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Now, modern science is showing that fasting can be a powerful addition to an overall healthy lifestyle. It can support weight management, metabolic health, and cellular repair. In fact, in laboratory and clinical trials<\/a> conducted on animals, restricting calories is one of the few strategies that have been reliably found to increase longevity. \u200b\u200b(Our view on the use of animals in medical research is here<\/a>.)<\/p>\n\n\n\n There are many different types (or \u201cflavors,\u201d if you prefer irony) of fasting. These include intermittent, water-only, and fasting-mimicking diets. Each method comes with its own set of benefits, risks, and challenges. <\/p>\n\n\n\n In this article, we\u2019ll look at how fasting works. We\u2019ll explore the science, identify and evaluate various fasting methods, and share tips for safe and effective fasting.<\/p>\n\n\n\n <\/p>\n\n\n\n Fasting refers to voluntarily abstaining from food and sometimes drinks for a specific period. It can range from short daily fasts (like skipping breakfast) to multi-day fasts.<\/p>\n\n\n\n As fasting has moved into the wellness mainstream, many varieties and \u201cbrands\u201d have emerged. Here are some of the most popular.<\/p>\n\n\n\n Intermittent fasting (IF)<\/strong> is about giving your body regular breaks from digestion.<\/p>\n\n\n\n Many of us do this without realizing it; the first meal of the day is called \u201cbreak fast\u201d for a reason. However, IF can extend the period of fasting or adjust its schedule. <\/p>\n\n\n\n The key difference between all the various IF methods is how long you go without food. Popular forms of IF include:<\/p>\n\n\n\n Unlike some other IF approaches that involve full fasting days or significant calorie reduction, TRE aligns food intake with the body\u2019s circadian rhythms and may be more sustainable for long-term use. <\/p>\n\n\n\n Read more about intermittent fasting here<\/a>.<\/p>\n\n\n\n In addition to intermittent fasting approaches, other types of fasting involve more intensive restrictions and are often used for detoxification or therapeutic purposes. <\/p>\n\n\n\n When you water fast<\/strong><\/a>,<\/strong> you abstain from all food and caloric beverages, drinking only water for a period of anywhere from 24 hours to several days or more. Most experts recommend that water fasts of longer than three days be done only under medical supervision. <\/p>\n\n\n\n Juice fasting,<\/strong> also known as juice cleansing, allows fruit and\/or vegetable juices<\/a> while eliminating solid foods. The goal here is to give your digestive system a break while flooding your body with micronutrients. <\/p>\n\n\n\n Another variation is the mineral broth fast,<\/strong> where only bone or vegan broth is consumed for nourishment and gut support. Bone broth has gained popularity in recent years, but it does come with potential downsides<\/a>. <\/a><\/p>\n\n\n\n Vegetable broth<\/a>, especially when homemade, is a low-calorie, nutritious option that can be consumed during fasting, helping to curb cravings and provide hydration.<\/p>\n\n\n\n These methods are typically short-term and more restrictive than intermittent fasting. <\/p>\n\n\n\n Why is fasting associated with improved health? What\u2019s going on inside your cells and organs when you give your digestive system a vacation? It turns out that there are a bunch of good things that can happen. <\/p>\n\n\n\n Your body has three basic sources of fuel to draw upon to keep you alive and moving. The first is the carbohydrates you eat, which are quickly converted into glucose and transported into your bloodstream, where they are carried to every cell in your body. <\/p>\n\n\n\n Using carbohydrates as fuel comes with two big benefits. First, they provide quick access to the energy you need. Second, glucose is the main source of energy for your brain.<\/p>\n\n\n\n The second source of fuel is glycogen, which consists of the carbohydrates that you don\u2019t burn right away. Your biggest store of glycogen is in your liver, and it gets tapped when you need energy between meals. <\/p>\n\n\n\n The third source is your body fat. When you\u2019ve used up your stored glycogen, which can occur between 12\u201324 hours of fasting, that fat starts to break down, not into carbohydrates or simple sugars, but into ketones<\/a>, which your brain and body can use as an alternate fuel source to keep you going when food calories aren\u2019t available. This metabolic shift \u2014 from glycogen to fat and ketones \u2014 is a fundamental aspect of fasting. <\/p>\n\n\n\n And it\u2019s what allows many of the health benefits of fasting to occur, such as cellular repair (autophagy), improved insulin sensitivity, and potential anti-aging effects, as we\u2019ll see. <\/p>\n\n\n\n Fasting triggers autophagy<\/a>, a process where damaged cells are broken down and recycled. Think of an old house with a fireplace as the only source of heat. If the inhabitants can\u2019t get more firewood, they\u2019ll start looking for other sources of wood to burn. They\u2019ll prioritize broken chairs, rickety shelves, and other damaged items, which can later be replaced by new ones.<\/p>\n\n\n\n In this way, autophagy (which comes from Greek words for \u201ceats itself\u201d) helps clear out dysfunctional proteins and promotes regeneration<\/a>. There\u2019s some evidence that this may reduce risk factors for neurodegenerative diseases<\/a> like Alzheimer\u2019s and Parkinson\u2019s.<\/p>\n\n\n\n When your insulin sensitivity is high, your body’s cells respond efficiently to insulin, allowing sugar to enter for energy and keeping your blood sugar levels balanced. If you’re insulin resistant, the sugar has trouble opening the door to each cell. This leads to high blood sugar and forces your body to produce even more insulin, which, over time, can develop into type 2 diabetes.<\/p>\n\n\n\n Water-only fasting has been shown to lower insulin levels<\/a>, helping the body become more insulin sensitive<\/a> over time. A 2018 study<\/a> found that TRE improved insulin signaling and glucose metabolism.<\/p>\n\n\n\n Those improvements aren\u2019t necessarily long-lasting, though. What you eat after a fast (known as the \u201crefeeding\u201d phase) is crucial in retaining the benefits of the fast. A 2022 study<\/a> found that overweight adults who underwent prolonged water-only fasting followed by a plant-based refeeding diet experienced sustained improvements in weight, blood pressure, cholesterol levels, inflammation, and markers of fatty liver disease. <\/p>\n\n\n\n Direct evidence that water-only fasting extends human lifespan is still scarce, but intriguing research suggests some promising effects. Prolonged fasting appears to kickstart powerful processes in the body, boosting cellular repair, lowering inflammation, and sharpening metabolic health. A study involving 12 healthy volunteers<\/a> who undertook a 7-day water-only fast observed significant changes in approximately 3,000 proteins in their blood, impacting every major organ in the body. These sweeping changes could very well set the stage for a longer, healthier life.<\/p>\n\n\n\n A 2023 study<\/a> found that a single 36-hour water-only fast led to significant changes in the plasma lipidome. No, that\u2019s not a stadium in a dystopian sci-fi series. Your plasma lipidome refers to all the \u201cfatty\u201d vehicles that travel through your bloodstream, including cholesterol, triglycerides, and a bunch of others that you may not have heard of because they can\u2019t afford a good public relations firm. Specifically, certain lipids associated with inflammation and metabolic dysfunction decreased, while others linked to cellular signaling and longevity increased.<\/p>\n\n\n\n Fasting has also been shown to significantly reduce levels of IGF-1<\/a>, a growth hormone that, at high levels, is linked to aging, inflammation, and cancer progression. <\/p>\n\n\n\n Remember that when you run out of carbs and glycogen, your body starts burning its fat to produce ketones. That process, called ketosis<\/a>, occurs in both IF and prolonged fasting. Over time, it can significantly reduce body fat<\/a>, particularly visceral fat (the stuff that surrounds your organs and is much more harmful than subcutaneous fat, or the fat that\u2019s just under your skin). (For more on the pros and cons of a ketogenic diet, see our article here<\/a>.)<\/p>\n\n\n\n Water fasting<\/a> has been shown to lower blood pressure<\/a>, cholesterol, and triglycerides.<\/p>\n\n\n\n A 2024 study conducted at the Buchinger Wilhelmi Clinic<\/a> (a fasting clinic in Germany) observed that participants who underwent a 12-day medically supervised water-only fast lowered their total cholesterol, LDL (\u201cbad\u201d) cholesterol, and triglycerides. Notably, the most artery-clogging particles decreased and remained lower even one month after fasting. <\/p>\n\n\n\n BDNF (brain-derived neurotrophic factor) is a protein that helps keep your brain cells healthy and supports learning, memory, and overall brain function. Think of it as a kind of \u201cfertilizer\u201d that allows your brain cells to grow stronger and better connected.<\/p>\n\n\n\n Fasting increases the production of BDNF<\/a>. And while research on humans is limited, animal studies suggest that intermittent fasting may reduce oxidative stress<\/a> and inflammation in the brain.\u200b\u200b Animal studies also suggest that IF may reduce risk factors for neurodegenerative diseases<\/a> like Alzheimer\u2019s and Parkinson\u2019s by improving how the brain uses energy, reducing inflammation, and helping nerve cells survive longer. <\/p>\n\n\n\n Researchers discovered<\/a> that people who fasted for 24 hours once a week over 6 months had higher levels of a protein called galectin-3 than those who didn\u2019t fast. Galectin-3 helps repair cells and may reduce inflammation in the body.<\/p>\n\n\n\n IF helps reduce inflammation by lowering the activity of NF-\u03baB<\/a>, a protein that triggers harmful immune responses. More sluggish NF-kB means lower levels of inflammatory molecules, which can compromise gut health and tip your immune system into imbalance. <\/p>\n\n\n\n In a 2023 study<\/a>, participants showed a remarkable drop in inflammatory activity within their immune cells after a 36-hour water fast, compared to when they had eaten a regular meal. Not eating gave their immune system a chance to calm down and reset.<\/p>\n\n\n\n Other fasting studies have found relief from chronic conditions like IBS<\/a> and autoimmune flare-ups.<\/p>\n\n\n\n A 2025 study<\/a> put 20 middle-aged volunteers on a medically supervised 10-day water fast, followed by a 5-day refeeding period. They experienced weight loss, a metabolic shift into fat-burning mode, improved fat processing in their bodies, and even a reduction in amyloid beta proteins, which are linked to brain plaques.<\/p>\n\n\n\n In this and some other studies, a marker of inflammation called CRP has been seen to rise during fasting. Researchers theorize that the rise may be due to a temporary increase in stress-related hormones<\/a> like adrenaline.<\/p>\n\n\n\n On the other hand, a different inflammatory biomarker called ESR (erythrocyte sedimentation rate) was found to decrease significantly. And periodic fasting has been shown to clinically improve symptoms of rheumatoid arthritis<\/a>, suggesting that fasting typically leads to decreased inflammation over time.<\/p>\n\n\n\n And because visceral fat itself releases inflammatory chemicals<\/a>, the reduction in belly size through fasting is also likely to lower inflammation levels in the long run.<\/p>\n\n\n\n We\u2019ve seen that water fasting, in particular, offers a powerful, evidence-backed way to support detoxification, weight management, metabolic health, and longevity. But it isn\u2019t for everyone. The following groups should probably attempt water fasting only under medical supervision, if at all:<\/p>\n\n\n\n <\/p>\n\n\n\n Fasting for less than 24 hours typically does not require supplementation, as long as you are healthy and maintain adequate hydration. During short fasts, your body\u2019s electrolyte levels generally remain stable, and drinking a normal amount of water will support your basic physiological functions.<\/p>\n\n\n\n That said, in certain situations, you may have to supplement to maintain your electrolyte balance. These include intensive physical activity or heat exposure, and if you have trouble retaining electrolytes or fluid.<\/p>\n\n\n\n Engaging in intense exercise or being in a hot environment can lead to increased sweating, which means electrolyte loss. Supplementing with electrolytes like sodium, potassium, and magnesium can help maintain hydration and prevent muscle cramps and fatigue. <\/p>\n\n\n\n I\u2019d strongly recommend not scheduling your water fast for the day you run an ultramarathon in Death Valley in July, though! All kidding aside, please save your intense workouts for days when you\u2019re not water fasting.<\/p>\n\n\n\n If you have a health condition that affects your electrolyte balance or ability to retain fluids, such as kidney dysfunction or heart failure, consult with a healthcare provider to determine if you should supplement when fasting. <\/p>\n\n\n\n If you do decide to add electrolyte supplements<\/a> to your water during fasting, opt for products that are free from added sugars and calories to avoid breaking the fast. Plain water, herbal teas, and zero-calorie electrolyte solutions can be good ways to stay hydrated without interrupting the fasting state. <\/p>\n\n\n\n Fasting for more than 48 hours or engaging in repeated fasting cycles can increase the risk of deficiencies in key electrolytes<\/a>, such as sodium, potassium, and magnesium, as well as certain vitamins, particularly if your diet lacks nutrient-dense foods.<\/p>\n\n\n\n Extended fasting depletes essential electrolytes because you\u2019re excreting them, but not replenishing your supplies from food. Sodium and potassium levels, in particular, can drop rapidly during the early stages of fasting. <\/p>\n\n\n\n That\u2019s because decreased insulin levels cause the kidneys to excrete more sodium, leading to a loss of both sodium and potassium through urine. Such losses can, over time, result in symptoms like fatigue, muscle cramps, and dizziness.<\/p>\n\n\n\n Prolonged fasting can also lead to deficiencies in vital vitamins, including B vitamins like thiamine (B1). If you just pick up eating normally after an extended fast, you run the risk of something called refeeding syndrome<\/a>: a potentially life-threatening condition characterized by sudden shifts in fluids and electrolytes. <\/p>\n\n\n\n This syndrome is associated with deficiencies in phosphate, potassium, magnesium, and thiamine, and can lead to complications such as cardiac arrhythmias, muscle weakness, and neurological issues. <\/p>\n\n\n\n While that sounds alarming, it\u2019s much more of a danger for people who have been suffering from prolonged malnutrition<\/a>, whether from lack of access to food or inability to digest it. In medically supervised therapeutic fasting, most participants are far from malnourished.<\/p>\n\n\n\n The risk of nutrient deficiencies during fasting is higher if your regular diet is poor, consisting of highly processed foods that are low in micronutrients. Consuming a diet rich in whole, unprocessed foods, such as vegetables, fruits, nuts, seeds, whole grains, and legumes, can help replenish vital nutrients and mitigate any risks associated with prolonged fasting.<\/p>\n\n\n\n Recommendations<\/strong><\/p>\n\n\n\n By paying attention to electrolyte and vitamin intake and choosing a balanced diet when you do eat, you can support your health during fasting practices.<\/p>\n\n\n\n Salt may<\/em> be risky post-fast if:<\/p>\n\n\n\n Salt is beneficial and often recommended<\/strong> in the following post-fast scenarios:<\/p>\n\n\n\n Clinical fasting centers<\/strong> (like TrueNorth Health Center<\/a>) often use low-sodium refeeding protocols<\/strong> in the first day or two, gradually reintroducing sodium over time.<\/p>\n\n\n\n One downside of long water fasts is muscle loss. When you don\u2019t eat for a long time, your body may start converting its muscle tissue into energy. Therefore, some of that weight loss is likely to be due to muscle loss.<\/p>\n\n\n\n <\/p>\n\n\n\n The Fasting Mimicking Diet (FMD) is a type of eating plan designed to replicate the physiological effects of fasting, while still allowing you to eat. (Talk about the best of both worlds!)<\/p>\n\n\n\n Developed by Dr. Valter Longo<\/a> and popularized through the ProLon Fasting Mimicking Diet<\/a>, the FMD allows limited calorie intake while still triggering many of the beneficial metabolic processes associated with water-only fasting.<\/p>\n\n\n\n While ProLon offers scientific rigor along with ease and convenience, you can save money by approximating the protocol and availing yourself of its benefits by taking a DIY approach. <\/p>\n\n\n\n If you decide to do your own FMD, the ideal approach is to use fresh, whole foods, such as vegetables, fruits, and beans. You can put together your own <\/strong>low-calorie, low-protein, low-carb, high-fat diet designed to \u201ctrick\u201d the body into a fasting state while still allowing you to consume food.<\/p>\n\n\n <\/p>\n 2. Macronutrient Breakdown<\/strong> 3. Some DIY-Friendly Food Options<\/strong> <\/p>\n <\/p>\n Day 3 (~800 kcal)<\/strong><\/u> Day 4 (~800 kcal)<\/strong><\/u>What Is Fasting?<\/strong><\/h2>\n\n\n\n
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What Happens in the Body During a Fast?<\/strong><\/h2>\n\n\n\n
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Glycogen Depletion and Ketone Production<\/strong><\/h4>\n\n\n\n
Cellular Autophagy and Detoxification<\/strong><\/h4>\n\n\n\n
Improved Insulin Sensitivity<\/strong><\/h4>\n\n\n\n
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Anti-Aging and Longevity Effects<\/strong><\/h4>\n\n\n\n
Weight Loss and Fat Burning<\/strong><\/h4>\n\n\n\n
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Cardiovascular Health<\/strong><\/h4>\n\n\n\n
Enhanced Mental Clarity and Neuroprotection<\/strong><\/h4>\n\n\n\n
Inflammation Reduction<\/strong><\/h4>\n\n\n\n
Is Fasting For Everyone?<\/strong><\/h2>\n\n\n\n
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Do You Need Supplements While Water-Only Fasting?<\/strong><\/h2>\n\n\n\n
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Longer or Repeated Fasts<\/strong><\/h4>\n\n\n\n
Vitamin Deficiencies and Refeeding Syndrome<\/strong><\/h4>\n\n\n\n
Importance of Diet Quality<\/strong><\/h4>\n\n\n\n
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What about Salt After Fasting?<\/strong><\/h3>\n\n\n\n
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Loss of Muscle Mass<\/strong><\/h4>\n\n\n\n
What is a Fasting Mimicking Diet?<\/strong><\/h2>\n\n\n\n
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Pros of the Fasting Mimicking Diet:<\/strong><\/h4>\n\n\n\n
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Cons and Considerations:<\/strong><\/h4>\n\n\n\n
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Do-It-Yourself Fasting Mimicking Diet (DIY FMD)<\/strong><\/h4>\n\n\n\n
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\n DIY FMD Guidelines<\/strong><\/td>\n \u00a0<\/td>\n<\/tr>\n \n Guidelines<\/strong><\/td>\n 1. Caloric Targets<\/strong>
Day 1: 1,100\u20131,200 calories
Days 2\u20135: 700\u2013800 calories\/day<\/p>\n
Carbohydrates: ~40\u201350%
Fats: ~40\u201350%
Proteins: ~10%<\/p>\n
Healthy Fats:<\/em> Avocados, olives, macadamia nuts, almond butter
Low-GI Carbs:<\/em> Zucchini, kale, broccoli, carrots, berries (small portions)
Plant-Based Protein:<\/em> Chia seeds, hemp seeds, small servings of nuts
Soups:<\/em> Homemade vegetable broth, mushroom soup
Drinks:<\/em> Green tea, herbal teas, black coffee, lemon water<\/p>\n<\/td>\n<\/tr>\n\n Sample DIY-FMD Meal Plan<\/strong><\/td>\n \u00a0<\/td>\n<\/tr>\n \n Days 1\u20136 Meal Plans<\/strong><\/td>\n Day 1 (~1,100 kcal)<\/strong><\/u>
Breakfast:<\/strong> Green tea or lemon water, 1 tbsp almond butter, 1 avocado with lemon, 1 small apple or \u00bd banana
Lunch:<\/strong> Butternut squash & leek soup, baked sweet potato round, flaxseed cracker, sunflower seeds
Dinner:<\/strong> Steamed broccoli & zucchini, \u00bd avocado, flaxseed in veggie broth<\/p>\n
Day 2 (~800 kcal)<\/strong><\/u>
Breakfast:<\/strong> Herbal tea, chia seeds in warm water with cinnamon
Lunch:<\/strong> Carrot-ginger soup, \u00bc avocado, small fruit, pumpkin seeds
Dinner:<\/strong> Cauliflower mash, steamed kale & mushrooms, walnut pieces<\/p>\n
Breakfast:<\/strong> Dandelion root tea, almond butter, walnut halves
Lunch:<\/strong> Roasted red pepper & tomato soup, steamed Swiss chard, hemp seeds, \u00bd avocado
Dinner:<\/strong> Roasted carrots & Brussels sprouts, salad with lemon & sunflower seeds<\/p>\n
Breakfast:<\/strong> Herbal tea, flaxseed meal with mashed banana
Lunch:<\/strong> Celery & zucchini soup, \u00bd avocado, ground chia seeds, almond butter
Dinner:<\/strong> Steamed bok choy & turnips, mashed cauliflower, crushed almonds<\/p>\n