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Fasting Mimicking Diet: How It Works, Benefits, and More


Are you wondering which fasting approach is right for you? Different fasting protocols exist, such as the 16:8 fast and 20-hour fast, and they’re all linked with weight loss, reduced blood pressure, and increased autophagy. Maybe you’ve heard of the Fasting Mimicking diet (or FMD for short), an option for people who cannot tolerate a no-calorie fast.

This article covers how the FMD diet works, who should do it, potential side effects, and commonly asked questions on the topic.

What is a Fasting Mimicking Diet?

The Fasting Mimicking Diet is a modified fast that varies from traditional fasting because it allows for some calories, but you’ll still reap the benefits of a calorie-free fast. It’s essentially low-calorie, low-protein, low-sugar, moderate-carb, and moderate-fat.

The FMD diet runs for 5 days, and it’s actually a program that was first developed by Dr. Valter Longo, the Director of the Longevity Institute at the University of Southern California (*).

The ProLon Diet — Dr. Longo’s program and the first fast mimicking diet on the market — is not a keto-friendly plan because it allows for moderate carbs, but it can still lead to ketosis and fat-burning.

If you’re on a keto diet and want to try the FMD approach, you can tweak it a bit by lowering carbs and increasing fat while keeping protein low (as with the standard FMD plan).

For those who are not keto and would rather try the fasting mimicking diet without ordering ProLon’s 5-day fasting nutrition program, you’re also free to do it. Just keep in mind to prepare your food in advance based on the recommended calorie intake.

How the Fasting Mimicking Diet Works

Throughout a 5-day period, you are only allowed to consume about 34-54% of your usual calorie intake (*).

As for the fasting mimicking diet calories:

On day 1,  you eat 1,090 kcal with the following macros: 10% protein, 56% fat, and 34% carbs.

For days 2-5, you drop your calorie intake to 725 kcal with the following macros: 9% protein, 44% fat, and 47% carbs.

See the table below for your reference:

Day  Calories Protein Fat  Carbs
1 1,090 kcal 10% 56% 34%
2-5 725 kcal 9% 44% 47%

Another thing to note is that all your foods (breakfast, lunch, dinner, and snacks) should be plant-based. For those who subscribe to the ProLon’s kit, you can expect to receive:

  • Nut bars (e.g., macadamia, coconut, honey)
  • Dietary supplements, such as vitamins, minerals, and omega-3 fatty acids
  • A fruit-flavored drink
  • Herbals teas with no caffeine
  • Easy-to-prepare soups
  • Snacks, such as olives and kale crackers

While Dr. Longo’s 5-day FMD protocol discourages replacing the above-mentioned foods and drinks with other options, some may prefer doing this if they dislike the taste.

After the 5th day, you’re going to resume your normal diet.

Potential Health Benefits of the Fasting Mimicking Diet

A fasting mimicking diet offers similar advantages to regular intermittent fasting. The ProLon website mentions various key benefits, from cell renewal to fat loss. Let’s discuss each below:

benefits of fast mimicking diet

1. Cell renewal or autophagy

Autophagy is expected to happen on the third day of a fasting mimicking diet as stated on the ProLon website’s FAQs. This is after you’ve depleted your glycogen stores and entered a metabolic state of ketosis (* , *).

Autophagy is your body’s “cleansing system” in which damaged cell parts that contribute to chronic diseases are removed and replaced (*). In other words, autophagy plays a vital role in keeping you healthy.

You may not feel autophagy physically, but you may notice symptoms like reduced appetite and weight loss.

2. Reduced blood pressure

A FMD diet was introduced to a small cohort of patients with prostate cancer.

Post-intervention, many of their metabolic factors improved, including their blood pressure. Their systolic BP was reduced by 9.52 mmHg while their diastolic BP was reduced by 4.48 mmHg (*).

In another study, participants ages 20-70, who were all generally healthy, were placed on a five-day fasting mimicking diet for 3 months.

The results showed that their systolic BP dropped by 4.5 mmHg while their diastolic BP dropped by 3.1 mmHg. Additionally, their IGF-1 (or insulin-like growth factor 1) decreased, helping to reduce cancer risk (* , *).

3. Enhanced mental clarity and mood

For those seeking the mental benefits of fasting, the FMD is capable of improving brain function through autophagy (*).

According to a mini-review article in Frontiers in Psychiatry, restricting your calories short-term induces autophagy, which has anti-depressant effects in humans (*).

Another study focusing on intermittent fasting found that one week of fasting significantly increases spatial planning and memory (*).

4. Increased fat loss

Since the FMD puts your body in a fasted state, it promotes weight loss — a common reason people follow Dr. Longo’s program.

Although keep in mind that intermittent fasting strategies like the 16:8 diet also result in weight loss, followed by a sustained fat loss if you make fasting (plus eating healthily, exercising, and other healthy habits) part of your lifestyle.

In a 2017 randomized controlled trial, Dr. Longo and other researchers divided 100 generally healthy participants into two groups. One group followed a diet with no restrictions for 3 months, while the other group followed a fasting mimicking diet for 5 days per month over the course of 3 months (*).

Based on the results, the FMD group experienced a reduction in their body weight and total body fat (*).

5. May change your hunger response

A common misconception about fasting is that it makes people extremely hungry, resulting in bingeing.

The reality is that fasting leads to temporary hunger, but this happens only a few hours after your last meal — let’s say 4-8 hours. This hunger wave will peak but it eventually disappears the longer you fast.

Ultimately, fasting decreases ghrelin (the hunger hormone) and your desire to eat, while increasing your feeling of fullness (*).

The difference is that with the fasting mimicking diet, you’re able to eat meals and snacks for 5 days, only that they’re limited in calories.

6. Lessens the risk of prolonged water-only fasting

Doing a water-only fast (no food and drinks except for water) for more than 48 hours is generally well-tolerated and safe under medical supervision (*).

However, a lot of people who are new to extended fasting may experience fatigue, electrolyte imbalances, nausea, and headache.

The good news is that you get to avoid these potential issues with the fasting mimicking diet since you’ll still consume a small number of calories each day.

Potential Side Effects of a Fasting Mimicking Diet

As with traditional calorie restriction and fasting strategies, the fasting mimicking diet can result in short-term side effects. These include increased hunger, cravings, tiredness, headache, brain fog, and low blood sugar.

Minimize these side effects by avoiding any strenuous workout during your 5-day fast. Pairing fasting and exercise is fine as long as you keep them light. Walking, gentle yoga, and stretching are great examples.

The ProLon program also mentions (on their FAQs page) that people may experience bloating, cramping, gassiness, constipation, and diarrhea. These symptoms could result from any sudden change in your diet, including adding high amounts of fiber too quickly (*).

If you are taking medications for lowering blood sugar and blood pressure, speak with your doctor before you do a fast mimicking diet.

Who Should Do a Fasting Mimicking Diet?

The FMD diet is an option for those who cannot tolerate or choose not to undergo extended fasts without some food.

It’s for individuals who love the idea of a plant-based diet or are already following it since the FMD protocol involves consuming plant-based foods and beverages.

Last but not least is anyone who is eager to achieve weight loss and other FMD benefits discussed earlier in this article, such as autophagy, better mood, and lowered blood pressure.

Is Fasting Mimicking Diet Safe?

In a nutshell, yes, it’s safe for most people — although it’s important to discuss the FMD with your healthcare provider if you have any concerns. This is especially true if you have a medical condition or you’re taking medications.

For those who subscribe to the ProLon program, stop consuming your plant-based products right away if you experience allergy symptoms.

Some plant-based ingredients (nuts, for example) may trigger allergies. Watch out for edema (or swelling), skin redness, tingling of the mouth, runny nose, digestive symptoms, and trouble breathing (*).

What Do You Eat on a Fasting Mimicking Diet?

The fasting mimicking approach focuses on low-calorie, low-protein, low-sugar, moderate-carb, and moderate-fat options that are plant-based. Within a 5-day period, you consume the following:

  • Soups: quinoa, mushroom, tomato, butternut squash, etc.
  • Nut bars: almonds, macadamia nuts, pecans
  • Snacks: olives with herbs, olives with sea salt, almond and kale crackers, etc.
  • Supplements: vegetable powder with vitamins and minerals, algal oil (oil from marine algae) which has omega-3 fatty acids
  • Drinks: hibiscus tea, spearmint tea, spearmint lemon tea, and L-drinks (ProLon offers this as fruit mixes with vegetable glycerin, which is supposed to protect your lean mass while in a fasted state).

Some people may not find these foods and drinks appealing, including those embracing a meat-based diet. Alternatively, you could start a ketogenic diet, which also mimics a fasting state, or try other types of fasts.

If you decide to proceed with the FMD plan but do not want ProLon’s 5-day kit, you can go the do-it-yourself route. You could swap some of the options from the list above with homemade versions. Feel free to replace some of the veggies and grains with those you can tolerate.

How to Start a Fasting Mimicking Diet

Preparation is key to a successful fast. Before starting the FMD, talk to your healthcare provider and ask if there are changes to be made to your medications.

Since the fasting mimicking diet involves meals with specific calories and macros, prepare these 5 days’ worth of meals in advance so you’ll simply heat them or open them.

It’s also a good idea to ease your way into a 5-day fasting mimicking diet by slightly reducing your calorie intake (especially calories from carbohydrates) days before the fast. This will help you get used to fewer carbs in general and avoid blood sugar swings during the fast.

Consider doing lab tests before and after your fast to note any differences. You might also want to check blood glucose, ketone levels, and changes in your weight.

Fasting Mimicking Diet Sample Meal Plan

Here’s what your meals would look like on the FMD plan. Feel free to make substitutions based on what you’re not allergic to and what’s available. The general rule is to keep them plant-based, unprocessed or minimally processed, and sugar-free.

Day 1 — 1,090 kcal

Breakfast: nut butter bar and herbal tea (spearmint tea, hibiscus tea, or ginger tea)

Lunch: tomato soup and kale crackers

Afternoon snack: nut butter bar

Dinner: cauliflower and spinach soup

Day 2-5 — 725 kcal

Breakfast: nut butter bar and herbal tea (spearmint tea, hibiscus tea, or ginger tea)

Lunch: broccoli and asparagus soup

Afternoon snack: nut butter bar

Dinner: mushroom soup and green olives

Note that you can follow the standard 10% protein, 56% fat, 34% carbs on day 1 and 9% protein, 44% fat, 47% carbs on day 2 if you’re not on the keto diet.

For keto dieters, lower your carbs and slightly increase your fat without necessarily affecting the recommended calories in a day.

How Long Should You Do a Fasting Mimicking Diet?

The fasting mimicking diet is meant to be practiced for only 5 days once a month, for 3 months to experience its weight loss and health benefits.

When you’re not fasting, it’s important to resume your usual calorie intake, but make sure to meet these calories from nutrient-dense foods.

You could also start eating a diet that’s lower in carbohydrates and higher in healthy fats so that your next FMD is easier. An added benefit is that this helps you continue losing body fat without having to restrict your calories.

Who Should Not Do a Fasting Mimicking Diet?

This fasting plan should be avoided by pregnant and breastfeeding women, children, and those who are underweight and have a history of an eating disorder.

Remember to discuss it with your doctor if you’re taking any medications for blood sugar and blood pressure.

Frequently Asked Questions

Here are frequently asked questions on the fasting mimicking diet:

How much weight can I lose on a fasting mimicking diet?

It’s possible for you to lose as much as 5 pounds doing the FMD once a month for 3 months.

However, everyone loses weight at different rates even when they consume the same number of calories due to other factors, such as the overall quality of their diet, sleep, age, and current health condition.

What’s the difference between fasting mimicking and intermittent fasting?

The main difference between these approaches is that fasting mimicking involves eating foods that are low in calories throughout the day, while intermittent fasting alternates between periods of eating and not eating.

Furthermore, fasting mimicking is plant-based while intermittent fasting foods (during your feeding window) can include a wide variety of options, such as meat, seafood, eggs, avocados, and berries.

Does a fasting mimicking diet put you in ketosis?

Yes, it can induce a metabolic state of ketosis since it’s a prolonged fast. The same is true for regular short-term intermittent fasts, especially when you start and break these fasts with meals that are low in carbohydrates.

Can you drink coffee on a fasting mimicking diet?

Black sugar-free coffee is allowed on fasts; however, you need to limit yourself to only one cup of 8-12 ounces of black coffee on a fasting mimicking diet. You may sweeten your coffee with stevia or monk fruit while avoiding creamers.

The Bottom Line

The fasting mimicking diet is a powerful tool to experience the benefits of fasting without completely giving up food. Although this is done only once a month, for up to 3 months, it’s best paired with a healthy diet in between, such as keto.

As mentioned in this guide, this method leads to weight loss, autophagy, lower blood pressure, and many other benefits of fasting in general. You might want to consider other types of fasts as well if you can comfortably go without food for hours.

Overall, the fasting mimicking diet is safe and tolerable, but consult a healthcare provider if you have concerns and you’re currently on medication.

17 References

ProLon. The ProLon Fasting Mimicking Diet is your secret to fasting.

Brandhorst S et al. A Periodic Diet that Mimics Fasting Promotes Multi-System Regeneration, Enhanced Cognitive Performance, and Healthspan. 2015 June 18

ProLon. Frequently Asked Questions.

Lopez N et al. System-wide benefits of intermeal fasting by autophagy. 2017 October 26

Lopez N et al. System-wide benefits of intermeal fasting by autophagy. 2017 October 26

Watt V et al. The impact of a fasting mimicking diet on the metabolic health of a prospective cohort of patients with prostate cancer: a pilot implementation study. 2022 March 21

Gersema E. Scientifically designed fasting diet lowers risks for major diseases. 2017 February 16

Shanmugalingam T et al. Is there a role for IGF‐1 in the development of second primary cancers?. 2016 October 13

Gassen N et al. Is There a Role of Autophagy in Depression and Antidepressant Action?. 2019 May 15

Gassen N et al. Is There a Role of Autophagy in Depression and Antidepressant Action?. 2019 May 15

Farooq A et al. A Prospective Study of the Physiological and Neurobehavioral Effects of Ramadan Fasting in Preteen and Teenage Boys. 2015 April 1

Wei M et al. Fasting-mimicking diet and markers/risk factors for aging, diabetes, cancer, and cardiovascular disease. 2017 February 15

Wei M et al. Fasting-mimicking diet and markers/risk factors for aging, diabetes, cancer, and cardiovascular disease. 2017 February 15

Ravussin E et al. Early Time-Restricted Feeding Reduces Appetite and Increases Fat Oxidation But Does Not Affect Energy Expenditure in Humans. 2019 August

Myers T et al. Potential Effects of Prolonged Water-Only Fasting Followed by a Whole-Plant-Food Diet on Salty and Sweet Taste Sensitivity and Perceived Intensity, Food Liking, and Dietary Intake. 2022 May 3

ProLon. Frequently Asked Questions.

Patel R et al. Peanut Allergy. 2022 July 5


18 thoughts on “Fasting Mimicking Diet: How It Works, Benefits, and More

  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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