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For doctorsWhat is the optimal fast frequency?
, medical content by Dr. Jason Fung, MD
in Insulin, Intermittent fasting, Q&A 
What is the optimal fast frequency? Can you fast with low blood pressure? Is type 2 diabetes caused by fat plugging the pancreas or via high insulin levels in blood? 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.
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.
Dr. Jason Fung
Fat plugging pancreas vs. high insulin levels in blood
Dr. Fung: Your books are a revelation for a person with type 2 diabetes for many years. I’m now fasting.
One thing gnaws at me. You make great sense to me that the 0.6 g (I think you said) of fat clogging the pancreas is the reason beta cells are not performing.
But, contrarily, you indicate that there are already high levels of insulin in the blood and that it’s the insulin in the blood that’s the real problem – high blood glucose is a symptom.
How can both of these statements be true?
Again, “you had me at ‘reversible.'”
Thank you,
Steve Brock
The underlying problem of type 2 diabetes is too much insulin. This drives glucose into cells, and drives de novo lipogenesis. The liver exports the fat to the pancreas which gets clogged and this decreases insulin production. This is the body’s compensatory response.
Insulin is too high (usually due to diet) and the body is trying to fix it by clogging up the pancreas. This lowers insulin, but does not fix the root problem. In the mean time, glucose goes up in the blood, which then gets dumped out the kidney. This gives us the symptoms of diabetes. But again, this is the body trying to fix the problem.
There is too much glucose coming in (diet) so it is trying to dump it out through glucosuria. But neither of these compensatory responses fixes the root problem (diet).
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
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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