By Nils Osmar © 2018. This article should not be construed as offering either formal or informal medical advice. The content is intended solely for informational purposes. Any changes in your lifestyle or diet should be done in consultation with your doctor or health care professional.  Edit

Most people, when they hear the word “fasting,” think of a water fast (drinking only water, and abstaining from food and other drinks for a set period of time). 

But fasting, by definition, can involve abstaining from ANY nutrient. 

One popular approach to fasting, which was created by Dr. Valter Longo, is called a FASTING MIMICKING DIET (abbreviated FMD).  It was developed carefully and methodically by Dr. Longo and his associates after a great deal of experimentation.

Longo’s goal in creating the FMD was to come up with a diet that would provide most of the benefits of a prolonged water fast, including autophagy, apoptosis, and stem cell regeneration, but still allow people to take in some calories and nutrients.

He speculated that allowing people to eat some food during their fasts would result in greater compliance (people actually finishing the prescribed five to seven days), and that the nutrients the FMD allows people would safeguard against problems such as micronutrient deficiencies, which can a danger for those who do a lot of water fasting.

The easiest way to do a fasting mimicking diet is to order a box from ProLon, then follow the directions. The box includes soups, crackers, nuts and seeds, and other foods with the recommended macronutrient breakdown. (Dr. Longo helped set up ProLon, but does not profit or benefit from sales of the product).  To be clear, ProLon‘s is the ONLY method of doing an FMD that Dr. Longo recommends. He does not endorse any other version of the FMD.


The difficulty with having only one version of the FMD is that some people may not be able to participate because of (1) the cost, and/or (2) being unable to eat some of the ingredients in the ProLon diet. (For example, I could never do it because it contains wheat and nuts, which are allergens I can’t have in my diet). Some folks have looked into the FMD, studying its ingredients and analyzing its macronutrients, to see if they can come up with alternative versions.

If you’re playing around with variations, or trying to make up one of your own, remember that whatever other changes you make, it’s vitally important to keep your protein 16 grams or less per day (after the first day, which can be a little higher). This is because one of most profound effects of the FMD is deepening a natural process called AUTOPHAGY. 

The body uses 15 or 16 grams a day just to maintain basic body functions such as keeping your heart beating, so has no “motivation” to go into autophagy if you’re providing more than that in the diet. (It makes its own proteins, during autophagy, by scavenging debris out of your cells, and then by destroying senescent cells; the point of fasting is to motivate it to keep doing so). (So, for example, eating bone broth during a fast would be bad because by providing ample protein, it would turn off autophagy.)

Some alternative versions to the FMD allow 20 or 30 grams of protein, and even call for adding bone broth. People following these versions would probably not experience autophagy, so would not get the most profound benefits of doing an FMD.

This website describes one approach to creating your own FMD.  It gives the basics of the FMD diet as:

  • DAY 1: Eat 1090 calories, with this breakdown: 10% protein (27 grams), 56% fat (68 grams), 34% carbohydrates (93 grams).
  • DAYS 2 through 5: EAT 725 calories per day, with this breakdown: 9% protein (16 grams), 44% fat (35 grams), and 47% carbohydrates (85 grams).

I tried eating these macros the first time I tried eating an FMD, but found that it was way too high in carbohydrates for me. It just didn’t work for me to be shoveling in all of those carbs. So I started looking for versions closer to the diet my body’s grown accustomed to.


One variation which has been gaining a little traction in the keto community is a low-carb version of the FMD. I tried this myself and found it to be too low in carbs and high in fat to be palatable.  But hard core keto dieters might not have a problem with it:

  • PROTEIN: 16G (64 CAL) 
  • CARBS: 10 (40CAL)  
  • FAT: 70G (630)

The above version didn’t work for me. I’d rather just fast on water, than struggle to find foods that fit these parameters. The only way I could make it work was to pour a small pitcher of cream in my coffee (i.e., do a “coffee and fat” fast for a few days). I wasn’t crazy about this version.


My version is a cross between the keto version and the Prolon version. The macronutrient are:

  • PROTEIN: 16G (64 CAL) 
  • CARBS: 40G (160 CAL)  
  • FAT: 55 G (495 CAL)

This version let me eat lots of broccoli, mushrooms, cauliflower, sauerkraut, and other low carb, low protein plant-based foods (they pretty much have to be plant based, to keep the protein that low –– so think of it as being a temporary vegan).

All three versions come to roughly the same calorie counts. My goal, when I use my version, is to be eating highly nutritious meals that are low in protein (so as not to stop autophagy or apoptosis), and also have some carbs and lots of healthy fat.