AMA #11: All things fasting

**Peter Attia** (0:11)
Hey, everyone, welcome to a sneak peek, Ask Me Anything or AMA episode of the Drive podcast. I'm your host, Peter Attia. At the end of this short episode, I'll explain how you can access the AMA episodes in full, along with a ton of other membership benefits we've created.
Or you can learn more now by going to peterattiamd.com forward slash subscribe.
So without further delay, here's today's sneak peek of the Ask Me Anything episode.
Welcome to a special AMA episode focusing on my recent seven-day fast, in addition to a deep dive on fasting in general. As this is a topic we get so many questions on, we figured dedicating an entire AMA to it would be of value. So we hope you enjoy. I'm once again joined by my head of research, Bob Kaplan. So without further delay, here's today's special AMA focusing on fasting.

**Bob Kaplan** (1:03)
Hello, and welcome to a fasting edition of Ask Peter Anything. Peter, how are you doing?

**Peter Attia** (1:16)
Doing all right.

**Bob Kaplan** (1:17)
And this is Bob Kaplan. So let's just jump right into the questions around fasting. You obviously get a lot of questions on fasting. And I thought before we get into fasting, maybe you could discuss what fasting is, a definition of fasting. So we get a lot of questions around what is IF, what is TRF, what is ADF, what's a fasting mimicking diet, and what is prolonged fasting, even what's an overnight fast.
So I can remind you of all those.

**Peter Attia** (1:47)
Okay, why don't you give them to me one at a time?

**Bob Kaplan** (1:49)
Okay, so I think maybe the first one is overnight fast. When somebody refers to an overnight fast, what is that?

**Peter Attia** (1:55)
So that, as its name suggests, is sort of the standard fast that almost by definition, everybody does between dinner and breakfast. So if you finished dinner at seven o'clock in the evening, rather, and you had breakfast at seven o'clock the next morning, you would have just undergone a 12-hour overnight fast.

**Bob Kaplan** (2:13)
Okay, and TRF, time-restricted feeding. Some people call it TRE, time-restricted eating.

**Peter Attia** (2:19)
That is an idea where you increase that window from just an overnight fast into a slightly longer window.
So if the overnight fast that I used a moment ago were to be put into time-restricted feeding nomenclature, you would call it a 12-12, meaning 12 hours of fasting, followed by a 12-hour window, say seven a.m. to seven p.m. in which one would eat. You can extend that and you could say a 14-10 window or a 16-8 window or an 18-6 window where the first number generally refers to the period of time that has no nutrient exposure and then followed by the window in time in which one would be able to consume food, typically ad libitum, meaning without restriction.

**Bob Kaplan** (3:09)
Okay, so rolling into the next one, alternate day fasting.

**Peter Attia** (3:14)
So again, as the name suggests, alternate day fasting is when every other day a person does something other than their traditional ad libitum eating. Now, the most strict way that one could do an alternate day fast, which would be quite difficult to do over the long haul would be to literally consume nothing every other day.
More commonly when people do alternate day fasting, they have a hypocaloric day. So they might on alternate days consume say a thousand calories and on the non fasting day, they would consume whatever they consume ad libitum and that might be say 2,500 to 3,000 calories.

**Bob Kaplan** (3:54)
So I know that you're somewhat of a stickler on the definition. So in that case, it's almost like alternate day calorie restriction on the opposite day. Yeah, one way that I think about that, actually a couple of ways that I think about it is if you're looking at a calendar for a strict alternate day fast, if you're going to start it in January, January 1, let's say you're going to eat in January 2nd, you're going to fast, you can mark off every even day of that month, and you know that you're fasting on that day, and then on the alternate days, you're eating. And I sometimes think about it in terms of when you talked about TRF or time restricted feeding or time restricted eating, you think about it in the context of a 24-hour clock.
With alternate day fasting, it's almost like a 48-hour clock on the alternate days. And I think it can actually, it can vary quite a bit on your feeding days that you might do a one meal a day, which would be almost like a 47-1.