Fast Health
Disclaimer: This article is for educational purposes and not medical advice. Consult with a healthcare provider before beginning any fasting protocol. This article is supported by evidence but relies heavily on my personal experience. Use caution and reason when proceeding.
Who doesn’t want something FAST? The purported benefits of fasting seem too good to be true and while individual experiences can vary wildly, keep in mind that healing WILL occur—it’s just a matter of how you go about your strategy.
Let’s look at the different types of fasts, the benefits associated with each and the strategy which I created for myself and what I believe to be one of the best and most potent ways to achieve real health and wellness.
Benefits Overview
For a deeper dive into the benefits, scroll down to the Comprehensive List 👇
Metabolism: fat loss & body composition, blood sugar & insulin, metabolic rate & hormones
Cellular & Longevity: autophagy, stem cell activation, genetic & mitochondrial
Immune System: overall function improvement, Inflammatory markers lowered
Cardiovascular
Brain & Cognitive: mental performance, mood & mental health
Digestive System: gut health, liver & detox pathways
Disease Prevention & Treatment: cancers, chronic diseases, injuries
Physical Performance & Recovery
Weight & Appetite Regulation
Skin & Appearance
Energy & Vitality
Economic & Practicality
Spiritual & Psychological
Types of Fasts
So, why would you do any one fast over another? It depends on your goals and starting point. If you’re not fat adapted or used to fasting then you need to start small and build small. You wouldn’t go into an intense training regimen recklessly, so be smart about entering the fasting game.
Water Fasting
The most common type of fast and the one most people think of when they hear the term “fasting”. This style involves drinking only water; no solid foods, no juices, nothing with calories. Ideally the user would have no coffee or tea either. However, most people still have these items during their water fast. The prime factor is being as close to 0 cal as possible.
Juice Fasting
Juice fasting involves drinking only juice (preferably fresh squeezed) during your fasting window. The rationale behind this approach is partly informed by the work of Dr. Walter Kempner, whose famous Rice Diet at Duke University (1939-2002) demonstrated that extremely high sugar and carbohydrate intake in the absence of dietary fat produced paradoxical health improvements—including in diabetic patients (even with Type I).
Some practitioners report a paradoxical reduction in hunger and stabilization of blood sugar after the first day or two of juice fasting. Additionally, the high water content of juices (sugar carries approximately 3-4g of water per gram when stored as glycogen) provides substantial hydration, particularly beneficial for colon health.
Important caveats: Prolonged or frequent juice fasting has been associated with potential liver and pancreas stress in some cases, though this is relatively rare and usually results from extreme or poorly planned protocols. Additionally, high-oxalate vegetables like raw kale and spinach may be problematic for individuals prone to kidney stones or oxalate sensitivity, so fruit-based juices may be preferable for extended juice fasts.
Restricted Eating
A fast is just abstaining from one or more things so if you restrict your eating in any way, you’re technically fasting from something. A popular example of restricted-eating is what is commonly known as the sardine fast where you just eat sardines, usually for 3 to 5 days. Another is olive oil fasting where, you guessed it, you just ingest olive oil for some period of time.
This can be beneficial for people who may require calories to get through work/life at that time or simply can’t commit to a fast lacking any calories, while still getting autophagy benefits, and other unique nutritional value.
Intermittent Fasting
Any of the above fasts can be used with any of these strategies; intermittent, long, super long or ultra long windows. Intermittent fasting is simply restricting the feeding window each day. It does not have to be consecutive days; for example, you might do an intermittent fast just once or twice a week.
The point is these are short fasts. They can have incredible value and benefit while fitting into a busy lifestyle. Here are some of the most common time windows:
16:8 — the strategy usually involves simply skipping breakfast then either having a big lunch and moderate dinner or vice versa. This is a great option for people new to fasting. Doing it daily or almost every day will help the user adapt to the fasting lifestyle without giving up too much. Many women say that they prefer something closer to a 14:10 or even 12:12 for hormonal balance. Test things out for yourself.
20:4 — this isn’t so much a one or two meal strategy, but rather a small “feeding window“ which means you can take your time getting in all the calories you require. People who are making use of intense training protocols while still desiring the benefits of longer fasting on the daily love this strategy.
OMAD — one meal a day is really a 23:1 window and is very difficult for most people to adapt to or stay on for long periods of time unless they are obese. Personally, I can pack in 3000 to 4000 kcal in less than 30 minutes. There might be discomfort the first week or two but I generally adapt quickly and find the extra couple hours fasting give me noticeable benefits over a 20:4 strategy, but this is generally not recommended for most people who are already fit…experiment.
Alternate day feeding — this is a successful strategy for anyone who wants to lose weight. If you’re more than 50 pounds overweight, this can be done for some period of time safely. I have also experimented with this strategy at very lean (10% or less) body fat levels and was able to sustain it for about three months and I feel confident I could go for much longer, but I don’t think it’s a good remedy for most people unless they have a considerable amount of weight to lose.
Long Fasts
I would consider anything longer than 48 hours to be a “long” fast and really anything over 24 hours will be long for most. Again, the more weight you have to lose, the more often you can fast and the longer you can fast without certain negative side effects. For those of us whose primary concern isn’t fat loss the benefits are as follows:
48 hours: entering autophagy, deep, ketosis, fat breakdown and growth hormone is secreted by 5X, insulin sensitivity increases and inflammation drops markedly. Mental clarity peaks.
72 hours: autophagy peaks, immune system regeneration begins, stem cell activation begins, and growth hormone is up to 10X. You can also expect up to 1-2 actual fat pounds lost, not water weight
96 hours: deep immune system clearance, autophagy maximized, gut lining repair acceleration, metabolic reset and antiaging effects begin to take place.
120 hours: the immune system is completely regenerated, stem cell production is maximized and peak longevity benefits solidify.
Super Long Fasts
I would consider a super long fast anything between 7 and 21 days. Most people will never venture here and might not need to. It really depends on the issues they would like to solve and the lifestyle they have available to them. Most people can continue working during a 3 to 5 day water fast, especially after they’ve adapted to the lifestyle. The same cannot be said for super long fasting. The strategy can take a lot out of you. It becomes imperative that strategic salt-loading is employed (adding in high quality sea salt, potassium, baking soda and magnesium to at least 1-2L of ingested water daily), consider obtaining medical supervision and ensure that re-feeding + recovery is planned out in advance then strictly adhered to, else serious harm could become of you (even death in rare cases).
However, many super long fast practitioners purport the only way to heal certain diseases or conditions lies in much longer fasting than most people will ever consider.
Ultra Long Fasts
Anything over 21 days is ultra and reserved for only the most serious devotees to the fasting lifestyle. While there likely are diseases that can only be healed over 21 days of fasting, most ultra long fasters do this as a spiritual practice. The toll on the body is considered a necessary condition of this radical measure.
Dry Fasting
I saved the best for last. Dry fasting is obviously the most hard-core style and involves no intake whatsoever. No food. No water. No supplements of any kind. Just you and your willpower. Most people mistakingly, believe that it is unhealthy to go without water, and that humans cannot survive more than three days without ingesting it. Aside from common sense in realizing that our ancestors would’ve likely gone for days (if not a week or more) at a time without water, there are no shortages of anecdotes and studies showing the benefits of short and even long dry fasts.
It is often touted (although lacking absolute scientific credibility) that for every day of dry fasting, you’re getting three days of water fasting benefits—more-so you’re also obtaining benefits that no amount of water fasting can give you. The state of dry fasting is certainly more intense for most which represents the main limiting factor and barrier to entry.
I highly recommend being adapted to water fasting for at least 6 to 12 months before embarking on a dry fasting journey, although many would say it is better to start with super short dry fasts in the 12 to 24 hour range. Personally, I stuck with water fasting for years before getting into dry fasting so I can only speak from my own experience. The more I delve into dry fasting, though, the better it gets.
Keep in mind that the rules may be slightly different when it comes to not ingesting water and one of the most critical factors is stem cell regeneration windows. The Russian research by Filonov and colleagues indicates that days 4, 6 and 8-10 are days which should NOT be broken as it could interfere with the stem cell regeneration process and potentially cause negative side effects. This is why they recommend breaking the fast on day 3, 5, 7 or 11+ and that after 11 days this rule becomes void. This has not been verified outside the Russian research circles but I think it’s generally a good rule to follow.
Obviously, you don’t want to jump into a longer dry fast without being ready for it. Both longer water fasts and dry fasts over 48 hours require specific re-feeding strategies to avoid what is known as re-feeding syndrome, which can cause unnecessary damage and discomfort. Small sips of water spaced out over hours, ingestion of things like kefier and white fish like sardines, bone broth, and baking soda water must not be rushed. The longer you have dry fasted the longer your re-feeding window must be. Be cautious with sugars, even good natural sources such as juices because it may not make your pancreas happy.
For any dry fasts lasting about 1 to 3 days, you can get away with having moderate sugars within a few hours of breaking the fast. For 3 to 5 day dry fasts moderate sugars can be ingested the day after or on the third day. After a 7+ day dry fast there needs to be a few days of water/liquid-only ingestion followed by easy to digest foods like scrambled eggs. The refeed/recovery period should last about as long as the fast.
Considerations
Who Should NOT Fast
Pregnant/breastfeeding women
Children and adolescents
People with eating disorders (although some claim that fasting cured their disorder)
Those with certain medical conditions (diabetes on medication, etc.)
Underweight individuals
Exercise During Fasting
For intermittent and long-ish water fasts you can continue exercising but keep in mind the longer you go the more risk you have of harming yourself with a muscle strain or too much load on the heart. General guidelines:
Light activity is usually fine
Intense exercise may need to be reduced
Listen to your body
For dry fasting, in general, and super long water fasts I can’t say I recommend too much movement, although I don’t recommend NO exercise whatsoever as we want to signal to the body to keep as much muscle as possible. Walking at an easy pace, 10% effort or less exercises as normal (ex. if you can do 10 push-ups normally just do 1…).
Common Side Effects
Don’t push yourself too hard. Allow your body to adapt but know the following side effects are very common and usually not serious:
Headaches
Fatigue
Dizziness
Bad breath
Sleep disruption
Hunger waves
Measuring Success
Ultimately, the most important aspects of fasting are achieving your goals (fat loss, clarity, mood improvement, healing injuries, spiritual development, etc.) but there are many ways to track the progress if you want to ensure that you’re in ketosis, losing weight, etc.
Ketone monitoring
Blood glucose tracking
Body composition vs. scale weight
How you feel (energy, mental clarity, etc.)
Blood and/or fecal testing
My Personal Recommendations—an Optimized Strategy
Intermittent fasting (16:8) for 1 to 3 months: acclimating to less meals and learning how to properly hydrate without food intake (finding the perfect ratio of water and salts).
OMAD (23:1) for 1 to 6 months: the strategy does not need to be employed every day of the week, but keep in mind the more often you do it the faster you will adapt and be ready for the longer fasts.
Biweekly long fast for 3 to 6 months: water fasting for 3 to 5 days or dry fasting for 1 to 3 days every other week if you have a decent amount of fat to lose or conduct one monthly if you’re already relatively lean.
Quarterly super long fasts for as long as you need to do them to become acclimated: this could include 7 to 14 day water fasts, or beyond, and 3 to 7 day dry fasts. These strategies are for healing injuries and giving the body complete rejuvenation.
Yearly ultra long fasts: only for the serious—more than 21 day water fasts (and 11 day or beyond dry fasts) for spiritual cleansing.
Of course, you can mix strategies as you go but I would recommend going off all fasting every so often to reset your system and give it something different for a while. This will ultimately make the entire process more productive and prevent burnout. Here’s an example of what I mean:
After adapting to OMAD, keep eating 3-7 days a week with this strategy, then add in bi-weekly/monthly long fasts.
Continue this plan until you’re ready to do a super long fast—every third month simply replace your long fast with a super.
After a year or more you may decide to try an ultra long water or dry fast (or other kind of your choosing). I’m not sure if I can recommend doing more than one ultra per year but that is entirely up to you and your goals.
Final form—OMAD 3-7 days/week + bi-weekly/monthly long fasts + quarterly super long fasts + a yearly ultra long fast. Take time off this strategy for 1-3 months per year (doesn’t have to be all in a row) to reset metabolic function and keep it guessing—usually time off around the holidays so you’re not that freak in the corner judging everyone 😂
In Closing
If you decide to do some type of intermittent fasting, just sparingly, or not at all—after you’ve adapted—and desire to do a long fast quarterly, or even yearly, this is fantastic.
So, where do the other fasting styles fit in here? What I laid out is more of an on-boarding process but you obviously don’t have to follow it religiously. Find what works best for yourself. You may want to take a long time dabbling with juice fasting before doing a water fast. This is your adventure, part of the fun is in the mystery. You can think of yourself as more of a scientist here, an “n=1” if you will. If you really want to know something, then you’ll have to record your progress and then maybe you can share it with others someday!
Any amount of fasting is better than none (unless you do too much before you’re ready) so give yourself a pat on the back and thank yourself for all the free healthcare!
Comprehensive Fasting Benefits List
Metabolic
Fat Loss & Body Composition
Fat oxidation: body shifts to burning stored fat for fuel
Preservation of lean muscle mass: growth hormone elevation protects muscle during fasting
Visceral fat reduction: particularly effective at reducing dangerous belly fat around organs
Improved body composition: better fat-to-muscle ratio
Blood Sugar & Insulin
Insulin sensitivity improvement: cells become more responsive to insulin (up to 20-31% improvement)
Blood glucose stabilization: fasting glucose levels decrease and stabilize
Reduced insulin resistance: key factor in preventing/reversing type 2 diabetes
HbA1c reduction: long-term blood sugar marker improves
Pancreatic rest: allows insulin-producing beta cells time to recover
Metabolic Rate & Hormones
Growth hormone increase: up to 5x at 48 hours, up to 10x at 72+ hours
Norepinephrine elevation: increases metabolic rate by 3.6-14%
Metabolic flexibility: enhanced ability to switch between fuel sources (glucose/fat)
Thyroid optimization: T3 conversion can improve (though extended fasting may temporarily reduce)
Leptin sensitivity: improves hunger hormone signaling
Cellular & Longevity
Autophagy (Cellular Cleanup)
Damaged protein removal: cells break down and recycle dysfunctional proteins
Organelle renewal: mitochondria and other cellular components regenerate
Cellular debris clearance: removes accumulated waste products
Anti-aging effects: slows cellular aging processes
Cancer cell resistance: autophagy helps identify and eliminate pre-cancerous cells
Neuroprotection: brain cell cleanup and protection
Stem Cell Activation
Stem cell production: significant increase starting around day 3
Immune cell regeneration: hematopoietic stem cells create new immune cells
Tissue repair: enhanced healing and regeneration capacity
Organ rejuvenation: multiple organ systems benefit from stem cell renewal
Genetic & Mitochondrial
Gene expression changes: upregulation of longevity genes (SIRT1, FOXO)
Mitochondrial biogenesis: creation of new, more efficient mitochondria
DNA repair: enhanced cellular repair mechanisms
Telomere protection: may slow telomere shortening (aging marker)
Reduced oxidative stress: lower free radical damage
Immune System
Immune Function
Immune system reset: complete regeneration after 72+ hours
White blood cell regeneration: old immune cells cleared, new ones produced
Reduced inflammation: systemic inflammation markers drop significantly
Autoimmune modulation: may help calm overactive immune responses
Enhanced pathogen resistance: improved ability to fight infections
Lymphatic system cleansing: better waste removal from tissues
Inflammatory Markers
C-reactive protein (CRP) reduction: key inflammation marker decreases
TNF-alpha reduction: pro-inflammatory cytokine decreases
IL-6 reduction: aecondary inflammatory marker improves
Reduced chronic inflammation: addresses root cause of many diseases
Cardiovascular
Blood pressure reduction: significant decreases, especially in hypertensive individuals
Cholesterol improvement: LDL may decrease, HDL may increase
Triglyceride reduction: dramatic drops in blood triglycerides
Heart disease risk reduction: multiple cardiovascular risk factors improve
Arterial plaque reduction: evidence of atherosclerosis reversal
Improved heart rate variability: marker of cardiovascular health and stress resilience
Brain & Cognitive
Mental Performance
Mental clarity: sharp, focused thinking (especially after adaptation)
Increased BDNF: brain-derived neurotrophic factor promotes neuron growth
Neuroplasticity: enhances brain's ability to form new neural connections
Neuroprotection: protection against neurodegenerative diseases
Improved focus: sustained attention and concentration
Enhanced memory: both short-term and long-term memory improvements
Mood & Mental Health
Mood stabilization: reduced anxiety and depression symptoms (after adaptation)
Increased alertness: heightened awareness and energy
Stress resilience: better ability to handle psychological stress
Potential for treating depression: evidence for mood disorder improvement
Spiritual clarity: many report enhanced introspection and mindfulness
Digestive System
Gut Health
Gut rest: digestive system gets complete break
Gut lining repair: intestinal barrier function improves
Microbiome reset: beneficial bacteria can rebalance
Reduced gut inflammation: IBD, IBS, and other conditions may improve
Improved digestion: better enzyme production and nutrient absorption post-fast
Elimination of food sensitivities: temporary relief, helps identify triggers
Liver & Detoxification
Liver regeneration: liver cells renew and repair
Enhanced detoxification: improved clearance of toxins
Reduced fatty liver: non-alcoholic fatty liver disease improvement
Bile production optimization: better fat digestion post-fast
Disease Prevention & Treatment
Cancer
Reduced cancer risk: multiple mechanisms may lower cancer development
Chemotherapy protection: protects healthy cells during treatment (under medical supervision)
Cancer cell sensitization: makes cancer cells more vulnerable to treatment
IGF-1 reduction: lower levels associated with reduced cancer risk
Chronic Diseases
Type 2 diabetes reversal: potential for complete remission
Metabolic syndrome improvement: multiple risk factors addressed simultaneously
Reduced Alzheimer's risk: neuroprotective effects may prevent cognitive decline
Parkinson's protection: some evidence of reduced risk
Asthma improvement: reduced airway inflammation
Arthritis relief: reduced joint inflammation and pain
Skin condition improvement: eczema, psoriasis, acne may improve
Physical Performance & Recovery
Enhanced fat adaptation: better endurance through fat burning
Improved VO2 max: cardiovascular efficiency increase
Better recovery: reduced inflammation speeds healing
Injury healing: accelerated tissue repair from stem cells and autophagy
Tendon/ligament repair: enhanced healing of connective tissue injuries
Weight & Appetite Regulation
Appetite normalization: hunger hormones (ghrelin/leptin) rebalance
Reduced cravings: especially for sugar and processed foods
Food relationship reset: better awareness of true hunger vs. habit
Portion control improvement: stomach may shrink, easier to feel satisfied
Breaking food addiction: helps overcome compulsive eating patterns
Skin & Appearance
Skin clarity: acne and blemishes often improve
Reduced puffiness: less water retention and inflammation
Anti-aging effects: cellular renewal shows in skin appearance
Brighter complexion: improved circulation and detoxification
Hair and nail health: may improve after fasting cycles (with proper refeeding)
Energy & Vitality
Stable energy levels: no blood sugar crashes (after adaptation)
Increased energy: many report feeling more energetic than when eating
Better sleep quality: deeper, more restorative sleep
Reduced need for sleep: some people need less sleep while maintaining energy
Enhanced vitality: overall sense of well-being and vigor
Economic & Practicality
Time savings: no meal prep, cooking, or eating time
Money savings: significant reduction in food costs
Simplified life: fewer decisions about what/when to eat
Increased productivity: more time and mental energy for other activities
Food appreciation: enhanced taste and enjoyment when eating resumes
Spiritual & Psychological
Enhanced willpower: builds mental discipline and self-control
Spiritual clarity: used in many religious/spiritual traditions
Increased mindfulness: greater awareness of body and mind
Emotional release: processing of stored emotions
Self-discovery: deeper understanding of relationship with food
Sense of accomplishment: pride in completing challenging fasts
Dry Fasting-Specific Benefits
Accelerated autophagy: estimated 3x intensity of water fasting
Enhanced anti-inflammatory effects: more pronounced reduction
Metabolic water production: body learns to produce water from fat
Deeper detoxification: cells forced to release water and toxins
Stronger stem cell activation: more intense regenerative signals
Antimicrobial effects: bacteria and pathogens need water to survive
Rapid healing: injuries and inflammation may resolve faster
Sources
General Fasting Benefits
Autophagy: Alirezaei et al. (2010) "Short-term fasting induces profound neuronal autophagy" - Autophagy journal
Growth Hormone: Hartman et al. (1992) "Augmented growth hormone (GH) secretory burst frequency and amplitude mediate enhanced GH secretion during a two-day fast in normal men" - Journal of Clinical Endocrinology & Metabolism
Insulin Sensitivity: Halberg et al. (2005) "Effect of intermittent fasting and refeeding on insulin action in healthy men" - Journal of Applied Physiology
Immune System Regeneration: Cheng et al. (2014) "Prolonged fasting reduces IGF-1/PKA to promote hematopoietic-stem-cell-based regeneration and reverse immunosuppression" - Cell Stem Cell
Stem Cell Activation: Mihaylova et al. (2018) "Fasting Activates Fatty Acid Oxidation to Enhance Intestinal Stem Cell Function during Homeostasis and Aging" - Cell Stem Cell
Metabolism: Longo & Mattson (2014) "Fasting: Molecular Mechanisms and Clinical Applications" - Cell Metabolism (comprehensive review)
Metabolism: Anton et al. (2018) "Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting" - Obesity journal
Dry Fasting
Filonov's Work: "Dry Medical Fasting: Myths and Reality" by Dr. Sergey Filonov (book)
Professor Yuri Nikolayev: “Starvation for Health” (Russian: “Голодание ради здоровья”)
Immune System: Papagiannopoulos, I.A. et al. (2013) “Immunological and haematological effects of dry fasting” - Proceedings of the International Conference on Nutrition and Health
Dr. August Dunning: “The Phoenix Protocol” (book)
Metabolism: Cahill, G.F. Jr. (2006) “Fuel metabolism in starvation” - Annual Review of Nutrition
Intermittent Fasting
16:8 Benefits: Sutton et al. (2018) "Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress" - Cell Metabolism
Alternate Day Fasting: Varady et al. (2013) "Alternate day fasting for weight loss in normal weight and overweight subjects" - Nutrition Journal
Health: De Cabo & Mattson (2019) "Effects of Intermittent Fasting on Health, Aging, and Disease" - New England Journal of Medicine
Metabolism: Patterson & Sears (2017) "Metabolic Effects of Intermittent Fasting" - Annual Review of Nutrition
Refeeding Syndrome
Refeeding syndrome risks: Mehanna et al. (2008) "Refeeding syndrome: what it is, and how to prevent and treat it" - BMJ