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The One True Fast – Comparing Water-only Fasting, Intermittent Fasting, and Fasting Mimicking Diets

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The One True Fast – Comparing Water-only Fasting, Intermittent Fasting, and Fasting Mimicking Diets

Dr Frank Sabatino DC, PhD 

Before the American Natural Hygiene Society became the NHA, a number of iconic Hygienic physicians, including Drs Shelton, Vetrano, Esser, Benesh, Sidhwa, Gross, Scott, and Burton, redefined alternative, natural health care by helping countless thousands recover their health with water-only fasting. As a beautiful example of time binding, all of the modern day fasting doctors and scientists are fortunate to stand on the shoulders of these dedicated physicians from the past, and walk the road that was paved by these remarkable Hygienic pioneers.

Through the years, the interest in fasting has often waxed and waned with cautious approval, misinformation, and unfounded concerns, while currently achieving a huge, renewed interest and popularity with the general population, as well as a variety of physicians and scientists. However, since we live at a time when so many people are looking and hoping for short-cuts and quick fixes for all aspects of life, including therapeutic interventions, a variety of approaches, like intermittent fasting (IF) and fasting-mimicking diets (FMD), are being talked about and marketed as viable alternatives to the more rigorous demands and challenges of water only fasting (WF). Yet, while these approaches have some value for health and weight loss, I do not feel that they can provide or replace the remarkable, profound benefits of short or extended water fasts. And to truly appreciate, compare and contrast these different approaches, it is important to have some basic understanding of WF and these alternatives.


Water-only Fasting

By definition, WF is the complete abstinence from all food and liquids, except water, for some extended period of time. After all the years of fasting care, there is an extensive body of clinical evidence supporting the use of WF for a wide range of health problems including obesity. A growing body of scientific evidence over a number of years has also reinforced these beneficial effects and continues to shed light on the cellular mechanisms that promote these changes.

The incredible clinical results of WF are the direct result of unique and remarkable changes that occur in the body as a direct result of food deprivation. When you begin to fast, blood sugar levels drop, insulin is decreased, and the hormone glucagon is increased to replenish blood sugar from the sugar reserves (glycogen) in liver. However, after  the first day of WF, the sugar in the liver is exhausted and the body begins to create energy from body fat and protein. By the third day of WF, protein is used more sparingly as the body shifts to fat metabolism to meet its energy needs. The decrease in insulin and the increase in glucagon during the fast promote this increase in fat metabolism (lipolysis). And between days 3-10 of the WF, fat metabolism increases significantly, to produce ketones (ketogenesis) that provide energy for the body and brain. The loss of protein and the depletion of blood sugar is tempered and controlled by resting  as much as possible during the fast. If the person attempts too much activity on a fast, body responses can be more unstable, including more rapid muscle loss, increased blood pressure, and blood sugar decline.

It is important to understand that WF is a deep, physiological, resting process that harbors energy for healing, repair, and regeneration. When dietary nutrients are eliminated, cells shift from a typical growth phase to a phase of energy conservation, maintenance, and repair. As evidence of this, insulin, growth hormone and the growth factor, Insulin-like growth factor 1(IGF-1) (abnormally increased  by eating excesses of high protein animal products, fat and sugar laden junk food), that can promote cancer and tumor growth in adults, are reduced during WF. This reduction of IGF-1, combined with the process of autophagy (self-digestion) that occurs during WF, protects normal cells while promoting the reduction or elimination of tumor cells and cancer growth. In fact, a short period of WF (3 days) before conventional, high-dose cancer chemotherapy has been shown to reduce the debilitating, adverse effects of drug treatment (1), while increasing the efficacy of chemotherapy against a variety of cancers(2, 3).

Every second of every day, the cells of the body are taking in nutrients and producing waste and by-products of routine metabolism. In addition to this internal toxemia (toxic chemicals in the bloodstream), there are a variety of fat-soluble chemicals/poisons that come into your body from the outside, e.g., pesticides, pollution, additives in foods, toxic foods, and drugs that you may be taking. Fat cells can also store this metabolic waste and the toxic fat-soluble chemicals we are routinely exposed to. But eliminating these chemicals from the body can improve our quality of life and health.

Therefore, the energy that is harbored in the fasting process enhances the mobilization of waste from fat cells, for removal through organs and tissues of elimination in a process of detoxification. The lungs, with their extensive surface area, and the skin are the largest organs of the body. So it is very common to see discharge, drainage and symptoms of elimination via these organs including mucous discharge, cysts, rashes, and boils. In WF, the enhancement of detoxification and elimination is profound, and completely under the body’s brilliant, intelligent, and selective control.

When nutrients are restricted, the miraculous process of cellular housekeeping, autophagy, is set in motion. In the cells of the body there is a unique enzyme called mTOR that is the primary regulator of cell growth, energy production, and cellular aging. When cells are deprived of nutrients, this enzyme is turned off as the cell switches from cell division and growth to maintenance, repair, and housecleaning. In autophagy, worn out parts of cells, fragmented proteins, damaged mitochondria, and bacteria and viruses contained in cells are engulfed by cellular structures called autophagosomes and transported to lysosomes in our cells, and digested so that raw materials and building blocks are available to support and restore vital body parts. During WF, and the transformative process of autophagy, the body uses what it needs least to provide support for what it needs most. It needs heart, and lungs, and kidneys, and bowels, etc., but it doesn’t need cysts, tumors, stones, and growths. So, through autophagy, it can discard old worn out cells, break down tumors or cysts, take what it can use to support the vital organs of the body, and eliminate the rest. That’s why we often see cysts, tumors, and stones routinely break down and dissolve during fasting.

What makes WF even more beneficial is that while many pathological conditions are improved, including chronic inflammation, hypertension (4), allergy, asthma, autoimmune disease, certain forms of cancer etc., there is also significant fat and weight loss. Weight loss is typically 1-2+ pounds a day during WF. However, this weight loss can taper off to some degree if the fast continues over a period of weeks. But I have seen people lose 20 pounds in two weeks of fasting, and as much as 30 pounds or more in a month.

WF is not a mystical process, but it has been used by a variety of spiritual traditions as a tool for introspective evaluation and spiritual growth. As mentioned above, WF is truly just a profoundly, simple process of deep, physiological rest. The goal is to harbor as much energy as possible for the healing work at hand. That means rest on every level, including all the senses. The more time spent being quiet, serene, and introspective the better. Even making your fast a bit of a digital fast and taking a break from all electronic devices has great value. Sometimes, only by slowing everything down and stepping back from the chaos and distractions around us, can we feel, question and change the patterns and choices of our lives. For this reason fasting is also a profound tool for creating a more mindful self-aware life, and resolving compulsive addictive behavior.

WF promotes fat breakdown, detoxification, and repair like nothing else. It enhances the balance and function of the hormonal (endocrine) system, while significantly improving the metabolic efficiency of the liver and digestive systems, thereby promoting improved calorie use and fat loss across time. WF reboots the immune system, and in just 4 days of fasting there is a stem cell activation of new white blood cells. WF also activates the genetic expression of repair enzymes for cellular / DNA repair and support. It is  also one of the most powerful approaches for resolving inflammation and the complications of autoimmune disease. The body-mind changes evoked by the fasting process make it one of the most efficient and powerful tools to jump start any health program in general, and a significant and successful long term weight loss program in particular.


Intermittent Fasting

The use of the term intermittent fasting (IF) is actually a misnomer. As we have seen, true fasting doesn’t really begin until the sugar reserves of the body are used up and the body is forced to switch from glucose to fat metabolism, which takes between 1-3 days of fasting. Even though the body can achieve some ketogenesis and fat loss with IF, IF does not promote the level of food restriction required to enter a sustained, true fasting state, and should not be considered a true fast. Typically most IF programs are really a time controlled pattern of eating / food restriction, and are most often done in the following ways:

  1. A 5/2 day program, eating your normal diet for 5 days and doing 2 days of significant calorie restriction of approximately 500-600 calories per day (5).
  2. Some form of a time-restricted pattern of eating, usually eating during a 4, 6, 8 or 10-hour period, while avoiding any food intake for  20, 18, 16 or 14 hours respectively. In fact, at my Balance for Life Retreat all eating guests participate in IF daily. Dinner is served between 5:30-6:30pm and breakfast is at 8:15-9:00am. So that all eating guests are basically on a 14:10 cycle, eating in a 10-hour window while avoiding food 14 hours a day.

While this is not a true fast, and does not provide the extensive autophagy and benefits of longer water only fasts, there are still major benefits for health and weight loss that can be accomplished with this approach.

A recent review article on the benefits of IF, published in the New England Journal of Medicine, stated that eating in a 6-hour period and fasting for 18 hours can trigger a metabolic switch from glucose-based to ketone-based energy with increased stress resistance, increased longevity and decreased incidence of chronic diseases including cancer and obesity (6).

While many benefits have been chronicled in animal studies, the suggested human benefits include some reduction of abdominal belly fat / obesity, heart rate, blood pressure, and inflammation as well as improvements in endurance and cognition. And similar to water fasting, IF promotes some autophagy, DNA repair, and ketogenesis while decreasing insulin and mTOR  activity.

So the ongoing participation in IF may promote some long-term improvements in insulin sensitivity, gut microbiota, while reducing some risky body fat, blood pressure and inflammation thereby increasing resilience and disease resistance.

Just keep in mind, that because you are still eating on a daily basis, the sustained benefits of ketogenesis, detoxification, and autophagy that we routinely see in days to extended weeks of WF cannot even hope to be matched by IF. But for people going through the routine pressures and strains of daily life, and who cannot surrender to the resting demands of WF, regular IF can potentially get you back on a healthy track, promote some weight regulation, and help restore your connection with the normal diurnal rhythms and cycles of your body and the natural world  around you.


Fasting Mimicking Diets

Fasting mimicking diets (FMD) were made popular by Professor Valter Luongo, a leading researcher of longevity and the mechanisms of fasting. In his book, The Longevity Diet, Professor Luongo describes a do it yourself 5-day FMD composed of vegetables (broccoli, tomatoes, carrots, pumpkin, mushrooms etc.,) and a small amount of olives, nuts, seeds, and olive oil, that can be purchased in any grocery store, along with supplements of vitamins and essential fatty acids (7).

He also created a FMD program called ProLon that is a 5-day  program containing  pre-packaged plant-based soups, veggies, olives, crackers, nut-based bars (containing a variety of different nuts, coconut oil, and dark chocolate), honey, herbal teas, and supplements of vitamins and amino acids. Since, his packaged program contains a fair amount of added salt, refined oil, saturated fat from coconut oil, and honey, it is certainly not consistent with a healthier, more ideal whole food plant-based diet without added salt, oil, and sugar.

The FMD is a 5-day program of significant calorie restriction. Typically, the program provides about 1,100 calories on the first day and 700-800 calories on days 2-5, and provides food that is supposed to mimic the effects of a 5 day WF by basically tricking the body into thinking that it is fasting.

In research with this FMD conducted at the Longevity Institute at USC, and the Diabetes and Obesity Research institute, 3 cycles of ProLon, 5 days per month over a 3 month period, produced several significant metabolic effects at 1 week after the last cycle. It is not clear in his online presentation which results are statistically significant but some of  the possible changes are listed as increased autophagy, decreased body fat / weight (an average of 5 lbs of weight loss per 5 day cycle), cell repair and rejuvenation, healthy levels of bone density, and the maintenance of lean body mass.

The FMD is sold as a tasty, more comfortable alternative for people that Dr Luongo feels will most likely not want to comply with the more rigorous demands of WF or experience any of its potential disturbing symptoms. With all due respect to Dr Luongo, he does not have experience in conducting extensive human water fasts. But he knows enough to realize that people on fasts can sometimes be uncomfortable, experiencing headaches, light-headedness, nausea, and even pain. Yet, even though some of these changes can be disturbing, it is important for people to realize that many of the  symptoms that may occur are typically a necessary part of their detoxification / recovery that demands a mindful surrender to rest .

A FMD is supposed to be a safer, more comfortable alternative for people that can still participate in their normal routine at home, and may not want to go to a fasting center to get the benefits of a stricter 5 days or longer water fast. The assumption is that it is difficult, if not impossible, for people to comply and accept the more rigorous demands, and potentially more dramatic symptoms of WF.

Those of us that routinely conduct fasts of 1-3 weeks, or even longer, know that this is an unfair and inaccurate assumption. Under the ideal conditions provided by fasting centers, where proper monitoring is done, people are carefully guided through the profound changes / symptoms of fasting and are often transformed by their ability to process through their discomfort and pathology.

Furthermore, even though some data suggest that both IF and FMD promote weight loss and some beneficial cellular / metabolic changes similar to water fasting, and can be used by people maintaining their normal active lifestyles, there is no evidence that either IF or FMD can promote the widespread beneficial effects on metabolism, inflammation, blood pressure, the immune system, hormonal regulation, and cancer that are promoted by the intense, extended ketogenesis and autophagy of both short and long term WF.

Very often, the conditions that people are seeking to resolve with WF require the combination of rest, food abstinence, detoxification, and introspective self-examination that only WF can provide whether it is for just a few days or weeks at a time. And if it is done in a proper, comfortable, and relaxed setting, with the proper and necessary support and monitoring, it is an incomparable health promoting and life changing experience.                                                                


  1. Raffaghello L, Lee C, et al. Starvation-dependent differential stress resistance protects normal but not cancer cells against high-dose chemotherapy. PNAS June 2008.
  2. Lee C, Luongo V. Fasting cycles retard growth of tumors and sensitize a range of cancer cell types to chemotherapy. Sci Transl Med, 2012 March 7, 4(24): 124-27.
  3. Safdie F, et al. Fasting and cancer treatment in humans. Aging 2009.
  4. Goldhamer A, Lisle D. Medically supervised water-only fasting in the treatment of hypertension. J Manipulative Physiol Ther 2001 Jun; 24(5): 335-39.
  5. Mosley M, Spencer M. The Fast Diet: The simple secret of intermittent fasting. Short Books, UK 2013.
  6. Castro R, Mattson M. Effects of intermittent fasting on health, aging and disease. N Engl J Med, Dec 16, 2019, 381: 2541-51.
  7. Luongo V. The Longevity Diet. Penguin Publishing Group, 2018.

Dr Frank Sabatino is a Chiropractic physician with a PhD in cell biology and neuroendocrinology from the Emory University School of Medicine. While an assistant Professor at the Health Science Center of the University of Texas School of Medicine, he conducted extensive landmark research on calorie restriction, stress and aging, and has published a number of major scientific papers in some of the most well-respected peer reviewed journals in the fields of cell biology, endocrinology, and neuroscience. He has also written numerous articles for lay magazines and journals in the areas of clinical nutrition, healthy weight loss, women’s hormones, stress management, addiction, and healthy aging. Dr Sabatino is the recipient of the prestigious Brookdale Fellowship.

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