Basics of the Fasting Mimicking Diet: What It Is and How It Works
A beginner-friendly overview of the Fasting Mimicking Diet (FMD): what it is, where it comes from, how it works, and what to expect if you decide to try it.
What Is the Fasting Mimicking Diet?
The Fasting Mimicking Diet (FMD) is a short, structured eating protocol designed to trigger many of the same biological effects as water-only fasting while still allowing a small amount of food. The idea is simple: by keeping calories, protein, and carbohydrates very low—but not zero—the body enters a “fasting state” even though you are eating.
Most versions of the diet last five days.
- Day 1: Slightly higher calories.
- Days 2–5: Lower calories with very limited protein.
- The diet is usually plant-based and higher in healthy fats.
The FMD is not meant to be followed continuously. It is done in cycles a few times a year.
Who Invented It?
The diet was created by Dr. Valter Longo, a longevity researcher and professor at the University of Southern California (USC). His work focuses on how nutrition, fasting, and cellular repair processes influence aging, metabolism, and long-term health.
The goal behind the FMD was to create a fasting approach that is easier, more practical, and safer for most people than complete fasting—while still activating many of the same beneficial mechanisms.
How the FMD Works
During the FMD, your body receives just enough energy and nutrients to function while still detecting a state of scarcity. This shifts metabolism away from growth and towards repair.
Key mechanisms include:
- Lower insulin and blood sugar levels
- Reduced activity of growth pathways
- Increased fat burning and mild ketone production
- Activation of cellular repair and stress-resistance processes
- Temporary reduction of inflammation markers in some studies
In simple terms: you keep eating a small amount, but your body behaves as if you are fasting.
What You Typically Eat
Because the exact formulas are patented, different DIY versions vary. A common pattern includes:
Allowed Foods
- Vegetable-based soups
- Leafy greens and non-starchy vegetables
- Nuts and seeds (small portions)
- Olives and olive oil
- Herbal teas
- Small amounts of fruit or vegetable snacks
Foods to Avoid
- High-protein foods
- Sugary foods or large carb portions
- Animal products
- Heavy meals or intense exercise during the fasting period
Who Might Benefit
Research suggests the FMD may help:
- Support metabolic health
- Improve markers like blood sugar or triglycerides
- Support weight management
- Promote cellular repair processes
- Support healthy aging pathways
Many people also use it as a structured “reset” once every few months.
Who Should Avoid It
The FMD is not recommended for:
- Pregnant or breastfeeding individuals
- People with a history of eating disorders
- Children or adolescents
- Individuals with chronic diseases unless supervised by a healthcare professional
- Anyone taking medications that affect blood sugar or blood pressure without medical guidance
Practical Tips
- Plan the five days ahead of time.
- Drink plenty of water and herbal teas.
- Avoid heavy workouts; stick to light movement.
- After day five, transition slowly back to normal eating.
- Most people repeat the protocol a few times per year.
Summary
The Fasting Mimicking Diet is a short-term, plant-focused approach designed to give the benefits of fasting while still allowing small amounts of food. Created by longevity researcher Dr. Valter Longo, it combines low calories with low protein and low carbohydrates to trigger metabolic and cellular repair processes. It can be a useful tool for health and longevity when used responsibly and with proper preparation.
Fresh experiments from the FMD team.