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What does a 72 hour fast do to your body?

Author

William Rodriguez

Published Jan 18, 2026

72+ hours. Once you've been fasting for three days or more, your body enters a deep state of ketosis. All the previous benefits: Autophagy, the uptick in the production of beneficial chemicals and hormones, fat loss, and mental clarity continue to increase.

What happens to your body when you fast for 3 days?

What To Expect When Fasting For 3 Days? Fasting can result in vitamin and mineral deficiencies, muscle breakdown, and diarrhea. Other Side effects of fasting include dizziness, headaches, low blood sugar, muscle aches, weakness, and fatigue.

How often should you do 72 hour fasts?

Nutrition and therapy researchers such as Dominic d'Agostino recommend 5-day long fasts two to three times per year to reboot your immune system due to stem cell-based regeneration.

How much weight can you lose on a 3 day water fast?

Because a water fast restricts calories, you will lose a lot of weight quickly. In fact, research shows that you may lose up to 2 pounds (0.9 kg) each day of a 24- to 72-hour water fast ( 7 ). Unfortunately, a lot of the weight you lose may come from water, carbs, and even muscle mass.

What happens if you fast 7 days?

There are many potential side effects to a 7-Day Water Fast, including rapid heartbeat, dizziness, and fatigue. The two most severe side effects are dehydration and muscle loss/weakness. When it comes to weight loss, progress is made by inches, not miles, so it's much harder to track and a lot easier to give up.

24 related questions found

Do you poop when fasting?

Yep, in some cases intermittent fasting can totally throw your bowel movements out of whack. Constipation isn't the only possible side effect of intermittent fasting. Others have also claimed they've experienced the opposite issue, like diarrhea, in some cases. Don't fret if poop probs happen to you, though.

How long can you starve yourself before losing weight?

This process will affect your muscles and can carry your body along for about three days of starvation before metabolism makes a major shift to preserve lean body tissue. To prevent excessive muscle loss, the body begins to rely on fat stores to create ketones for energy, a process known as ketosis.

Is a 3-day fast safe?

Is Fasting Safe? Fasting for a few days probably won't hurt most people who are healthy, provided they don't get dehydrated. Your body needs vitamins, minerals, and other nutrients from food to stay healthy.

What should I eat after a 3-day fast?

Gentle foods to break a fast

  • Smoothies. Blended drinks can be a gentler way to introduce nutrients to your body since they contain less fiber than whole, raw fruits and vegetables.
  • Dried fruits. ...
  • Soups. ...
  • Vegetables. ...
  • Fermented foods. ...
  • Healthy fats.

How do you do a 72 hour fast?

Preparing for an Extended Fast

  1. Decide how long you will fast. ...
  2. Drinking coffee and tea during a 3-day fast is fine. ...
  3. You can have more than just water during a 72-hour fast. ...
  4. A 3-day water fast takes longer than three days. ...
  5. Don't eat a final meal heavy in carbohydrates. ...
  6. Let family or roommates know you're fasting.

Can you workout during a 72 hour fast?

Yes, it is OK to work out while fasting because the key to weight loss and muscle gain is not just calories and exercise, but hormone optimization. Studies demonstrate amazing benefits to intermittent fasting alone, but combining fasting with sprint training takes the benefits of each to a whole new level.

Can I exercise while fasting 72 hours?

When you're fasting for longer periods of time, over 72 hours, exercise should be avoided. You do not have enough fuel in your body to power through the workout. Even if you feel like you're up for it, any positive benefit from your workout will be severely diminished.

Can you drink coffee on a 72 hour fast?

During fasting periods, zero-calorie beverages or drinks that are pretty close to zero calories—like tea and lemon water while fasting—are OK. An eight-ounce cup of coffee contains about 100 milligrams of caffeine, negligible macronutrients, and about two calories. Black coffee can be good for you.

Can a 3 day fast reset your immune system?

The Source featured research by Valter Longo of the USC Leonard Davis School on how fasting for three days can improve a person's health. The six-month study was done on subjects going through chemotherapy.

What are the stages of fasting?

The four phases include the fed state, early fasting state, fasting state, and long-term fasting state (starvation state). Each phase varies based on the primary source of energy used for the body, as well as how it affects your metabolism and levels of specific hormones.

How long can I safely fast?

To keep yourself safe, especially if you are new to fasting, consider limiting your fast periods to 24 hours or fewer and keeping a snack on hand in case you start to feel faint or ill. If you do become ill or are concerned about your health, make sure you stop fasting straight away.

What should I eat after a 72 hour fast?

We like to poultry or fish following a fast. Having a small portion of protein at your first meal such as salmon or chicken can be a good option because they provide essential amino acids to help rebuild and repair the body.

Are eggs good to break a fast?

Eggs are a great way to break your fast.

An egg is a whole food that contains lots of proteins, vitamins, and nutrients. Egg gets digested quickly, is low in calories, and rich in proteins.

Can you drink coffee on a 3 day fast?

No food is allowed during the fasting period, but you can drink water, coffee, tea and other non-caloric beverages. Some forms of intermittent fasting allow small amounts of low-calorie foods during the fasting period. Taking supplements is generally allowed while fasting, as long as there are no calories in them.

What does your body feel like in starvation mode?

It has been shown that your body temperature lowers when you don't consume enough calories. You feel lethargic. Without enough calories, you will quickly experience feelings of fatigue because your body doesn't have enough calories to burn and generate energy.

How do you know if your body's in starvation mode?

If you don't eat enough calories for a period of time, your body may go into starvation mode or adaptive thermogenesis.
...
The signs and symptoms of starvation mode may include:

  1. ​Lethargy. ​ Calories are, essentially, fuel for your body. ...
  2. ​Feeling cold. ...
  3. ​Constipation. ...
  4. ​Depression. ...
  5. ​Hair loss.

What are the symptoms of starving yourself?

Other symptoms of malnutrition include:

  • reduced appetite.
  • lack of interest in food and drink.
  • feeling tired all the time.
  • feeling weaker.
  • getting ill often and taking a long time to recover.
  • wounds taking a long time to heal.
  • poor concentration.
  • feeling cold most of the time.

How do you break a 3 day dry fast?

You should ideally break your fast with simple organic foods, such as a light salad or a probiotic smoothie which can help release even more toxins without placing too much pressure on your stomach all of a sudden.

Why do I get diarrhea after eating after fasting?

Causes of diarrhea during fasting

During a fast, diarrhea may occur because of an oversecretion of water and salts in the GI tract. A number of triggers can cause this, including drinking liquids high in caffeine, such as tea or coffee. Usually, fasting doesn't cause diarrhea on its own.

Does water with lemon break your fast?

Plain lemon water with only lemon juice is also allowed when following the intermittent fasting method. The drink contains almost zero calories and does not break your fast. Having one or two glasses of lemon drink, when following intermittent fasting can also help you burn fat and curb hunger.