My 5 Days on the Fasting Mimicking Diet
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By Leigh Wagner, PhD, MS, RDN
If you follow me on Instagram, you may have seen that I did my second round on the fasting mimicking diet this past week, after doing it for the first time last November. I gave a few quick glimpses of it in my instagram stories but wanted to do a deeper dive into the program here.
First, I want to give you the background and make it clear this is not a sponsored blog post (#ipaidforthis). I want to share with you the science behind the program, what it is, and who should and shouldn’t follow it.
Three reasons why I did a second round:
I wanted to see what a second round felt like compared to the first one.
I like to try things that I ask clients to try so I have personal experience and empathy for the process.
To be honest, I just turned 35 and I want some of those anti-aging benefits that I’m supposed to get from fasting (fingers crossed).
So, let’s get started.
What is the fasting mimicking diet (FMD)?
Dr. Valter Longo - a PhD researcher at USC who has studied longevity for 30+ years - designed the fasting mimicking diet based on his (and others’) research to provide the benefits of fasting without having to completely stop eating. L-Nutra is the company he started and ProLon is the 5-day (FMD) program he designed, studied and eventually made available to the public. I provide an overview of the diet below.
How was the fasting mimicking diet created?
Dr. Longo (per his book) created the FMD based on 5 pillars of the “Longevity Diet,” which (as far as I can tell) are the dietary principles of the FMD. This is the scientific/evidence-based foundation upon which the FMD stands:
Basic research and juventology, which is the study of what keeps people young.
Epidemiological studies, or studies focused on certain populations of people.
Clinical studies: Studies testing an intervention like a diet or drug to see if it’s safe and effective. This would encompass the lauded “double blind placebo-controlled trial.”
Centenarian studies, which are studies on people who live high quality, high functioning lives until they’re 100 years and older.
In his words, “the study of complex systems.” He describes this as taking an “engineering approach” to characterize how our complex human body (system) can be reduced down to a model to help understand the interactions between food, cellular function/damage, and longevity and aging.
Before I go further, I want to clarify some important groundwork. I like to visualize his work and diet like a pyramid. At the base of the pyramid are these 5 pillars. Out of his in-depth research, he was able to characterize a dietary pattern for longevity. So, atop this 5-pillar foundation are general dietary characteristics of his “longevity diet” (summarized below). Finally, at the peak of the pyramid is the carefully formulated 5-day “fasting mimicking diet” that are the specific foods of his studied “intervention.”
What are the potential benefits of fasting?
The physiological benefits of fasting include anti-aging (and even anti-cancer) activity by turning on a process in the body called “autophagy,” which triggers the body to “clean up.” In this process, our cells remove damaged contents so they can be metabolized and excreted from the body.
Autophagy is a natural way to get pathogens and abnormal contents in cells out of the body. You can find more background on autophagy at PubMed and Healthline. Autophagy provides anti-aging benefits and potentially even some anti-cancer benefits, because when cells act abnormally and replicate in an uncontrolled manner, that’s essentially how cancer develops. Autophagy removes these abnormal or damaged cells before they get out of hand.
So, fasting turns on autophagy and the fasting mimicking diet seeks to engage that process without having to stop eating completely. In short, you still eat food but calories are limited (800-1100 calories per day), and in theory you may still get the benefits of fasting.
Overview of the Longevity Diet Principles and the Fasting Mimicking Diet:
As I mentioned, Dr. Longo based his very specific FMD on the principles of what he calls the “Longevity Diet.” The general gist is that it’s very low protein, high complex carbohydrate, and moderate intake of high quality fats and oils. Here are the basic principles on which he bases the FMD:
Mostly vegan/plant based: High intake of whole grains, vegetables, root vegetables, beans.
Protein sources are mostly plant based: Beans, seeds, nuts, infrequent animal protein, fish or seafood.
Small amounts of fish, seafood and mollusks: These are some of the most nutrient-dense foods on the planet, not to mention they contain essential omega 3 fatty acids that our bodies cannot make, so we have to eat them.
Rarely animal protein/meat and small amounts of dairy: Mostly sheep or goat’s dairy.
Naturally low in saturated fats because you’re eating primarily plants.
Eat like your ancestors when possible.
Unlike his above-described Longevity Diet, which is more of a lifelong eating style that he suggests most people adopt most of the time, the fasting mimicking diet is a very specific, calculated 5-day program (a kit of packaged food) that emulates the principles of his Longevity Diet above. You can get more details in his book, but I’ll give an overview of his 5-day FMD here:
Day 1 (transition day): About half the food is complex carbohydrates and healthy fats (remember, low protein) in the form of packaged bars, soups and olives. You take a couple supplements (omega 3 and multivitamin). You have a few options for tea and can drink as much water as you want.
Days 2-5 (noticeably less food): The same balance of complex carbs and fats and tea or water to drink. These 4 days you also drink a glycerol concentrate combined with water. In an interview with Dr. Longo, he explained the inclusion of glycerol was due to their discovery that glycerol is elevated in the body during fasting, and he also suspects glycerol may have to do with why the body doesn’t breakdown muscle during fasting.
Can I create my own DIY fasting mimicking diet?
Dr. Longo summarizes the general principles of the FMD in his book but encourages people to use his specific diet. I’m sure that’s partially because he designed his exact plan very intentionally to meet his guidelines and also because – at least in part – money, right?
So, yes, you could make a calorie-restricted, plant based, very low protein, high quality fat diet that you follow for five days. You can actually get a free copy of his book to see what his guidelines are for this and create recipes based on that.
Who might benefit from FMD?
First off, I want to advise that if you’re considering the FMD or any other version of fasting, you should consult with your healthcare provider(s) to ensure you’re healthy enough to do so. Ok, so Dr. Longo would likely suggest that most of us could benefit from some form of fasting and certainly the FMD. I would agree that most of us would do well to give our bodies a break through FMD or a monitored fast.
I love that, historically, fasting has been a part of many religions and cultures. Also, humans have naturally gone through seasons of plentiful food (i.e. fall harvest) and famine (late winter). Our bodies have adapted to these seasonal variations in food intake.
For my clients, some of the best results have come from clients who have cardiometabolic (pre-diabetic and/or cardiovascular) disease risk factors. It is also easy because the program is clear and simple; everything you need is in a box. I know Dr. Longo is working on finalizing FMDs specifically for autoimmune disease and other conditions, but those aren’t yet available. I’ll be curious to test them when they are released.
My own experience with the FMD
Read on below for a bit about my own experience with FMD, what the food is like, how I felt, and all those soups.
Fasting Mimicking: Days 1-3
The food and drink: It’s prepackaged food, but for prepackaged food, it’s pretty good. For breakfast you eat a nut/granola-type bar, which is small but good.
Lunch and dinners are always soups and sometimes olives and/or flax crackers. At the end of a couple days you get some kind of weird chocolate thing with inulin in it, which I called the “fart bar.” The inulin is a prebiotic (fiber), which keeps the digestive tract moving along, but bloated me something fierce.
On days 2-5, you start drinking the proprietary glycerol concentrate with water. I put mine in the bottle they provided and added the bags of hibiscus tea to steep throughout the day. I found an interview with Dr. Longo where he says that the glycerol (which is the backbone of triglycerides - a type of fat) is elevated in people who are fasting and may be the reason that muscle is spared (very little to no muscle loss) during periodic fasting.
Supplements: They give you an omega 3 algae supplement and a multivitamin, which were fine, although I wouldn’t have put folic acid in the multi, but that’s a blog post for another day
Energy/hunger: The first time I did this last November (2018), I felt fine, at least on days 1-4. I couldn’t believe how well I transitioned into the fast. I didn’t notice any blood sugar crashes or hangry moments.
This second round, I had more headaches because I stopped caffeine (coffee), after day 1 because caffeine can kick you out of fasting. By days 4 and 5, I was clear headed and felt really good.
Mindset/food obsession: The first time around, I was really busy on days 1 and 2. I saw clients all day each day and had some evening activities, so I didn’t have much time to think about it, which helped. The second time, I made more intentional effort to keep busy and check a few things off my to-do list I had been putting off. I also asked for some personal cheerleading from friends.
One other random thing: I had some really vivid dreams and slept very deeply for the first 3 nights.
Fasting Mimicking: Days 4-5
The food/drink/supplements: Same bars, soup, crackers/olives. Some of these meals are even more sparse (just soup), and I would eat like small spoonfuls to draw out the meal longer than 90 seconds. The first round, I enjoyed the food. Round 2, I couldn’t look at another spoonful of soup. Maybe the novelty wore off?
Hunger: Round 1 (last fall): I found myself talking a lot about food by this point. Upon reflection, it was interesting because I hadn’t been that obsessed with food since I was deep in my disordered eating. My husband, Rob, would tell you that I was talking about food a lot. Round 2 (last week): I was okay, but more just wanting to quit and eat real food. I didn’t feel like I was obsessing about food the way I was during round 1.
Both rounds I was ready to quit on Day 4. I’m laughing because both times I was texting with my friend and colleague Amy who’s done FMD and had a good experience (herself and with her clients). I told her that I was going to quit and would maybe finish a day early. She encouraged me to keep going. She reminded me that the program was designed to mimic fasting and was an evidence-based approach to facilitate autophagy, which is basically the body cleaning up dead cells. She also reminded me that I’ve done other harder things in my life. So, thanks to Amy, I made it through day 5.
Energy/temperature: The fifth and final day, I remember wearing an extra layer of clothes because I was cold during round 1 (during the fall/winter). And I cut my typical walking route with my dog short because I didn’t have the energy.
Round 2, it was a hot week in September, so I haven’t noticed temp changes as much as last fall.
Day 6 “Refeeding” Day: They tell you to start by drinking liquids like broths and juices, which went well. Round 1: I tried some sweet potato and venison chili Rob had made a couple days before for lunch, and had a teeny bit of gurgling in my stomach, which was likely it waking up after several days. That evening I had some scallops and steamed broccoli and a glass of wine, which went straight to my head.
I was pleasantly surprised that my body adapted back to food so smoothly. I think one key is taking the morning slowly and not eating large amounts of foods or anything out of your typical norm of eating.
Round 2: I started transitioning a little bit on 5 day evening so that I would be able to eat mostly normally on Saturday. I’d say overall round 2 felt harder in some ways (sick of the food) and easier in other ways (kept myself busy and benefited from feeling clear headed and energized).
Final note: you must tolerate/like olives to do this. If you hate olives, you’ll likely be miserable because you eat them 4 out of the 5 days and sometimes twice a day!
Would I recommend the FMD?
Although I have done this two times and would likely do it again, maybe because I’m vain and want my skin to glow, and also because I want to live longer than my grandparents, I don’t think the fasting mimicking diet is for everyone.
Some things to remember:
First, please make sure you have a healthy relationship with food if you are going to try the diet.
Next, in terms of restrictions, this program should not be followed if you are pregnant, underweight, have low blood pressure, are generally “fragile” (Longo’s word), have diseases and/or are taking medications without first consulting with your doctor, people with diseases that inhibit their ability to make glucose (sugar) from protein, and athletes who are intensely training.
Dr. Longo gives other warnings, but the best approach would be to work with a healthcare provider who is well-versed in the risks and benefits of the program.
If you are already restricting caloric intake, then this may not provide the same benefits as someone who is eating a generally well-nourished, adequate caloric diet and then follows the FMD for only 5 days.
What the FMD is missing
As you can tell by its description, this is not a personalized nutrition program. If you’ve heard me speak, read my writing or followed me on instagram you know how important it is to get personalized nutrition advice. This program is a whole foods, evidence-based approach to fasting, but this boxed program is not able assess you and your individual needs. Remember, every single one of us has unique needs, not just at the biochemical or nutrient level but also from the perspective of our lifestyle, family and medical histories, emotional and mental health, cooking skill level, disease risk, metabolic health, genetics, financial health, stress, motivation, environmental and community support. The combination of all of these different needs within each individual make things a little more complex than a 5-day box of bars, packets of soup and a proprietary glycerol drink. Our nutritional needs are much more nuanced than that.
This program can never substitute for establishing a good relationship with a health care provider who can look at you, hear your story, assess your symptoms, measure your laboratory values and care about your wellbeing. As always, if you’re interested in working with me and live in the United States, you can request a discovery call.
What have been your experiences with the FMD or what questions do you have?