasting glucose, and some other risk factors. In short:

• Studies have been small and short, and many participants did not finish all cycles
• Effects on weight and risk factors were modest and varied between people
• There is no evidence yet that FMD prevents disease or extends life in humans
• Research in cancer and autoimmune conditions is early; some of it is in animals, and any use in these settings belongs within medical care and clinical trials
• Some of the research has been conducted by scientists with financial ties to the commercial product, which is worth keeping in mind

Effects on markers such as weight and IGF-1 appear to diminish after people return to their usual diet.

Home (DIY) Version

Home versions try to follow the published calorie and macronutrient targets using ordinary foods. The research was done with the specific commercial formulation, so a home version is an approximation, and results may differ.

Approximate daily targets based on the proportions above:

• Day 1: about 1,100 kcal, with around 25-30 g protein
• Days 2-5: about 700-800 kcal, with around 15-20 g protein

Typical food choices:

• Vegetables, especially leafy greens and non-starchy vegetables
• Vegetable soups and broths
• Olive oil, olives, and avocado
• Small amounts of nuts
• Small portions of beans or lentils
• Water, herbal tea, and plain coffee or tea in usual amounts

Usually limited during the 5 days:

• Meat, fish, eggs, and dairy
• Sugar and sweets
• Most fruit
• Alcohol

Because the plan provides little protein and few calories, it is not a nutritionally complete diet and is not meant to be followed for longer than five days. A basic multivitamin is sometimes used; check with a pharmacist if you take other medication.

Sample 5-Day Plan

This is an illustration of the kinds of meals involved, not a prescription. Portions need to be measured to stay near the targets.

Day 1 (about 1,100 kcal)

• Breakfast: vegetable soup with a drizzle of olive oil and a small handful of nuts
• Lunch: large salad with olive oil, half an avocado, and a small portion of lentils
• Dinner: roasted vegetables with olive oil and a cup of vegetable broth

Days 2-5 (about 700-800 kcal each)

• Morning: herbal tea and a small portion of nuts (about 15 g)
• Lunch: vegetable soup with olive oil and a green salad
• Dinner: steamed or roasted vegetables with olive oil and vegetable broth

Expect to feel hungry, tired, or cold at times, particularly on days 2 and 3. Keep physical activity light and drink enough fluids.

DIY vs Commercial Kits

• Commercial kits: pre-portioned with a set composition that matches what was studied, so no planning is needed; they are relatively expensive and consist of packaged foods
• Home versions: cheaper, use fresh foods, and can be adjusted to your preferences; they take planning and weighing, and the exact nutrient profile of the studied plan is not reproduced

No study has directly compared a home version with the commercial kit, so it is unknown whether the effects are the same. We do not recommend any particular product.

How Often People Repeat It

There is no established "right" frequency. In the main human trial, participants completed one 5-day cycle per month for three months. People who use FMD outside research often repeat it a few times a year. More frequent cycles mean more days of very low intake, which may not be appropriate, especially for people who are lean, older, or trying to maintain muscle. If you are considering repeating it, discuss the plan with your healthcare provider.

Returning to Normal Eating

Because some food is eaten throughout, returning to normal eating after FMD is generally simpler than after a multi-day water fast. It is still sensible to ease back in:

• Day 6: smaller, easily digested meals such as soups, cooked vegetables, rice, eggs, or yogurt
• Following days: return to your usual balanced meals
• Avoid a very large meal or heavy drinking straight after the five days
• Keep drinking enough fluids

See our refeeding recipes and how to break a fast for meal ideas.

Frequently Asked Questions