I thought today would be a particularly good day to write this post because I’m currently 68 hours into a 3-day fast. It’s a good time to show that I’m still functioning normally after nearly 3 days without eating and to ensure that I remember all my tips and tricks, in case you’re interested in trying it. If you’re thinking that multi-day fasting seems impossible or ill-advised, I hope that I can dispel some of the myths.

First, the myth is that it’s inherently unhealthy to not eat for long periods of time. If this were true, our species would’ve never survived winters before food preservation made access to food more regular. Instead, many religions carried forward fasting traditions after food became relatively abundant for their benefits, especially mental benefits. Mental benefits include detaching from the constant cycle of preparing and eating food, resetting hedonistic patterns (especially with junk food), and learning to appreciate our food instead of take it for granted. To me, the most compelling argument that fasting isn’t bad for you is that it is increasing in popularity, despite the fact that there’s no money to be made from not eating.

For physical benefits, alternating between feasting and fasting allows a natural cycle between periods of growth and periods of rest and repair. Many people think that if they don’t eat, then they’ll break down muscle for energy. However, this can’t be true because whenever our ancestors failed a hunt, they’d be weaker for subsequent hunts and more likely to fail. Our bodies are smarter than this. When people don’t eat for more than a day, their growth hormone surges, preserving muscle.

During the first day, though, you will burn some protein for fuel, but it’s mostly protein that the body is cleaning up through the process of autophagy. Autophagy is many people’s primary goal for multi-day fasts. It happens when your cells realize that there’s a lack of nutrients, so they start weeding out the old, inefficient organelles and misfolded proteins that are lying around and not pulling their weight. Autophagy is also why people who lose weight with fasting have less excess skin as they lose weight. The body recycles the proteins in skin to preserve muscle. This process has great benefits for mitochondrial (energy) and metabolic health.

After the first 12-24 hours of fasting, we primarily burn fat, which is why we carry around fat – for periods when food is scarce. If you are looking to reduce fat, this is why fasting is better than chronic caloric restriction. In chronic caloric restriction, especially if you eat every few hours, you’ll have too much insulin in the blood to burn primarily fat and instead burn a 50/50 mix of muscle and fat. Losing muscle mass is why chronic dieting, especially yo-yo dieting, causes people’s basal metabolic rate to plummet. I’ve heard of some women who can’t eat more than 1200 calories a day without gaining weight, whereas I eat 2100 calories a day without gaining weight. Anyone trying to reduce fat through fasting, though, should be on the lookout for disordered eating and ensure that they get enough nutrients in the long run.

What I do: I’ve been doing a 3- or 4-day fast at least every quarter for 2 years. I’ll eat dinner on day 0 like normal, not eat anything for 2-3 days, and have dinner on the 3rd or 4th day. For about six months when I was losing weight, I did a 3-day fast every month, which was probably a little much given that I was also doing 16-18 hours of fasting every day and 24-hour fasts every week. Still, I felt fine and wasn’t losing muscle.

3-4 days is the longest fast that I would attempt without medical supervision. However, if you have medications, especially those taken with food or related to blood sugar or blood pressure, you need to consult with your doctor before attempting any multi-day fast. Fasting is also not beneficial for children, those who are pregnant or breastfeeding, or anyone who cannot handle extra stress on their body.

What to Expect

• Day 0, 0-12 hours: If you start fasting after dinner on day 0 like I do, then this part should feel normal.
• Day 1, 12-24 hours: This is the hardest part for me as my body adjusts. I feel mostly normal but hungry, especially at mealtimes. After this point, you will feel less hungry as you switch more to fat burning. I also lose 2-3lbs of water (and electrolytes with it) as I use up glycogen (the storage form of glucose that stores 4g of water for each gram of glycogen).
• Day 2, 24-48 hours: This is the easiest part for me. My energy is still good, and I mostly don’t feel hungry. Don’t get me wrong, food sounds good, but I’m much less attached to eating it. I also run out of breath easier because it takes more oxygen to burn fat than glucose for energy. Towards the end of the day, I’ll start to feel cold as my body becomes thrifty with its energy expenditures. Sometimes I’ll sleep poorly on this night as my body produces a little extra cortisol to make sure I’m alert for any opportunities to eat.
• Day 3-4, 48-72/96 hours: This part is like a lower-energy day 2. I’m bad about having enough electrolytes, so I’ll often get lightheaded when I stand up because my blood pressure is lower. My body tries to conserve energy by telling me that I’m tired and weak, but I have just as much energy and strength as I do any other day. I typically do a short strength training session each day to make sure my body knows I need my muscles, and the only difference I feel between fasting and non-fasting is running out of breath faster.
• For the week after: Dinner on Day 3 or 4 tastes amazing, and you’d be surprised how quickly you feel full. This effect persists for a couple days. I’ll typically lose ~5lbs by the end of the fast, but I also gain most of the weight back quickly, as I regain glycogen and water. All in all, I typically take off about ~1lb of fat from a 3-4 day fast.

Tips and Tricks

The only things you NEED to do on a multi-day fast is get adequate rest, drink lots of water (I do 96-128oz), and take in some electrolytes (I prefer LMNT packets). After that point, what you include is more about your preferences and what makes it easier. I won’t lie, multi-day fast is tough, especially at first, but it’s not nearly as tough as people think it will be. With a few tricks, it can be much easier.

The most common questions about fasting are what counts as breaking the fast. The answer mostly depends on your goals. If your goal is rest, repair, and autophagy, then you want to avoid calories, especially from protein. Most people will continue to drink tea and coffee, though you might watch your caffeine intake because your cortisol will already be elevated. I avoid bone broth because it has protein, which can dampen autophagy, but many people who are trying to lose weight will include it.

To keep my gut microbiome happy, I’ll take activated charcoal and fiber pills once a day. The fiber gives the good bacteria in your gut something to eat while you’re not. The activated charcoal helps to clear out unhelpful things from the gut, like bad bacteria that thrive on sugar and are starving during the fast.

In preparation for a fast, I’ll do a few things. First is to just mentally prepare and make sure you’re setting yourself up for success (have time to rest, aren’t going to family dinner). I also eat close to keto the week before so that my glycogen stores are lower and my fat-burning system is ramped up. On the first day of the fast, I do a longer (60-90 minute) cardio session to burn through glycogen faster and get deeper into the fast more quickly.

Regular movement will help you maintain muscle mass. Magician David Blaine did a 44-day fast in a glass box and lost a lot of muscle because he had no room to move around. Obviously, 3 days is quite different, but muscle is always a use-it-or-lose-it tissue. Any sort of low-impact activity that doesn’t do much muscle damage is good (e.g., walking not running, climbing stairs not jumping, band-based resistance training not hypertrophy-style resistance training). Your body will tell you to conserve energy, but it doesn’t know when your next meal is — you do.

If you’re really struggling and are thinking about quitting, try eating high-fiber veggies (like celery or leafy greens). The fiber will make your gut happy, and the minimal carbs won’t absorb fast enough to affect insulin much. You can even cook them in fat because fat doesn’t interfere with the autophagy system (aka stimulate mTOR). A few times, especially my first few fasts, I’ve eaten a serving of leafy greens cooked in oil to avoid quitting a fast. Sometimes I’ll also eat celery just to have something to chew on. These things have minimal impact on the fast but can significantly improve the experience.

As I mentioned, fasting isn’t easy, which can make it difficult to tell if you should cut the fast short. Some normal symptoms include lightheadedness, headache (especially if caffeine is reduced), nausea, and fatigue. These symptoms, however, should not be chronic, and they should not feel extreme. If you can’t function normally, then you should probably stop. In addition, if you feel dehydrated despite drinking lots of water or shaky, then your blood sugar is probably too low to continue. When I first started, I also had lower back pain on my 3rd day, which is often a sign of kidneys processing too much protein. If you start to experience lower back pain, you should probably stop within several hours.

When you break your fast, you’ll be more insulin sensitive than normal. This means that you should not eat a lot of carbs or high-glycemic foods. I usually break my fast with 5-8oz of steak and a side of roasted brussel sprouts with olive oil, which is about 800 calories. The next few days, I’ll focus on high-fiber/low-sugar plants and nutrient-dense foods to rebuild my gut microbiome, refuel my body, and avoid spiking insulin.

Are you ready? If you can do a 24-hour fast, then you can probably do a 2-3 day fast without much fuss, especially if you use these tips. For further information about multi-day fasting, you can get a lot of the basics from Dr. Jason Fung and a lot of the more nuanced questions answered with evidence-based information from the Buchinger Wilhelmi Clinic. There’s not one video that I’d recommend, but both sources have many videos on YouTube.

For more blog posts about wellness, return to the wellness series page.