Tuesday, August 9, 2016

When Should You Eat While Doing Intermittent Fasting?

Ask Dr. Jason Fung

There are tons of questions about intermittent fasting, like these:

  • When should you eat while doing 16/8 intermittent fasting? Lots of snacking during the eating window, or as few times as possible?
  • How do you avoid starvation mode?
  • How much salt do you need to avoid side effects?

Dr. Jason Fung is one of the world’s leading experts on fasting for weight loss or diabetes reversal. Here are a his answers to those questions and more:

When should you eat during a 8 hour eating window?

Hi Dr. Fung – when following 16/8 fasting protocol – and looking to minimise insulin response during 8-hour eating window – and assuming macro-nutrient volume (calories) and ratio equal – would it be better to eat say two large meals (lunch and dinner) with bigger insulin spikes but then levelling out between meals – or smaller more frequent meals/snacks during 8-hour eating window but with lower insulin spikes throughout?

I assume bigger and and infrequent option better but please confirm. Also understand largely dependent on macronutrient ratio. I’m following circa 0-50gr/day carb protocol so understand protein component important in determining insulin response. Many thanks!


Dr. Jason Fung: If you confine to an 8 hour eating window, I don’t think there will be enough of a difference. Do whatever you prefer. My own bias is towards 2 large meals.

How do you avoid starvation mode?

Thank you so much for everything you do – you’re helping to make IF mainstream! I’m active on an on-line support group and quite a few of us are doing some form or another of IF – many for weight loss, some to control their T2D.

There is quite a bit of confusion on how to keep REE [Resting Energy Expenditure] up while doing a combo of daily 18-24 hour fasts with 2-3 longer fasts per week. (Most of us are also on LCHF).

Eating to satiety (especially as the fasting and LCHF both tend to decrease appetites) for one or two meals per day 4-5 days per week results in a fairly significant decrease in net calorie consumption – thus the concerns about REE.

Any clarification you can give would be greatly appreciated.

Thank you again for all your work!


Dr. Jason Fung: It’s not about calories. It’s about insulin. Reducing calories but not reducing insulin results in metabolic slowdown. Reducing calories and insulin does not.

How much salt do you need to avoid side effects?

After doing various fasts and eating LCHF for a few months, I still struggle with lightheadedness when I stand up. I understand this is most likely due to low salt intake and my electrolytes? Is there a type of pill that I could take or a daily amount of salt or something else that you recommend to alleviate this problem? It’s seems to happen more when I do a 2-3 day fast, but it also happens when I eat just one meal a day. I workout 6 days a week (cardio and strength training), in a fasted state. Does the timing of when I would take this pill or this salt make a difference? For instance, before working out of after? Thank you.


Dr. Jason Fung: You can check your blood pressure when sitting and standing. If you are on medications, you should consult your physician. Otherwise, yes, we often increase salt intake. Some use salt in water. Some use broth.

Thank you. I’m not on any medications. Do you have any recommendations as to how much salt is optimum? And is it best to take before I workout or does that even matter?

Dr. Jason Fung: For regular people it seems that somewhere between 3-5 gram/day is optimal, which happens to be about the average American intake. It likely makes no difference when you take it.


More questions and answers

Many more questions and answers:

Intermittent Fasting Q&A

Top Jason Fung videos

Full IF Course >


Read Dr. Jason Fung’s new great book The Obesity Code for many more insights:

The Obesity Code

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