Fasting, Longevity, and the ProLon 5-day Fasting Mimicking Diet

After completing two rounds of the ProLon Fasting Mimicking Diet, I chronicled my experiences on Instagram (here, here, and here, also on YouTube). In the videos, I also shared the results of my research of the benefits (and potential drawbacks) of fasting, as it's become somewhat of a health trend, especially in the "biohacking" space. (In other words, manipulating your environment to enhance your biology.)


In this post, I've consolidated everything I've shared on fasting, including at the end of the post, my thoughts on how you can receive some of the biggest benefits of fasting with the least amount of restriction or inconvenience. As with most health trends, for the majority of people, I advocate at least starting with the more doable, sustainable, and often safer approach. While short periods of really targeted focus or intention can help jumpstart healthier habits, remember that it's what you do "most of the time" over time that makes the biggest difference!


If you've been curious about or have tried fasting, I'd love to hear from you!


*Please note that if you are interested in doing ProLon yourself, you can get $20 off your purchase using my discount code. Additionally, I do offer health coaching sessions to help you prepare for + get the most out of your experience, so feel free to email me at liz@lizbarnet.com to discuss.

What is fasting + why is it practiced?


The term "fasting" generally refers to restricting or refraining from food (and therefore calories) for a period of time. Although fasting has become somewhat of a health trend, it's certainly not a new practice.


Humans have fasted for literally millions of years, for both voluntary + involuntary reasons. Many religions + cultural practices include fasting, such as during the Christian lenten season, Jewish Yom Kippur, and Muslim Ramadan. Medically, patients are often advised to fast before blood work or surgery.


In fact, until very recently in human history, we did not have constant access to such an abundant amount of both natural + processed food. (For many people, food scarcity is still a very real concern, including in the United States.)


Of course, fasting can been used negatively as a tool for deprivation or punishment, inflicted upon others (see also: the cult NXIVM) or upon oneself, as in the case of eating disorders. (Please note: If you have a history of eating disorders or disordered eating, fasting is probably not for you; please consult with a medical or mental health provider before exploring fasting, even for health purposes.)


But only recently has fasting more mainstream in the world of "health + wellness" (which arguably positions itself as the more holistic, self-care focused version of "diet + weight loss"). Historically, popular diet culture (as well as the oft-cited law of thermodynamics) dictated that one must reduce caloric intake in order to lose weight (meaning body fat); we've forever been advised to eat small meals, more frequently, presumably in an attempt to keep hunger at bay + maintain balanced blood sugar. (Spoiler alert: for most people, this actually achieves the opposite, undesired effect of increasing hunger + deranging blood sugar.) We've been berated into eating every 2-4 hours like clockwork, lest we risk "slowing down our metabolism" (another myth for another day). Similarly, we're assured that breakfast* is the absolute most important meal of the day, and should be consumed immediately upon waking - or else we destine ourselves to a live of being hungry + fat. (*Of course, the term "breakfast" quite literally means to "break the overnight fast," when we somehow survive without eating for 8 hours, give or take. Personally, I do think believe how one approaches breakfast helps set the tone for the day, but that every person is unique in what will work best for them.)


So if not for weight maintenance or reduction purposes, why fast?

Research on the Health Benefits of Fasting


Dr. Valter Longo PhD is a professor of gerontology (the study of aging) + biological sciences and the Director of the Longevity Institute at the University of Southern California, one of the leading centers for research on aging + age-related diseases. Longo is something of a "fasting guru" and is a frequent podcast guest + documentary expert on the topic. (Google his name + "fasting" to access a number of compelling research papers; if you want to understand the details of the science, but don't have much experience or interest in weeding through the detailed results, I highly recommend his book The Longevity Diet. It's a very digestible - pun intended - read summarizing his research + recommendations on fasting, as well why he advocates following a Mediterranean Diet-type style of eating.)


To summarize the research I have done on fasting, a good portion of which is produced by Dr. Longo, the potential benefits of fasting focus on the concept of cellular autophagy, or what Longo colloquializes as "cellular rejuvenation." According to Healthline:

"Auto" means self and “phagy” means eat. So the literal meaning of autophagy is “self-eating”...

Autophagy is an evolutionary self-preservation mechanism through which the body can remove the

dysfunctional cells and recycle parts of them toward cellular repair and cleaning..."

In short, cell become damaged over time; an excess of damaged cells can be very problematic, contributing to aging + diseases, and so occasional "cellular cleanups" could be beneficial to longevity.


Fasting promotes cellular autophagy, therefore supporting:

  • blood sugar regulation

  • weight maintenance + body composition improvements

  • chronic disease treatment + prevention, including diabetes, heart disease, cancer, Alzheimer's + neurodegenerative diseases and inflammatory + autoimmune diseases

I talk more about the science + benefits of fasting in this video:

Fasting has the potential to be beneficial for other reasons - but also runs the risk of backfiring:

  • Fasting is a hormetic stressor, which refers to the idea that "that which doesn't kill us, makes us stronger." Occasional, properly dosed bouts of stress teach the body to be resilient. Other popular examples of applying intentional hormetic stress include infrared saunas, ice baths, and intense breath work. (Of course, a lot of the benefits of hormesis occur during the "recovery" period, which is why chronic calorie restriction is not advised. This is also why I advise clients to plan accordingly when possible, and not add stress on top of stress. For example, if you are chronically sleep deprived, intermittent fasting + high-intensity interval training = a very, very bad idea.)

  • Fasting means we are consuming fewer or no calories, which hypothetically allows the body to tap into it's stored form of calories: body fat. If you have a goal of improving your body composition by reducing your body fat, strategic fasting could be helpful; in the case of daily intermittent fasting, it could help reduce your overall daily calories. (On the flip side, if skipping breakfast means you overcompensate later, but in a shorter window, you're sort of missing the point. Additionally, chronic calorie deprivation can lead to a loss of lean muscle mass, which is not helpful for metabolism, longevity, or simply, achieving a "toned" appearance.)

  • It's sort of obvious, but if you are eating less overall, you may have a better chance of limiting or avoiding consuming unhealthy foods. (Unless, of course, you are someone who worships at the alter of a macronutrient-focused diet plan such as IIFYM - literally, "if it fits your macros" - and only care about overall caloric intake + macronutrient distribution. No surprise here, I advocate prioritizing nutrient-dense foods first, and then leaving room for occasional thoughtful, indulgences.)

Popular Fasting Strategies

There are as many fasting strategies as there are purported benefits. Commonly practiced styles of fasting include:


Intermittent fasting, also known as "intermittent energy restriction" or "IF," is somewhat of an umbrella term for following particular schedules of eating vs. non-eating, generally that are for shorter periods of time (hours vs. days).


Two popular formats of IF are: alternate-day fasting + daily time-restricted feeding.

  • Alternate day fasting also has a number of established variations, but generally includes alternating between days of "normal" caloric intake + low or no calories. (e.g. the 5:2 diet, where 2 days a week one is limited to just 500 calories.)

  • Daily Time-Restricted Feeding features a daily "compressed" eating window; in other words, each day you would restrict when you begin + finish eating. A popular version is the 16:8 diet, where you fast for 16 hours (so overnight and for whatever relevant waking period), and only eat during an 8 hour window (e.g. 10am-6pm). From a practical perspective, daily time-restricted feeding (depending on the number of fasting hours" is arguably the more "doable" version of IF - depending on how you do it. Personally, I think this variation has tremendous potential benefits for weight maintenance, general health + longevity, which later in this post I will discuss how to practically apply.

Quite literally by definition, intermittent fasting should mean occurring at irregular intervals + not repeatedly; of course as often occurs in health + wellness, people make up their own rules as they go along, and IF is sometimes practiced very regularly (as in daily time-restricted feeding). Here's an IG post I did on Intermittent Fasting for more of my thoughts on the topic.


Compared to intermittent fasting, prolonged fasting is a period of calorie reduction or restriction generally lasting more than 48 consecutive hours. The only specific format of prolonged fasting that I will discuss (and that in good conscience, the only one I would recommend), is ProLon, the 5-day Fasting Mimicking Diet developed by Valter Longo.

ProLon 5-Day Fasting Mimicking Diet

Dr. Longo develop a program known as the "fasting mimicking diet," and a product called ProLon. (Pro...Long...Prolonged... get it?!) With a fasting mimicking diet (FMD), you consume significantly fewer (but not zero) calories for an extended period of time; because you do consume some food + specially formulated supplements, it is arguably safer + more manageable.


ProLon is formulated as a 5-day restricted calorie diet, with Day 1 including approximately 1100 calories, and days 2-5 including 700 calories; the program includes nut-based bars, olives, soups + teas which provide nutrients. All items are gluten-free + dairy-free. The idea is that you can experience the benefits of fasting, while still eating (some) food. Another important distinction between ProLon and fasting that just focuses on calorie restriction is that ProLon is intentionally very low protein - 15g per day only on days 2-5. Without looking at the research, this might be confusing; isn't protein good for us? Doesn't it help build muscle, boost our metabolism, and satiate our hunger? In short, yes. But protein also activates a particularly pathway called MTOR, and the short + sweet explanation is that MTOR promotes growth + aging, and is connected to certain diseases such as cancer + neurological diseases. While there's no way to avoid MTOR completely (nor should you try to), the idea is that with periodic protein fasting, your body gets a break from MTOR.


According to Longo's research, 3 consecutive monthly cycles of the 5-day fasting mimicking diet (FMD) resulted in:


"...reduced body weight, trunk, and total body fat; lowered blood pressure; and decreased insulin-like growth factor 1 (IGF-1). No serious adverse effects were reported...[B]ody mass index, blood pressure, fasting glucose, IGF-1, triglycerides, total and low-density lipoprotein cholesterol, and C-reactive protein were more beneficially affected in participants at risk for disease than in subjects who were not at risk. Thus, cycles of a 5-day FMD are safe, feasible, and effective in reducing markers/risk factors for aging and age-related diseases."


In terms of long term health, that's pretty compelling stuff!


To summarize, here are what I find to be the unique differences between ProLon and other fasting protocols:

  • Takes advantages of benefits of prolonged fasting (mainly, cellular autophagy), but without as many risks or consequences (since you are eating some food + taking in supplements to prevent deficiencies).

  • Food is provided (so you don't have to think about it) + specially formulated based on scientific research

  • Developed with intentional fasting from protein (to enhance benefits)

  • ProLon offers support via online resources + health coaching

That said, it's not cheap! A single 5-day ProLon program is $249; if you purchase multiple kits, there are incentive discounts. Additionally ambassadors (such as myself) may have additional discount opportunities.


*Please note that if you are interested in doing ProLon yourself, you can get $20 off your purchase using my discount code. Additionally, I do offer health coaching sessions to help you prepare for + get the most out of your experience, so feel free to email me at liz@lizbarnet.com to discuss.


If you want to find out more about what to expect while on ProLon, check out my video recap:

Health-Related Risks of Fasting


Pretty much nothing in life is without risks. But for the majority of generally healthy individuals, the physical risks associated with strategically planned short-term fasting are minimal:

  • dizziness

  • headaches

  • low blood sugar/hunger

  • weakness

  • fatigue

  • irritability

Keep in mind that for most of human history, we did not have the luxury (or perhaps burden) of eating every few hours; it's completely "normal" to abstain from food. That said, if you are used to eating a particular range of calories (especially from carbohydrates), at a certain frequency, it's not surprising you might experience such symptoms. I would highly suggest making sure you are staying hydrated with water + herbal tea, and avoiding too much caffeine while fasting.


*If you have one of the following conditions or concerns, you should not pursue any form of fasting without first consulting a healthcare professional:

  • diabetes: blood sugar should be watched carefully + medications adjusted appropriately

  • hypoglycemia

  • neurological issues related to dizziness, loss of balance, or fainting

  • low blood pressure or heart rate: as fasting can further lower

  • electrolyte imbalance concerns: from medications such as those for blood pressure or heart disease

  • history of eating disorder or disordered eating

Keep in mind that just because some fasting might be good, that doesn't mean more fasting is better. Even Longo asserts that chronic severe caloric restriction is not a good idea, despite whatever the laboratory research suggests in terms of cellular health. (That doesn't mean, however, that chronic caloric overconsumption is beneficial - especially when paired with inactivity.) In fact, although Longo recommends a relatively lower protein - particularly from animal sources - diet, after age 65, his recommendations change to a higher protein diet, especially from well-sourced animals. That's because as we get older, the consequences of age-related sarcopenia (loss of muscle mass + function) outweigh the supposed risks of consuming animal protein.

If you are interested in learning more about Longo's approach to how to eat "most of the time," check out his book The Longevity Diet, summarized here.

Strategic, Sustainable Fasting Solutions

If I've learned anything over my 12+ years as a health coach, is that people say they just want to be told what to do. (Of course, they don't always like what they hear..) Additionally, many people gravitate toward more seemingly extreme practices, as they ping pong their way from being "perfectly good" to "hopelessly bad" - as in, "oh what the hell, I had 1 slice of pizza so I might as well finish all the cookies + ice cream in the house."


If that's you, please take note: fasting might not be for you. It's not a quick fix, magic bullet, or band-aid for your behavioral sins. It can be a very powerful tool for improving health, no doubt - but it's not for everyone. That said, here are a few fasting-inspired strategies I think most people can benefit from:

  • Limit your daily eating window to between 8-12 hours; 10-12 hours is very doable + still incredibly beneficial. Research suggestions even the more generous eating windows can support blood sugar regulation, improve digestion, and reduce overall caloric intake when followed properly. (In other words, no binging to "make up" for time fasting.)

  • Aim for your "fast" to occur while you sleep, which should be an easy way to accumulate at least 8 hours of fasting. As if you needed more reason to prioritize getting good quality sleep: studies show that sleep deprivation can lead to an average daily additional calorie intake of almost 400 calories; if for no other reason, common sense would dictate that the more hours you spend awake, the more opportunity you have to eat! Additionally, the brain tends to crave carbohydrates for fuel, which might explain less-than-healthy late night snacking.

  • Try to eat your last meal as early as possible, and make it as light as possible. While delaying or skipping breakfast is popular, I think this can backfire for several reasons. Anecdotally, people who skip breakfast tends to overcompensate later; as the day goes on and we get more busier + more fatigued, it's difficult to make "good decisions" - especially if we're "hangry." Additionally, our digestion slows down as the day goes on; eating a heavy meal close to what should be bedtime can lead to indigestion or other digestive distress. When we're sleeping, our body has a lot of repair work to do, and digestion shouldn't interfere.

  • Eat "reverse vegan-until-dinner." If you are interested in reducing your animal protein intake for one reason or the other, you may have heard of the "vegan until dinner" movement, popularized by food writer Mark Bittman. It's pretty self-explanatory: no animal protein until your last meal of the day. However, one of the benefits of animal protein is it's satiety factor; unlike foods like processed carbohydrates, there's an inherent limit to how much animal protein is appetizing. (My husband may disagree, but that's another story...) By making dinner vegan, you can take advantage of the positive effects of animal protein during the day, while reducing your overall animal protein consumption and potentially improving your evening digestion. (Additionally, if the idea of dinner being a big piece of meat, a starch, and a vegetable is ingrained into your psyche, this provide a nice challenge to your habits.)

  • Eat a little more on the days you are more active, and less the days you are more sedentary. Food really is fuel, and on the days you are especially active, you might notice that you're more hungry. On the flip side, if you are more sedentary some days, you don't necessary need as much food. (And if you are generally very sedentary and would like to lose body fat, you may want to consider lowering your overall intake incrementally.)

If you are interested in optimizing your health, there are additional strategies you could employ; the key is to do so occasionally, and not chronically:

  • Calorie cycling: This is more extreme version of the last general population bullet point, and a less structured variation of alternate day fasting. If you find yourself with a lazy Sunday on your hands, perhaps skip dinner or try to reduce your overall intake so your body can tap into it's fat stores.

  • Carb cycling: This is similar to calorie cycling (and may occur simultaneously), but applied to the macronutrient carbohydrate. If you are very sedentary + want to lose body fat, there is plenty of research supporting the benefits of a lower carbohydrate diet, especially in terms of satiety (as fat _ protein are more satiating). Additionally, by reducing your carbohydrate intake, your body will eventually utilize fat as a fuel source. Generally, you would want to increase your carbohydrate intake on active days, and reduce it on more sedentary days. Additionally make sure your carbohydrate sources are primarily from whole foods sources such as starchy vegetables, legumes, fruit, and whole grains. It's beneficial to time your carbohydrate intake intentionally post-exercise, as your body should use that to replace diminished glycogen stores (which is the stored form of glucose in the liver + muscles).

  • Occasional protein fasting: While the research on the benefits of protein fasting is in its infancy, given what we know from Longo, I think this is worth exploring. Maybe that looks like going vegan once a week, or taking an entire month to experiment eating completely plant-based. (Know that I don't recommend a vegan diet for most people, mainly due to the challenge of ensuring adequate nutritional intake, e.g. B12, zinc, protein, Omega 3 fatty acids. I do support it as an individual choice, and believe it can be executed in a healthy way with proper planning. As an FYI, Longo recommends seafood + legumes as the main source of protein.)

  • ProLon: Clearly, I'm a fan because ProLon is developed based on research, structured to be user-friendly, and formulated so that you don't feel like you're starving. Keep in mind that the part of what's essential to achieving the benefits of cellular rejuvenation is both the length of the fast (e.g. a 1-day fast won't cut it), as well as the lack of protein (to prevent MTOR).

As someone who is both very active + loves delicious food, I feel that doing ProLon quarterly or twice a year is "easier" + more effective than more chronic restriction.


To find out about my "results" after 2 rounds of ProLon, check out my video recap below:

Thank you for reading! If you have further questions, require additional support, or just want to chat, feel free to email me at liz@lizbarnet.com, or follow along with me on Instagram.

*Please note that while this blog post was not sponsored, I am a ProLon ambassador, and do receive discounts if you purchase the program using my code.


**This blog provides general information and discussions about health and related subjects. The information and other content provided in this blog, website or in any linked materials are not intended and should not be considered, or used as a substitute for, medical advice, diagnosis or treatment. This blog does not constitute the practice of any medical or other professional health care advice, diagnosis or treatment. It is not meant to diagnose conditions, provide second opinions or make specific treatment recommendations.


If you or any other person has a medical concern, you should consult with your health care provider or seek other professional medical treatment immediately. Never disregard professional medical advice or delay in seeking it because of something that you have read on this blog, website or in any linked materials. If you are experiencing a medical emergency, please call 911 or call for emergency medical help on the nearest telephone immediately.

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