A fast is a voluntary practice in which people go for extended or structured periods without eating and drinking for spiritual, medical, or weight loss reasons. Others fast to protest or raise awareness for causes. Fasts vary widely depending on the type you're following. Some fasts allow water, tea, coffee, or other fluids during the fasting period, but dry fasts go without. A fast may be intermittent, or it may extend for multiple days.

Fasting is not starvation. For those who fast for health reasons, fasting is just a more structured way of eating. Fasting is sometimes followed by feasting, especially around religious holidays. Some people may find fasting challenging, but there are many types of fasting regimens and protocols from which to choose.

Many of the world's major religions and cultures have a rich history of fasting. Fasting has long been promoted as a natural means to boost health and deepen spiritual awareness. In some sects of Buddhism, fasting is a regular part of the monastic lifestyle and enhances meditation. In the Judaeo-Christian and Islamic religious traditions, fasting is an act of observance, atonement, penance, self-control, or preparation for rituals or holidays. Therapeutic fasting dates back to Hippocrates, who prescribed it for many ailments. At the time, it was the only successful way to reduce seizures in epileptic children and remained so until the 20th century.[1]

Health Benefits of Fasting

Although much of the clinical research related to fasting is limited to animal studies, the abundance of first-hand accounts from people who fast is remarkable, exciting, and encouraging. Many people find that fasting sharpens their mind and provides mental clarity. Interestingly, many of the benefits of fasting don't result directly from fasting itself, but from the effects of reduced calorie intake, decreased fat composition, better sleep, less diet-related inflammation, and lower intake of salt.

Tempers Blood Pressure and Fluid Balance

Blood pressure tends to fall during the fasting state, primarily during the first week of fasting. This effect seems to result from a lower salt intake and a detoxification of accumulated salt through the urine. Since excess sodium causes your body to retain water, lower sodium levels lead to better fluid balance in your tissues.[1]

Encourages Normal Blood Sugar Levels

Since you don't need as much insulin while you're not ingesting sugar, your body's production of insulin drops during fasting.[2, 3]

Protects the Brain

Fasting and calorie restriction inhibits the production of free radicals and irritating proteins like inflammatory cytokines. Interestingly, evidence suggests that free radical and inflammatory cytokine production slow down during fasting and protective cytokine production increases and protects the brain from oxidative damage.[3]

Moderates Appetite

Fasting causes leptin levels to drop. However, as you lose weight, your response to leptin signaling increases, making it easier to eat healthier foods and smaller portions since you'll feel more satisfied after a meal.[3] Some weight loss authorities think leptin resistance might be a factor that prevents people who are significantly overweight from dropping pounds because they don't get that hormonal signal telling them that they're full.

May Help You Live Longer and Healthier

There is an evolutionary theory that may explain why animals that are fed low-calorie diets tend to live longer than their "well-fed" counterparts. The leading idea holds that when an organism endures challenges like famine, it responds by dedicating more resources to survival.[4] This is kind of like a factory shuffling equipment and labor around to produce a different product while also finding new ways to be more efficient.

Helps Burn Fat

Alternating windows of fasting and eating with regular resistance training leads to greater fat loss than either alone.[5]

Promotes Healthy Immune Function

Fasting triggers the recycling of old white blood cells — the cells that comprise much of your immune system. Recycling these immune cells leads to a more competent immune system. It works by triggering the regeneration of the stem cells that become your platelets, red blood cells, and white blood cells when you begin eating again.[6]

May Increase Resistance to Mental Stress

In animal models, researchers found that the effects of fasting on blood sugar and insulin levels also improves the brain's response to mental stress and protects it from stress-related damage.[7]

Different Types of Fasting

Fasting methods and protocols vary widely depending on the specific fast. Even within the fasts described below, there are at least a couple of ways of conducting the fast. When deciding which to pursue, consider your goals and which will help you get there.

Diagnostic Fast

This fast may be a bit more difficult because it's not something most people elect to do. Your doctor may prescribe a fast before a medical procedure such as surgery or a blood test. It's important to stick to the recommended protocol for safety and accurate test readings.

Dry Fast

Arguably the most straightforward kind of fast, dry fasting involves not eating or drinking anything during the fasting period. A diagnostic fast may also be a dry fast. I do not advocate dry fasting for extended periods of time. Beyond making you feel lousy, dehydration can have serious side effects on your blood volume and tissues, making it difficult for your body to detoxify itself.

Liquid Fast or Water Fast

When liquid fasting, you only drink fluids and avoid eating solid foods. Liquid fasts can include broth, water, or concoctions made with water, like the Master Cleanse. Water fasts only permit water during the fasting period. These fasts can last anywhere from a day to several days.

Juice Fast

Juice fasting, or juice cleansing, is a type of liquid fast lasting 3-5 days. It's usually conducted with detoxification or weight loss in mind. Juice fasts include organic, cleansing fruit and vegetable juices.

Partial Fast

There are two kinds of partial fasting. The first type is similar to liquid fasting except you may eat small amounts of solid food for the duration of the fast. The second type excludes certain foods for an extended period. Many people give up carbohydrates, alcohol, or red meat during this fast.

Intermittent Fast

Intermittent fasting is alternating periods of fasting and eating during the same day. This pattern may persist every other day, a few days at a time, or you may choose to adopt this style of fasting into your everyday life for an extended period. The food you eat while intermittently fasting may not change at all, or people may feast during the eating window. Some people simply eat all their meals within a small window of time in the afternoon or evening.

There are many ways to conduct an intermittent fast. Religious intermittent fasts typically prohibit eating between dawn and dusk, and meals are only taken in the evening. Athletes, dieters, and bodybuilders tend to customize their intermittent fasting schedule to their daily schedule to get the most out of their fast. Some evidence indicates that longer periods of fasting increase weight loss and produce better results in blood glucose and insulin balance.[8]

Alternate-day Fast

Alternate-day fasting is a much more intense fasting regimen than other fasting methods. This fast seems to be especially helpful for losing weight and maintaining weight loss progress. To qualify as an alternate-day fast, you must fast for at least 24 hours. Some people choose to extend alternate-day fasts up to 36 hours. Make sure to drink plenty of water or tea during an alternate-day fast.

Extended Fasting

Extended fasts are usually 48 hours without eating, but they can last up to a week or longer. People may conduct this fast a few times a year or every month. These fasts are usually only conducted by people who have a high body mass index or who have trained their metabolism to adjust to long periods of fasting. Depending on the length of the fast, it may be necessary to add nutritional supplements to your water to keep your vitamins and minerals in balance.

Ketogenic Fast

Ketogenic fasts push your body into the fat burning state known as ketosis. A ketogenic fast is similar to a partial fast in that it includes a small amount of food. The two differ in the types of food consumed. On a ketogenic fast, you only consume fatty foods to shift your body into ketosis. Check out my ketogenic fast for a vegan take on this fast. You can try it for five days to begin to feel the benefits or go as long as three weeks.[9]

Important Considerations While Fasting

Fasting takes planning and preparation. Before beginning any fasting regimen, you must get a handle on your schedule, stress, and nutrition. Be realistic about your goals when conducting a fast. Inadequate sleep, unhealthy or emotional eating patterns, and insufficient stress management can impede weight loss or undo any advances you make.[3]

Stay hydrated while fasting. Before your body adjusts, you may experience mild but unpleasant symptoms for the first three days. Hunger, irritability, slight headache, and disorientation are common while you're adjusting. Around day four on a restrictive fast, you should begin to feel significantly better than you normally do when not on a fast.

Some people should not fast. Children, pregnant and lactating women, and diabetics should avoid fasting unless instructed to do so by their trusted health care advisor. It's also a good idea to converse with them and get an informed opinion that's personalized to your needs and situation before radically changing your diet or going on an extended fast.