What is the optimal fast frequency?
, medical review by Dr. Bret Scher, MD
in Insulin, Intermittent fasting, Q&A 
What is the optimal fast frequency? Can you fast with low blood pressure? And, can a low metabolic rate be reversed?
It’s time for this week’s Q&A about intermittent fasting and low carb with Dr. Jason Fung:
Fast frequency
I’ve found through various of your articles and videos that the 24-hour fast can be performed daily (Warrior Diet). I’ve also found the “mixing up” the duration of fasts is good so that the body doesn’t adapt. My question is on what frequency are three-day and seven-day fasts acceptable? For example, one 7-day fast per month and three 3-day fasts per month, 24-hour fasts the remainder? If you’re in general good health, a of couple weeks into the keto diet, 40 pounds (18 kilos) overweight having lost 20 pounds (9 kilos) already?
Mark
That’s a great question, but one with no easy answer. It all depends upon the person. It depends upon the specific reason you are fasting, how your body responds to it (some people do better than others), and how easy it is for you. I just saw somebody who did a 61-day fast, and the very next person said she couldn’t do 12 hours. The answer is different if you are at your ideal weight or severely diabetic and 100 pounds overweight.
You can find more details in Diet Doctor’s guide on fasting.
Dr. Jason Fung
Fasting and low blood pressure
Hi Jason,
Is it safe to start fasting if you have low blood pressure?
Thanks,
Adam
It is not an absolute contraindication but you need to speak with your own doctor. Some people during fasting can feel faint, especially if they are not staying hydrated, so the low blood pressure may exacerbate that problem.
You can read more about low blood pressure in Diet Doctor’s guide.
Dr. Jason Fung
Can a low metabolic rate be reversed?
I have been a yo-yo dieter for years. last year, following a diagnosis of diabetes, I started on the BSD (800 calories a day). I have lost 50 pounds and my blood sugars are much improved. My metabolic rate is definitely low, it probably was before I started even on 800 calories. I have reached a plateau having been on 800 calories and low carb for nearly three months. I have just started intermittent fasting and generally understand that this, in itself, does not lower metabolic rate but what if you already have a low metabolic rate – can this be helped? I have your books on fasting, obesity and diabetes and they have helped me to understand the aetiology of diabesity, but I don’t think they address this specific enquiry. Could you elaborate?
Sue
You can hear more about resting metabolic rate in the Diet Doctor Podcast with Kirsty Woods.
Dr. Jason Fung
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More with Dr. Fung
Dr. Fung has his own blog at idmprogram.com. He is also active on Twitter.
Dr. Fung’s books The Obesity Code, The Complete Guide to Fasting and The Diabetes Code are available on Amazon.1
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I do not expect you to answer my question direct but maybe to ever one who follows you like I.
Thank you
You mention milk in your post. You wouldn't want to use milk to get your fat since the carb count is rather high. High fat cheeses, meats, cream, vegetables like avacados, and good quality oils would make up a lot of your fat intake. Eggs, bacon, walnuts, pecans are also good choices - just make sure you aren't overdoing the protein.
You can sign up for our free two week challenge!
https://www.dietdoctor.com/low-carb/get-started
I saw recently that some women are complaining of what is called keto crotch. What is your opinion of this? Is it really a ph balance issue or is it the body correcting itself so it takes some time to adjust?
Gall bladder, or not having one, should not have any impact on keto or fasting. If you do find you are having trouble with the higher fats, you can look for a digestive enzyme.
You may want to make sure that your meal a day is keto/low carb! That can help as well. You can use any of the recipes from our website.
I m fasting from when I was 5 years old I hv lots to talk to you I hv fasted for a year with alternate fasting it’s a religious custom which we hv to do once a year I hv fasted for 16 days only on boiled water that also for 10 hrs again this is a religious custom
I hv done lots of fast the warrior diet etc I am so happy to see you helping the whole world
Today for the first time I hv started fasting for health I hv started a 21 day fast with 50 calories of vegetable broth as I am a vegetarian and few supplements
GNC woman’s ultra
GNC Salmon oil
GNC PRIMOSE
GNC COLLAGEN
DERMAFIT
VITAMIN C
ONCE A WEEK VITAMIN D
B complex
Magnesium
Any advice you want to give me
Thanks
Pooja Goyal
Here is a link to our Diet Doctor guide to Time Restricted Eating https://www.dietdoctor.com/intermittent-fasting/time-restricted-eating
I have been experimenting with fasting for weight loss the last 1/2 year and the protocol I have arrived at that seems to be working well for me is doing a 72 hour fast, a 48 hour fast and a 24 hour fast each week (so I'm essentially eating 5 meals a week). I find this manageable with consuming coffee with heavy cream and bone broth while I'm fasting. I'm losing roughly 2 lbs per week with this approach, and I'm projecting I will need to sustain this for another 6 - 8 months to get to an ideal weight.
My question is: are there any potential long-term negative side effects to this approach? I appreciate your time in answering!
The long-term side effects would be even less severe than well-known keto side effects since I assume you're having carbs on your feeding days.
Scott, you can check out the risks and benefits associated with extended fasting here. https://www.dietdoctor.com/longer-fasting-regimens
What about the thin people who are pre-diabetic?
I’ve been on ketogenic diet 80% fat diet along with intermittent fasting for 5 years and while my blood glucose stabilized my BMR remains much lower than its supposed to be for my age. At 35 years old, 5 ft 11 and 140 lbs I can only eat 1200 cals/day or I gain weight. I exercise too. What gives? It seems like the the law of diminishing returns is at play?!
Fasting is not recommended for people with a low BMI. You can accomplish the same results when it comes to blood glucose control through eating a low carb diet without added fasting.
https://www.dietdoctor.com/low-carb/get-started
( I hadn't started with the bone broth. Relevant? How much of that is appropriate?)
If I should counter stomach tantrums with a small amount of coconut oil, does that blow the autophagy effects?
Are the cautions I see about "fat fasts" over 5 days, ie muscle loss from lack of protein -- confirmed, or simply conjectures like similar cautions about 'real' fasting?
Here is a video from Dr Fung about what breaks a fast:
https://www.dietdoctor.com/video-post-what-breaks-a-fast
Additionally, if you are having stomach issues, coconut oil may make those worse. You can read more about normalizing blood pressure at this link:
https://www.dietdoctor.com/blood-pressure
Dr Fung recommends medical supervision for fasts longer than a day, especially if you are on medication. Please check in with your doctor before engaging in extended fasting.
Thank you very much for this website and the opportunity to post a question on it to someone, seemingly, well informed 🙂
I have started an experiment to see if i can fast 5 days a month, not for loss weight reasons, but purely out of curiosity to see if it’s difficult/easy to sustain over a year, what the benefits might be and what the better way might be to do those 5 days - once a week, or 5 consecutive days in a row, or a few days here a few days there (with the idea if it is easy to go 60 days a year without eating and should then many more were also to do similarly - eating whatever we liked in between -, could that have positive implications on the planet’s resources and our effect on it? Presuming the science that says we are having such an ill effect due to our consumption and farming is correct).
I’m 48, in good health and eat a balanced, pescatarian diet.
I’ve done 5 consecutive days a couple of times in my life and I didnt find it a struggle then, but I haven’t done it every month for a year
My question is, if I was to do this with a slightly scientific/mindful mind to verify it was/wasn’t safe/beneficial… what key factors should I look out for, or test for periodically and what else would you recommend, eg keep a food diary, literature to possibly read, etc..? The other question I should probably ask is whether, in your informed understanding, would this be something sustainable year after year..?
Many thanks again
Steven