Is a five-day fasting program any more efficient than other types of intermittent fasting? We wanted to know whether we had to fast for five full days or could get the same benefits in a shorter period. What happens to your body when you fast? After researching, for fun – and our health - my husband and I survived the five-day fast, and here is what we found out about the optimal length to fast.
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Fasting has been in practice since the dawn of humankind and in all cultures and religions. We don’t hear about it as often now, but perhaps our ancestors were on to something…
In addition to its spiritual benefits, implementing a fasting program into an already-healthy diet has been shown to have a significant effect on our long-term health.
For someone who loves to eat, I wanted to fast for the minimum amount of time and get the most benefits. My parents both died of cancer, so my focus is preventing this awful disease, in particular.
A little starvation can do more for the average sick man than can the best medicines and the best doctors”
– Mark Twain
What are the benefits of fasting?
Forcing your body to cope with the stress of no food, can help our bodies enhance DNA repair, eliminate toxins, increase brain cells, lose fat, reduce inflammation, and combat diabetes, cardiovascular diseases, obesity, cancer, and cognitive impairment.
The benefits, also listed in the image below, have been studied by some of the most trusted researchers today. Of course, many of the fasting studies have been done on mice and other animals – even Labrador retrievers (who lived longer) – but the results have been confirmed on human studies as well. Testing diets is always more difficult to do on humans, but I have learned that putting your body under stress, as in fasting, is something that most of us should do consistently – but with a solid plan.
What is a ‘fast’?
At D2D, we have written about intermittent fasting. This is where you don’t eat for a period of time each day or week to ‘reset’ your body. For instance, you can fast for 14, 16, or 18 hours each day and then only eat during a 10-, 8-, or 6-hour window. Or, once a week, you can fast for 24 hours, for example from dinner to dinner. Maybe you want to do the 5:2 fast, which is fasting for two days each week.
What I wanted to know more specifically is: what happens to my body during the different phases of fasting? And what is the optimal timing to achieve the maximum benefits? Is it 16 or 24 hours? Is it really five days? And…could I do it for five days?
Our 5-day experience
Our son and his fiancé inspired us to try the 5-day fast-mimicking program they do from time to time called Prolon. This specific one was developed by Dr. Valter Longo, professor at USC Davis School of Gerontology, Department of Biological Sciences, and Director of the USC Longevity Institute. For my husband and me, it sounded challenging but appealing because Dr. Longo has carefully researched and constructed a nutritious diet to follow for each of the five days. Dr. Longo was one of the select few awarded a grant from the National Institute on Aging, part of the National Institute of Health, to research fasting, cell regeneration, and disease protection.
Prolon sent us a box of plant-based food so we could dutifully follow the protocol which ‘tricks’ our bodies into thinking we were fasting. This means we ate a modest 1100 calories the first day and then between 700-800 calories on days two to five.
The food consisted of caffeine-free teas, an energy drink, fasting bars, crackers, and soups. For instance, one day we would have a bar for breakfast, watery soup for lunch and watery soup and a bar for dinner. All day, the Prolon directions encouraged us to hydrate and keep our energy up by drinking their glycerin ‘L-Drink’ mixed with the tasty teas.
We did it!
We decided to go from Sunday to Thursday. Honestly, I was nervous as we approached the date. I already do the 15-16 hour fasting and that is pretty easy because I know a good meal is coming that very day. I was curious about how I would do on such limited calories for five days without a real meal in sight. I wanted to make sure I kept my muscles, so I planned on continuing my workouts. Would I have enough energy?
Plus, I was worried about losing too much weight. So I did what most people don’t do — I bulked up beforehand and happily gained three pounds. My sister said that I should be more thoughtful and approach this with peace and mindfulness. She was probably right…my husband just plowed right into this experience without any hesitation or trepidation.
What happened? After seriously overthinking this, basically, we were…fine. We had plenty of energy to work out, we were not tired and while we were hungry, we weren’t “hangry”, so the entire five-day period was only modestly unpleasant. Although, I was very excited to eat a ‘real meal’ on day six!
But the benefits from Prolon are only studied and proven if one does this once a month for three consecutive months. Really? Do I have to do this again? I am wondering if there is a shorter version to gain the same benefits.
Your body’s response to fasting
While there are multiple benefits to intermittent fasting, they can be categorized in three areas: burning fat, increasing brain activity, and preventing disease. How long you fast determines the benefits.
Each cell in your body needs fuel to function. That fuel comes from carbohydrates ranging from fruit to vegetables to grains. After a meal, the glucose from your meal is used for energy and the fat is stored as triglycerides. When you fast, your liver converts fatty acids to ketones, a major source of energy for many of your body’s organs.
According to a study by Mark Mattson, a neuroscientist from Johns Hopkins, who has studied intermittent fasting for 25 years, “more than just burning fat, ketones regulate the expression and activity of many proteins and molecules that are known to influence health and aging.’
Your brain loves ketones. Ketones help generate a hormone called BDNF which strengthen neural connections and promote new nerve cells in the brain for learning and memory. In turn, this may help prevent Alzheimer’s and other neurodegenerative disorders. Clinical trials have shown that caloric restriction improves verbal memory, executive function (memory, flexible thinking, and self-control), and global cognition.
After a period of fasting, your cells go through autophagy. This is a cleanup of waste and damaged components in the cells. During autophagy, your cells repurpose some of the proteins and other cell parts and then direct them to where they are needed. This is where your body begins to flush out cells exhibiting early-stage diseases such as cancers and Alzheimer’s. Exercise also enhances autophagy, and even more so while fasting.
Inspired by Nimsdai Purja, who climbed 14 peaks in an incredible 7 months, we agree that ‘Nothing is Impossible’.
What kind of fast is right for you?
What type you choose depends on your lifestyle, your microbiome, your goals, and your ability to manage hunger. And don’t forget to check with your doctor – mine was a little curious about the five days.
For me, fasting will now become a way of life – and hopefully for my husband. As a result, I have decided to do an 16-18 hour fast each day with a three or four day fast about four times a year. If I am extremely motivated maybe I will do Prolon again. Overall, I think this approach is balanced if my diet remains healthy during my eating periods. I am also pleased to know that while traveling if there are not good food options, I can skip a meal and my brain and body might even thank me.
The key to success is to make sure you eat healthy meals during your non-fasting time. I have heard of some people diving happily and overeating with cheeseburgers, ice cream and beer. Maybe not the best choice on an empty stomach and a ‘refreshed’ body. Instead, lots of vegetables, fruits, healthy fats, whole grains, and proteins are a better bet. And stay away from sugary foods and drinks.
For more detailed information on this here are some credible and helpful resources:
- My brother in law gave us the book “Lifespan” by David Sinclair, Professor of Genetics and co-director of the Paul F. Glenn Center for Biology of Aging Research at Harvard Medical School, which gave us a great understanding of “what happens to our cells when we age and why we don’t have to”.
- Mark Mattson, professor of Neuroscience at Johns Hopkins University School of Medicine.
- Andrew Huberman, neuroscientist and tenured Professor in the Department of Neurobiology at Stanford University School of Medicine, has some great podcasts on the effects of fasting and time-restricted eating on fat loss and health.
- Satchidananda Panda, PhD, a professor at the Salk Institute, La Jolla, California, has researched time-restricted eating in a narrow eating window.
- Chris Kresser, M.S., L.Ac., is an expert, clinician, and educator in the fields of functional medicine and ancestral health explains intermittent fasting with studies as references. He also wrote “The Paleo Cure”.
- Eric Berg, chiropractor, is an educator and has some helpful videos.
The Bottom Line
Fasting seems like a miracle solution to ensuring good health and longevity. Determination is the key to success as being hungry is not easy. However, research shows it burns fat, increases brain activity, and sloughs off the cells that begin disease.