Dr Jason Fung on Intermittent Fasting medical review by Dr. Andreas Eenfeldt, MD
https://www.dietdoctor.com/intermittent-fasting Updated October 15, 2019
Intermittent fasting is a way to cycle between periods of fasting and eating. It’s currently a very popular method to lose weight and improve health.
Intermittent fasting might actually be an ancient secret of health. It is ancient because it has been practiced throughout all of human history.
It’s a secret because this potentially powerful habit had until recently in many ways been virtually forgotten especially regarding our health.
However, many people are now re-discovering this dietary intervention. Since 2010, the number of online searches for “intermittent fasting” has increased by about 10,000 percent, with most of the increase happening in the last few years.
Intermittent fasting might provide huge benefits if it is done right, including loss of excess weight, reversal of type 2 diabetes and many other things.
Plus, it can save you time and money.
The goal of this beginner’s guide is to provide everything you need to know about intermittent fasting, in order to get started.
Intermittent fasting – isn’t that starvation?
No. Fasting differs from starvation in one crucial way: control. Starvation is the involuntary absence of food for a long time, leading to severe suffering or even death.
It is neither deliberate nor controlled.
Fasting, on the other hand, is the voluntary withholding of food for spiritual, health, or other reasons. It’s done by someone who is not underweight and thus has enough stored body fat to live off. Intermittent fasting done right should not cause suffering, and certainly never death.
Food is easily available, but you choose not to eat it. This can be for any period of time, from a few hours up to a few days or – with medical supervision – even a week or more. You may begin a fast at any time of your choosing, and you may end a fast at will, too. You can start or stop a fast for any reason or no reason at all.
Fasting has no standard duration, as it is merely the absence of eating.
Anytime that you are not eating, you are intermittently fasting. For example, you may fast between dinner and breakfast the next day, a period of approximately 12-14 hours. In that sense, intermittent fasting should be considered a part of everyday life.
It is perhaps the oldest and most powerful dietary intervention imaginable.
Consider the term “break fast”. This refers to the meal that breaks your fast – which is done daily. Rather than being some sort of cruel and unusual punishment, the English language implicitly acknowledges that fasting should be performed daily, even if only for a short duration.
Intermittent fasting is not something queer and curious, but a part of everyday, normal life. It is perhaps the oldest and most powerful dietary intervention imaginable.
Yet somehow we have missed its power and overlooked its therapeutic potential.
Learning how to fast properly gives us the option of using it or not.
To get started, either watch our brief video course on intermittent fasting, or keep reading below.
It is important to realize that this is normal and humans have evolved to fast for shorter time periods – hours or days – without detrimental health consequences.
Body fat is merely food energy that has been stored away. If you don’t eat, your body will simply “eat” its own fat for energy.
Life is about balance. The good and the bad, the yin and the yang. The same applies to eating and fasting. Fasting, after all, is simply the flip side of eating. If you are not eating, you are fasting. Here’s how it works:
When we eat, more food energy is ingested than can immediately be used. Some of this energy must be stored away for later use. Insulin is the key hormone involved in the storage of food energy.
Eat Food -----à Increase Insulin ------àStore Sugar in Liver, Produce Fat in Liver or Muscle
Insulin rises when we eat, helping to store the excess energy in two separate ways. Carbohydrates are broken down into individual glucose (sugar) units, which can be linked into long chains to form glycogen, which is then stored in the liver or muscle.
There is, however, very limited storage space for carbohydrates; and once that is reached, the liver starts to turn the excess glucose into fat. This process is called de-novo lipogenesis (meaning literally “making new fat”).
Some of this newly created fat is stored in the liver, but most of it is exported to other fat deposits in the body. While this is a more complicated process, there is almost no limit to the amount of fat that can be created.
So, two complementary food energy storage systems exist in our bodies. One is easily accessible but with limited storage space (glycogen), and the other is more difficult to access but has almost unlimited storage space (body fat).
Burn Stored Sugar or Fat ß------Decrease Insulin ß----- No Food or Fasting
The process goes in reverse when we do not eat (intermittent fasting). Insulin levels fall, signaling the body to start burning stored energy as no more is coming through food. Blood glucose falls, so the body must now pull glucose out of storage to burn for energy.
Glycogen is the most easily accessible energy source. It is broken down into glucose molecules to provide energy for the body’s other cells. This can provide enough energy to power much of the body’s needs for 24-36 hours. After that, the body will primarily be breaking down fat for energy.
So the body only really exists in two states – the fed (insulin high) state and the fasted (insulin low) state. Either we are storing food energy (increasing stores), or we are burning stored energy (decreasing stores). It’s one or the other. If eating and fasting are balanced, then there should be no net weight change.
If we start eating the minute we roll out of bed, and do not stop until we go to sleep, we spend almost all our time in the fed state. Over time, we may gain weight, because we have not allowed our body any time to burn stored food energy.
To restore balance or to lose weight, we may simply need to increase the amount of time spent burning food energy.
That’s intermittent fasting.
In essence, intermittent fasting allows the body to use its stored energy. After all, that’s what it is there for. The important thing to understand is that there is nothing wrong with that. That is how our bodies are designed. That’s what dogs, cats, lions and bears do. That’s what humans do.
If you are eating every third hour, as is often recommended, then your body will constantly use the incoming food energy. It may not need to burn much body fat, if any. You may just be storing fat.
Your body may be saving it for a time when there is nothing to eat.
If this happens, you lack balance. You lack intermittent fasting.
Intermittent fasting’s most obvious benefit is weight loss.
However, there are a many potential benefits beyond this, some of which have been known since ancient times.
The fasting periods were often called ‘cleanses’, ‘detoxifications’, or ‘purifications’, but the idea is similar – e.g. to abstain from eating food for a certain period of time, often for health reasons. People imagined that this period of abstinence from food would clear their bodies’ systems of toxins and rejuvenate them. They may have been more correct than they knew.
Some of the purported health benefits of intermittent fasting include:
Fasting offers many important unique advantages that are not available in typical diets.
Where diets can complicate life, intermittent fasting may simplify it. Where diets can be expensive, intermittent fasting can be free. Where diets can take time, fasting saves time. Where diets may be limited in their availability, fasting is available anywhere. And as discussed earlier, fasting is a potentially powerful method for lowering insulin and decreasing body weight.
Here are even more reasons to try it, along with more details: The 7 practical benefits of intermittent fasting
Intermittent fasting offers plenty of flexibility. You can fast for as long or short as you like, but fasts longer than a few days may require medical supervision. Here are some popular regimens. Generally, shorter fasts are done more frequently.
This way of doing intermittent fasting involves daily fasting for 16 hours. Sometimes this is also referred to as an 8-hour eating ‘window’. You eat all your meals within an 8-hour time period and fast for the remaining 16 hours. Generally, this is done daily or almost daily.
For example, you may eat all your meals within the time period of 11:00 am and 7:00 pm. Generally, this means skipping breakfast, but some people prefer to skip dinner instead. You typically eat two or three meals within this 8-hour period.
This involves a 4-hour eating window and a 20-hour fast. For example, you might eat between 2:00 pm and 6:00 pm every day and fast for the other 20 hours. Generally, this would involve eating either one meal or two smaller meals within this period.
Learn more about shorter fasts
This way of doing intermittent fasting involves fasting from dinner to dinner (or lunch to lunch). If you eat dinner on day 1, you would skip the next day’s breakfast and lunch and eat dinner again on day 2. This means that you are still eating daily, but only once during that day. This would generally be done two to three times per week. Learn more
This is the version of intermittent fasting that has the most scientific support, as most studies on intermittent fasting has featured similar advice.
Dr. Michael Mosley popularized this variation of intermittent fasting in his book ‘The Fast Diet’.
5:2 involves five regular eating days and two fasting days. However, on these two fasting days, you are allowed to eat 500 calories on each day. These calories can be consumed at any time during the day – either spread throughout the day or as a single meal. Learn more
Another related approach to 5:2 is to have “fasting” days with 500 calories not just twice a week, but every other day. Learn more
This involves fasting for the entire day. For example, if you eat dinner on day 1, you would fast for all of day 2 and not eat again until breakfast on day 3. This is generally 36 hours of fasting. This might provide a more powerful weight loss benefit. The other great benefit is that it avoids the temptation to overeat dinner on day 2. Learn more
first rule of extended fasts is to always check with your health care provider
to ensure you are not at risk for fasting complications.
Generally for fasts greater than 48 hours, I recommend a general multivitamin to avoid micronutrient deficiency. The world record for fasting is 382 days (although we don’t recommend this!), and going 7-14 days may be possible for some people.
I discourage people from fasting for more than 14 days due to high risk of refeeding syndrome, a dangerous shift in fluids and minerals that can occur when food is re-introduced after a long fast.
Learn more about longer fasts
You should not do intermittent fasting if you are:
You can probably fast, but may need medical supervision, under these conditions:
Not likely. This is the most common myth about intermittent fasting, and generally it’s not true.
In fact, some studies indicate that intermittent fasting may even increase the basal metabolic rate (at least initially) and might potentially improve overall body composition.
Yes. You can continue all your usual activities, including exercise, while fasting. You do not need to eat before exercising to provide energy.
Instead, your body can burn stored energy (like body fat) for energy.
However, for long duration aerobic exercise, eating before exercise may increase performance.
This is good to know if you’re competing.
Keep in mind that it may be important to drink fluids and replenish sodium (salt) around exercise when fasting. Learn more
There can be a number of possible nuisance side effects of intermittent fasting.
Here’s what to do if you encounter them:
Taking some extra salt often helps mitigate such headaches.
A more serious side effect is the refeeding syndrome. Fortunately, this is rare and generally only happens with extended fasts (5-10 days or more) when one is undernourished. Learn more
While this does not happen with everyone, it can occur due to hormonal changes that occur during intermittent fasting. Your body is producing sugar in order to provide energy for your system. This is a variation of the Dawn Phenomenon and in general is not a concern as long as blood sugars are not elevated the rest of the day.
The most important thing to realize is that hunger usually passes like a wave. Many people worry that hunger during intermittent fasting will continue to build until it is intolerable, but this does not normally happen.
Instead, hunger comes in a wave. If you simply ignore it and drink a cup of tea or coffee, it will often pass.
During extended fasts, hunger will often increase into the second day. After that, it gradually recedes; and many people report a complete loss of hunger sensation by day 3-4.
Your body is now being powered by fat. In essence, your body is ‘eating’ its own fat for breakfast, lunch and dinner and therefore is no longer hungry. Learn more
That depends on the person and the duration of the fast. During fasting, the body first breaks down glycogen into glucose for energy. After that, the body increases fat breakdown to provide energy. Excess amino acids (the building blocks of proteins) are also used for energy, but the body does not burn its own muscle for fuel unless it has to.
Some studies, however, suggest that leaner individuals are at higher risk of lean body mass loss, and even reduced metabolic rate. Yet it appears this is less of a concern with obese subjects.
In my experience with over 1,000 patients on various intermittent fasting regimens, I have not yet seen a single case of significant muscle loss.
Here are the nine top tips, briefly:
Learn more practical intermittent fasting tips
Gently. The longer the fast, the more gentle you might have to be.
Eating too large a meal after fasting (a mistake that we have ALL done, myself included) can give you a stomach ache. While this is hardly serious, people usually learn quickly to eat as normally as possible after a fast.
Not necessarily. This appears to be an old misconception, based on speculation and statistics, and it does not hold up when it’s tested.
Skipping your morning meal gives your body more time to burn fat for energy. Since hunger is lowest in the morning, it may be easiest to skip it and break your fast later in the day.
Yes, but there are exceptions. Women who are underweight, pregnant or breastfeeding should not fast.
Furthermore, for women trying to conceive, be aware that – perhaps especially for athletic women with low body fat percentage – intermittent fasting might increase the risk of irregular menses, and lower the chance of conception.
Other than that, there is no special reason why women should not fast.
Women can have problems during intermittent fasting, but so can men. Sometimes women do not get the results they want, but that happens to men, too.
Studies show that the average weight loss for women and men who fast is similar.
Learn more about women and intermittent fasting
No, not necessarily. Fasting can reduce the time you spend eating and primarily addresses the question of “when to eat”.
Calorie reduction addresses the question of “what and how much to eat”. They are separate issues and should not be confused with each other.
Fasting may reduce calories but its benefits extend far beyond that.
It is almost inconceivable that you will not lose weight if you do not eat.
In theory it’s of course possible to eat more after fasting, cancelling out the weight lost. But studies generally show that people tend to end up eating significantly less overall.
I call intermittent fasting “the ancient secret of weight loss” because it might be one of the most powerful dietary interventions for weight loss, yet it has been mostly ignored by doctors and dieticians for a long time.
– Updated September 10, 2019
Here you can find common questions about intermittent fasting with answers from our top expert, Dr. Jason Fung.
Choose a topic below or scroll down for every question and answer.
1. Who can use intermittent fasting (IF)?
2. Different variants of IF
3. Things to consider during fasting
4. Blood sugar and other tests during fasting
5. Dietary advice between fasting periods
6. Weight loss problems and IF
7. Type 2 diabetes and IF
8. Positive effects of IF beyond weight loss and type 2 diabetes
9. Potential negative effects of IF and LCHF
10. IF and ketosis
11. Recommendations on blood tests
Do you have other questions about fasting for Dr. Jason Fung? Watch our in-depth interview with him or ask him directly on our membership site (free trial).
Fasting is not an option for children. My advice is to severely restrict added sugars and snacking. Reducing down to 2 meals per day is also possible, but not longer duration fasting.
Not only is it safe, but training in the fasted state has several theoretical benefits that many elite level athletes are using. So, yes, it is highly recommended.
I don’t advise fasting during pregnancy or breast feeding. Short term (<24 hrs) fasts may be OK for some, but definitely not longer term fasts. There is a concern of nutrient deficiency which I think far outweighs any potential benefit.
Should there be any differences between intermittent fasting on training days and non-training days? And during the fasting periods – or days – is it advisable to take supplements such as BCAA’s to prevent muscle loss?
There are many different schedules. Most people fast for 24 hrs and then do their training – this is called ‘training in the fasted state’. Since growth hormone is high, you theoretically will recover and build muscle faster in this state.
There is minimal muscle loss during short term fasting, so BCAA is not needed, but often used by bodybuilders. It’s efficacy is unknown, with mostly anecdotal evidence. Many athletes follow a schedule of 24 hr fast, then exercise, then breaking the fast with a high protein meal.
Not appropriate. Certainly occasional short fasts, (less than 24 hours) are fine but not longer ones. Even most religions do not make children fast because their bodies require more nutrients to grow.
You can certainly try although we don’t have good data one way or the other. Fasting should not be used during pregnancy however.
The main difference, as you may suspect, is that shorter fasting periods are less effective and are usually done more frequently. So a 16:8 fast is often done daily, whereas a 24 hr fasting period is done 2-3 times per week. For more severe insulin resistance, I tend to prescribe longer fasting periods, whereas for maintenance I tend to prescribe shorter ones.
Periods of fasting less than 24 hours (20 hours fasting, 4 hr eating) or ‘Warrior’ style fasting can be done daily. The term ‘healthy’ always depends upon what your goals are. If you are simply trying to lose weight, then fasting can be done as needed for that. There are no known negative health consequences to eating only during 4 hours of the day.
I am not aware of any good data on this, but personally, I believe that it is much better to switch things up so that the body does not have a chance to adapt. However, sometimes this inconsistency leads to people not fasting at all, which is also bad.
So it all depends upon your ‘style’. If a regular routine works better for you for compliance reasons, then do so. However, physiologically, I think changing things up all the time works better.
Both are acceptable fasting regimens. It only depends upon which one you prefer and which one gives you the best results. We use both regimens. My own feeling is that the 24 hr fast 2-3 times per week is stronger than the 16:8 regimen, but you must decide which is best for you.
I am also interested about feeding window, isn’t it the same when I eat from 10:00-18:00 as if I eat from 13:00 – to 21:00? when I go to bed 22:00-23:00 ? I mean isn’t it better to eat sooner the day so the energy will be used better or is it just another myth that evening eating leads to weight gain?
People working night shifts often have problems with sleep deprivation and disturbed circadian rhythms. This may result in elevated cortisol that makes it difficult to lose weight. This pathway is separate from the insulin pathway that is typical in most people.
The time of day you eat probably matters, but only a little. Some advise eating in the morning, others at night, so there is little consensus. I think it is more important to try both and see which works best for you, both from your lifestyle perspective and weight loss.
There is no set limit. It depends upon how you are feeling and your goals. We have had people go as long as a month, but this is under direct medical supervision. We have many people doing 10 day to 2 week fasts as well, but again, under supervision. There are many people who do a 1 week fast themselves or as part of a ‘cleanse’.
However, I cannot provide personalized advice and you would need to make your own decision with your physician.
I don’t think there is any link. You can certainly try skipping breakfast 2-3 times per week and working upwards from there. Some people prefer to work themselves in slowly, and others to jump in with both feet. Kind of like a swimming pool. Some wade in, others cannonball right in. Your choice.
Some people tend to overeat and indulge in foods before sunrise and after sundown. I would recommend to not eat before sunrise and eat as normally as possible after sundown. Some studies of Ramadan have shown weight gain during this period for that reason.
You should try to eat as normal a dinner as possible. You will eat slightly more than usual, but as you get used to the fasting, it should get better. This is quite common. Many people will find that the overeating will cause some stomach upset.
Yes – Bone broth is highly recommended. It contains numerous minerals and vitamins and is quite ‘filling’ in terms of reducing hunger pangs. The other benefit is that you can add a good amount of sea salt to it. The other fluids taken during a fast – water, tea, coffee – don’t have sodium and you can become dehydrated. Mild dehydration, for example may lead to cramps and headaches during longer fasting.
So, yes, bone broth is highly recommended (recipe). Also very ‘Paleo’ in the sense that this is a very traditional food with a long tradition.
Technically, the milk does not fall within the guidelines of a true fast, but the small amount of milk/ cream added to coffee improves compliance tremendously for some people. So in our program, we absolutely allow milk/ cream in coffee, but no sweeteners or sugar.
Yeah, I was more thinking along the lines of 1-2 teaspoons, not the whole carton. Because cream still contains milk protein, it will stimulate insulin which defeats the point of fasting. Pure fat, such as coconut oil, will be less.
Tea (all kinds), coffee, and bone broth are all acceptable. I allow a small amount of cream or coconut oil in coffee for compliance sake, although technically, it would not be allowed. I don’t worry about the caffeine content.
There is little information on the sugar alcohols including xylitol. So I don’t really know if they are acceptable or not. However, when in doubt, my position is that these are not traditional, real foods, so best avoided.
If you feel better taking the soup, then, yes, I wouldn’t be too concerned about the small amount of carbs.
Fiber is often our first approach, but if that fails, we often use laxatives such as milk of magnesia or senna tea. Constipation is common and often bothersome. Stool softeners often help with the problem.
I don’t recommend counting calories. After the fast, I would try to eat as normally as possible. That would be your usual dinner but perhaps a slightly larger portion of it.
Remember that protein intake on a fasting day will be much lower than normal. On your eating day, you can simply make up for it by taking higher dose, although most people eat at least 3-4x as much protein than what is needed for normal health.
Dr. Jason Fung: Yes, both are acceptable. Drinking 2 tbsp at night lowers morning sugars
In uncomplicated hypertension, I generally don’t advise a low salt diet – just a regular salt diet. With bone broth, the amount of sodium is still going to be far less than what is taken on a regular eating day, so I would not worry.
We often see this drop during fasting.
This is quite common, and due to breakdown of glycogen or production of new glucose in response to some of the hormonal changes of fasting. It is neither good nor bad.
Think of it this way. Your body is simply moving sugar from its stores (glycogen and fat) and pushing it into the blood. Here your body has a chance to burn it off.
Listen to your body. If you feel unwell, then stop. Otherwise, if you are worried, reduce the fasting duration.
What do you suggest about using Whey Protein Powders and what is their impact on insulin? Mark Sisson (who sells it) wrote whey can lower insulin yet often heard is that as a concentrated Dairy, whey protein raises insulin.
I advise against using whey powder for the main reason that it is a highly processed chemical, not a real food. Whey stimulates insulin highly, but also is very satiating, so effect on weight likely closer to neutral.
If you eat a diet predominantly of whole, unprocessed, real foods, then no, it is not necessary.
I know that I will ruffle some feathers, but I am quite skeptical about the gut micro biome theory with regards to obesity. So, there are no food I recommend for that reason.
With regards to rice and potatoes – these are not necessary in any diet. Personally, I eat both, simply because I enjoy them occasionally. However, I am not trying to lose weight. If I were, yes I would restrict rice and potatoes.
It is not carbs per se that cause obesity, but insulin. While starches raise insulin, there are ways to bring it back down. You can add protective factors such as fibre and vinegar. You can also alter meal timing (intermittent fasting) and adding natural fats.
[Editorial note: While fiber, fat and even vinegar can slow down the absorption of some carbohydrates and delay or blunt the resulting glucose rise, this does not mean it completely prevents the glucose and insulin spikes. Furthermore, even though it may delay the spike in blood sugar, it can extend the overall time blood sugar remains elevated. Therefore, we do not recommend this technique as a “safe” way of eating more carbs. If you are absolutely craving that potato and are going to have it one way or the other, then by all means take these steps to make it somewhat “safer”. But to get the benefits of a low-carb diet you are still better off not having it to begin with.]
Except in certain medical circumstances, sodium restriction is not necessary. This was recently shown by Dr. Salim Youssef in the New England Journal of Medicine.
There is ongoing debate about the need for sodium restriction, but for otherwise healthy people, I do not worry about restricting sodium.
2) I once made the dumb decision to drink a bottle of red wine during a longer fast on day 6 or 7 (or something like that). I really felt horrible that night but in the morning… no problem anymore. Can drinking alcohol during a longer fast be dangerous? And: does the body ONLY burn alcohol while being drunk? (I remember feeling cold and extremely hungry that night…)
I generally advise patients to stop alcohol during the period that you are trying to lose weight/ reverse diabetes for the simple reason that the body can burn the alcohol for fuel, and we are trying to get the body to burn stored sugar. I’ve also heard it ‘stops ketosis’ for a similar reason.
Yes, where most people have a carb-centric view of obesity, I have an insulin-centric view of obesity. That is, carbs are a large part of insulin, but not the whole picture.
I don’t think fibre is inherently toxic. Actually, I think that it may help protect against insulin spikes. I don’t think fibre is bad for the gut. I also don’t agree with the acid/alkaline theory.
I am of the opinion that the main issue is high insulin levels. Therefore, fibre, which tends to reduce insulin, should not be counted and think that the net carbs (carbs minus fibre) concept makes good sense.
None that I am aware of.
I don’t believe it dangerous, but it sure is uncomfortable. That is generally why it is easier to plan a small ‘break fast’ meal. A handful of nuts, a small salad and then give yourself at least half and hour to digest.
The initial rapid weight loss seen in fasting is often water. Since you have followed LCHF, you are not losing much of the water weight. After that, it averages 1/2 pound of weight loss per day of fasting. So, your weight loss is a little bit lower than average, but not unheard of. If a pound of fat is 3500 calories and you normally eat 1800 calories, then 2 full days of fasting will produce 1 pound of weight loss. It is possible that your metabolism runs a little slow and therefore you only get 0.2-0.3 pounds of weight loss.
If you are not getting the results that you desire, you can try to change your regimen. Do the fasting on a regular basis. Try longer fasts. Try shorter more frequent fasts. There is no ‘best’ regimen. The key is to try it and find the one that suits you and gives you results.
I have two questions:
1) Will adding a high fat source to a protein meal reduce the insulinogenic effect of the protein meal? For example, if I was eating a 6 oz. steak for dinner, would the insulin response be reduced if I included a high fat item such as avocado or sour cream as opposed to just eating the steak?
2) I know you have stated that the best fasting regimen for each person is the one they can maintain, but if a person is suffering from extreme insulin resistance, would a longer fasting period be more helpful? And, if so, do you believe in that situation a longer fast of at least a week or more would have a significantly better effect than say a 3 day fast every now and then added to regular intermittent fasting?
1. I would replace some of the steak, which is high in protein with the avocado or other natural fat. Protein can still stimulate insulin, as opposed to fat, which does so to a much lesser degree.
2. Longer duration fasts are much more effective than shorter one. We routinely start longer duration fasts for people on higher doses of medications because of their higher insulin resistance.
If you are taking blood sugar medications, then you must be very careful to avoid low sugars (hypoglycemia). Otherwise, your body should be able to manufacture new glucose during fasting, although in rare cases, some people still develop hypoglycemia.
Sugars should normally be low during fasting and ketones increased. This is the normal situation as ketones are produced as energy for the brain.
Ketones are produced by the body when insulin levels are low for the brain to use as fuel. Some people measure it to make sure that their diet is sufficiently low in carbohydrates
An eGFR of 80 is pretty close to normal. The only way to prevent diabetic kidney disease is to get rid of the diabetes. Anything else is just rearranging chairs on the Titanic
The SGLT2 inhibitors get rid of sugar in the urine, which works well with the fasting. With fasting, we encourage the body to burn off the sugar. The drugs make you urinate out the sugar.
There are, however, side effects, as with any drug, especially urine infections, but in general, I think it is a good drug.
If you are seeing good results, then clearly this approach is working for you and I wouldn’t change it. In general, I advise following an LCHF diet with intermittent fasting. Your approach clearly qualifies.
I cannot legally give you advice for your personal situation, but in our clinic, we try to keep blood sugars in to 8-10 range. This is higher than normal because it is far more dangerous to become hypoglycemic during fasting.
For this reason, we carefully monitor sugars during fasting and we always advise that it is better to take less insulin than more. If you take too little, you can always take more.
If you take too much, you will need to take sugar to reverse the hypoglycemia, which defeats the whole point of fasting in the first place.
There is no ‘best’ fasting regimen. More intensive regimens produce faster results, but are not ‘better’. Some prefer to go slow and others fast. Some will find shorter duration fasts better and others find longer is better. Please see my ‘Fasting’ series of blogs on my website for more information.
Metformin stops the process of gluconeogenesis. So, yes, it does nothing to prevent fatty liver.
I can only say that we often hold metformin during fasting in our IDM clinic due to GI upset. This is OK as long as blood sugars remain in a good range. I cannot comment on whether you should take them yourself.
1. Is it common for a very IR
individual to have to go to this extreme measure to begin producing ketones?
2. If extended fasts (4-ish days) are performed between 2 and 4 times per month, and a LCHF diet is followed when not fasting… in your experience, how long might it take to resolve or at least dramatically improve this level of IR?
1. Ketones are produced by the body to feed the brain instead of using glucose. If you have enough glucose coming out of storage, there is no reason for your body to make ketones. So, yes, that is normal, and likely due to your IR.
2. There is no normal and depends upon the individual. Some people reverse their IR within weeks and others take more than a year.
That is certainly our experience. If you are recently diagnosed with T2D, it generally reverses quickly. If you have had it for 17 years, it will take more than a few months at least.
Yes this is a common problem and is to do with the Dawn Phenomenon. Your body has a surge of ‘counter regulatory’ hormones just before waking that pumps sugar into the blood. This is why your fasting sugar is high despite not eating.
This reflects your body’s insulin resistance. In essence, your body is moving too much sugar from storage into the blood. It just means that your body has too much sugar overall.
You could either continue your fasting schedule and give it more time, or you could increase duration of fasting if you want to speed it up.
I consider diabetes to be reversed when you are taking no medication and able to maintain an A1C of less than 6%.
My guess is that there are two main effects. One, the focus on real food rather than highly processed ones is very important to maintain normal function of the GI system. Two, losing weight often improves symptoms of reflux.
The link between BP and diet is not quite as tight as with blood sugars. I think trying a 16:8 IF sure couldn’t hurt.
It is quite rare for renal function to improve. It has happened perhaps to one person in 300. While the diabetes (type 2) can be reversed, the kidney function cannot. Even in studies of pancreas transplant of type 1 diabetes, the kidney does not improve for 10 years after normalization.
There is not much literature about fasting and change in thyroid dosing, so I can’t help you there, but I have heard several anecdotal cases of the same thing happening where thyroid function suddenly improves. With the high blood sugars, the only thing to do is to continue with your plan. It certainly seems that you are now mobilizing some of that stored sugar.
Yes. Both types of diabetes would improve on LCHF compared to a standard 50% carbohydrate diet. The reasons are entirely different in the two types, though.
No, it is not normal to be cold – it means your REE is going down. Try to eat sufficiently on eating days.
I am sure the study was not done with low carb diets so there is that. What do you think?
This was an animal study and I would ignore it. Most studies ‘proving’ that you must eat all the time prove nothing of the kind. Eating all the time to lose weight? I don’t think so.
There is minimal protein loss is a 16:8 regimen or even after 4 days of fasting. It is only a myth. I cover intermittent fasting in depth on my site starting with part I.
Why would your body store energy as fat if it starts burning protein (muscle) for energy? The answer is that it does not. It is only a myth.
We have not yet had any problems with gallstones or biliary colic during fasting. I have not yet found any discussion of gallbladder problems with fasting, and literally millions of people fast regularly
Fasting does not cause hypothyroidism unless you become severely iodine deficient. Hashimoto’s disease is an autoimmune disease and is not much related to diet, good or bad.
There are many problems that occur with fasting, though. The most common are constipation, headaches, and hunger pangs. There are strategies to deal with these. Many medications can also cause problems on an empty stomach and should be discussed with a physician.
Anything more serious than that is not part of normal fasting and should be investigated.
Unless you have type 1 diabetes, the ketones are normal and are produced by the body for the brain to use instead of glucose.
No, it does not. I address Fasting physiology in a multi-part series here.
In the first 24 hours after eating, you will use amino acids (from dietary protein) as substrate for gluconeogenesis. Afterward, glycerol from the breakdown of triglycerides provides the substrate. Protein (muscle etc.) is conserved during fasting.
Ask yourself this. Do you believe that Mother Nature designed us to store excess energy as fat, but as soon as we need it, we start burning protein instead of fat? No, protein is conserved and fat is burned for fuel during fasting.
Yes, in the diabetic situation it is possible to get both high and low blood sugars. This should always be undertaken with physician supervision. As you point out, in the non diabetic, this hypoglycemia does not happen, but in diabetics, with their high baseline insulin levels, it is a strong possibility.
We have seen this before, where diabetics who were taking a very high dose of insulin were able to get off their medications, but became hypoglycemic off all medications. It typically passes in a few weeks time, but in the meantime, clients can become symptomatic.
The body will start producing glucose when it gets too low to prevent hypoglycaemia, except if you are taking medications. We do occasionally see hypoglycaemia on people taking no meds, but this is usually when people have just recently stopped insulin and presumably, the mechanism for gluconeogenesis is ‘rusty’. This usually improves within a few weeks although can last longer.
Everything you eat or do not eat will affect your gut bacteria. Whether it is important is a different question. I tend to think that it is of minor importance, but evidence is so far scarce.
If you are feeling well, there is no contraindication, except in children, pregnant and breastfeeding. Also, if diabetic, medications may need to be adjusted.
The most common reason is other medications especially iron and aspirin. Check those. Otherwise, you can try to build up to the longer fasting periods.
It is certainly possible. If it happens, then he should stop.
They say that leptin is connected with our consumption and if we start to eat too late that whole process is disrupted then, and leptin and cortisol does bad values then, …..
Also about fasting they are saying that prolonged periods without food (more than 8 hours) are too stresfull and bad for your cortisol control. and that it can raise stress levels.
They say that cortisol then protects the body fat, and etc. My question is do you have some studies about cortisol and fasting? Do you measure cortisol in your clients? I suggest that If I measure blood glucose and it goes low during fasting like to 3,8 molar then I don’t have problems right? its normal not to be hungry in the morning isn’t it?… and I don’t have to stuffed myself with food my body obviously don’t want at that time.
If you are not hungry in the morning, then I think you should not eat. This is called ‘listening to your body’. It doesn’t mean your hormones are messed up, it means your body is telling you that you don’t need to eat. So you should not.
Leptin is not likely affected by skipping breakfast. This sounds like something that is made-up. It is not necessary to eat constantly. Neither does missing a meal increase cortisol. I fail to see how forcing yourself to eat when you are not hungry is going to help you lose weight.
There are actually very few studies on cortisol and fasting and they are mostly contradictory. I do not measure cortisol in our clinic patients. If your problems are cortisol (stress) related, then changing your diet is not going to be very effective. Instead, you need stress relief (meditation, yoga, massage, pain management etc.) I try to stick to diet related issues.
Cortisol is normally raised in the morning as part of the circadian rhythm. This is normal and found in everybody. This helps release some of the stored sugar in the morning to give your body some energy for the upcoming day.
Therefore, you do not ‘need’ to eat because your body has already given you energy. You have plenty of sugar available for whatever you need to do in the morning without eating. Since you are ‘tanked up’, you do not feel hunger. Most of morning hunger is trained through decades of eating as soon as we get up.
There is no connection, unless you do not stay hydrated. It is important to consume enough water as well as salt/ electrolytes during fasting. This will help prevent kidney stones.
I would not be concerned. As a nephrologist, I am referred all cases of RTA and I have perhaps seen only 3 or 4 cases in the last 15 years – all of which were not related to diet. RTA would be amongst the very lowest of my concerns with a ketogenic diet.
The tests I focus on are the fasting glucose and the hemoglobin A1C. I also test ALT to look for fatty liver and Triglycerides (indicates a diet very high in carbs).
Cortisol excess can be difficult to diagnose for certain, but most people will know if they are under excessive stress (psychological, physical, chronic pain etc).
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