In previous podcasts and articles on this site Chris discussed some of the factors to consider when deciding if intermittent fasting is the right approach for you. While the decision to use intermittent fasting as a strategy to improve or optimize health should be considered carefully, it is a powerful tool when used appropriately. In this article, I want to discuss some of the potential benefits offered from intermittent fasting.
Intermittent fasting is a general term used to describe a variety of approaches that change the normal timing of eating throughout a day, with short-term fasts used to improve overall health. In other words, the one consistent theme of intermittent fasting is that individuals periodically fast for a longer duration than the typical overnight fast.
Some approaches to intermittent fasting include skipping one meal of the day, extending the duration of the overnight fast to anywhere from 12 to 20 hours. This may also be referred to as time-restricted feeding because it shortens the feeding window. Some people prefer whole-day fasts that usually involve fasting for 24 to 30 hours, performed anywhere from once to twice per week to just once or twice per month. Most of the research on intermittent fasting more specifically uses alternate-day fasting, where participants fast for 24 hours every other day, alternating days of eating without restrictions (1).
Intermittent Fasting Is Associated with Decreases in Body Weight and Body Fat Percentage
Several studies have shown that intermittent fasting is associated with weight loss (2, 3, 4, 5, 6). While many of the patients I see are more concerned with overall reduction in weight, I also see a lot of patients who want to gain weight, specifically lean body weight or muscle mass. And some of these patients express concern that intermittent fasting may lead to a decrease in muscle mass. Fortunately, research shows evidence that intermittent fasting causes a favorable shift in metabolism that preserves muscle.
Here’s why …
During the most common fasting duration of about 18 to 24 hours, our cells shift from using glucose as their primary fuel source to using fat (7, 8, 9). This means that our fat stores, namely triglycerides, are broken down and used for energy. The breakdown of proteins for fuel does not begin until the third day of fasting. Thus, intermittent fasting remains an option for optimizing health even in those wanting to maintain or gain muscle mass.
Without going into too much of the science here, the shift in metabolism from glucose to fat may be most pronounced after about 18 hours of fasting, suggesting potential benefit from occasional whole-day fasts (8).
Improved Cardiovascular Disease Risk Profile
Several studies show intermittent fasting may lead to a reduction of total cholesterol by about 20 percent (7, 2, 4, 5, 10). This becomes even more impressive when we look at the breakdown of the effects on LDL, HDL, and triglycerides.
The following is an over-simplification, and Chris has written extensively about cholesterol and lipids in the past, but for the purposes of this article:
- LDL is the “bad cholesterol” (the worst is small, dense LDL, and the less offensive form is large, fluffy LDL).
- HDL is the “good cholesterol” (we don’t want to see HDL decrease, and most often we would prefer it actually increase).
- Triglycerides are a type of fat used to store excess energy from our diet, and high levels may be associated with cardiovascular disease and insulin resistance (we want low levels of triglycerides).
Since the total cholesterol on a blood panel is derived from a formula including LDL, HDL, and triglycerides, we want to make sure that a decrease in cholesterol comes from reductions in LDL or triglycerides, and not lowered HDL.
So, What Happens to Cholesterol with Intermittent Fasting?
Not only does LDL decrease by about 25 percent after eight weeks on an alternate daily fast, but even better, we actually see a decrease in small LDL particles (10, 11, 12). And remember, small, dense LDL particles are associated with an increased risk of cardiovascular disease when compared with an equal number of large, fluffy LDL particles. (Note: small, dense LDL is best viewed as a proxy for LDL particle number, which, as Chris explained here, is a more significant risk factor for heart disease than total or LDL cholesterol.) Thus, intermittent fasting favorably shifts LDL both by decreasing total LDL and also by decreasing the small, dense LDL particles.
We also see decreases in triglycerides by as much as 32 percent below levels measured prior to implementing intermittent fasting (2, 7, 10, 13).
And, as hoped, with intermittent fasting, there is no significant decrease in HDL (14).
Intermittent Fasting Is Associated with Decreases in Inflammation
A study published this month investigated the effect of intermittent fasting on a marker of inflammation, specifically looking at NRLP3 inflammasome activation (15). The results indicated a decrease in this measure of inflammation with fasting.
Another study evaluated the effect of alternate-day fasting in adults with asthma and found a decrease in symptoms along with striking decreases in markers of oxidative stress and inflammation (7).
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Intermittent Fasting May Improve Brain Health
One interesting study published earlier this year investigated the effect of intermittent fasting on motor coordination skills, protein, and DNA damage in specific regions of the brain in middle-aged rats (16). This study also measured markers of cell metabolism, cell survival pathways, and synaptic plasticity (you can think of synaptic plasticity as a measure of the ability to learn).
The findings indicated that intermittent fasting was associated with improved motor coordination and learning response and a decrease in oxidative stress (think of oxidative stress as what we often consider “normal” age-related change). So, intermittent fasting may improve healthy aging of the brain and decrease the cognitive decline that is generally considered a normal part of aging.
Intermittent Fasting May Be Associated with Decreases in Neuroinflammation
Chronic neuroinflammation is increasingly associated with neurodegenerative diseases like Alzheimer’s and mood disorders such as depression. One study published earlier this year looked at the role of intermittent fasting on markers of neuroinflammation in rats and found that this dietary approach actually changed gene expression to allow for an adaptive response (17). These results suggest that intermittent fasting may have a beneficial role in conditions associated with neuroinflammation.
While there are even more potential benefits to intermittent fasting, like improving insulin sensitivity and promoting a normal migrating motor complex (important in preventing SIBO as discussed here), I’ll have to save further discussion for another post to prevent this one from becoming too long. But hopefully at this point it’s clear that intermittent fasting can provide a number of measurable benefits.
Intermittent Fasting Is Not for Everyone
There can be risks associated with intermittent fasting, and I would strongly recommend that it be pursued with the guidance of a qualified healthcare provider or nutritionist who understands the risks and benefits and can help determine if it’s right for you.
Intermittent fasting should always be avoided during pregnancy and breastfeeding and should generally be avoided during times of increased stress that contribute to Adrenal Fatigue Syndrome, or more precisely, hypothalamic-pituitary-adrenal (HPA) axis dysfunction.
Additionally, there are health risks associated with diets that are too low calorie, including concerns of nutritional deficiencies, electrolyte abnormalities, and potentially more serious risks if extreme diets are undertaken without appropriate supervision. Intermittent fasting can be a great strategy for weight loss and overall health during the right time for you and when approached cautiously.
About Amy: Amy Nett, MD, graduated from Georgetown University School of Medicine in 2007. She subsequently completed a year of internal medicine training at Santa Barbara Cottage Hospital, followed by five years of specialty training in radiology at Stanford University Hospital, with additional subspecialty training in pediatric radiology.
Along the course of her medical training and working through her own personal health issues, she found her passion for Functional Medicine. She works with patients through a Functional Medicine approach, working to identify and treat the root causes of illness. She uses nutritional therapy, herbal medicine, supplements, stress management, detoxification and lifestyle changes to restore proper function and improve health.
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I have adrenal fatigue and according to the tests I did with my functional medicine my cortisol levels are way to high. Would therapeutic and intermittent fasting make my cortisol worse?
Oh I thought intermittent fasting doesn’t work, but it does. Thank you for sharing the post! This information helps me understand more about intermittent fasting. Gonna find one schedule, which is suitable for myself.
Should intermittent fasting be done while working out? Will it help me lose weight and add muscle?
I recently did read an article about a guy doing it for a year and it did help him become stronger and leaner.
What’s ur take on it? Is it risky?
I began the year weighing in at 290 lbs on Jan 9th. I weighed in today at 233 lbs on April 7th. Down 57 lbs in less than 90 days. I have fasted every day for a minimum of 16 hours and a maximum of 22 hours. My calorie intake has been max of 2000 calories a day during the eating window beginning at 8AM. I have also worked out on elliptical, rowing machine, and bowflex max (stairclimber) as well as walking for 87 of those days sometimes 2 a day. I have had no fatigue, I have had no injuries or impediments. Oh by the way I am 50 yrs old. Once down to 200 I will add weights workout. I have not lost much muscle ( I worked out with weights in the past) also I incorporate at least 20 minutes of my workouts are HIIT – High Intensity Interval Training on any of the aparatus above. Hope this helps. Best of luck
I have been on an intermittent fast of at least 16 hours every day of 2017. I have lost a total of 40 lbs as of 2-24-17. That is 40 lbs lost in less than 60 days. I realized it was time and had previously lost 40 lbs in 4 months some two years back and then relapsed into my bad habits – There is no ravenous eating as my appetite has me consuming less than 2500 calories a day and for a 240 lb male that is not bad. I alter my fast times based on events and functions but easiest is to follow during the work week. Fast starts betweem 12 noon and 2 PM and first meal of the day is at 8AM. There is an occasional hunger pang at night but it does not carry over to the mornings. Green tea (specifically matcha) is helpful – no cream or sugar. Also I have worked out in the mornings some 35 days of the new year but none all to strenuous. This is the magic bullet from everything I have researched and you would be surprised how many people still adhere to the false belief that they will waste away to nothing. We have adaptive features in our bodies that prevent this as well as multiple bodily functions that are never triggered because we are NEVER in a fasted state including autophagy, HGH production and high levels of alertness as well as preventative measures against Alzheimers et al… Give it a go – start 16 hours per day for 3 days a week – go all work week if you can. Best to do it every day as it gets hard to get back on the wagon after a weekend away. Am measuring my biomarkers after 4 months – had hypertension before this as well as breathing issues and fatigue – Fatigue and breathing issues are gone will test hypertension in April – BEST of LUCK
I lost 10 lbs on a ketogenic diet and another 15 lbs on intermittent fasting… And I’m still losing weight. I eat from 5pm to 10 pm, 1500 calories. 200 of those calories is fish oil. 20 caps might not be healthy long term, but for now the weight is coming off.
Hi, what are your thoughts on fasting and constipation and eating disorders?
Hi Lynda, I would recommend Martha Christie’s book on “your own perfect medicine ” she had suffered from chronic constipation all her life and explains in her opening chapter how it all changed permenantly. It will really open your eyes I promise you.
Will this book you recommend run through the effects that fasting has on constipation though? I work in the area of constipation and am reluctant to advise fasting in fear that it may exacerbate the problem.
One of the reasons I started IF was to help promote regularity of my BM’s. I’ve been experiencing constipation since a pelvic floor collapse 2 years ago. Fasting has made my BM’s softer and regular. Hope this helps!
I try to keep an eye on my weight throughout the year, and use the 5:2 diet only if my weight ticks over a certain threshold. The first couple of fast days can be difficult, but I keep at it because I know I won’t need to do it for long to get back in shape. I find this approach to be very effective.
From what I have read about intermittent fasting in the USA bears no resemblance to the yoga idea of fasting I have followed from my twenties. This form of fasting involves preparing your body in advance (say 2 or 3 days prior) bearing in mind the body responds to every thought you have that on such a day you will avoid ALL food, liquid or solid for 24 hrs minimum drinking only water, plenty of it. And if you REALLY want to help your body consume your own urine during the day. It is full of amino acids vitamins, mineral antibodies and strengthen your immune system in the process.(for further info on u/t read Martha Christie “Your own perfect Medicine.
I use IF as a staple choice. I never experienced any troubles. It comes naturally to me. But this is not for everyone. I never get used to 6 meal a day type of a diet. I use 16h fast and 8h feed window. But I also tried Warrior diet and I was fine but IF is for me. Especially for workouts in the gym or on the golf course. I recommend everyone that try this diet.
I have found fasting every other day greatly helps my general health especially my Trigeminal Neuralgia and depression. I no longer take any meds for my Trigeminal Neuralgia.
How long did it take for the fasting to take away your TN pain?
I’m interested in trying IF, but I’m confused. I always thought fasting was not eating, but everyone talks about eating during their fast. What do I need to do or what’s acceptable? I have a lot of gut issues that I need to fix (hoping that IF will fix them), and I’ve been having issues getting into and staying in ketosis. I’ve been low carb strict paleo for 2 months now but my blood sugar is higher now at 110 than it was when I started at 94. Perhaps IF will get that ship righted as well. Any help would be much appreciated.
See my comment read Martha Christie and your problem will disappear her book is based on the most up to date scientific studies or look at ancient Ayurvedic texts.
Living half the year in an 11hr time difference And–Only eating when i’m hungry—has created a lifetime habit of intermittent fasting.
(I do add 2 this mix B-12 injections and Multiple B Complex injections that I administer myself.)
How old wld u b if u didn’t no how old u r? I don’t feel any age whatsoevr.
One of my other habits is workin out and adding a physically challenging sport-few yrs ago it was skiing n now it’s squash (which is addictive!).
I’m wanting Chris’ expert nutrition as I only have any health complications with food in the US! Lydia Bach
I began a system of IF every other day in early August. On fasting days I did have about 500 calories. I found that I could easily skip breakfast, have about half my calories in proteins for lunch and then sip on juice, fruit, vegetables, etc throughout the rest of the day. It was challenging, but I came to look forward to fasting days. On eating days, I also reconsidered choices. I became ill (probably due to a new immunosuppressant) in early November, so I focused on addressing those issues and gave up fasting. After reading these posts, I think I will launch a new IF routine. Thank you for the information. Any input is appreciated.
Chris has written previously that he does necessarily approve of IF to address sugar imbalances (see here: http://chriskresser.com/to-intermittent-fast-or-not-to-fast-that-is-the-question/ and here http://chriskresser.com/intermittent-fasting-cortisol-and-blood-sugar/)
I’m curious if his position (or yours, Amy) is still consistent with this. Great article!
Kept looking for a baseline anchorage. Isn’t it implicit that diet during regular non-fasting periods is unchanged in all respects ?
I pracited IF, lost 5 lbs/week for the first month so 20lbs that month. Contunued to lose a total of 50lbs over the course of 6 months, all while lifting weights. I was the strongest I had ever been, and felt better (had better moods) than I ever have. If you wanna lose weight and mostly body fat I highly recomend this. First few days are pretty tough tho.
Intermittent fasting really does help in losing pounds of weight. I remember I was watching an interview with Hugh Jackman (yeah, the Wolverine) where he confessed about the hellish diet regimen he used. He coined it “The Wolverine Diet”.
He told the interviewer that he would eat for about 8 hours and fast for 16 hours. It even went on a water dehydration diet where he deprived himself with fluids just to so he can be as ripped and cut as possible.
What you are doing right now Brian is totally impressive. It is great to hear that you are lifting weights as well. For everyone who is interested in building muscles fast, check out http://www.musclebuildingmasters.com/
Thanks for the article Amy. Your contribution to the community is truly appreciated.
I have been fasting for 18 months now and I do once a week 24-36 h. The biggest improvement was that I got of my meds for restless legs syndrome. If I cheat for a week I have to take meds again, so for me I can’t be without fasting! Thanks to Dr Moseley for the tv show about intermittent fasting.
I have heard about IF and I really want to start because of my weight issues. However, I am hypoglycemic and when I try fasting, even if I eat every 3 hours, I am dizzy, tired and cannot function throughout the day. What would you suggest to keep from feeling so hypoglycemic and ‘absolutely starved’ during a fasting day?
How can you be fasting if you’re eating every three hours?
I was on a low carb diet for over a year before I started using IF. I started skipping breakfast two days a week, then having a bullet proof coffee and skipping lunch two days a week, then skipping both breakfast and lunch two days a week, then not eating two days a week, then trying longer fasts (many three day fasts, one five day). I still eat low carb, and additionally I’ve increased my fat content as much as I can per day. Doing this, I’ve lost about another 30 pounds since about March of this year. I like IF so much that I no longer eat breakfast.
Anytime you enter into a fast and you get dizzy or light headed, that means your electrolytes are low. especially if you are Keto or Low carb. Its an easy fix, just eat some salt. 1/2 teaspoon, usually chicken or beef broth will do the trick. Takes about 30 minutes to recover. The better approach is to automatically drink the broth when you start the fast.
I am also hypoglycemic, I still practice IF when I wanna lose weight. Hint: vitamin waters. They provide your brain with sugar witch is what our hypoglycemic brains need, and I found the IF still works, im assuming because its not solid food.
I’m also to the degree that blood glucose swings would cause heart arrythmia. However this was self- inflicted due to a high carb diet which was not usual during human evolution. Adapting to a low carb diet permanently fixed the problem. Its difficult to get large glucosec swings when there are no glucose jolts caused by starch and sugar. I’m probably keto adapted because missing meals or not eating for a day are not an issue. If you eat a species-appropriate diet you really can get busy and forget to eat.
Based on the information you’ve provided I would not recommend you try intermittent fasting at this time. It sounds like it could be a worthwhile investment to work with a health care practitioner for adrenal testing, and/or a nutritionist to help you find a strategy that works better for you. You might be able to practice intermittent fasting in the future, but it sounds like right now is not a good time for this approach. You should not feel dizzy or unable to function with IF.
I’ve been hypoglycemic my whole life, now 73. Getting light-headed for me is a normal result of not eating often if I eat the traditional American diet. I’ve been tested and I have normal reactive hypoglycemia. You should be tested, very simple, takes about 4 hours. Reactive Hypoglycemia is normal for millions of people, particularly with a North and Western European and Native Indian heritage. If this is the case you need to eat a lower carbohydrate and higher fat and protein diet. Thenyou don’t get light-headed when you fast because your body is adapted to what is its normal mode for your genetic make-up. Instead of running out of fuel you automatically metabolize body fat stores. During WW2 the Partisan couriers of Crete were so well adapted they could run a double Marathon, 50 miles, through the mountain passes without eating or resting. First step is to have your Doc order up the test for reactive hypoglycemia, you may well be just acting normally for your genes.
Thanks for sharing the WW2 couriers story. I suspect that you already know about Tim Olson, the low carb, high fat Ultra runner. (Ultra races are 100 miles long trail races over mountains.) In case you don’t, here’s good article on him. http://www.meandmydiabetes.com/2012/08/11/western-states-100-low-carber-wins-ultramarathon-steve-phinney-and-jeff-volek-study/
I’ve been this way my whole life and I discovered going LOW CARB first was the key. The issue is your too insulin resistant and you have unstable blood sugar and insulin. Once I went low card I was able to do IF no problem and I feel 10 times better when low carbing or fasting and never have any of the hypoglycemia issues and unless I have too many carbs.
I have tried intermittent fasting and found it works great! I do eat healthfully: EVOO, wild salmon, avocadoes, organic chicken, organic fruits and vegetables. I also drink lots of water and have a “green” drink most days. I typically eat my first meal around 10:00am or so and my last meal around 6:00. My cholesterol levels, triglicerides and glucose levels have been excellent. My question is that I recently was diagnosed with arrhythmia and have an implanted defibrillator. I have to take medications twice a day. I am wondering if I can still do IF and take my meds, too, in a timely fashion. Thanks for your thoughts and your inspiring columns.
I have roasted periodically all my life ranging from whole day to several days 1week and.three weeks taking one yoghurt a day at meal times with my family. I have always found it beneficial. I have recently been diagnosed with ITP with a platelete level of 3000 (they should be a minimum of 150,000) I refused further treatment as steroids and IV/ig had no results they had remained at 3000 for some months until I took a 7 day fast with urine therapy and water. This kick started the immune system (ITP is an autoimmune challenge) and they are now rising steadily. The point here is the fasting as urine therapy by itself didn’t do it. I am 75+ been a vegetarian for over fifty years. Had atrial fibrillation for over twenty years but BP of a twenty year old. Fasting enables the body to go into repair mode. Urine therapy returns aaminos.vitamins protein etc etc to the body. Let go your fear and go for it