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For doctorsWhy is blood glucose elevated when fasting?
, medical content by Dr. Jason Fung, MD
in Diabetes, Intermittent fasting, Q&A 
Why is blood glucose elevated when fasting? Do you need keto macro guidelines when fasting? What is the optimal way of breaking a fast? And, can you talk about the psychological part of fasting?
It’s time for this week’s Q&A about intermittent fasting and low carb with Dr. Jason Fung:
Fasting & elevated blood glucose
Type 2 diabetes for 20+ years. Started keto with intermittent fasting in January 2019. Why would my fasting blood glucose numbers during my 18-24-hour fast be elevated, then come down to normal ranges after eating?
Mindy
Fasting can definitely raise blood glucose. This is due to the effect of insulin falling and the rising counter-regulatory hormones including increased sympathetic tone, noradrenaline, cortisol and growth hormone, in addition to glucagon. These all have the effect of pushing glucose from liver storage into the blood. This is normal. If you are not eating, you want to use some stored glucose. The question is this – if you are not eating, and your blood glucose went up, where did that glucose come from? It can only have come from your own body (liver). So, it’s a natural phenomenon, and the fasting now allows your body to use some of the glucose for energy.
Dr. Jason Fung
When combining keto and 5:2 intermittent fasting on fasting days, do you still follow the macro guidelines for keto?
On the two days of fasting, should the 500 calories consumed be of the same macro proportions as followed on the normal keto days? Or can you consume 500 calories of any food without going out of ketosis?
Andrea
I don’t generally recommend people to count calories. Fasting means not eating anything at all, so there is no ‘counting macros’. Dr. Mosley’s 5:2 diet allows 500 calories of whatever you like. But that’s his diet, not mine. I advocate intermittent fasting, with no calories.
Dr. Jason Fung
Veggies or fat or protein
I was taught to eat my salad first, then the meal… but I read that you advised to break a longer fast with ¼ cup of Macadamia nuts, and an hour later a salad. Ivor Cummins talked about the veggies doing their thing in the upper intestine, and the fat and protein in the lower. My question is which should I eat first to receive the best benefit. I eat once a day while fasting at least 24 hours. When 24 hours comes past 8 pm, I wait until the next day around lunch, then move ahead one hour each day and repeat.
William
I think you should eat the salad first. There is some data to suggest that eating the veggies first reduces insulin.
Dr. Jason Fung
Will fasting for long periods of time activate the famine/fat protocols in the body?
Hi Dr Fung,
I’m very interested in intermittent fasting and keto for weight loss, I am however concerned about the “starvation” factor – not so much physiologically but also mentally. I’ve just finished reading Jon Gabriel’s book where he talks about fat programs in your body and the importance of not “dieting” or denying yourself food because it activates the fat programs. I’m worried that fasting will “switch on” the “famine/fat program” and there will be more weight gain in the long run. Can you help me understand how fasting will not activate the “fat/famine” protocol in my mind and body?
Kerren
Yes, the psychological part of fasting is hard. Fasting is supposed to be a part of everyday life – that is why we have the word ‘break-fast’. Most people think they can’t do it, but the truth is that people have fasted throughout history. We only think we can’t. As with anything else, it is about getting the right education and the right support group. From a physiological standpoint, fasting allows you to burn body fat, which is a storage form of food for your body when no food is available. This is what most people want.
Dr. Jason Fung
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Is your fat really just fat? You may have tumors.
I lost my pancreas due to necrosis after trying to lose weight and after a long 5 years, getting a lap band. It immediately caused my body to get necrosis. I lost my gallbladder first in a week with the lapband. Then, my pancreas was mostly removed, and infection tore through my intestines and liver. I didn't eat by mouth for 3 months. I was horribly I'll with infection.
I have type 3C Diabetes and with the small piece of pancreas, chronic pancreatitis. Eating to starve started part of this cycle. I was on a protein sparing diet. I was in ketosis for 2 years with minimal weight loss. Guess what? I have Dercum's Disease!!! I have painful fat tumors all over my body. Not one person checked to see if my fat was actually regular fat. I died on the operating table and was on a ventilator with 3 tubes coming out of my body. All anyone cared about was how I looked. I was fat! Or was I?
Now I have a insulin pump. It's supplies are not covered by insurance. And to heck with salad. I now have gastroporisis, and diverticulitis.
Many illnesses that cause issues that lead to weight gain are probably caused by the lymphatic system. Also, most people are eating not enough nutrition. People need to sleep. Doctors need to cure illness and not just treat symptoms. Everyone should go back to school and reevaluate their Lymphatic system!!!
Without a healthy Lymphatic system, nutrition, sleep, and more than basic health care, no one will stay healthy and lose weight.
I had teeth going bad at the hospital and my back injury from a car accident wasn't tended to. I went through a pregnancy with a car accident injury. All anyone was concerned about was my weight.
People get you minds straight. Weight is not the issue. Getting the care you need, taking time to care for yourself, getting nutrition, and emotionally being supported is better than just a fast. If you have all your needs met, than sure the fast may work. It dang near killed me before. Now I'm forced to go days with only watered down gatorade to eat because I'm nauseated with pancreatitis everyday of my life and the stuck with insulin dependant Diabetes.
Starving yourself isn't a long time solution.
Take better care of yourself and others.
Love and aloha, Kai
Awaiting your kind response
Thanks
That least (H a 1c ) normal
What can I do ??
The best thing you can do is keep track of your blood sugar before a meal and then 1 hour after. That will help identify any problem foods or meals that may be keeping your blood sugar high.
If you are trying to gain weight, you would not want to incorporate fasting. You can read our guide to gain weight here.
https://www.dietdoctor.com/low-carb/gain-weight
You want to eat foods low in carbohydrates.
That likely indicates the foods you are eating may be too high carb. Ideally you will see a minimal raise about an hour after eating a meal. If your blood sugar rises too high after a meal, that is counterproductive.
Letting your liver "clean house" is a good thing. Eating low carb will also slowly reduce the liver's glycogen stores, but it's a gentler and more comfortable way to go. The soluble fiber in low carb vegetables is useful because it can absorb released toxins on its way through the digestive system. Eating some good fats helps remind the liver to keep digesting fats. Eating a diet too low in fat can cause gallbladder issues and even fatty liver.