How Fasting Impacts Your Ability to Focus

00:00:00.000 | [silence]

00:00:03.060 | Your ability to focus,

00:00:04.260 | and in fact, your ability of neurons

00:00:06.180 | to encode specific information in your environment,

00:00:08.980 | that is to represent what's out there in the world,

00:00:11.660 | is actually related to your blood glucose level.

00:00:14.600 | Now, here I'm setting aside the discussion

00:00:17.220 | of ketosis and ketogenic diets for the moment,

00:00:20.380 | but there's a beautiful study

00:00:21.400 | that was published in "Neuron" not long ago

00:00:22.980 | that showed that the tuning,

00:00:24.020 | that is the precision with which neurons in the brain

00:00:26.860 | will represent things in our environment,

00:00:28.900 | is actually much greater

00:00:31.240 | when there is sufficient glucose in the brain.

00:00:33.540 | Translated into English,

00:00:34.620 | this means that when we are fasted,

00:00:36.560 | or when our blood glucose is very low,

00:00:38.520 | we aren't able to perceive

00:00:40.380 | and think about things as clearly.

00:00:42.540 | Now, there's a twist to this, however.

00:00:44.260 | Many people who practice intermittent fasting,

00:00:46.340 | and I should say,

00:00:47.180 | I practice a sort of pseudo-intermittent fasting.

00:00:48.940 | I generally eat my meals

00:00:50.140 | between the hours of 11 a.m. and 8 p.m.,

00:00:52.380 | although sometimes there's some wiggle around that.

00:00:54.420 | Occasionally, I have an early breakfast.

00:00:55.780 | I'm not super rigid about it,

00:00:57.220 | but I know there are a number of people

00:00:58.580 | who are doing longer fasts,

00:00:59.740 | so they're eating in a six-hour window.

00:01:02.180 | We did an entire episode about fasting.

00:01:04.340 | You can, again, find that at hubermanlab.com.

00:01:06.500 | We'll likely have Sachin Panda,

00:01:08.260 | who's an expert in intermittent fasting, on the podcast.

00:01:11.300 | Intermittent fasting

00:01:12.760 | has a lot of different potential benefits.

00:01:15.560 | For some people, it's a convenient way

00:01:16.980 | to restrict their calories.

00:01:17.960 | For other people, it's a convenient way to avoid eating.

00:01:20.180 | That is, it's easier to not eat

00:01:21.700 | than to eat a small portion,

00:01:22.820 | so they opt for intermittent fasting,

00:01:25.020 | and so on and so forth.

00:01:26.400 | But one of the things that you hear very often

00:01:28.220 | is that some people like being fasted

00:01:29.940 | because they like the clarity of mind that it provides.

00:01:33.300 | Here's the situation.

00:01:34.580 | Neurons, unless you're in a ketogenic diet,

00:01:36.520 | really thrive on glucose.

00:01:38.060 | They love glucose.

00:01:39.660 | And as I mentioned before,

00:01:41.180 | your ability to think and perceive things

00:01:43.020 | is actually enhanced

00:01:44.380 | by having sufficient glucose in your bloodstream.

00:01:46.580 | So why would it be that some people experience

00:01:48.980 | a heightened state of mental clarity when they are fasted?

00:01:51.620 | I've certainly experienced that before.

00:01:53.460 | Well, I should say that provided you're well-hydrated enough

00:01:56.060 | and you have enough electrolytes in your system,

00:01:58.000 | what tends to happen is that when you ingest food,

00:02:00.620 | there's a shift in your nervous system

00:02:02.140 | towards so-called parasympathetic mode.

00:02:04.200 | That is, the more relaxed,

00:02:05.700 | you've probably heard it as rest and digest,

00:02:07.300 | although it does other things,

00:02:08.140 | the more relaxed mode that can indeed make us very sleepy.

00:02:11.020 | If we have too many carbohydrates,

00:02:12.340 | it actually can make us quite sleepy.

00:02:13.960 | However, if we have any food, if we have enough of it,

00:02:17.660 | that is, if our gut is full,

00:02:19.260 | it diverts blood to our gut and we become sleepy

00:02:21.700 | and we can't focus as well.

00:02:22.940 | So a lot of people really like fasting

00:02:24.900 | in the state of being fasted for focus and concentration

00:02:28.200 | because they don't have as much

00:02:30.440 | of that parasympathetic activation,

00:02:32.420 | they're just not as sleepy.

00:02:33.460 | And in fact, under those conditions,

00:02:35.060 | half as much caffeine will give you just as much lift

00:02:37.840 | as twice as much caffeine will give you

00:02:40.000 | on a full belly of pasta.

00:02:41.240 | And that's just the way that caffeine interacts

00:02:43.000 | with blood glucose.

00:02:43.880 | So what I'd like you to imagine

00:02:45.440 | is if you had a measure of focus from zero to 10,

00:02:48.800 | these are arbitrary units,

00:02:49.920 | 10 being maximally focused and zero being not focused at all,

00:02:53.480 | imagine a U-shaped function, right?

00:02:56.540 | Where if you're very fasted,

00:02:58.380 | you're going to have a high degree

00:02:59.620 | of focus and concentration.

00:03:01.360 | But then if you ingest some food and your belly is full,

00:03:03.860 | your focus and concentration is reduced.

00:03:06.200 | But having enough blood glucose

00:03:08.740 | and maybe even elevated blood glucose

00:03:10.820 | will increase cognitive function.

00:03:12.340 | So there are two ends of the spectrum.

00:03:13.580 | On one end of the spectrum,

00:03:14.820 | blood glucose is relatively low and you're fasted

00:03:17.660 | and you can think and behave in a very concentrated way.

00:03:21.220 | And on the other end of the spectrum,

00:03:22.820 | you have a lot of blood glucose

00:03:24.220 | or I should say sufficient blood glucose.

00:03:25.660 | You never want your blood glucose to be too high.

00:03:27.940 | And that allows your neurons to encode and perceive

00:03:31.700 | and basically allow you to think really clearly.

00:03:33.940 | So you sort of have to pick your condition.

00:03:36.020 | What do you want for your bouts of focus and concentration?

00:03:39.300 | I actually do both.

00:03:40.340 | So what I do is, as I mentioned before,

00:03:41.860 | I eat my meal sometime around 11 a.m.,

00:03:43.820 | my first meal typically,

00:03:44.940 | unless I'm very hungry when I wake up.

00:03:46.860 | And so I will do my workout and one bout of focused work.

00:03:51.020 | I always think of this as my hard work early in the day.

00:03:54.060 | And I do that fasted.

00:03:55.460 | I'll be consuming water with electrolytes,

00:03:57.740 | maybe Element or other electrolytes,

00:03:59.180 | maybe some caffeine as well in the form of Yerba Mate

00:04:02.460 | or coffee.

00:04:03.680 | That's my first focus bout of 90 minutes or less.

00:04:06.860 | That is essentially done fasted.

00:04:08.340 | And then I'll eat.

00:04:09.380 | And then I do notice after I eat,

00:04:11.220 | I actually have a diminished capacity to focus.

00:04:13.420 | But then again, in the afternoon,

00:04:14.720 | I will do another 90 minute bout of focus.

00:04:16.700 | And I'll talk about some of the tools I use

00:04:18.220 | to make sure that that bout of focus is optimal

00:04:20.620 | for getting the most amount of focused work done,

00:04:23.940 | whether or not it's mental work or physical work,

00:04:25.820 | although I tend to do my physical work early in the day

00:04:28.060 | and my mental work both early and late in the day.

00:04:31.060 | So to make this very simple or as simple as I can for you,

00:04:34.860 | being fasted is great for focus and concentration,

00:04:38.540 | provided you're not thinking about food the entire time.

00:04:41.620 | And being fed is terrific for focus and concentration,

00:04:44.740 | actually can improve neuronal function,

00:04:47.040 | provided that you didn't eat too much food.

00:04:49.460 | So one way to manage this is if you're going to have a lunch

00:04:52.760 | to make sure that you don't stuff yourself at lunch,

00:04:54.900 | that you're not overeating and to not get quite so full

00:04:58.260 | that you push your nervous system

00:05:00.220 | into this parasympathetic mode

00:05:01.660 | and make it hard to focus in the afternoon.

00:05:03.740 | I know a lot of people experience a dip

00:05:05.100 | or even a crash in energy in the afternoon

00:05:06.820 | that make it really hard to focus.

00:05:08.420 | For that reason, I'll just remind people of a tool

00:05:10.420 | I've talked about many times before,

00:05:12.140 | which is based on the biology of adenosine and caffeine,

00:05:14.460 | et cetera, which is to delay your first caffeine intake

00:05:17.620 | to 90 to 120 minutes after waking up.

00:05:20.180 | I know that can be painful for certain people.

00:05:22.220 | I violate that rule when I'm working out

00:05:24.200 | very early in the morning,

00:05:25.300 | I'll drink my caffeine before my workout,

00:05:27.780 | which often occurs within 30 to 60 minutes of waking.

00:05:31.700 | But in general, unless I'm working out very early,

00:05:34.460 | I will ingest my caffeine 90 to 120 minutes

00:05:37.460 | after I wake up.

00:05:39.020 | So again, I want to emphasize

00:05:40.420 | that if you hear somebody out there say,

00:05:42.660 | being fasted is optimal for focus and concentration,

00:05:46.140 | well, that is true in one context

00:05:48.740 | and perhaps ideal for a certain part of the day.

00:05:51.300 | And other people will say, no, you know,

00:05:53.300 | neurons run on glucose,

00:05:54.500 | you need glucose in your bloodstream

00:05:56.380 | in order to get those neurons to be tuned,

00:05:58.900 | that is to respond with electrical activity

00:06:01.060 | in the optimal way when you're reading something

00:06:03.460 | or when you're trying to perform exercise.

00:06:04.740 | Well, that's also true.

00:06:05.820 | And of course, you can incorporate both.

00:06:07.860 | I, in fact, as I just described,

00:06:10.300 | incorporate both fasted states and fed states

00:06:13.620 | in order to optimize my concentration and focus.

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How Fasting Impacts Your Ability to Focus | Dr. Andrew Huberman

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