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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Thank you so much for this article. I do some IF and will do more from now on, only thing i noticed sometimes when I do IF is that I get cold hands and feet. I would make coffee with some butter and MCT oil or just have black coffee and then occasionally like I said i do get cold hand and feet to the point where it’s two steps away from being uncomfortable.
Do you have any suggestion on this? Its my understanding that its thyroid issue and that more carbs can usually make it better.
It sounds like it would be a good idea to run a thyroid panel to evaluate if low thyroid function is contributing to your symptoms.
I am a big fan of IF. However, I “cheat” by having about 40oz of coffee with grass fed butter, coconut oil and MCT oil, which allows me to go a full 16-18 hours with no “glucose” fuel.
NOPE! Not for me! I get horrible symptoms from trying to IF. A high fat/low carb diet are also disastrous to my body. I’m surprised so many people here are having such great success!
Well…maybe it depends on how you approach the diet. I eat protein and good fats, EVOO, flax seed oil, avocados, bacon, ham, eggs, tuna, chicken salads, etc. This diet keeps me in Ketosis 24/7. All my sinus allergies have completely disappeared (after 50 years of suffering) and I no longer have to take an inhaler for lung inflammation. I also take numerous vitamins and minerals (in pill form) to compensate for not eating fruits and vegetables. I’ve been on this diet for almost 2 years and have had numerous “full work up” blood tests and they all come out great. Since being on this diet my resting pulse rate has decreased from 99-102 down to high 70s low 80s. My cholesterol is great, I have plenty of energy and my Diverticulitis symptoms have completely disappeared. It’s like a “fairy tale”.
I guess I’m doing something right, I’m not sure how good I’d be doing if I wasn’t taking the vitamin and mineral supplements. I’ve always been slender ad actually had to stop exercising to keep from losing too much weight. The funny part is that on my “old” carb/sugar diet I used to exercise for an hour a day (cardio) and my resting heart rate wouldn’t go below 97/98 (it was scary!!) but on the low carb/lo sugar diet my resting heart rate is much, much better even though I haven’t exercised in over a year!!
So what does your supplement regimen look like?
By “supplements” I’m going to assume you mean everything that is not food?? For example, because I don’t get much fiber I take 4-5 Citrucil tablets with each meal (gotta have fiber). So I’ll list everything I take that is not food. Let’s see:
Lots of Water
Calcium 1200mg daily
Potassium 1100mg daily
Vit D3 5000IU Daily
Lots of water
Magnesium 500mg Daily
One Adult (over 50) multi-vitamin daily
Vit C 1500mg daily
Lots of water
Flaxseed Oil 3600mg daily
4 Tbls of EVOO (there are many different ways EVOO is produced/manufactured, do some research and get the cold pressed with the least additives!!).
EVOO and Flaxseed oil are extremely important in this Caveman diet because these oils (just like avocados) help make your cholesterol levels correct and actually fight the bad cholesterol. You can actually eat much more bacon (I eat 25 strips every morning) because the good oils will negate the effects of the bad oils/fats. Of course…I only buy bacon that has the most good oil/fats and the least bad oil/fats. You also have to make sure you get enough “good” fats/oil because this is what your body will burn instead of carbs/sugar. In the absence of fats/oil/carbs and sugars the only thing left in the human body that can used as energy (fuel) is “protein” and you don’t want to burn protein (muscle).
If you want to gain weight you simply increase your intake of EVOO, if you want to lose weight you simply decrease your intake of EVOO. Since this a “good” oil/fat it won’t do you any harm, in fact, I think the EVOO is one of the reasons by pulse rate dropped down to normal, along with a BIG decrease in inflammation (Ketosis).
And with respect to the term “supplement”….I frequently eat an avocado with my evening meal (steak, pork chop, grilled sausage). So in essence, I’m getting even more “”good oils” in my body than listed above.
And lastly, you also have to eat enough protein to sustain your muscle mass, very important!!!
Cheers – much appreciated!
What about decrease metabolic rate as a result of IF and thyroid function. Is it necessary to have a higher carb eat up day to restore leptin and thyroid?
Thank you, Amy. I thought I’d weigh in here, as a woman who’s had great success with IF. I’m 61 and post-menopausal, which could affect things, but my 27-year-old daughter has had similar success, so maybe it’s partly genetic. In any event, I have only bulletproof coffee (Kerrygold butter, MCT oil, and cinnamon) in the morning and am not hungry until early afternoon. I eat when I’m hungry, usually between 1:00 and 2:00 p.m., and when I’m again hungry, usually between 6:00 and 7:30 p.m. Aside from the butter (and occasional cream or cheese), I’m pure Paleo, since February 2013, and have been doing the IF (feeding window approach) since August 2013. I generally run ketone levels between 1.3 and 1.8 mm/dL. When last tested, my triglycerides were 30, LDL 35, and HDL an astonishing 118. I weigh 130 and feel amazing. I’d like to experiment with multi-day fasting (for its potential anti-cancer effects, as my fasting serum glucose tends to run around 85), but even though I’m fat-adapted, when I’m hungry, I’m hungry, and so far I’ve wimped out on dealing with the “pain” of fasting beyond about 20 hours.
Do you have a dedicated blood ketone meter?
And do you eat really low carb in the feeding window?
Not a dedicated meter. The Precision Xtra takes both glucose and ketone strips, which I got online from Canada, as they can be pricey. I do eat fairly low carb, but I’ve never calculated exactly how much. I suspect I’m under 50 grams most days, but I don’t really know. I never eat grains or potatoes at all. But I eat some fruit occasionally (mostly berries), and have red wine at least a few times a week. I often have a sweet potato after my weekly weight lifting (in the style of Doug McGuff), because they are delicious. So it’s low carb, but not obsessive. Clean meats and fish, lots of veggies, lots of good fats, and nuts. I don’t feel deprived; I feel awesome.
Thank you, Naomi!
Naomi – today, I turned 59 and am drawn to your comments for a variety of reasons, not the least being that I long for a generational tribe! How I wish I could ‘pick your brain’ since we seem to be on the same wellness path, although I’m just taking my first tentative fasting steps – and feeling so full immediately when I start eating after a 7pm – 10 or 11 am fast.
Happy birthday! Mine’s next Monday, 01-11. I don’t know if this is Kosher, but I, too, would love to be in touch with like minded folks my age, so here goes: [email protected]. Have a great day!
I fast once a week. It breaks my weight loss stalls. I am ketogenic also ~ for the last 15 months. Keto makes it easy to fast. I have some much energy when I fast. I do 36 hours fasts, basically I skip a day of eating. I do a strict water fast.
I once did a 35 day fast with just water and the occasional carrot and celery juice bc I was so overloaded with prescription drugs and was not getting any better so Being raised with parents who fasted from time to time and after doing research on how to do it properly, I went on the fast. I felt so much better after and had lost 25 lbs. (I was overwt.) that I was glad I did it. I do not take meds anymore except occasionally and do short fasts from time to time. The way the body heals is to stop dumping garbage into it as does a body of water. Nature heals itself.
I would like to know did you eat anything during the day when you did the fast ? As I have also taken lot of prescription drugs and would like to stop them . These doctors here have no idea about anxiety and they are pill pushers ? Please let me know how you did it ? Would appreciate greatly .
I sent a detailed description a day or so ago about my three-months experiences with intermittent fasting, but received no reply.
Hi Ian I replied to your mail scan down to your mail and you will see.
Great article Amy!
I was excited and relieved to see the disclaimer at the end for clients that have adrenal stress. I’ve never run an adrenal profile on someone that is NOT under some sort of adrenal dysfunction/fatigue.
If we get to the IF stage of the nutrition program, I usually make it based around a good dose of healthy fats in the mornings to keep them feeling good, just nothing added to spike insulin levels.
Keep up the good work!
I am 60 years old with metabolic syndrome. I am also a shift worker. I go from working four 12 hour nights to working 12 hour days with a couple days off in between. Almost impossible to get normal sleep but I work hard at it. About two years ago my weight peaked at 214 lbs (I am only 5′ 4″). I couldn’t walk more than about 50 years without having to sit down and then I developed a very bad autoimmune skin condition. My doctor’s solution was to increase the pills I was taking.
I started walking about 50 minutes 5-6 xs per week and began to use intermittent fasting along with generally improving my diet. Avoiding processed food and cutting back on sugar and carbs. Because I work 12 hours shifts (and lots of them at night), I would eat a good healthy dinner shortly after arriving at work and then stop eating (but drink lots of water). I would get off shift and go right to sleep so by the time I woke up I would already have been fasting about 18 hours. The only time I got hungry was about 4-6 hours after I ate dinner but that was easy to ignore. It was very easy to do. I would walk before going to work while still fasting and eat when I got there.
I lost more than 50 lbs. and improved all my blood markers. I got off Lipitor, got a handle on my blood sugar, eliminated one BP pill and cut the other in half. It’s been two years now and I have 5xs the energy. Whenever I start feeling sluggish and start gaining weight I go right back to IF. It’s been a wonder for me. I would recommend it.
I was diagnosed with Graves Disease resulting in I-131 ablation of my thyroid. After some tweaking, I seem stable on daily synthyroid. 2X a week I exercise without breakfast, resulting in a 16-18 hour fast. I feel fine and functional. my doctors are against it, but then, they want me to eat low fat and 1200 calories a day (back to 1950s) but I need to deal with them until new health insurance kicks in. Does the exercise (1 hour of aquafit) really make a difference? I’m not losing weight , but I am finally starting to build muscle after losing so much during the thyroid fiasco…. It’s been a couple years to heal my metabolism.
It amazes me how backwards doctors are. A recent study showed that doctors are, on average, 17 years behind the latest studies. The reason? They don’t have time to read new information. Instead, the study found that 86% of over 13,000 doctors in the study, said they get ALL their information from Big Pharma.
Thats like getting ALL your information about the car you’re buying….from the car salesman.
In addition to following my own nutrition plan, Paleo with some variation, I have been doing intermittent fasting with excellent results. My goals are fitness and reduction of fat %. Right now, I am 57 years old, 163 lbs and body fat around 8%. What amazed me is, I can keep up my training schedule and fast. My workouts are 2-5 hours at a time with a heavy emphasis on the high intensity biking and core fitness burning 2 to 3k cals sometimes more. Sometimes, when I really push the length of my workout, I will drink some diluted Gatorade. However, 90 % of the time, just water. Amazing!
Wow, amazing, info, I am still off work sick (1year now), however as I have not used any strong muscles for this length of time and I am still a couple of kilos overweight, and due to my problems I cannot work out (I am doing some exercises at home) where if I have any problems I can stop and rest.
I was wondering along with starting a new eating programme if Fasting or Detoxing would be good for me.
I want to return to work ASAP and need to gain strength again to do my job, which is physical.
My Drs just want to keep me on Meds which have crazy side effects, non of which I take any more. So dieting, changing eating habits, careful exercise, and fasting sound like a way forward.
I’ve been doing intermittent fasting for about two years now. I don’t do it to lose weight – I’m skinny – I do it to control IBS and associated symptoms. I eat two meals per day – a good breakfast about 7 a.m. and then again around 2 p.m. Since I have digestion issues with carbs and anything sweet – including fruit – I also eat a reduced carb diet. I don’t get hungry as long as I eat enough fat. I’m 62, very active with a farm and I also do constroction work off the farm.
Stop gluten and dairy, and you’ll cure your IBS. PS, your doctor won’t know anything about it. Read the studies yourself.
If only curing IBS were that simple- glad it works for you.
How about using “bulletproof coffee” as your first meal of the day? Does that mimic IF? I feel great when I have high fat coffee just 1 or 2 mornings out of the week and don’t eat my first meal until around noon. I also do morning workouts in a fasted state.
Jacqui-I do the same in A.M. since I adapted the Nutritional Ketogenic. I do 20oz BPC in the morning and bring it to work. I wasn’t familiar with this IF till I noticed that not hungry for breakfast till around 1pm. My energy cognitively is sustainable all morning without sluggishness.
I have been reading an interesting book on the subject of diet and heart disease called “Epi-Paleo Rx” and Dr Kruse explains how it is the oxidised cholesterol that is the big issue. He states it is very important to have breakfast and if you are going to miss meals to miss lunch. What are your thoughts? I have been a 2 meal a day person for 30 years yet got metabolic syndrome. When I went to 3 meals a day I felt much better though now I eat mainly paleo.
Does the IF have to be done with regularity to be effective? For anyone who does on-call work (I’m a midwife) it would be hard to keep a set schedule for eating when sleeping at odd times.
You can absolutely benefit from intermittent fasting even if it’s done only sporadically. And you’re right to acknowledge that when working such long or irregular hours it can be difficult, and may even do more harm than good, to aim for longer fasts.
What is your definition of “fast”?
Is there any evidence that intermittent fasting could help aid in the treatment of Small intestinal bacterial overgrowth (SIBO)?
It can regulate the MMC
I vaguely recall reading that the benefits of fasting may not be the same for both men and women. Were the studies gender balanced?
IF works very well in regards to weight loss, mental clarity, energy and mood for myself. While I agree that you can maintain lean muscle mass with IF, gaining significant muscle requires more precise timing with when one eats or fasts in relation to workouts and their intensity.
Certainly, working out in a fasted state will accelerate fat loss and convert the body to burn fat as fuel but strength will be diminished in such a situation. Also, post-workout recovery for optimal muscle gain and protein synthesis after resistance training will be somewhat inhibited. This might be a factor of you have a goal of significant gains in muscle or have difficulty gaining muscle. In consideration of these factors, IF can be utilized within a muscle gaining agenda by only partaking in it 36-48 hours after an intense resistance training workout and after proper nutritional recovery and cortisol suppression.
Personally, I benefit from IF once or twice a week when I train 3 or 4 days a week with the above mentioned time constraints.
Great article! Thanks!