My Valter Longo Inspired Potential Cancer Risk Reduction Fast

As I wrote in my “Thoughts on Fasting” post I am primarily looking to perform these multi-day fasts for cancer avoidance purposes. There is some evidence that a 3 day fast can help cut cancer risks. It is not a guarantee but the cost and risk associated with doing these things is small enough to make doing these things once or twice a year worth it even if it turns out to not have the cancer fighting benefit. A big part of the body of research I’ve followed on fasting has come from coverage of the works of Dr. Valter Longo . For years he has been an advocate for periodic multi-day fasts and avoiding excessive protein intake to increase longevity and cut down on cancer risks. This post highlights how I’ve designed my cancer avoidance fast around his techniques and research.

The usual disclaimer applies: I am not a doctor, trainer, dietitian, nutritionist, or any other expert in any related field. I’m talking about my amateur and anecdotal experiences here and none of this should replace expert medical advice.


My first introduction to Longo’s specific fasting protocol came in the 2013 BBC Horizons episode “Eat, Fast & Live Longer” . The show covered more than just fasting, and perhaps I’d write about the other calorie restriction protocols discussed in the future. In that episode though the host Michael Mosley did one of Valter Longo’s fasts as part of the documentary. You can see the relevant subsection fo the documentary here . Longo’s fasting plan laid out there is simple: three days of not eating anything with calories all day and allowed one cup of broth with 50 calories in it for dinner. This was the exact plan I put into action when doing my first three day fast . I tried something comparable but for four full days on my next one.

Since airing the airing of that episode in 2013 Longo and his team had been working on ways to make fasting more approachable to people. Both the host, Mosley, and Longo himself said they dread the idea of needing to do it again. It was a no pain no gain thing for them. A formula which Longo found was worth doing even though he thought it sucked and which Mosley did not. But Longo wanted to make those benefits available to all so research he had been doing afterward looked at creating a “fast mimicking diet”. Which he spelled out in his book The Longevity Diet . This diet is more like a drastically reduced calorie plan for a week. What you eat during those five days are soups, shakes, or health bars specially formulated by ProLon , a company that Longo is associated with but he says he does not get any financial benefits from.

In Chapter 6 of The Longevity Diet, the five day Fast Mimicking Diet fundamentals are laid out bare, without any details about the ProLon formulated associated products. Day #1 is an 1100 calorie day with 500 calories from complex carbohydrates, 500 calories from healthy fats, and 25 grams of protein, and a multivitamin. The fasting days are at 800 calories which is essentially 400 calories from carbs, 400 calories from fats, and a multivitamin. Day 6 is the transition diet day whwich is very broadly try to eat a healthy carb heavy day.

While I appreciate the concept of the fast mimicking diet I’m not sure it is for me. I could later find it useful if doing the three day fast too onerous but for now I don’t consider it a huge imposition to do that 1-3 times a year. I’m primarily doing this for cancer risk reduction benefits. There is more research on the three day real fasting than on the fast mimicking diet. While The Red Pen Review of The Longevity Diet gives it mostly high marks, it does state that some of the benefits of the fast mimicking diet are overstated (along with evidence that protein needs to be generally cut to as much as Longo states).

I therefore want to stick with the three day fast but I want to dial in my transition into and out better. My first three day fast was reckless on both entry and exit, especially exit. Three day fasts are short enough that risk of refeeding syndrome for someone not malnourished, nutrient deficient, or with metabolic disregulation, is very low. Thanks to my iron gut I didn’t suffer adverse consequences from my gluttonous days before and after the fast. But I want to maybe get some added benefits to the entry/exit and maybe a little extra fasting window without adding a complete additional day of complete fasting. I’ve therefore taken the basic three day fast and the information on the fast mimicking diet to create my own fasting schedule.

Preparation for the Fast

As I stated in my “Thoughts on Fasting” post, one should make sure they are in good physical health and ready to do a multiday fast. That means having seen your doctor recently and had blood work and have successfully worked up to at least a full day of fasting. A more immediate preparation step for the fast would be to eat really healthy for a good week leading up to the fast and tracking your nutrition in something like Cronometer to get a sense of where your nutrient levels are on a regular basis, how much water you are consuming and where/when that water is coming from.

The Fasting Plan

The performance of this fast takes a total of five days:

  • Day 1 (Transition In Day): The transition in day should be an 1100 calorie diet with a macronutrient profile of about 500 calories from carbohydrates, 500 calories from healthy fats, and about 100 calories from protein. Along with the standard foods a high quality multivitamin will be taken. The last calorie consumption should be no later than 7 pm. The remainder of the evening one can consume calorie-free beverages.
  • Days 2 - 4 (Fasting Days): On fasting days one should be sure to stay hydrated with non-caloric beverages. This can include things like seltzer water, coffee, tea, etc. Things like coffee and tea cannot have any sugar or creamers added to them. In order to help mitigate electrolyte imbalance issues one can use electrolyte packages like LMNT Raw Unflavored Electrolyte Packets . Optionally, if it helps with staying power a couple of cups, less than 50 calories, of vegetable broth can be used instead of electrolyte packets.
  • Day 5 (Transition Out Day): This day will begin with a cup of broth at 9 am. Two to three hours later, at late morning or lunch time, a cup of healthy vegetable soup will be consumed. More eating of smaller snacks/meals can progress through the day with a normal sized dinner if you aren’t feeling gastrointestinal distress. A multivitamin will be taken as well. The macronutrient profile for the day should be 800 calories with most of that being an approximately equal balance of carbs and fats. Minimal protein should be consumed.
  • Day 6 (First Post Fast Day): No calorie restriction or macronutriet ratios but following the FMD’s exit day criteria of a diet rich in complex carbohydrates (veggies, fruit, rice, and past/bread/grains preferrably of the whole grain variet). A minimal amount of fish, meat, and dairy should be consumed as well.

Assuming that one keeps with the eating schedule specified on the transition days this creates a total fasting duration of 86 hours or just over 3.5 days. If one eats dinner a few hours earlier and doesn’t eat until lunchtime on the transition day that can extend to 3.75 days.

Expected Implementation

With the general plan laid out the way I am hoping to implement it this go around is as follows. I have a recipe for a vegetable soup that is very close to the target macronutrient composition for the transition out day. You can find the post with the recipe here . By adding a couple of ounces of raw nuts it also matches the target macronutrient composition for the transition in day. I already have the electrolyte packs purchased as well. Whether I can use that as needed versus having a couple cups of broth at dinner on the fast days remains to be seen. I am going to try though! If it turns out I don’t need either because I’m not experiencing headaches then I will try to take neither. In terms of beverages to drink during the whole run I’m going to try to limit it to coffee (regular and decaf), tea (black and green), Perrier/Pelegrino, seltzer water, and water. I am a big diet soda junkie so that may be easier said than done. My stretch goal though is to not use the broth or artifically sweetened beverages during the entire fasting window.

The day before the fast is the 4th of July. I’m expecting that I’ll be eating a lot that day and maybe drinking a bit of alcohol too. Having that really clean transition day will be nice. So the first day of the fast will be the 5th of July. The core pure fasting days will be the 6th, 7th, and 8th. The 9th will be the transition out day following the listed protocol. Since I’ll have a giant batch of soup but need to be trying to eat more slowly my plan is to make the soup in the morning after I have my broth. I’ll have a small cup of it for lunch. Assuming that goes well I’ll continue doing that every hour or two until I’ve consumed half of it. I’ll then have the second half for dinner.


I know I can do three and four day fasts pretty easily. These tweaks with a Fast Mimicking Diet inspired introduction and exit days may provide a little extra benefit. In the end this whole fasting thing only has the potential to reduce my cancer risk. As laid out here it is something very achievable by me and probably others.