The 5 Day Fast. How and Why?

The science of fasting is becoming more and more compelling.  Studies are demonstrating the benefits of occasional short-duration fasting, such as staving off Alzheimers and heart disease, improved insulin sensitivity and brain function, a stronger immune system, and increased longevity.

I have a lot to get done in my life, and I’m going to need some extra years to make sure it all happens.  My main goal in trying the 5-day fast mimicking diet was 2 -fold. First, I was curious. I wanted to scratch my own itch.  Second, I’m hoping following this protocol a couple times per year will push me well into my centenarian years.

I knew the benefits of a 5 day water only fast, but I also knew the consequences.  I work hard and at a relative high intensity in the gym. I wanted to minimize the catabolic (muscle-wasting) effect of my fast.  Enter the 5-Day Fasting Mimicking Diet (FMD). 

What is the Fasting Mimicking Diet?

In a study that was published in Cell Metabolism (and funded by the National Institute of Aging), researchers found that cutting daily calories in half for just four days every two weeks reduced biomarkers for aging, diabetes, heart disease and cancer with no adverse effects. FMD was tested on yeast, mice, and humans and the results remained consistent among all three groups.

The FMD describes itself as:

…made from healthy, natural ingredients that you will eat for five days. Your body, however, does not recognize that it is being fed. This causes the body to enter a fasting mode.

Dr. Valter Longo is the founder of the FMD and sells a kit with everything you need for your 5 day FMD.  The brand name of the kit is ‘ProLon’, and if you’re so inclined you can buy one here.  Being the owner of a budding small business I decided to do some research and figure out how I could follow the same protocol as ProLon without paying $250 (to not eat…).  Proceed at your own risk, I’m not a doctor and there very well could be key micro-nutrients that I missed in my version. If you want to play it safe, buy the kit!

My Version of the Fasting Mimicking Diet

The nutrition rules of the FMD are given in Dr. Longo’s book The Longevity Diet:

  • Day 1: Total caloric intake of 4.5 to 7 kcal/lb of body weight (10% protein, 56% fat, 34% carbs)
  • Days 2-5: Total caloric intake of 3 to 5 kcal/lb of body weight (9% protein, 44% fat, 47% carbs.

Here are the specific numbers I hit with my FMD:

Fasting Mimicking Diet Nutrient Guidelines:

  • Low protein and low carbohydrate, with no animal based products.
  • High vitamin/mineral content 
  • All proteins from plant-based sources
  • Carbohydrates from complex carbohydrate plant sources
  • Fats primarily from coconut oil/olive oil and/or nuts (almonds, walnuts)
  • No/Low Sugar

My FMD Meal Plan

After some research I found a great plan that I adapted from Quantified Bob.  I adapted his plan to me and got pretty close to the target macronutrient requirements, which I split into 3  “meals.” You can see everything I ate and graphical results of my data here.  I also found this useful list of Fasting Mimicking Diet recipes.

My primary nutrition sources were avocados and sweet potatoes.  I also had some cauliflower, coconut oil, and green superfood. I also had sea salt on my avocado and sweet potato, as well as some swigs of pickle juice to help with electrolytes during the fast. 

I drank 2+ liters of spring/high alkaline water daily along with an occasional cup of chamomile tea. Each morning I also had 1 cup of black coffee.

My Results


I was quite surprised with what happened to my body over the course of 5 days.  As you can see in the data, my body fat went up 1.4% and my muscle mass dropped 4 lbs through the 4th day.  I also lost about 6 pounds of body weight.

I believe the increase in body fat percentage was actually caused by my muscle loss.  As I lost muscle mass, I’m left with a higher percentage of body fat making up my total weight.

This is a good a place as any to say I WOULD NOT recommend this plan for weight loss, even though you will lose weight.  I had an extremely difficult time getting back to eating normally after the fast ended. It felt like my body could not get enough food for almost a week after my fast.  I went back up to my normal weight, except with a higher body fat % and lower muscle mass than before I started within about 10 days. Not good!


Mentally this was an amazing exercise.  I love anything that forces me to get uncomfortable, I see these types of exercises as mental toughness training.  Mentally is by far where I got the most benefit out of my FMD.

After the third day there was a sense of clarity that’s hard to come by.  I could hyper focus on any activity I was performing, and distractions were a thing of the past.  I was ‘in the zone’ for pretty much the entire 4th and 5th day.

The other benefit is the realization that I don’t need nearly as much food as my brain tells me I do.  Half the time I’m eating out of boredom, or because ‘I should eat’. There’s something freeing in knowing you can go a day or 2 without food and everything is still going to be just fine.

Conclusions/What’s Next?

Overall, I was happy my FMD results. The positive mental benefits outweighed the negative immediate physical benefits.  But remember, the real physical benefits are seeds to be sewn when I’m 100!  The hardest part was staying out of the gym for 5 days. I missed my workouts.

Dr. Longo suggests that the overall benefits of fasting (lowered inflammation and increased immune system function) will increase after each FMD cycle. I plan on repeating the FMD every 180 days, incorporating some of the tweaks I outlined.

Please let me know if you have done some form of fasting or plan to fast in the future – would love to hear about your experience!



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