FASTING MIMICKING DIETS – an alternative for folks who can’t yet do a water fast

by Nils Osmar. 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.  

Most people think of abstaining from all food and just drinking WATER during a fast. But a fast, by definition, can involve abstaining from ANY nutrient. And of course some people, such as those with a low BMI or health condition that contraindicates fasting, should not do a water fast.

For these people, an alternative to a full blown water fast is the FASTING MIMICKING DIET, or FMD, which was created by Dr. Valter Longo.  It was developed carefully and methodically after a great deal of experimentation.

Longo’s goal was to come up with a diet that would provide most of the benefits of prolonged fasting, including autophagy and stem cell regeneration, but still allow people to take in some calories and nutrients. Dr. Longo felt that allowing people to eat some solid food would result in greater compliance (people actually finishing the full five to seven days), and that the nutrients the FMD allows people would safeguard against problems such as micronutrient deficiencies, which can a danger in prolonged water fasting.

The easiest way to do a fasting mimicking diet is to order a box from ProLon, then follow the directions. (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 approach. 


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 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). So some folks have looked into the FMD, studying its ingredients and analyzing its macronutrients. When Longo published originally in Europe, he encouraged people to come up with their own versions, if they wanted to, in consultation with their doctors; but he soon came to feel that this was a mistake, because the diets bore little resemblance to his. He does not currently endorse ANY versions of the FMD other than his own. Nonetheless, numerous versions have sprung up on the web.

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. 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 it would turn off autophagy.) Some variations on the FMD allow 20 or 30 grams of protein, and even call for adding bone broth; people following these revisionist versions would probably never experience autophagy.

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. It just didn’t work for me to shovel 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 steam in the keto community is a low-carb version of the FMD. I tried this myself and found it to be way too low in carbs and high in fat to be palatable. It’s so low in carbs that it’s lacking the plant nutrients that Longo feels are necessary. 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 pitcher of cream in my coffee. So I wasn’t fond of this version. But hard core keto dieters might not have a problem with it:

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


My version is a cross between the keto version and the official version.

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

This version let me eat lots of broccoli, mushrooms, cauliflower, 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. Your goal is to be eating highly nutritious meals that are low in protein (so as not to stop autophagy or apoptosis, which are the main benefits to be expected from a successful fast or FMD), and also have some carbs and lots of healthy fat.