More practical tips for fasting

This is a continuation of practical tips for fasting. Let’s start with some common questions.

Will fasting make me tired?

In our experience at the Intensive Dietary Management Clinic, the opposite is true. Many people find that they have more energy during a fast—probably due to increased adrenalin. Basal metabolism does not fall during fasting but rises instead. You’ll find you can perform all the normal activities of daily living. Persistent fatigue is not a normal part of fasting. If you experience excessive fatigue, you should stop fasting immediately and seek medical advice.

Will fasting make me confused or forgetful?

untitled-3No. You should not experience any decrease in memory or concentration. The ancient Greeks believed that fasting significantly improved cognitive abilities, helping the great thinkers attain more clarity and mental acuity. Over the long term, fasting may actually help improve memory. One theory is that fasting activates a form of cellular cleansing called autophagy that may help prevent age-associated memory loss.

I get dizzy when I fast. What can I do?

Most likely, you’re becoming dehydrated. Preventing this requires both salt and water. Be sure to drink plenty of fluids. However, the low-salt intake on fasting days may cause some dizziness. Extra sea salt in broth or mineral water often helps alleviate the dizziness.

Another possibility is that your blood pressure is too low—particularly if you’re taking medications for hypertension. Speak to your physician about adjusting your medications.

I get headaches when I fast. What can I do?

untitled-2As above, try increasing your salt intake. Headaches are quite common the first few times you try a fast. It is believed that they’re caused by the transition from a relatively high-salt diet to very low salt intake on fasting days. Headaches are usually temporary, and as you become accustomed to fasting, this problem often resolves itself. In the meantime, take some extra salt in the form of broth or mineral water.

My stomach is always growling. What can I do?

Try drinking some mineral water.

Since I’ve started fasting, I experience constipation. What can I do?

PrintIncreasing your intake of fiber, fruits and vegetables during the non-fasting period may help with constipation. Metamucil can also be taken to increase fiber and stool bulk. If this problem continues, ask your doctor to consider prescribing a laxative.

I get heartburn. What can I do?

Avoid taking large meals. You may find you have a tendency to overeat once you finish a fast, but try to just eat normally. Breaking a fast is best done slowly. Avoid lying down immediately after a meal and try to stay in an upright position for at least one-half hour after meals. Placing wooden blocks under the head of your bed to raise it may help with night-time symptoms. If none of these options work for you, consult your physician.

I take medications with food. What can I do during fasting?

There are certain medications that may cause problems on an empty stomach. Aspirin can cause stomach upset or even ulcers. Iron supplements may cause nausea and vomiting. Metformin, used for diabetes, may cause nausea or diarrhea. Please discuss whether or not these medications need to be continued with your physician. Also, you can try taking your medications with a small serving of leafy greens.

Blood pressure can sometimes become low during a fast. If you take blood-pressure medications, you may find your blood pressure becomes too low, which can cause light-headedness. And, of course, if you take medications that lower your blood sugar, you have to be extra careful and work with your physician before starting a fasting routine.

Always consult with your physician about adjusting your medications.

I get muscle cramps. What can I do?

Low magnesium levels, particularly common in people with diabetes, may cause muscle cramps. You may take an over-the-counter magnesium supplement. You may also soak in Epsom salts, which are magnesium salts. Add a cup to a warm bath and soak in it for half and hour. The magnesium will absorb through your skin.

What if I have diabetes?

Special care must be taken if you have diabetes or are taking diabetes medications. (Certain diabetes medications, such as metformin, are used for other conditions such as polycystic ovarian syndrome.) Monitor your blood sugars closely and adjust your medications accordingly. Close medical follow-up by your physician is mandatory. If you cannot be followed closely, do not fast.

Fasting reduces blood sugars. If you are taking diabetes medications, or especially insulin, your blood sugars may become extremely low, which can be a life-threatening situation. You must take some sugar or juice to bring your sugars back to normal, even if it means you must stop your fast for that day. Close monitoring of your blood sugars is mandatory.

Low blood sugar is expected during fasting, so your dose of diabetes medication or insulin may need to be reduced. If you have repeated low blood sugars it means that you are over-medicated, not that the fasting process is not working. In the Intensive Dietary Management Program, we often reduce medications before starting a fast in anticipation of lower blood sugars. Since the blood sugar response is unpredictable, close monitoring with a physician is essential.


Close monitoring is essential for all patients, but especially, for people with diabetes. You should also monitor your blood pressure regularly, preferably weekly. Be sure to discuss routine blood work, including electrolyte measurement, with your physician. Should you feel unwell for any reason, stop your fast immediately and seek medical advice. In addition, people with diabetes should monitor their blood sugars a minimum of twice daily and record it.

In particular, persistent nausea, vomiting, dizziness, fatigue, high or low blood sugars, or lethargy are not normal with intermittent or continuous fasting. Hunger and constipation are normal symptoms and can be managed.

Top 8 intermittent fasting tips

  1. Drink water: Start each morning with a full eight-ounce glass of water.
  2. Stay busy: It’ll keep your mind off food. It often helps to choose a busy day at work for a fast day.
  3. Drink coffee: Coffee is a mild appetite suppressant. Green tea, black tea, and bone broth may also help.
  4. Ride the waves: Hunger comes in waves; it is not continuous. When it hits, slowly drink a glass of water or a hot cup of coffee. Often by the time you’ve finished, your hunger will have passed.
  5. Don’t tell anybody you are fasting— except your doctor: Most people will try to discourage you, as they do not understand the benefits. A close-knit support group is often beneficial, but telling everybody you know is not a good idea.
  6. Give yourself one month: It takes time for your body to get used to fasting. The first few times you fast may be difficult, so be prepared. Don’t be discouraged. It will get easier.
  7. Follow a nutritious diet on non-fast days: Intermittent fasting is not an excuse to eat whatever you like. During non-fasting days, stick to a nutritious diet low in sugars and refined carbohydrates.
  8. Don’t’ binge: After fasting, pretend it never happened. Eat normally, as if you had never fasted.

The last and most important tip is to fit fasting into your own life! Do not limit yourself socially because you’re fasting. Arrange your fasting schedule so that it fits in with your lifestyle. There will be times during which it’s impossible to fast: vacation, holidays, weddings. Do not try to force fasting into these celebrations. These occasions are times to relax and enjoy. Afterwards, however, you can simply increase your fasting to compensate. Or just resume your regular fasting schedule. Adjust your fasting schedule to what makes sense for your lifestyle.

What to expect

The amount of weight lost varies tremendously from person to person. The longer that you have struggled with obesity, the more difficult you may find it to lose weight. Certain medications may make it hard to lose weight. You must simply persist and be patient.

You’ll probably eventually experience a weight-loss plateau. Changing either your fasting or dietary regimen, or both, may help. Changing the fasting protocol is often what’s required to break through a plateau.

Fasting is no different than any other skill in life. Practice and support are essential to performing it well. Although it has been a part of human culture forever, many people in North America have never fasted in their lives. Therefore, fasting has been feared and rejected by mainstream nutritional authorities as difficult and dangerous. The truth, in fact, is radically different.

Jason Fung


Do you want to know much more about intermittent fasting? Check out our full guide:

Intermittent fasting for beginners

Top videos about fasting

    The 2 big lies of type 2 diabetes
    The top 5 myths of fasting
  • The 7 benefits of fasting
    The cause of obesity

Earlier with Dr. Jason Fung

Practical tips for fasting

The Common Currency in Our Bodies Is Not Calories – Guess What It Is?

Why the First Law of Thermodynamics Is Utterly Irrelevant

How to Fix Your Broken Metabolism by Doing the Exact Opposite

More with Dr. Fung

Dr. Fung has his own blog at He is also active on Twitter.

His book The Obesity Code is available on Amazon.

The Obesity Code


  1. bill
    Way too much time spent on Diet Doctor
    now on fasting.

    How about discuss the idea that
    a high fat diet mimics the best effects of
    fasting without the concomitant issues
    as delineated above.

    Fasting is not necessary for the vast
    majority of people if they would follow
    healthy LCHF nutrition.

    Reply: #3
  2. Dr. Andreas Eenfeldt, MD Team Diet Doctor
    I agree with all except the first paragraph. :)

    It's equally true that the vast majority of people would not require a strict LCHF diet if they did some fasting once in a while.

    Personally I think it's a great combination.

    Replies: #4, #5, #11, #19
  3. Pierre
    I agree with you, I see no need to fast if you follow a LCHF diet.

    My last meal is around 6 PM and the next morning around 7 AM I get my breakfast. That's why it is called break fast.

    So I fast ~12 hours a day, so what is the point to do 24 hours?

  4. bill
    Dr. E: Will you also concede that not
    following an LCHF diet makes fasting
    much more difficult and increases
    odds that one will experience some of
    the symptoms delineated above e.g.
    excessive hunger, lightheadedness, lack
    of energy, all due to the phenomenon of
    blood glucose crashing, which doesn’t happen
    nearly as much on LCHF nutrition? I have
    not seen you emphasize this.

    Your site is losing focus.

    Reply: #8
  5. Marianne G
    I agree with you, Andreas, LCHF/Keto and IF are a great combination. LCHF is sometimes not enough for some people, particularly those with extreme insulin resistance and metabolic impairment. IF can be a way for them to heal and increase insulin sensitivity. I do not agree that Diet Doctor is losing focus, I think it is becoming more inclusive of different people with different needs. Thanks for your fantastic work and the help you bring to so many!
    Reply: #12
  6. Helen
    I have done LCHF for over 12 years, in the beginning it was really easy to loose weight and keep it off, now it requires a little more effort. I am also in the small group of people who have above normal cholesterol levels and therefore need(?) to limit certain saturated fats (is high cholesterol actually bad, I don't know). Anyway, I have cut back on saturated fats and use olive oil rather than butter. So far I have fasted only a few times and lost a few pounds each time. Fasting was easier than I imagined and I think it will benefit me.

    We are all different and Diet Doctor covers different topics, if you think too much time is given to fasting then ignore these articles and read or watch something that interest you. :)

  7. BobM
    I found that I was eating too many times per day on low carb, and IF helped with that. In particular, protein causes an insulin response and I was eating 4-5+ times per day, sometimes with strictly protein. I lost 20 pounds with low carb, another 30 pounds by IF+LCHF, and am continuing to lose now (now keeping a ketogenic diet + IF). Also, IF tends to clear fat from the pancreas and liver faster than does low carb.

    Now, I vary my routines all the time. I may eat breakfast but not lunch; I may not eat breakfast or lunch; I may not eat for a few days; I may eat three meals (as I did yesterday). And if I go on vacation and eat off of low carb, I'll use several days of fasting to get me back on track and in ketosis.

    I do find that eating more fat is also helpful, but I also have to eat protein, which causes an insulin response. It's difficult to not eat protein. For instance, to get 2 grams of Omega 3 fatty acids in fish, you're talking 20+ grams of protein, easily. Unless you gobble fat down (and I eat plenty of homemade mayo, butter, olive oil, etc.), you need protein, and protein causes an insulin response.

    Reply: #9
  8. BobM
    Bill, I combine LCHF and fasting all the time. My measured ketones were 0.8 (blood) this morning after a weekend during which I did not eat until about 1pm on Saturday, ate three meals yesterday, and won't eat again until Wednesday at lunch. I do use pickle juice for salt sometimes when fasting, but I do the same while on LCHF. There is absolutely no reason one cannot combine LCHF and fasting (IF).
  9. Cindy C
    I get my omega 3 fat from cod liver oil every day, instead of getting it from fish. On some days, I have fish instead of fatty meat, and still take the cod liver oil.
  10. gbl
    Helen, few people have a cholesterol level higher than mine and at 74 I have no cardiovascular disease. I eat high fat and always have, but also until recently, too much carbs. Now, just the high fat. This study discusses women and cholesterol:
  11. bill
    Dr. E: Why would you want to encourage someone
    not to eat LCHF nutrition? Isn't this site supposed
    to be Low Carb High Fat, not, try this so you don't
    have to eat Low Carb High Fat? (Your reasoning,
    not mine) Lots of people are
    looking for reasons they wouldn't have to stay LCHF.
    This just plays into that.

    That's what I mean when I say this site has lost its focus.

  12. bill
    Marianne: You completely missed what
    the good doctor just said: If you fast, you
    don't have to stay LCHF. Why he promotes
    this way of thinking, I couldn't say. And,
    apparently, neither can he.
    Replies: #13, #15
  13. Dr. Andreas Eenfeldt, MD Team Diet Doctor
    Actually, I did not say that. Read it again, please.

    I said that MOST people would probably not need a STRICT low-carb diet if they sometimes fasted.

  14. Daci
    I've combined fasting with hflc and it's worked out very well.I really
    can't complain .
  15. Marianne G
    No, Bill, I did not misunderstand. No one here is saying that IF is an alternative to LCHF. It is being presented and discussed as a complement to the diet. LCHF is a tool, not a religion. We do not have to be fundamentalist about it. I like that a variety of viewpoints and options are offered here within the parameters of low carb - i.e., strict, moderate or liberal low carb, keto, IF. It's up to us to decide which approach works best for our particular situation.
  16. Patrick
    Hello. I would like to add some info about fasting. I started fasting regularly with my wife 2 years ago to accompany her in her chemotherapy. Fasting helps a lot with chemo since it reduces side-effects in a lot of people and increases the stress specifically on cancer cells. So the therapeutic index of chemo is hugely increased by fasting. Now we fast 4 days, 4 times a year. My point is that weight loss should be viewed as a bonus of fasting, by teaching your body that your "storage guy" need to learn to look for where he has stored all that fat and why.
    The main advantage is the drop of bio-available IGF1 in your system which has several beneficial impacts on your body. First, you teach your normal cells that they can live "without" glucose (in fact much less glucose is more correct). Once your system has learned this important lesson, you can exercise with fat fuel, hence with a much greater autonomy. Second, you upset your cancer cells or pre-cancerous cells which largely depend on glucose for striving. Once upset, these cells may enter programmed cell death or autophagy. Third, you boost your stem cells, hence rejuvenate, especially the blood system including the immune cells.
    Finally, about headaches. I get them each time on the second day. I always drink a lot, Vichy water with a good electrolytes balance. So I think the headache in my case is related with the drop in blood glucose. Once down from 5 mM to 2-3 mM, and stable, the headache is gone and I can even go running for more than an hour on day 3 or 4.
    Keep up the good work.
  17. Richard S Stone
    Fasting and Low Carb is not an either/or, or a binary, kind of issue: The idea, as I see it, is to get the most out of the entire conceptual package. First, there is serious evidence regarding the destructive nature of excessive consumption of refined carbohydrates, mainly wheat flour. Rice is similar, but maybe not quite as bad. Such refined carbohydrates are too quickly and too easily converted into sugar in the body. Alternative carbohydrates, such as potatoes, sweet potatoes, fruit, etc., have a reduced impact. Why is this a serious issue? Because sugars are the main triggers in telling the body (pancreas) to produce insulin, the fat storage hormone. The other trigger is protein, but the reaction to protein is not as strong as to sugar. In this situation the body cannot tell a snickers bar from a muffin. Controlling this with a lchf diet is a good start. If you do this you will most likely lose weight, for a while.

    And in this context, insulin production leads to insulin resistance, which is, in effect, diabetes.

    Second, fasting takes your insulin production to zero. Unless you do that your body's metabolism will not access your fat stores, and you will continue to store fat. This will happen even if you exercise seriously and suffer. In addition, no exercise is necessary to lose weight while fasting, because the body's need to maintain its base metabolic rate will require use of stored fat. What other source of energy does it have?

    Again, in this context, reducing insulin greatly has a beneficial effect on the problems caused by excessive insulin production, such as heart disease and circulatory issues, cancer, etc., caused in part by "growth factors' related to insulin. (Cancers live on sugars, and the insulin-related growth factor is part of the basis for tumor growth.) Further, in the continued absence of nutrients (more than 15-18 hours?) the body will go into a higher level of autophagy, amounting to a more serious pursuit of fat and damaged proteins throughout the body.

    Third, the complementary nature of the process changed diet and fasting results in a better outcome over-all. There is no point in eating excessive amounts of carbohydrate and protein, when you know that the main effect of doing that is actively harmful to yourself and to the public at large. Avoiding the consumption of additional and unnecessary calories, in preference to eating only those required results in better (public and individual) health and an improved environment on the planet. It also results in fewer individual (and unfortunate) health problems, like diabetes, high blood pressure, CHD, and cancer. Where is the downside?

    And, amusingly, it is essentially free. You don't have to buy pre-packaged food to fast or take any special and expensive pills. There are fewer dishes to wash. More time in which to do what you like to do.

  18. Al
    The claim that bathing in Epsom salts relieve suffering as it is absorbed by the skin has no proof. It is a folk belief.
    Reply: #21
  19. Cindy
    I also believe and have found that Keto and other LCHF plans work well with IF. I do a 36 hour or 48 hour fast occasionally.
  20. Theresa ( Gidget ) Woods
    Can you fast with bpc. Like have it in the morning then eat your omad around 7. And how will I get and see comments on this Post
  21. Wanda
    He didn’t say muscle aches, it was cramping. He said soaking in epsom salt would cause you to absorb magnesium which could relieve the cramping
  22. carol
    is a 12 or 13 hour fast enough to lose siginificant weight....i have been doing keto for about a month and not seeing the incredible results others have. I have introduced intermittent fasting into my keto and hope this will help.

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