What is a “fasting mimicking diet”?

Fasting is very “on-trend” at the moment. It’s cheap to do, no special meal preparation is required and there is ample evidence highlighting its benefits for anti-aging, weight loss and combatting chronic disease.  Fasting is not a new idea. Various religions and cultures have been practicing fasting for centuries. Even our cavemen ancestors had to fast, as there was often no food available for days on end. If fasting is such an amazing longevity and fat loss hack, why isn’t everyone doing it? One reason is because our relationship to food is complex and being ravenous for any length of time can be very unpleasant.

Even though proponents of fasting claim that hunger is not as big of a deal as people think, the bottom line is most people like food and they like to eat. It is a pleasurable part of our day and relationships are nurtured when sharing meals with friends and family. Food gives us nourishment, energy and when made correctly, is delicious and satisfying. For these reasons, fasting can be a reasonably hard sell.

Fasting can be even more difficult for sugar-burners, i.e. those on high carb diets, who lack metabolic flexibility to switch over to the burning of body fat for fuel when calories are restricted.  On the flip side, those who already follow a ketogenic or low carb diet and are fat-adapted might find fasting easier.  The natural suppression of appetite that comes with a diet lower in carbs is also helpful when attempting to fast.


When is a fast a true fast?

Time restricted feeding, where one goes without food for 12 to 16 hours as well as intermittent fasting for 1 day here and there, is just the tip of the iceberg when it comes to fasting protocols. While this type of short duration fasting is certainly more manageable and has its advantages for weight loss, healthy blood sugar control and increased metabolism of fatty acids and ketones, it is not considered a true fast according to Dr Valter Longo, Director of the Longevity Institute at the University of Southern California.

True biological fasting only begins once the body has been free of food for over 24-30 hours. Why? Because digestion takes time. Only once your stomach is completely empty does biological fasting begin. When biological fasting begins, warning signals are triggered throughout the body. These signals tell the body that its survival is at risk. Fat stores start being broken down and ketones are produced to provide the body with calories and nutrients.  This process happens over 1 to 2 days and is considered phase 1 of survival mode. Weight loss and some level of metabolic optimization occur.

Phase 2, which is days 3 to 4 of a fast, is when things get more serious and autophagy is triggered. Autophagy is a detox process the body undergoes to clean out damaged cells and regenerate new ones. When autophagy is activated, the aging process is slowed down, inflammation is reduced, the onset of neurodegenerative diseases is prevented or delayed and the body’s natural ability to function is given a boost.

After 4 to 5 days of no food the body is under severe stress and starting to freak out a little. This third phase is when the body increases the number of circulating stem cells to create new tissue that is young, efficient and strong. Studies in mice have shown that this process has the potential to prevent or even reverse some chronic diseases.

Another approach to fasting is ongoing caloric restriction, which has been shown to improve longevity, but the downside is that constant hunger and deprivation is a pretty miserable way to live.  One also doesn’t benefit from the refeeding phase, which is where the magic happens in terms of cellular renewal. Other potential side effects of ongoing caloric restriction is a weakened immune system and prolonged wound healing.  This method of continued fasting is therefore not ideal.

What if there was a way to get all the benefits of a 3 to 5 day water fast, while still being able to eat? 

If the notion of going without food for a few days leaves you in a cold sweat, you may want to explore the option of the Fasting Mimicking Diet (FMD).  The Fasting Mimicking Diet was developed by Dr. Valter Longo, an expert in aging, fasting and how diet and lifestyle regulate longevity. The goal of Dr Longo’s research was to find a way to maximize the benefits of biological fasting, while minimizing the downsides like ravenous hunger and loss of lean body mass, to make it more accessible for everyone.


What does a fasting mimicking diet entail?

The Fasting Mimicking Diet is slightly different to fasting in that instead of going long periods without food, one eats small portions that amount to roughly half one’s daily calorie intake for a 5 day period.  The diet is low protein, low sugar, vegan and contains good fats. One eats between 800 and 1000 calories a day in total. For best results the 5-day fast should be repeated monthly for 3 months. Thereafter, it can be used a few times a year or as needed. Dr Longo’s patented Fasting Mimicking Diet was developed after 20 years of his own research in the field. He claims the FMD nourishes the body while producing the same beneficial effects as water fasting. This includes autophagy, protection of healthy cells, weakening of cancer cells as well as stem cell and immune system regeneration and more.

For those wanting convenience in a box, you can purchase Dr Longo’s ProLon diet (short forPro-longevity) and receive 5 days’ worth of packaged food containing vegetable soups, which you eat twice a day, olives, vegetable chips, nuts, bars made of nuts, supplements and specialized drinks and teas.

“When you fast under the right conditions and for the right period of time, an incredible biological transformation is triggered – a renewal – which takes place at a cellular level deep within the body.” – Dr Valter Longo


DIY Fasting Mimicking Diet

If you feel the $249 per box price-tag is a little too steep or if they don’t ship to your country of residence, you can follow his guidelines and attempt your own diet plan. While achieving exactly the same results as Dr Longo’s ProLon diet cannot be guaranteed, it is definitely worth a try, especially if a 3 to 5 day water fast is beyond your capabilities. Use a food tracking App like MyFitnessPal for the full 5 days. In the App set your calorie goal to between 800 and 1000 per day. Set macronutrients as follows: Protein 9%, fat 44% and carbs 47% of daily intake. Fats should be from olives, avocados, nuts and seeds. The carbs come from nuts, seeds, legumes, and gluten-free grains. Ensure you choose protein from plant-based sources only. You could “Bantify” the eating plan if wanting to avoid certain foods, but it could be a challenge getting protein in. You could try chia seeds, almonds and lots of dark green leafy veggies like kale and broccoli as sources of plant based protein.


What can one expect?

One can, during the first few days of the fasting programme, experience headaches, fatigue and probably a degree of hunger. After day 4 one should start feeling much better as energy levels and mental clarity improve.

After completing three 5-day cycles over three months, one can expect weight loss due to the calorie restriction. Other benefits include improvements in cholesterol, triglycerides, blood pressure as well as inflammation and insulin resistance. Dr Longo’s animal and human clinical trials also indicate, as with a water only fast, that deep cellular renewal and optimization is achieved.

Note:  Pregnant women, seniors over 70 years of age, breast feeding mothers, children and those with eating disorders, adrenal fatigue, liver and/or kidney disease should not fast.


Article written by Nicky Perks for Lose It magazine  (Volume 29)

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Reference sources:












About Nicky Perks

Passionately sharing information about the paleo/primal, high fat/low carb lifestyle that will rock your world! I am on my own journey to good health and a slim body. My goal? To enjoy the ride as life on this beautiful planet is just too short to do it any other way.

Posted on May 3, 2019, in Primal 101 and tagged , , , . Bookmark the permalink. 1 Comment.

  1. Good info on fasting. I’ve been doing 14 hours fasting 10 hours on. It has helped for me to time it with an app and it makes me not snack after dinner!! Just tea. It really has helped in that regard

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