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What does a 5 day fast do to your body?

Fasting has become an increasingly popular way to lose weight, improve health, and simplify life. While there are many different fasting protocols, 5 day fasts are one of the more common durations. A 5 day fast gives your body plenty of time to start reaping the benefits of fasting, without being overly long or difficult to stick to. Here’s an in-depth look at what happens in your body when you fast for 5 days.

Hours 0-8 of Fasting

Once you stop eating and enter into a fasted state, your body will first start burning through its readily available glycogen stores for energy. Glycogen is the stored form of carbohydrates, mostly found in your liver and muscles.

There are approximately 2000 calories worth of glycogen stored in the human body. Depending on your metabolic rate and level of activity, it takes around 8-12 hours to deplete your glycogen stores.

While your body is still burning through glycogen, you may experience hunger, irritability, weakness, and fatigue. This is the toughest part of fasting for many people. However, hang in there because once your body switches to burning fat for fuel, hunger and weakness will dissipate.

Tips for Getting Through the First Hours of Fasting

  • Stay busy and try to limit time spent thinking about or preparing food
  • Drink water, herbal tea, or black coffee to help curb hunger
  • Avoid being around food or watching food commercials
  • Go to bed earlier as you’re more likely to cave and eat when tired

Hours 8-24 of Fasting

Once your glycogen energy stores have been depleted, your body switches to burning fat for energy in a process called ketosis. Ketones are produced when your liver breaks down fatty acids for energy. Ketosis kicks in fully around the 24 hour mark of a fast.

One of the main benefits of fasting is that it accelerates the process of ketosis and fat burning. During this time, you will start to feel less hungry as your blood sugar and insulin levels begin to stabilize.

Your fat cells will start releasing glycerol to help produce glucose for energy. You may experience an increase in focus and mental clarity during ketosis as well, since your brain actually functions more efficiently when running on ketones versus glucose.

Signs Your Body Has Entered Ketosis

  • Reduced hunger and increased focus/energy
  • Fruity or metallic taste in mouth
  • “Ketone breath” that smells a bit like acetone
  • Increased urination as ketones are excreted through urine

Hours 24-72 of Fasting

This is where the deeper healing magic of fasting starts to kick in. With your body in full blown ketosis and cells clearing out damaged proteins and old cellular debris, you start to feel the benefits.

Autophagy ramps up, which is your body’s natural process of renewing and recycling damaged cells and proteins. Fasting stimulates autophagy, which is why it’s linked to anti-aging and longevity benefits.

Your body’s inflammation levels will decrease rapidly during this time as white blood cell counts fall. Your blood pressure can drop during extended fasts as well.

Growth hormone levels increase up to 5 times their normal rate during fasting since there is less glucose and insulin in your blood inhibiting it. This is connected to improved muscle gain and fat loss when combined with regular strength training.

Benefits of Fasting Hours 24-72

  • Increased autophagy
  • Reduced inflammation
  • Lower blood pressure
  • Increased growth hormone

Hours 72-96 of Fasting

The final stretch of a 5 day fast is where you start to reap the real rewards. As the body switches into deep conservation and self-healing mode, some of the most remarkable benefits occur during this time.

Studies show the final 24-48 hours of extended fasts result in cardio-protective and anti-diabetic benefits. Fasting cycles help reduce blood sugar spikes by rebooting your insulin sensitivity and glucose metabolism.

Nerve cell growth in the brain ramps up during fasting cycles as well. Animal studies show fasting’s ability to stimulate brain-derived neurotrophic factor, which encourages new neural connections. This effect contributes to the cognitive benefits of fasting.

Fasting for 3-5 days has been found in studies to regenerate the immune system. White blood cell counts fall initially but rise dramatically after 72 hours as the body clears out damaged immune cells and produces new ones.

Hours 72-96 Fasting Benefits

  • Rebooted insulin sensitivity
  • Stimulated nerve cell growth
  • Immune system regeneration

Breaking Your Fast

After you’ve reached your desired duration, it’s crucial to break your fast gradually and strategically to avoid undoing the benefits and shocking your system. Here are some tips for ending a 5 day fast:

  • Stick to water and herbal tea for the first few hours off the fast, then try bone broth or vegetable juice.
  • Eat an apple or avocado, as they are easy on the digestive tract.
  • Don’t overeat initially or mix carbs and proteins in the same meals.
  • Chew food very thoroughly and eat slowly.
  • If you feel bloated or uncomfortable, take a break before eating more.

It can take a couple weeks for your digestive enzymes and acid levels to fully bounce back, so continue favoring gentle foods as you transition back to normal eating.


A 5 day fast gives your body ample time to deeply cleanse and renew itself while sparking fat burning and metabolic benefits. You’ll likely find hunger and weakness dissipating around day 3 as ketosis fully kicks in and your body adapts to burning fat-derived fuels. The final 2 days are when fasting’s “magic” truly ramps up, with autophagy, immune regeneration, blood sugar rebooting, and neurogenesis occurring. Just be sure to break your fast gradually with gentle foods over a period of 2-3 days.

While fasting for 5 days may sound daunting for some people, you can work your way up slowly. Start with intermittent fasting for 12-16 hours and progress to 24-36 hour fasts before attempting a full 5 day protocol. Supporting your body with mineral supplements can also help minimize side effects.

Achieving a 5 day fast generally requires patience, planning and self-discipline. But the research shows it can be well worth it – unlocking powerful cleansing, healing and anti-aging benefits that affect your whole body right down to the genes.

Common Questions About 5 Day Fasts

Is fasting for 5 days healthy?

Yes, studies show that fasting for 3-5 days can have profound health and anti-aging benefits. It puts the body into deep autophagy and regeneration mode. Just be sure you’re healthy enough to fast and ease into it slowly.

How much weight will I lose on a 5 day fast?

Most people lose between 5-8 pounds over a 5 day fast. However, weight loss varies a lot between individuals based on metabolism, activity levels, and body composition. Around 2/3 of the weight lost is usually water weight that will be regained once you resume normal eating.

What are the side effects of a 5 day fast?

Potential side effects of 5 day fasting include hunger, headaches, dizziness, irritability, fatigue, constipation, muscle aches, and brain fog. These normally dissipate within 1-3 days as ketosis starts. Staying hydrated and supplementing with electrolytes can minimize adverse effects.

Can I exercise during a 5 day fast?

Light walking and gentle yoga are fine during extended fasts. But most experts recommend avoiding strenuous exercise like cardio or weightlifting when fasting for over 24-36 hours. Listen to your body closely and rest when needed.

Is it safe to take supplements while fasting for 5 days?

Yes, supplements like multivitamins, electrolytes, probiotics and magnesium can help support your body and minimize side effects when fasting. Avoid supplements that contain calories or artificial ingredients.

What are the dangers of fasting for 5 days?

Dangers of longer fasts mainly include severe hunger, electrolyte imbalances, dizziness, and fatigue. People with health conditions like gout or diabetes should only fast under medical supervision. Seek help if you experience chest pain, difficulty breathing, racing heart rate, or feel faint.

How often should you do a 5 day fast?

Most experts recommend leaving at least 2-4 weeks between extended fasts like 5-day protocols to give your body time to recover. Listen to your body and don’t force it if you aren’t feeling up to fasting again soon.

Can I drink coffee during a 5 day fast?

Black coffee and unsweetened tea are fine to drink while fasting for 5 days. They provide minimal calories and can help curb hunger. But avoid adding cream, milk or sweeteners to your coffee as that will break your fast.

What are signs you should stop fasting after 5 days?

Stop your fast if you experience chest pain, difficulty breathing, a racing heart rate, dizziness that won’t resolve, or you faint. Severe, uncontrolled hunger, weakness or fatigue are also signs you should consider ending your 5 day fast early.