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Fasting Mimicking Diet: What It Is and How to Do It

It’s scientific, it’s nutrient-dense, and it may have huge advantages for your long-term health. The fasting mimicking diet is an alternative to full-on fasting and it might be worth giving it a try. 


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This article will cover what a fast-mimicking diet is, how to do it, how it’s different from normal fasting, and why you may want to do it.

What Is a Fasting Mimicking Diet?

Fast mimicking is a type of modified fasting. Instead of abstaining from food completely like a traditional fast, you consume small amounts of food — but you do it in a way that gives you the benefits of fasting. 

A fast-mimicking diet typically lasts about five days — you’ll keep your carb, protein, and calorie intake low and your fat intake high. Calories are kept at around 40% of normal intake. This keeps you nourished with nutrients and electrolytes. It also puts less stress on your body than normal fasting while still giving you the same benefits.

Long-term calorie restriction and long-term fasting can harmful, but fast mimicking is safer and more effective. First, look at how much it differs from traditional fasting.

Fast Mimicking vs. Traditional Fasting

Just like with intermittent fasting, there are many myths about these modified fasts: Your muscles will waste away, you’ll kill your metabolism, and it’s downright unhealthy.

The above might be true for someone who is actually starving, restricting calories for weeks, months, or years at a time, or doing no-food water fasting

These can lead to metabolic damage and are especially bad for people with underlying health conditions. But as mentioned, fast mimicking gives you all the benefits without these side effects.

Health Benefits of a Fasting Mimicking Diet

A fast mimicking diet can give you similar benefits to regular fasting. Some people call it the longevity diet because it helps increase your overall well-being. 

Some of the many benefits include:

8 Benefits of a Fasting Mimicking Diet
  • Supports the immune system[*]
  • Promotes stem cell regeneration[*]
  • Promotes healthy gut microbiota[*]
  • Increases stress resistance[*]
  • Promotes longevity[*]
  • Intervenes in the progression of diabetes[*]
  • Enhances cognitive performance[*]

How to Mimic Fasting

Fast mimicking essentially “tricks” your body into thinking you’re fasting — as such, you can potentially reap these benefits while still eating. Below are the basics of fast mimicking.

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How Long to Do It 

Most research on fast mimicking shows you’ll get the best results after about five days or when your glucose ketone index falls below 1.0, but anywhere between 3-7 days will work. You’ll get the most benefits if you repeat the FMD cycles twice per year, or as often as once a month.

How to Prepare 

You might want to measure certain biomarkers if you’re interested in tracking your fasting outcomes. This could be doing lab tests before and after your fast as well as measuring blood glucose, ketones, and weight changes each day.

Also, you might want to set up your environment for the fast:

  • Tell friends and family you plan on seeing during this time what you’re doing and why it’s important you have support.
  • Get rid of any snack foods at home or work that might tempt you.
  • Plan to give yourself more time for sleep, since you’ll likely be more tired than usual.
  • Plan for some physical activity each day, but only light stuff. Avoid intense exercise during this time.
  • Create a meal plan so you know exactly what you’re going to eat.

Fasting Mimicking Diet Basics

Some people ease into the fast by eating slightly higher calories the first day, around 50% of total intake. 

You can then reduce it to around 35-40% of total caloric intake for the remaining days. You also want to eat easily digestible foods in very small amounts.

One popular pre-packaged fast mimicking diet, called ProLon FMD, contains all five days’ worth of food for the fast. The food is all plant-based and one day looks as such:


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  • Breakfast: Tea and a nut bar 
  • Lunch: small serving of vegetable soup and a few kale crackers 
  • Snack: A few olives in the afternoon
  • Dinner: Small portion of soup 

You don’t need a pre-packaged box to do a fasting mimicking diet, though — especially if you want to keep your diet ketogenic. Just stick to the calorie percentages and consider how you’ll space them out each day. Make sure you plan out all the food for the entire fast so there’s nothing else to worry about.

Traditional Fast Mimicking Macros

Macros for traditional fast mimicking are: 

First Day:

  • 34% carbs
  • 10% protein
  • 56% fat 

Remaining Days: 

  • 47% carbs
  • 9% protein
  • 44% fat 

This is obviously different if you’re following a ketogenic diet. Black coffee and tea (a cup per day) are typically allowed, although not necessary. Make sure they don’t contain any added creams or sugars (coconut oil is OK if you factor it into macros).

Risk Factors

If you have any health issues, be sure to consult your medical practitioner before doing a fasting mimicking diet at home. This is especially important for anyone with blood pressure issues, blood sugar struggles (like diabetes), cardiovascular disease, or multiple sclerosis. 

It’s also important to supplement during your fast to ensure you’re getting enough nutrients and electrolytes. 

Supportive Supplements

Taking supportive supplements might help you ease into the fast, as well as provide enough nutrition throughout. Supplements might include:

  • Electrolytes like magnesium and salt to replenish from water loss
  • Grass-fed liver tablets to provide micronutrient support
  • Branch chain amino acids (BCAAs) to help prevent any loss of lean tissue
  • Greens powder to provide micronutrients
  • Algal oil or cod liver oil for omega-3 fatty acids

You can also take exogenous ketones if you’re trying to get into ketosis through a ketogenic diet. Speaking of ketones, fast mimicking is perfect for easing into ketosis before going fully keto. 

Fast Mimicking and Ketosis

Fast mimicking is a great preface to a ketogenic diet. That’s because it can help you get into ketosis faster. Plus, eating keto foods helps you stay in ketosis the whole time.

With ketogenic fast mimicking, you’ll want to keep your macros within the proper range of 5-10% carbs, 20-25% protein, and 70-80% fat. If in doubt, always choose something with more fat. 

When you’re fast mimicking on keto, you’ll want to eat extra low carb and high fat. Avoid choosing foods that are low-protein since that protein will give you energy and help sustain your muscles. 

What to Consume

See this four-day ketogenic fast mimicking done by Dr. Anthony Gustin. Each day, he consumed different amounts of bone broth, coconut milk, coconut oil, BCAAs, and exogenous ketones. Avocados and grass-fed butter are other ideas. This is a viable method to combine keto with fast mimicking, and it will help you get into ketosis faster than without any fasting.

Do It Safely 

Fast mimicking is a powerful hack to get the benefits of fasting while not completely giving up food. Still, this should only be a periodic diet. Even though some people like doing it once a month, you should pair it with a healthy, low-carb diet in between. 

Make sure you keep your calories low and properly supplement to stay in ketosis without health issues. Of course, it’s always best to eat whole foods on this diet to give your body the nutrients it needs. 

Combine a keto diet with fast mimicking to get into ketosis faster and get the most benefit out of both.


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18 thoughts on “Fasting Mimicking Diet: What It Is and How to Do It

  1. Will someone PLEASE tell me how many calories are consumed each of the 5-days? I even have the Prolon box and it does not say. Why on earth not? If this is so scientific why no details on what is actually in all the boxes. Even American processed food needs to contain calorie count for example. Ergh. Disappointed and starting to feel I got “taken” by this Prolon kit.

  2. The first day has 1090 calories and the next 4 days have 725 calories. this would be approximately 50% of usual calories the first day and 40% of usual calories the next 4 days.

  3. I am currently on day 3 of the 5 day ProLon FMD. I feel great! No cravings for anything.

    There is a glossy sheet included with the meal boxes that provides a food label for every food item in the box. Easy peasy to figure out calories for the day. Also, lists ingredients for each food item.

    With that said, let me comment on what is working and not working for me regarding the box plan. In general, I don’t care to eat “bars”, instead, I prefer real food. The dehydrated food is good. I develop nasal congestion for about an hour or two after eating some of the products; ? potato starch, inulin, natural flavors, not sure what’s causing the congestion but I know it’s something my body does not like. This does not happen when I eat real food. Also, I feel bloated after some of the meals and that does not happen when I eat real food.

    I am disappointed that cane sugar is in some of the products as it’s unnecessary (I don’t eat sugar in any form). The crackers are amazing, the olives are amazing, teas are amazing, the choco bars are amazing but have rice syrup (again, sugar), the breakfast L bar is so-so, too sweet for my taste, wish they would leave the sugar out of this bar or make a savory option for those of us who are sensitive to any type of sugar added to our foods.

    I plan to do the recommended full three sessions of FMD (1 every 3 weeks) but will not purchase the box for my next two fasts, instead, I will eat food and create my own diet plan. Glad I did not purchase all three up front!

    Hope this reply is helpful.

  4. I would love to see ur created meal plan..I too prefer food to bars. I try desperately to limit sugar.

  5. I too wish to do this fasting with real food. Can you please tell me which real food is appropriate for the 5 day mimicking fasting please. I am vegan. Tks

  6. For further info on the FMD, you should read “The Longevity Diet” by Dr. Valter Longo, the scientist who developed the FMD from 20 years’ research as well as the Prolon pre-packaged version of it. He goes into much more detail on contra-indications for it. And of course you can google his websites.

  7. The link to Dr Anthony’s four day ketone fast mimicking is not working. Page not found. Please fix, I really want to read that. Thank you.

    1. Hi Josh, we’ve checked on our end and it’s working fine. You may read the blog here: MY FOUR DAY FASTING RESULTS . If it’s still not working, we recommend to clear the cache on your current browser or try using a different browser. Thank you.

  8. The link for Dr. Anthony’s 4 day fast is not working nor is the second link you gave. I’m allergic to things in the ProLon plan and am looking for alternatives.

  9. You will feel less hunger if you just do a water fast for five days. No kidding. Its hard to believe but try it.

  10. I just did it and am now on day 6. My diet plan consisted of diced red and green bell pepper and zucchini sauteed in olive oil + walnuts for breakfast. I had a vegetable soup made from organic, low sodium vegetable broth and 10-12 different vegetables (cheated and bought from the frozen section as I’ve read that frozen vegetables still have the good stuff in them) and almonds for lunch, and then vegetable soup and hazelnuts for dinner with some steamed carrots. I also took a one-a-day and fish oil each day. Total calorie intake was 1100 the first day and 800 the remaining days for me, but this will clearly changed based on your BMR and how active you are leading up to the FMD. If I were not very active, as a 42-year-old female, I would typically only need about 1400 calories per day, meaning I would eat 700 calories the first day and then 500 each day after that. I am an active person so chose to increase the amount eaten, just using the nutrition info to identify how much soup, how many walnuts, etc. It was hard. I felt hungry more often than not, but I stuck with it and my ulcerative colitis definitely toned it down a notch. I have hope that maybe I can stay off Imuran for the long haul with this as this was my first time. I’ve read that with autoimmunity, it takes three of these to see the full benefits. I was truly impressed and amazed with how this went!

  11. Hmmm… I’m doing one meal a day intermittent fasting. I don’t ingest any sugar at all. The only carbs I ingest are from veggies. But I noticed in the video about this, they said during the 5 day fast to greatly reduce protein, and increase fat. So, that’s what I did. Just using real food for the one meal I eat per day that’s low protein, very low carb, and high fat.

  12. Thanks Jocelyn for the info!! I am doing keto and IM after cancer x3. He has interesting research. Never knew!! Ty for sharing!!!!!

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