The Benefits of Intermittent Fasting

June 9, 2012 in Categories: by

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Intermittent fasting, or IFing, is a very popular strategy for stimulating healing, increasing longevity, balancing hormones, increasing energy and mental clarity and losing weight.  If you’ve heard this term bantered around paleo circles and have been wondering what it’s all about, then wonder no longer!

How does Intermittent Fasting work?  Intermittent fasting provides a variety of health benefits, predominantly due to stimulating a process call autophagy.  Autophagy is the process by which a starving cell can reallocate nutrients from cell machinery that is not working optimally to fuel more essential cell processes. The cell degrades its own components, including damaged organelles, cell membranes and proteins, in a tightly regulated process.  Autophagy can destroy viruses and bacteria within the cell that are resistant to other ways a cell might destroy them.  It can even help the cell identify a viral infection that may have otherwise gone undetected.  Autophagy plays a crucial role in immunity and inflammation, balancing the beneficial and detrimental effects of immunity and inflammation, and thereby may protect against infectious, autoimmune and inflammatory diseases.  It may even prevent cells from becoming cancerous.  Autophagy plays a normal part in cell growth, development, and homeostasis, helping to maintain a balance between the synthesis, degradation, and subsequent recycling of cellular products.  In fact, failure of autophagy is thought to be one of the main reasons for the accumulation of cell damage and aging.  Turning on autophagy is extremely beneficial (whether it’s turned on by intermittent fasting, exercise, ketosis, or straight calorie-restriction).  The result is healthier, more efficient cells, which means a healthier, more efficient body. 

What are the benefits of Intermittent Fasting?  The benefits of intermittent fasting can be inferred from the effects of autophagy.  However, more and more scientific studies are being conducted to confirm the effects of Intermittent Fasting and also isolate the optimal strategy for putting it into practice.  Many of the benefits listed below have not been directly tested in humans using Intermittent Fasting; however, there is either strong evidence from animal studies or evidence from studies of autophagy itself, combined with anecdotal evidence to support these claims.  The benefits of Intermittent Fasting include:

  1. Increasing lifespan. 
  2. Increasing insulin sensitivity, which has many health benefits in and of itself.  Of interest, the resulting increase in insulin signaling in the brain is thought to be how fasting/calorie restriction works to increase lifespan.
  3. Lowering blood lipids, triglycerides and other markers of metabolic syndrome.
  4. Fighting/preventing cancer.  There is also some evidence that fasting before chemotherapy treatments can help reduce the negative side effects. 
  5. Increasing growth hormone secretion (which builds muscle and burns fat).
  6. Normalizing expression of the hunger hormone ghrelin, thereby reducing appetite.
  7. Promoting brain and peripheral nervous system health by increasing neuronal plasticity and promoting neurogenesis, which has a large variety of effects such as boosting mood, memory, and mental clarity.
  8. Increasing dopamine production, thereby boosting mood and increasing anticipation and response to rewards (meaning we get more enjoyment from less food). 
  9. Increasing energy through regulating metabolic hormones.

Intermittent Fasting is a little like hitting a reset button.  It can help curb sugar cravings, restore energy, and even promote deeper sleep.

How do you do it?  And how often?  There are many options, but in general fasting for at least 16 hours is required to receive any benefits.  Fasting beyond 24 hours doesn’t extend those benefits.  So consider a fast anywhere between 16 and 24 hours.  This includes sleep time, so a great way to intermittently fast is to simply skip breakfast.  Ideally, that also means skipping your morning coffee.  Drinking water is okay.  Expect to feel hungry when you fast.  This is different than simply listening to your body’s cues and waiting until you are hungry to eat (although many people are opportunistic about when they fast and simply choose days when they aren’t that hungry anyway).  If you want to fast for 24 hours, you can skip breakfast and lunch.  In terms of frequency, it is perfectly safe to fast 2 or 3 times per week (in the absence of health conditions that might complicate matters).  If you prefer a longer fast, then once or twice per week is fine.  Some people opt to have an 8-hour feeding window every day (see Leangains).  However, I would argue that a daily fast is no longer intermittent.  The body is able to adapt and predict the fast and many of the benefits are dulled.  I also want to point out that you can benefit from fasting even if you do it very infrequently.  Perhaps you only want to fast once per month, or once every few months.  There is no clear evidence that fasting frequently will dramatically improve your health.  Try it, see how you feel, see how you feel when you try it the next time, and then decide what is best for you. 

What should you break fast with?  When you are ready to eat, eat a balanced meal with lots of great protein and tons of veggies.  You probably won’t feel very good if you eat too many carbs, so I urge caution with starchy vegetables and fruit.  And don’t overdo the quantity you eat; try and aim for a normal meal (or only slightly larger than normal).  I actually found in my own experimentation that I wasn’t that hungry and would eat an unusually small meal to break fast (I would then have more appetite for the meal after that).

Is fasting for everyone? The answer to this is a resounding NO!  If you are not getting enough sleep or if your stress is not well managed, you may experience exaggeratedly high cortisol production in response to fasting, which can be detrimental.  If you have a history of metabolic derangement or adrenal fatigue, I urge caution for the same cortisol-spiking reason.  Women may be more likely than men to have an exaggerated cortisol spike in response to fasting (here‘s a great post reviewing women-specific responses to fasting).  If you are not currently eating a fairly low carbohydrate diet (say, less than 100g per day), then fasting may have some side effects that mask the benefits (like headaches, fatigue, and nausea, caused by high cortisol).  If you have any grains or dairy in your diet, you may experience a withdrawal-like effect because you aren’t consuming the opiate-like substances found in those foods.  If fasting does not feel good, then don’t do it.  If fasting feels good the first few times, but then stops feeling good, then stop.  My own personal experience with intermittent fasting led me to realize that I can only get away with doing a 16-hour fast once or twice per month.  Any more frequently and the cortisol spike stops weight loss, wrecks my sleep, and makes the whole experience completely pointless.   


I have a question for you, unrelated to fasting. My husband and I have been doing paleo and are trying to work 6 children into it.. What is your take on kids and almonds? Can they get too much of it? They are very used to the SAD, but not processed. I made lots of waffles, pancakes, and bread. All 100% whole wheat, then started leaning to gluten freee. Can kids get too much of almond baked goods? I was trying to limit it to once a day. Any suggestions would be greatly appreciated! Thank you.

Well, I certainly think that almond-flour baked goods are WAY better than grain-based baking. But I’m not a big fan of eating too many almonds (or other nuts high in phytic acid and omega-3 polyunsaturated fats). I try as much as I can to get my kids used to eating meat, veggies and fruit as the basis of their diet, but there are many times where some paleo baking makes the difference between them eating willingly and a complete battle (they like paleo toast beside their poached eggs, for example). And I have noticed that a nut-based snack (as opposed to a fruit-based snack) gives them much more even energy, especially in the afternoon. I try to mix it up with more coconut products and more nut-free baking as a way of minimizing the nut intake. And I am continually encouraging them to eat something like a piece of fruit and a hard boiled egg as a snack as opposed to a paleo granola bar. That being said, my kids do get something nut based anywhere between 1 and 3 times per day (with the intention that we will slowly wean off the nuts once the other aspects of them eating paleo are a little easier). I hope this helps!

Intermittent fasting is absolutely great! I’m doing it since November and let me tell you my personal experience. The first few ones were tougher, i felt dizzy and hungry.

After a couple fasts, my body got used to it and I even enjoyed my fast days. I was doing 2x24h per week. I am more focus on my work, it cleared my skin, i can see my abs now and it cuts the grocery bill by 10-20%. Great article!

Intermittent fasting is great! I’m doing it since November and let me tell you my personal experience with it. The first few ones, I felt dizzy and hungry. After a couple times, my body got used to it.

The benefits for me : more focused on my work, cleared my skin, a lot more energy during the day ( because there was no insulin spike) and reduced grocery bills.

Great article !

I too have seen wonderful results from fasting.. biweekly for 24 hours. and I feel great. I was taking vitamins the first few times then stopped.. large glasses of water really are essential to make it…great information!!!

I’m in my fifties and am in my perimenopausal cycle. Fasting puts my symptoms at a normal level… No night sweats, sugar spikes, water retention. 24 max with some afternoon walks for 30 minutes and I am loosing my belly fat. So girls, drink lots of fluids (no caffeine) , breathe deeply and I’ll see you on the other side of living young. 🙂

My worry with coffee is that both Ifing and coffee stimulate cortisol sectretion. If you’re someone with really great sleep and stress management and perfect cortisol regulation, the combination is likely beneficial. But, I think many people experimenting with IFing don’t have really tight cortisol regulation and the addition of coffee can derail efforts by causing cortisol to spike too high.

New to the whole Paleo and Fasting thing.. and my question is about tea during IFing. Does it have the same effect as coffee? I drink a LOT of whole-leaf, home-brewed black tea with no sugar or creamer, none of the “teas” that come pre-processed in tea bags. Just wondering how tea works with IFing, since it does have caffeine in it as well. Thanks, LOVE your information 🙂

Someone else had commented on this post and asked a similar question. Sarah’s reply: “Well, there’s less caffeine than coffee. I suppose you could try it and see how it works for you…” You can read the full reply by searching the page for the term “tea”. — Tamar, Sarah’s assistant

wow. where to start. just stumbled onto your site. I’ll have to write again later about my entire life of IFing!! I’m a 60+yr old plain ordinary paleo dad, professional plant ecologist (I know all about grains, legumes, and nightshades), who’s had amazing results with ‘standard’ paleo (my psoriatic nails – thickened, pitted, yellow, deformed, fall-off) are now at 1 year clean and clear, and i’ve had no arthritis symptoms since the end of week 2. EVERYTHING about my mind and body works better. More on all that later if you’re interested. But my asthmatic wife won’t go there. Would paleo help long term asthma’s effects? Should she perhaps even go AIP? She eats all the paleo meals I fix (most of the time as I’m also a stay at home dad with a 5 year-old stop doing the math), but still insists on her oats, pasta, bread, cheese, occasional potatoes, and cream her coffee (haha, I had to give up coffee on Day 3). Oh, and she’s a ‘super-taster’ so coconut stuff has to be toned way down (although she likes my home-made coconut milk ‘yoghurt’) . She’s practically there, but what alternative bread/scone/muffin type thing can I get her addicted to, and how can I get her to eat more meat? Maybe you have a recipe for Chinese paleo pork dumplings? and, my gosh, thank you for your site; I’ll probably be up all night now browsing.

Yes, paleo will help her. I’d try and get her onto standard paleo first (or nightshade-free paleo) before tackling the AIP. Check out my baked good recipes. Lost of bread and muffins to get you started.

Hi Charlie. I’m new to Paleo (9 months) and I have found it to have a dramatic impact on my asthma. When I started Paleo, I slowly noticed that I wasn’t reaching for my inhaler. Whereas before, I was dependent on my inhaler night and day. I rarely need them at all any more.

The biggest confirmation that what I was doing was working, was one day I went for a run and I didn’t take one puff of my inhaler before, during, or after. That was on heard of for me. And no, it didn’t happen every time I went for a run but one time was enough for to be convinced in the Paleo Approach. When before I would even wake up in the middle of the night needing it or even if I would laugh really hard that would trigger my asthma oddly enough.

Years ago the doctors told me that I would need to stay on oral meds, steroid inhalers, and other inhalers the rest of my life. They told me to take the meds even when I felt good. But I refused to believe that continued my search to find a way for my body to heal. Over the years, I’ve experimented with this and that but nothing had worked as well as starting the Paleo way of life and I’m not 100% Paleo yet but getting there. I’ve been in and out of the emergency room with asthma attacks.

I know everyone is different so I’m not recommending anyone to go off their meds, but for me the Paleo Approach was definitely the missing piece for my body to heal. I even notice a different in my symptoms when I am strictly AIP Paleo during the week and allowed myself one day on the weekend to eat whatever I wanted.

Due to a lot of life changes, I went back to my old ways of eating (breads, pasta, sugar, etc) and boy, did I notice a difference. Although my asthma did get triggered it was no where near the flare ups or attacks I use to get. So even having a short break from Paleo didn’t set me back too much. My body still seemed to retain the healing benefits from my months prior.

In saying all this, I would be surprised if Paleo eating didn’t help your wife. Hope this can inspire your wife to at least give it a try, if she hasn’t already.

And THANK YOU Sarah (The Paleo Mom) for all your efforts to get this information to all of us. Can’t wait for your cookbook in August! 🙂

You dont talk much about IF in parallel with working out. If I was wanting to do a shorter (16h) IF on a day that I was working out, what would the timing of the day before and the day of look like? (What time to stop eating the night before, what time to work out, etc) .. I typically do my workouts in the morning somewhere btwn 9-10a. And within the 8 hour window of eating, how much should I eat? Should I eat roughly the same amount of calories as normal? Or should I just eat my lunch, snack, dinner, snack same size as normal?

Take a look at leangains regarding the fasted workouts, rough scheduling on how to do your 16-8 fast with early morning / mid morning / evening workouts are posted. Remember though to do what works for you! Adjust the timings so they work and are convenient with your schedule … don’t force your schedule around your fasting times.

What do you think of so-called “Ketogenic” fasting, where one only eats fats such as ghee or coconut oil during the “fast”?

From what I understand they have many of the same benefits (well, at least in stimulating autophagy), but also suffer from many of the same problems (cortisol, insulin resistance).

Well, there’s less caffeine than coffee. I suppose you could try it and see how it works for you. Some people purposefully drink coffee during an IF in order to get the cortisol spike to help mobilize sugar, but knowing as much as I do about cortisol, this gives me the heebie geebies (that’s the technical term, right?)

Hi, great article and website!
I have hashimotos and had a total thyroidectomy and stage 1 papillary cancer and RAI therapy last year. Recently diagnosed with H.Pylori. My doctor tells me the H.Pylori is gone ( 4 months ago) but I still feel lots of the symptoms…anyway, I’m trying to get some balance back in my life and have just started AIP…3 days ago! My question is, is intermittent fasting ok with hashimotos? I was doing it a few months ago, but an wondering if its ok for me. What sort of changes need to be made during pregnancy if on AIP? Thanks so much! Your recipes are fantastic, can’t wait to ry the plantain pancakes:)

I’m not a big fan of IFing for autoimmune disease, but it has been shown to help some diseases (and make others worse). I think it’s fine to experiment with, but I recommend being very watchful for signs of cortisol responses. I also recommend checking out the article on about intermittent fasting for women.

No changes needed for pregnancy… just make sure you are eating enough food.

This is so interesting. You’re the first source on this topic that I’ve seen that DOESN’T recommend the 16hr period of fast as a daily routine. Your logic makes complete sense and makes me want to revise my practice.

Just to share some of my own experiences so far…

I do not have a diagnosed autoimmune condition, however I am using the Autoimmune Paleo Plan to target leaky gut syndrome after several years of increasing food allergies and intolerances, as well as after years of dealing with chronic sinus issues (nasal polyps) and starting to see new patterns of inflammation after I had surgery last year (joint & muscle pain, reddening cheeks). AIP with a mindfulness for salicylates does wonders to help with these symptoms when I’m staying on top of things.

I started experimenting with Intermittent Fasting just about a month and a half ago. I tend to only be able to stomach lighter foods in the morning anyway, so it wasn’t that big of a leap to hold off until lunch and eat my day’s nutrients in an 8 hour window. I was doing this daily for a couple of weeks.

Immediately, I felt loads of bloat dissipate, it felt like my digestion improved and I was assimilating nutrients better. I was sleeping better, I was losing cravings for foods that don’t serve me making it easier to stick to AIP 100%, I was burning fat and had loads of energy for my days.

And then I had a series of days where I was both struggling to eat my day’s calories and nutrients due to a sudden drop in appetite and, due to some personal stress, received significantly less sleep than I normally do. Reading your article, I’m not totally sure if that sleep struggle was a product of cortisol issues itself that had already begun or something else that simply exacerbated the cortisol problem, but I’m leaning towards the former. Within a couple of days of the start of that, I ended up ‘crashing’ really hard, fighting off an intense ear and sinus infection, being overloaded with (and giving into) starch and dairy cravings, and once again mucking through digestive bloat and distention, mucous, and brain fog.

I think I’ll revise down to 2-3 days a week of eating in an 8 hour window and go back to broth breakfasts for the other days and see how that goes. I’d love to learn more about cortisol production in the body and how it relates to autoimmunity or digestive issues if you have that information.

Thank you for the article!

Interesting! I also have an unrelated question. I am reading your book and following along on the blog etc. Have you ever heard of arthritis being triggered by pregnancy, particularly with a male baby? I was fine after baby #1 girl – showed arthritic symptoms after baby #2 boy – After baby #3 boy I was finally diagnosed with RA with a RF of 180……surprise baby #4 a girl – she will be 12 in April and RA is totally gone……?

As mentioned in The Paleo Approach, pregnancy can sometimes cause an AI condition to flare, or it can sometimes cause an decrease in symptoms. It really depends on the person. I don’t know if Sarah is familiar with any specific studies regarding pregnancies with boys vs. girls. — Tamar, Sarah’s assistant

I had RA before falling pregnant and went into remission both times and both were boys. Infact my husband knew I was pregnant before I told him as my symptoms went away.

If I have decaffeinated tea or warm water with lemon in the morning, is that considered breaking the fast? I have been doing IF for that past 5 months and have found great success (I found the info through Lean Gains), but have recently started having either one of those beverages before I would normally break the fast with an actual meal. I don’t want to screw it up!

The post itself says that it’s okay to drink water. Decaf tea is not caffinated, so that is probably okay. It’s best to experiment and see what works for you. — Tamar, Sarah’s assistant

Hi, Tamar. I think I should clarify. The water I drink has freshly squeezed lemon juice in it and I’m wondering, but having the lemon juice, if that breaks my fast.

Thank you.

I am really curious about all of the references to cortisol. I am new to the Paleo lifestyle. Where can I find more information about cortisol, specifically, how do you know if you have an issue associated with it?

Cortisol is discussed in many posts on the site, a few are: and and and in this excerpt from The Paleo Approach: If you use the search box to search for cortisol you will find many results. Cortisol is also discussed in detail in The Paleo Approach. You can learn more about the book (including watching a video tour) here: — Tamar, Sarah’s assistant

funny you just reposted this to Facebook. I’ve been doing “bulletproof IF” this week and having terrible ANGER. not sure what to change…

Up until recently I was unable to fast. I used to eat dinner around 8pm and on weekends I would sleep until noon. I would eat lunch then and my glucose would drop immediately. 1h after eating it was lower than the baseline. Around 50-60. Any idea why would this happen? It’s like my body would absorve the food right away. Maybe cortisol is involved?

Thank you for answering. I made an appointment yesterday. I believe it is indeed reactive hypoglycemia. When I was eating 5-6 meals a day before reading about paleo, I was constantly hypoglycemic. it used to happen 1h-2h after eating, I even passed out one time. I have Hashimoto’s so I am probably more prone to it. Since I switched to a paleo diet the hypoglycemia is pretty much gone, it happens only when I IF, the meal after the fast. It usually happens on weekends, since I fall asleep until lunch or closer to lunch time so I skip breakfast. I’m going to stop doing that! Instead I think I would benefit from eating just 3 meals a day (at the moment I’m eating 3 meals and a snack in the afternoon). What is Sarah opinion on snacking? Can you please tell me at what times should the meals happen? I can only manage to eat dinner at 8pm so what time should I eat lunch? What I mean is how many hours is it ok to go without eating without transforming it into fasting.

Hi. I am just delving into the AIP world, being newly diagnosed with Hashimoto’s. I have been practicing the leangains style of IF for a couple of months, but just read somewhere (I’m in a bit of information overload, so I don’t remember where) that people with an autoimmune disease should not IF or be in nutritional ketosis, what is your take on this?

*side note: I do show signs of adrenal fatigue, but do not have a doctor familiar with the testing for this and have not yet had further testing to determine if I also have celiac. So, to be on the safe side, I have stopped IF, at least until symptoms are under control, but would love to be more informed on the topic of IF as it relates to someone with autoimmune disease(s). Thanks!

Interested that you don’t recommend IF for autoimmunity issues. I am trying to deal with horrible allergic dermatitis, total body rashes and itching many times this year (finally biopsied as mast cell–autoimmune/high histamine). Trying to stay off prednisone and other poisonous Rx. A month now on histamine diet, lots of protein but no eggs, no dairy except cottage cheese and butter, olive and coconut oil and bacon. Tons of veggies but no nightshades…no legumes means no beans of any sort? I have limited my.fruit, stick mostly
with bananas, apples, blackberry pulp. No nuts or grains. Turmeric and flax. In the morning a glass of water with lime juice (hard to find lemons here Costs Rica) first thing. Was considering IF but don’t dare mess with cortisol, right? P s what about organic herb teas?

I love love love the intermittent fasting! The simplicity of it! Oh my! No meetings, no shakes, no food to buy and prepare! And I save $$. I feel great, my skin is clear, I have more energy than ever. And I think it’s healing my gut. I’m now doing two 24 hour fast per week. I’m down about 23 pounds as an added bonus. I have hashimotos and have never been able to lose much weight before now.

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