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EventsWhy does blood sugar increase during a fast?
, medical content by Dr. Jason Fung, MD
in Autoimmunity, Blood sugar, Dr. Jason Fung, Heart disease, Intermittent fasting, Keto, Q&A, Thyroid problems 
Why is my blood sugar increasing during a fast? Will reversing diabetes prevent arterial plaque production in the future? And can keto and intermittent fasting help reverse thyroid disease (Hashimoto’s)?
It’s time for this week’s Q&A about intermittent fasting and low carb with Dr. Jason Fung:
Increasing blood sugar when fasting
Why does my blood sugar level increase from 86 to 112 mg/dl (4.8 – 6.2 mmol/L) when I do a 20-hour fast? Is that normal? I’m on an LCHF diet.
Thank you doctor,
Alvaro
Answer:This is a normal process. When you fast, insulin levels start to drop and this triggers a surge of counter-regulatory hormones, including noradrenalin and growth hormone. This is normal, and meant to pull some of the stored sugar from the liver into the blood. If your liver is full of sugar, it may release lots of sugar into the blood, causing the blood sugar to rise.
So, yes, blood sugar may rise during fasting. The most important question to consider, though, is where this sugar came from. If you are not eating, the rise in blood sugar may only come from your own body. You are simply moving sugar from the liver to the blood. It means that there is too much sugar stored inside your body and you need to empty it out, either with LCHF diet or intermittent fasting
Dr. Jason Fung
Arterial plaque
Reversing diabetes and therefore inflammation should stop future arterial plaque production, right? Does reversing diabetes cause plaque to recede from arteries already affected? Are there any studies on this?
Kathleen
Answer: Diabetes is a very strong risk factor for heart disease and arterial plaque. Reversing diabetes should theoretically lower the risk of plaque disease, but there are no studies that conclusively demonstrate this. That is probably because most people consider type 2 diabetes to be a chronic and progressive disease, like aging. So, yes, I think it will reduce risk of heart disease, but no, there are no studies to prove this.
Dr. Jason Fung
Hashimoto’s, fasting and keto
I believe there is a way to reverse Hash! I feel so much better on keto and IF than any treatment over the past three years. Have you had any patients reversing Hashi with this program?
Thank you so much for all your work for all of us,
Martha
Answer: I don’t see Hashimoto’s very frequently so don’t have much experience. Fasting and low carb diets usually drop insulin so are effective for diseases of excessive insulin such as obesity, type 2 diabetes and PCOS. However, it may also have a smaller effect on inflammation so it may certainly benefit Hashimoto’s as well, but there are no studies to prove this, and I have only limited clinical experience with Hashimoto’s.
Dr. Jason Fung
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I am 45 years old and a T2D since 2003. I watched all the videos and started a keto diet, about 45 days ago. I incorporated intermittent fasting with the diet about 30 days ago. I was on Trulicity, Inovokana, and Metformin before the starting the Keto diet. Within a months time, I was completely off my medicines and my glucose levels were better than what I experienced while taking medicine. I am off my medications for 3 weeks now and continuing with strick keto a Intermittent fasting along with HIIT work out. Three weeks into it now I am observing high glucose levels, these levels are the same throughout the day (fasting 130 and 135 all day long) I am checking my sugar levels 3-4 times a day to keep a check. Not sure what is going on and why my levels are rising. Could you please advice on what could be the cause? Many thanks
Do you have experience with fasting with alopecia areata?
I 'm 37 years old and I have this disease for few years. But This disease starts in childhood..around 10years and after that with short episodes in stress periodes.
Three months ago I made a gut analysis and I have Zonulin over and other markers.. and seems to be "leaky gut".
I started a cure with probiotics and enzymes. For 2 months I make IF (16:8)...and now i'm in extended fast ...85hours until now.
My question is...is any chance to heal my gut and also my autoimmune disease???
Thank u a lot
I am having the same issue where BG levels are high during the fast mine is from 5.2 to 8.6mmol. My question is when eat doing omad. My BG drops to 4 to 5.6 on average. When I fast BG is up when I eat BG goes down. Any insight?
I'm a T2 24 hours into a 48 hour fast. After exercising my sugar went to 150. Should I continue to fast until it reaches 90 or less? Even if it requires me to go beyond the 48 Hours. Im not taking meds and normal diet is Keto 20 Grams <Carb/day??
As some above I do intermittent fasting three times a week. First time in 3 years, I saw an unusual extraordinary HIGH sugar spike when I tested at 7.45pm in the evening i.e. finishing the 24 hr fast, prior to eating dinner i.e. 8pm. Normally I am in range of 80 or 99mg/dl
I had a shock it showed 146mg/dl?? I immediately did 2nd test within 3 mins it was 99mg/dl, then as backup to see if I had two normal results, did a 3rd test i.e. result was 89mg/dl. Bascially the results were two normal non diabetic range, v. 1 diabetic abnormal range.
Should I view this as a one off situation, the temperatures had been soring and was 40 degrees time of taking the test? I had washed my hands as normal, no soap or other, simply warm water and dried thoroughly with clean towel.
Next day, concerned of course, I did another fasting test the normal out of bed, before breakfast at 8 hours after sleep, result was as I normally experienced 85mg/dl.
Could it be that the 24 hr fast for my body gives higher rating, it was the first time I had tried this test, I normally do the fasting day, and the next day I do the tests.
Curious as to how this happened?
Look forward to any guidance comments, and especially that with a 5 min period the levels dropped from sky high to normality?
Thank you.
That could vary based on many factors. Here is our guide for type 1 diabetes that may be helpful.
https://www.dietdoctor.com/diabetes/type-1
I read the Dr fung's report on keto, intermittent fasting and raised blood sugar levels during fasting and keto diet. My question is, do the raised sugar levels have a negative effect on my organs?
That is going to depend on how high your blood sugar goes, and for how long. If your blood sugar is going up significantly please work with your doctor to determine if you should break the fast or be on medication.
Anything longer than 24 hours is considered a "longer" fast and Dr Fung recommends doctor supervision. If your blood sugar drops drastically during a fast, it is time to break the fast.
My glucose levels at specific hours of fast were as follows:
36h: 59 mg/dL; 66h: 36; 88h: 40; and now at 112h: 56.
My ketones were:
24h: 2.6 mil/L; 36h: 3.8; 66h: 6.8; 88h: 6.8; and now at 112h: 4.5.
I assume that the drop in ketones would be due to my body getting better at utilizing them for fuel? But I am still quite curious what could cause the glucose to raise after all I assume by now my liver would be depleted of glucose.
Thank you!
From watching Dr. Fung's videos, I think I understand the principles of intermittent fasting. I'm a 62 year old Type 2, diagnosed 30 years ago, and obese with now a BMI of 38. I went on insulin about 5 years ago and have experienced significant weight gain. I also have Stage 4 kidney disease and have had an amputation, so I am coming to this information a bit late. I adopted a LCHF whole foods diet 90 days ago, and have lost 20 pounds. Lower extremity edema has resolved completely and I feel much better than I have in years. I still struggle with hypertension, as well as hyperglycemia.
Here is my question. I have started this new 90 day period (April 1) with some intermittent fasting, going with a 16/8 cycle for now. When I break my fast with a meal, should I be taking my mealtime insulin, or is it the "enemy", just adding to my problem? Do I need to fast longer? Pre-meal blood sugars are in the 160-180 range. When I ask my doctor, he tells me that fasting is "bad" and that I should just keep upping the insulin to fix my numbers. Any information you can give would be much appreciated.
This may be helpful for you! https://www.dietdoctor.com/low-carb/with-diabetes-medications
I'm in much the same position as you. I started 120 days ago. Before starting I was taking upwards of 200units of Lantus Solostar Basal Insulin and up to 75units of NovoRapid Bolus Insulin (depending on what I was eating) EVERYDAY, along with Sitagliptin/Metformin combo twice per day.
2 weeks into a Keto/LCHF Diet I had lost 15kgs (about 33lbs?) and significantly reduced to the point of completely stopping ALL of my Insulin and remained only on the Sitagliptin/Metformin tablets from that point
My HbA1c in December last year, just before I started Keto/LCHF was 9.2, the mid February followup HbA1c was 5.5 - lowest it's been in over 12 years as a Type 2 Diabetic. My daily BGL's were in the order of 5.0 - 6.3mmol (I think thats about 90-115 mg/dl?), down from my daily averages between 9-15mmol (160 - 270dg/ml)! WOW!
In Feb I started Time Restricted Eating... then started to throw in some Intermittent Fasting. While the weight continued to drop, now down by 32kg (70lbs) and still going.... i've noticed this past couple of weeks my daily BGL's have started to rise again.... i'm back in the order of a fasting BGL of about 8.0 or so, though today is was 10.4 (cross checked on two different meters). I did just yesterday start taking some B Complex Vitamins and Lecithin tablets to help improve my Liver Function - not sure if these have contributed to today's woeful BGL, so I will monitor to see what happens over the coming days.
From what I have been reading, an increase in BGL's at this time into a Keto/LCHF diet might be expected behaviour, especially if your Liver has had such a long period of neglect as in my case, this would be 35years+. I guess we cannot expect this to resolve itself in a few short months and time is required, along with patience and a degree of perseverance :).
I presume so long as the sugars are coming from my Liver and not from excess carbs being consumed (I am usually below 30gm/day, but have the odd spike here and there), then I guess i'm still far better off than I was 4 months ago!
I'm happy to see what happens over the weeks ahead and see if it just settles down by itself now.
Good luck with your Journey
This may be helpful for you! https://www.dietdoctor.com/blood-sugar/hba1c
It turns out after 5 Drs. She had allergies tested and she was allergic to many foods: wheat, dairy, shrimp, etc.
Our Dr. put her on a low dose Naltrexone 4.5 mg. I tab per day. Within 6 weeks her hair began to grow back. She has taken the medicine for 2 years. She has a thick head of hair now. Once the Dr. lowered the meds. And her hair fell out again.
He said the allergies up regulated her immune system and the immune system attached the hair follicles.
If you have leaky gut, that is many times caused by a food allergy. Good luck.
We have the medicine compounded, as it is a low does.
Please discuss any medication related questions with your doctor.
If your blood sugar levels have not come down, you may want to try eating a low carb diet in addition to the fasting. Please make sure and work with your doctor to monitor your blood sugar levels.
https://www.dietdoctor.com/low-carb