Fasting has gained attention as a potential tool for weight loss and better health.
It’s not just about skipping meals—it’s about:
Fasting involves reducing calorie intake on a schedule and can support everything from fat loss to better blood lipid levels (1).
But not everyone can—or wants to—go without food entirely.
That’s where the fasting mimicking diet (FMD) comes in.
It’s an approach that lets you “trick” your body into thinking it’s fasting while still eating small amounts of carefully selected foods. Some experts believe the diet offers many fasting benefits without the same level of restriction.
If you’re new to FMD, don’t worry. This guide will explain it and, more importantly, recommend what foods to focus on as you get started.
The fasting mimicking diet (FMD) is a unique approach that allows you to eat while achieving many potential benefits of traditional fasting. It’s a diet designed to mimic how your body reacts during a fast, even though you consume small amounts of food (2).
Researchers, including Dr. Valter Longo, developed the concept to make fasting more accessible and safer for various people.
The FMD is structured as follows, along with the fasting mimicking diet macros:
Macronutrient breakdown: 43% complex carbohydrates, 11% plant-based protein, and 46% mono and polyunsaturated fats. At least 7 ounces of water (3)
Macronutrient breakdown: 47% complex carbohydrates, 9% plant-based protein, and 44% mono and polyunsaturated fats. At least 7 ounces of water (3).
You’re encouraged to follow this diet once per month for up to six consecutive months.
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The primary purpose of FMD is to trigger your body’s natural fasting responses.
During a fast, the body typically switches from burning glucose (sugar) mainly for energy to burning fat primarily.
This switch has potential cellular benefits, such as improved repair processes and reduced markers of aging and inflammation (2, 4).
FMD recreates these effects by keeping calorie intake very low—usually 40-50% of normal—and primarily consisting of specific ratios of proteins, fats, and carbohydrates that are thought not to disrupt the fasting state (5).
Another theory about why FMD works is that it actively affects the body on a deeper cellular level by influencing its nutrient-sensing pathways (NSPs) (6).
NSPs are the body’s way of sensing whether it has enough nutrients to support growth and development (7). By manipulating these pathways, FMD may theoretically trigger beneficial responses (6).
Research on FMD and whether it works isn’t conclusive. Research suggests this diet could offer health benefits (2, 4). However, more studies are needed to determine its efficacy fully.
Read more: Intermittent Fasting Vegan Diet: What It Entails, Rules To Follow & More
The main difference between the Fasting Mimicking Diet (FMD) and Intermittent Fasting (IF) is that one allows you to eat during fasting, while the other does not.
FMD lets you eat small amounts of specific foods during fasting without breaking the fast entirely. With IF, you are typically not allowed to consume calories during fasting.
You must wait for a designated “eating window” where you consume all your daily food.
Notable differences between the two include:
IF: Time-restricted eating with strict fasting periods (e.g., 16/8, alternate days).
No food during fasting windows.
FMD: A multi-day plan (e.g., 5 days) allowing limited food intake, designed to mimic fasting.
IF: Limit all calorie intake to a designated window, lowering calories and promoting weight loss (8).
FMD: This diet follows a specific macronutrient and calorie intake designed to achieve fasting-like effects, which can lead to various potential health benefits (4).
IF: Reduces calorie intake, shifts the body to burn stored energy, and may promote autophagy with longer fasting windows (8).
FMD: May suppress nutrient-sensing pathways like mTOR and IGF-1 using calorie and nutrient restriction to trigger fasting-like repair and renewal processes (6).
IF: Eat whatever you want during the designated eating window.
FMD: For a set number of days, only select foods chosen for their specific macronutrient breakdown and ability to support fasting results.
IF: It can be sustainable in the long term with careful planning and adherence to calorie goals during eating windows.
FMD: Followed for short periods (e.g., 5 days), as it is more restrictive than IF and may not provide all necessary nutrients for long-term health.
IF: Simple and flexible with no food planning, but hunger during extended fasts can be challenging.
FMD: Structured and includes limited food, making it easier to manage hunger but less flexible due to specific guidelines.
Many ask, “What’s a fasting mimicking diet food list and meal ideas?”
The ProLon diet is the most well-known commercial version of the fasting mimicking diet. It is a 5 day fasting micking diet meal program to help people follow FMD rules without measuring or preparing food.
ProLon provides prepackaged, ready-to-eat meals, snacks, teas, and supplements designed to meet the protocol’s exact calorie and nutrient requirements.
This readiness eliminates much guesswork and makes it easier for beginners to get started.
While ProLon can be convenient, you don’t have to rely on it exclusively.
Understanding the principles of FMD lets you recreate the experience using homemade whole foods if you prefer.
On Day 1, FMD limits your intake to around 1,100 calories.
Of this, roughly:
On Days 2-5, your daily calorie intake drops to around 725 calories.
Of this, roughly:
Proteins (Low, Plant-Based)
Fats (Healthy, Mono- and Polyunsaturated)
Other Approved Items
While the FMD can be incredibly rewarding, there are specific foods and habits you’ll want to steer clear of to maximize its benefits.
High-Protein Foods
The FMD is intentionally low in protein to mimic fasting and potentially trigger cellular repair processes like autophagy (9). Consuming high-protein foods is thought to interrupt these benefits by activating growth pathways like mTOR (10).
Avoid the following:
Processed and Sugary Foods
Ultra-processed foods often contain unhealthy fats, sugars, and additives that may disrupt fasting-like effects and increase inflammation (11).
Stick to whole, nutrient-dense options and avoid these:
Habits to Avoid
Your approach to the diet matters just as much as your food choices.
Poor habits can undermine your efforts, so watch out for these:
Why These Rules Matter
The FMD works by tricking your body into thinking it’s fasting, even while eating.
High protein breaks this illusion, while ultra-processed and sugary foods may disrupt your metabolic state.
Overeating or deviating from the plan can prevent your desired cellular repair and fat-burning benefits.
Stay mindful and stick with the plan that uses precision to optimize results.
FMD experts recommend conducting it monthly, with participants completing a 5 day cycle every 30 days.
For significant results, adhering to this regimented pattern may be necessary for several months (3-6 months or more).
Once you have completed the initial 3 month round of FMD, you can reevaluate your goals and decide whether continuing a monthly cycle benefits you.
Some individuals may benefit from completing multiple rounds back-to-back, while others may follow a maintenance plan after achieving their desired results.
While the FMD diet can be an effective tool for weight loss, most experts advise against using it as a long-term solution due to its restrictive nature.
The fasting mimicking diet works well as a short-term intervention to kickstart cellular repair processes and supports overall health.
This 5-Day Fasting Diet Meal Plan lays out what to eat to maximize your fasting potential and boost your health.
Read more: Intermittent Fasting vs. Small Meals: Which Eating Style is Right for You?
Like any dietary program, the FMD isn’t without its side effects.
While most people tolerate it well, there are a few things to watch out for, especially if you’re new to the diet or have specific health concerns.
One of the most common side effects is feeling tired or sluggish during the 5 day period.
The FMD involves a significant calorie reduction, which means your body has less fuel than usual (12). As your system shifts into fat-burning mode, you may experience dips in energy, especially during the first couple of days. This lower energy is usually temporary and tends to ease as your body adjusts.
It’s no surprise that eating fewer calories can leave you feeling hungry.
During the initial days of FMD, you can expect hunger pangs. As the body transitions into a fasting-like state, cravings for high-calorie or sugary foods may intensify.
Drinking plenty of water and herbal teas can help manage these feelings (13).
The FMD mimics fasting and provides precise macronutrient ratios, but if followed repeatedly without proper planning, it may lack some essential vitamins and minerals.
Long-term or frequent diet cycles without nutritional balance during non-fasting days can risk B vitamins, iron, and calcium deficiencies. If you’re concerned, it’s a good idea to focus on nutrient-rich foods between cycles or consult a healthcare provider.
Reduced food intake can also affect your digestive system (14). During the FMD, some people report feeling bloated, constipated, or experiencing changes in their intestinal health. These issues are often temporary, but staying hydrated and including fiber-rich FMD foods can help alleviate discomfort.
Some people may experience headaches or mood swings due to lower calorie intake and potential shifts in blood sugar (12). These symptoms, often called “fasting headaches,” tend to resolve after the first few days. Drinking water and maintaining low stress levels can help manage these sensations.
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The focus on calorie restrictions and specific macronutrient ratios during the FMD might contribute to an overly rigid view of eating.
Some people may begin to associate food with guilt or feel anxious about deviating from the plan. This mindset can interfere with developing a balanced, intuitive approach to eating in the long run.
The highly controlled nature of the FMD can make everyday food choices feel overwhelming or “wrong,” further straining one’s relationship with food.
For some, the FMD can trigger cycles of strict adherence followed by overeating on non-fasting days. Fasting for extended periods is a hallmark of yo-yo dieting, where individuals shift between periods of extreme restriction and indulgence.
Over time, this cycle can lead to weight fluctuations and decreased metabolic efficiency, undoing the benefits gained during the diet.
The diet’s structured nature often requires purchasing expensive specialized meal kits, such as those offered by the ProLon program. This cost can add up quickly for many people, making monthly cycles challenging financially.
The FMD is not for everyone. Pregnant or breastfeeding women should avoid it, as reducing calories and altering macronutrient intakes might harm their nutritional needs. The same goes for children and adolescents.
Similarly, if you have a medical condition like diabetes, low blood pressure, or a history of eating disorders, consult a doctor before starting the diet.
It could pose risks by affecting blood sugar levels, energy balance, or overall health.
The Fasting Mimicking Diet isn’t suitable for everyone. Pregnant and breastfeeding women, children and adolescents, individuals with diabetes, low blood pressure, or a history of eating disorders should avoid it. Always consult your doctor if you have a medical condition before starting. Our previous blog on Intermittent Fasting Macros details balancing your fasting routine with the perfect macro ratios for optimal results. No, eggs are not allowed on the FMD. To mimic fasting the diet focuses on low-protein, plant-based foods with specific macronutrient ratios. A typical FMD breakfast includes plant-based, low-protein foods like nut bars or vegetable soups. It is small and nutrient-dense, aligning with the diet’s calorie restrictions. Yes, but only black coffee without sugar, cream, or milk. Herbal teas and plain water are also encouraged to stay hydrated.Frequently Asked Questions
Who should avoid the fasting mimicking diet?
Can I eat eggs on a fasting mimicking diet?
What is a fasting mimicking diet breakfast?
Can you drink coffee on a fasting mimicking diet?
The Fasting Mimicking Diet is a short-term intervention to support cellular repair processes and overall health. Like any dietary program, it can have side effects like fatigue, hunger, digestive changes, and nutrient deficiencies.
Before starting, you must approach the diet cautiously and speak with a healthcare professional if you have specific health concerns.
While the FMD might provide benefits in the short term, most experts will, due to its restrictive nature, advise against using the diet as a long-term weight loss solution. Instead, focus on incorporating balanced eating habits and exercise for sustained wellness.
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