My 5 Day Fasting Mimicking Diet Experiment

Diet can have a remarkable effect on you, it can reprogram your body and put it on a path to live longer.
— Dr. Valter Longo, The Longevity Diet

I first learned about the 5-day fasting mimicking diet (FMD) from Dr. Valter Longo's book, The Longevity Diet. I had no intention of fasting (the book was recommended to me by a fellow a cancer survivor whom I love, respect and admire), but what I learned about healthy aging and disease prevention from Longo's book was a revelation. Also, I was feeling like I'd hit a bit of a wall with my body composition (stalled at 15% body fat) and, more concerningly, my PSA had been ticking up steadily for the past year. I was looking for some additional natural interventions to address my chronic prostate inflammation as an alternative to a lifelong dependence on pharmaceuticals.

Longo, the Director of the USC Longevity Institute, is a biogenterologist and cell biologist who has synthesized research from diverse disciplines to derive what he claims to be the optimal diet for human health and longevity. Longo uses data from 5 research areas to weed out myth, bias and marketing from the diet wars:

  1. Juventology research: the study of preserving youth

  2. Epidemiology: the study of the causes and important risk factors for disease and other health-related conditions in defined populations

  3. Clinical studies: research performed on people aimed at evaluating the effectiveness of an intervention (medical, surgical, lifestyle)

  4. Centenarian studies: studies of long-lived populations, such as those that live in the so-called Blue Zones

  5. Complex systems: the application of an engineering approach to analyze human health issues to better understand the complex interactions between food, cellular damage, and aging

Using research from these different disciplines, Longo developed the ideal lifestyle to minimize disease and maximize a healthy lifespan. Since I was already following most of his recommendations -- a whole-food, plant-based diet with low but sufficient protein (mostly from fish), minimal bad fats and sugars, lots of good fats and complex carbohydrates, plenty of exercise (including strength training) -- I decided to try what Longo calls the fasting mimicking diet.

In his book Longo lays out a very compelling argument for why humans should periodically fast. Fasting, it turns out, can trick our bodies into triggering the kinds of evolutionary adaptations that we've developed, over hundreds of thousands of years, to survive periods of food scarcity such as occurs during famine or a bad harvest season. Calorie restriction, Longo has found, reduces inflammation by lowering the levels of C-reactive protein (CRP) in the blood; CRP is one of several markers associated with cardiovascular disease (my father, David Sloane, who died of prostate cancer in 2015, also suffered from heart disease. Strike two.).

Longo claims that his own patented fasting mimicking diet (which he branded Prolon FMD) helps people reap the health, wellness and longevity benefits of a full 5-day fast without feeling like they're starving themselves. He contrasts the FMD with all other kinds of fasting approaches, including intermittent fasting, which all promote weight loss but which don't place the body into biological fasting long enough to experience the biological changes that it experiences during phases 2 and 3 of the body's survival fasting mode.

According to Longo, the FMD promotes longevity and resistance to disease by activating the following biological processes:

  • Switching all cells to a protected anti-aging mode

  • Promoting autophagy (self-eating of parts of the cell) and replacing damaged cell components with newly generated functional ones

  • Killing damaged cells in many organs and systems and replacing them with newly regenerated cells from activated stem cells

  • Shifting the body into an abdominal/visceral fat-burning mode, which continues after returning to a normal diet (probably due to epigenetic changes, which are modifications of the DNA and proteins that bind DNA)

Think of the Prolon FMD as a 5-day calorie-restricted diet. Over the 5 days you consume between 670 and 1065 calories per day. Those calories come from a proprietary food formulation, with specific nutrients designed to minimize hunger and protect lean muscle mass, which Longo's company, L-Nutra, delivers to you in the mail (NB. Longo donates 60% of his share of L-Nutra profits to the Create Cures Foundation). The recommended protocol is a 5-day fast once a month for three months, and then a couple times a year thereafter. Longo stresses that 5 days is sufficient to get the full benefits of the fast; any longer and the returns diminish.

I just recently finished my first FMD. And although I haven't had my PSA re-tested yet I can attest to the powerful physiological effects the fast has had on my body. Over the 5-day fast I lost 9.4 lbs. and 1% body fat. However, I also lost 6 lbs. of lean muscle mass (good thing I had built a surplus from decades of strength training). The "before" photo on the left was taking on the first morning of the fast, while the "after" photo on the right was taken the day after I came off the fast.

Almost as important as the physiological effects of the FMD were the mental effects: I proved to myself that I could endure a days-long fast without dramatically impacting my normal mode of operation. I continued to work and socialize (even sitting with friends as they ate and drank) and even managed to stay somewhat active (Longo recommends avoiding vigorous exercise while on the FMD, a recommendation which I observed). My only challenging day was the second one, when I needed a short nap in the afternoon. But on all the other days I felt energized, clear-headed and devoid of food cravings. Even more than that: I felt in control of my body.

I look at the FMD is another hack, a powerful tool in my arsenal of lifestyle interventions. Prolon FMD makes it easy by delivering all that's needed for a 5-day fast right to my door. It appeals to my experimental mindset, and it makes intuitive sense to me: it's only relatively recently in our history that we humans have enjoyed an abundance of calorie-rich food, which has led to us eating more than our bodies can handle, adding weight, accelerating biological aging and promoting disease.

I plan on completing the recommended protocol, which includes two more 5-day fasts over the next two months. I'll definitely let you know how it turns out!

The human fasting mimicking diet (FMD) program is a plant based diet program designed to attain fasting-like effects while providing micronutrient nourishment (vitamins, minerals, etc.) and minimize the burden of fasting.
— Dr. Valter Longo