This is a blog post by Dr. Don Brown.

Last year, LifeOmic employees (the creators of your LIFE apps!) tried the ProLon five-day modified fast for metabolic health. This year, our CEO Dr. Don Brown tried another five-day fast using a few new strategies that he found worked best for him. Read on to learn more about the rationale behind multi-day fasting and what you can expect if you try a prolonged fast yourself! Don is an experienced intermittent faster and often fasts for 24-48 hours and longer. Talk to your physician and practice shorter fasts before trying a multi-day fast.

Why Try Multi-Day Fasting?

I stumbled upon the scientific basis for intermittent fasting about three years ago, while I was finishing up a graduate degree in biotechnology at Johns Hopkins University. I’ve long been familiar with the purported benefits of caloric restriction, which basically means living on about 1,200 calories a day for life. But I knew that was something I could never do. I was tremendously excited to come across a paper by Valter Longo strongly suggesting that even greater benefits could be realized by simply fasting a few hours several times per week. Now, that was something I could actually see myself doing!

I quickly began to fast for sixteen hours most days (from dinner at 6 pm until breakfast around 10 am). I found that it got easier and easier with time. Soon, I was doing a 24-hour fast once a week fairly comfortably.

Over the course of the first few months of my intermittent fasting practice, my weight dropped without effort back to where it was when I graduated from high school and all of my biomarkers (fasting glucose, cholesterol, c-reactive protein, etc.) moved in the right direction. My doctor was stunned at my annual physical to see that my fasting insulin level had fallen to 2, indicating that my body was exquisitely sensitive to insulin and needed very little of the stuff to do the job.

Still, it gnawed at me that I might be missing out on some of the benefits of longer fasting periods. The original Longo paper that had kicked off my interest in fasting indicated that going 3-4 days with minimal calories caused the body to break down old white (immune) cells in droves and replace them with brand new ones.

An Immune Regeneration

A common problem during aging is that the immune system becomes overly inflammatory – ready to send in the army at the first sign of trouble. White cells fall into two major categories – myeloid and lymphoid. The myeloid is the “old school” branch. Myeloid immune cells, including macrophages and neutrophils, have sort of a scorched earth mentality. They literally eat up invading bacteria as well as body cells that have been infected by viruses or that have been otherwise damaged. The lymphoid branch of immune cells is more sophisticated. If the myeloid cells are poorly trained infantrymen with a hair trigger, lymphoid cells are special forces – much more discriminating and highly trained.

When we’re young, our bodies have essentially a 50/50 mix of myeloid and lymphoid white cells. As we age, however, this balance falls out of whack – with the myeloid cells becoming dominant. This leads to a condition commonly called “inflammaging” – an overall increase in inflammation throughout the body as we get older. This greatly increases the chances of developing autoimmune disorders like lupus, rheumatoid arthritis and many others.

The fascinating thing is that fasting might be able to reverse that aging-induced imbalance between the myeloid cells and the lymphoid cells.

Valter Longo was one of the first researchers to show this impact of fasting in humans. But when he first tried to line up human volunteers to test the effect of a complete five-day fast on the immune system, he found that there were few takers. Perhaps people couldn’t fathom eating nothing for five days. He began to wonder if he could do better by pitching the intervention as a five-day “special diet” rather than a fast. This led him to develop what he now refers to as a “fasting mimicking diet” or FMD. He even started a company called Prolon to sell a packaged five-day FMD kit. The kit provides around 800 calories per day in the form of three tiny meals for each of the five days of the plan.

Overall, the FMD is mostly fat with a small amount of carbs and protein. This is because fasting moves the body into a fat-burning mode called ketosis. Longo found that his plan had an overall effect very similar to complete fasting, but was much easier to pitch to prospective participants in clinical trials and was easier for people to actually adhere to.

Fitting a Five Day Fast To Your Lifestyle

In the spring of 2019, most of the employees at our company voluntarily spent a week doing the Prolon “modified fast”. It was tough but most of us made it through with no ill effects. I personally felt incredible after completing it and resolved to do a similar five-day fast a couple of times every year. As 2020 rolled around, I began to plan my first attempt, wanting to get it out of the way in the first quarter of the new year. I finally picked the last week in January when I had no business meals planned and no conflicting personal obligations.

In biting off something as difficult as a five-day fast, it’s important to recognize your own limitations and to work around them. I live in a large house on a mountain in Park City, Utah and am fortunate to currently have three of my children, their significant others and my grand-daughter living with me. It’s a wonderfully chaotic environment with all sorts of great food around. For that reason, I thought it might be best to go away for a week to a place where I could more easily control what was around in order to minimize temptation. And although I love winter and the snow, I thought it would be a great time to spend a week at the beach. So I made plans to head off to Cabo San Lucas at the tip of the Baja peninsula in Mexico for a few days of sun and controlled starvation.

I resolved to start my fast on Sunday after dinner and break it with dinner on Friday night. I ate more or less normally all day on Sunday and finished with a homemade pizza for dinner, washed down with a nice India Pale Ale. It was 6:20 pm and I wouldn’t eat another real meal for the next 120 hours.

Five Days of Fasting – Hydrate and Enjoy Some Plant Fats

I got up Monday morning and recorded my weight – 156.0 pounds. I went into our office in Salt Lake City for our Monday roundtable where we do a videoconference with all 80 of our employees scattered around the US. After that, I stopped into a local climbing gym and bouldered for a couple of hours, getting a nice workout and ripping my hands up a bit. I didn’t even think much about the fast until after dinnertime.

I had decided to create my own “fasting-mimicking diet” this time rather than pay for the Prolon meal kit. So about 8 pm, I put a couple of cups of mixed greens in a bowl and sprinkled on a tablespoon of olive oil and some salt. I threw in a half-dozen almonds and ate my delicious “dinner” – about 250 calories altogether. Although it was far from satisfying, it took the edge off of the hunger and I was able to sleep fairly well Monday night.

On modified multi-day fasts, it won’t hinder your progress or kick you out of ketosis if you enjoy under around 500 calories of low-carbohydrate foods. Having some salt content in these fasting “meals” can also help you maintain your electrolyte balance during a long fast, which is very important. Focus on eating healthy sources of fat without a lot of protein during a modified fast.

Don’s daily fasting meal.

On Tuesday, I got up, had some black coffee and then flew off to Cabo where I would be staying until Friday in a house on the beach.

When I got in, I stopped at the grocery store and bought a large bag of mixed greens and a case of La Croix mineral water. After a two-hour walk along the beach, I took a bath and had the same dinner – mixed greens, tablespoon of olive oil, and a few almonds. I got to sleep just fine and actually spent a pretty restful night.

Don’s fasting arc in the LIFE Extend app.

When I weighed myself on Wednesday, I was surprised to see that I had already dropped three pounds. I spent the day catching up on email and doing some light reading. I found myself frequently calculating how many hours remained until Friday night and thinking about how I would break my fast. But I had another wonderful 2-hour walk in the sand along the Cabo beach and basked in the abundant Baja sunshine. The vitamin D my body was making seemed to help overcome the hunger pangs. But my evening salad felt even less satisfying than before and I had trouble getting to sleep. Going to bed hungry is the worst part of multi-day fasts. I find that the days go by pretty easily but getting to sleep with a growling stomach is no fun.

By Wednesday night, my resolve was starting to crumble and I increasingly found it necessary to negotiate with myself. As I lay in bed thinking about how badly I wanted to eat, I made the following deal. Get through the third night and next day. If things were really bad, I would cut the fast short at 96 hours and have a great meal at a nearby Mexican restaurant that I love. I mean, 96 hours is nothing to sneeze at, right?

It’s important to listen to your body during a long fast. A little bit of hunger that you can mentally work through is ok, but you shouldn’t deal with feeling dizzy or faint. It’s ok to end your fast before your desired goal! You’ve still earned a ton of health benefits in the form of autophagy (cellular recycling), gut rest and bringing your blood glucose levels down.

That bargain helped me resist breaking my fast Wednesday night. I woke up feeling good on Thursday and quickly got out into the sunshine. I felt wonderful after a long walk on the beach and slowly made up my mind that I could make it through another night. However, I found it helpful to make a new bargain with myself. If I could continue the fast through Thursday night, I would allow myself to break a few hours early by going to a great little local taqueria for lunch on Friday. That would give me a total fast of about 114 hours.

I’ll admit that Thursday night was tough. My little salad seemed to do more harm than good, making me even hungrier. Although my cravings tapered just a bit during the evening, I found it very difficult to get to sleep.

Having trouble sleeping while fasting? Be sure to monitor your blood sugar and ketone levels to make sure they stay in a healthy range. You can also try these sleep tips!

When I woke on Friday, the Cabo sun was streaming into the window and I smiled at the thought of being able to eat in a few hours. After a couple of cups of black coffee, I found that I was feeling great and not the least bit hungry. I dragged a yoga mat into the sun and spent a good hour stretching, doing some planks and working through a nice yoga lesson using the Alo Moves app. I had to head to the airport by 1 pm for the flight back to Utah, so if I was going to have lunch at the taqueria, I had to leave the house by 11:30 am to go to the restaurant. As I lay in the sun, I began to think that I might go for one last walk along the beach instead. I had come this far, why not make it for the full 120 hours?

After much mental debate, that’s what I did. I put in some earbuds, played Bombino’s ethereal Agadez album, and walked along the beach watching whales breach in the Pacific Ocean. I became acutely aware that I was experiencing a “ketone high”. I knew that my body was tearing down fat like crazy, breaking fatty acids out of their triglyceride containers and pumping them into the blood stream. Cells all over the body were absorbing the fatty acids from the blood and then burning them cleanly and efficiently in their mitochondria. And since fatty acids don’t easily penetrate the blood-brain barrier, the liver was taking in some, chopping them up into smaller fragments called ketones, and then pumping them back into the blood where they could flow easily into the brain.

Learn more about intermittent fasting, ketosis and ketones in this fasting mini-course.

It used to be thought that neurons could only use sugar (glucose) for energy, but now we know that the brain absolutely loves ketones. It can burn those even more efficiently than sugar. High ketone levels may even prompt the brain to produce a growth factor called BDNF that spurs the generation of new neurons and the formation of new connections between neurons called synapses. But at a subjective level, all I knew was that I felt a tremendous sense of calm and well-being. My brain seemed to be operating in a higher gear that I hadn’t even known was there. I spent an hour pushing through the heavy sand and luxuriating in the way my calves and other muscles reacted to it. I knew that I was ready to see this thing all the way through to the end.

Don’s fasting arc in the LIFE Extend app.

And so I boarded the flight from Cabo back to Utah at about the 116 hour mark in my fasting odyssey. Even the half-hour delay on the tarmac failed to upset my serenity. I had come to enjoy the growls in my stomach, knowing that the ghrelin (a hunger hormone) causing the sensation was sending a signal throughout my body to promote autophagy – a cellular recycling program that is better than any drug you can possibly buy.

I closed my eyes and tried to imagine my cells breaking down old proteins and tagging raggedy mitochondria for destruction. I could almost feel the fat cells around my body being depleted of their stored energy. My bone marrow seemed to hum from the effort of building millions of new immune cells while my spleen and other organs were breaking down old white (immune) cells, especially the highly inflammatory myeloid ones.

As the flight took off and made it up the peninsula back toward the snow-covered mountains of the mountain West, I felt a deep peace as well as strong sense of satisfaction at having accomplished such a difficult task. When the flight landed in Salt Lake City, I got in my car and made a beeline to an Indian restaurant, placing an order on the way. I picked up the fragrant mixture of vegetable Pakora, chicken Biryani, aloo saag and garlic Naan, put it in my car and drove home. Strangely, I didn’t even feel tempted to nibble any on the way. I got home, texted the kids about the culinary bounty I was bringing, and went inside.

Enjoy Your Food!

As I broke my fast about two hours later than planned, I remembered what a joy it is to eat. Rather than quickly stuff myself, I savored every bite and ate more slowly than usual. I could almost sense the relief my body felt as cells relaxed from their starvation mode and realized that it was now time to rebuild. Stem cells were already kicking into gear and synthesizing the new proteins that would allow them to divide in a few hours. My liver was storing glycogen to be used the next time I went more than eight hours or so between meals.

I had dropped almost 9 pounds over the course of the five-day fast. I knew that only about three pounds of that total was fat and the rest was water, but that was OK. A multi-day fast is a great way to spark some weight loss, but that wasn’t the main motivation for me. My hope is that doing these five-day fasts a couple of times a year will help kill off some senescent cells, rebalance my immune system and reduce my risk of cancer, diabetes and especially the awful neurodegenerative diseases like Alzheimer’s and Parkinson’s. These diseases are increasingly linked to overall inflammation as well as intracellular accumulation of misfolded proteins.

Don at the beach.

Going without food for prolonged periods of time isn’t easy nor is it fun. However, it definitely provides a sense of control. It’s pretty mind-boggling to realize that you can go multiple days without food and that you’re capable of tuning out the screams coming from your stomach. I’m convinced that over-nutrition is the biggest danger to our health in the modern world, and that intermittent fasting can activate an ancient program of turnover and renewal that is sitting there available to all of us.

Intermittent fasting can be a great health practice. It is also a luxury to be able to access food when we want it. If you have ever suffered from an eating disorder or from food insecurity, prolonged fasting is not recommended for you. Focus on strategies that can help you access and consume healthy foods on a regular basis.