The Matt Walker Podcast

Matt returns with Part 2 of his series on sleep and weight gain. This time around, he teaches us how a lack of sleep not only makes you eat more food, but changes what types of food you want to eat, and eat to excess.

First, Matt describes how underslept individuals that are limited to 4-5 hours of sleep for several nights will experience a 33% increase in the desire to eat obesogenic, sugary treats. In addition, they will suffer a 30% increase in craving for heavy-hitting carbohydrates, like pasta and pizza, and a 45% increased desire for salty snacks!

Matt goes on to explain that your brain plays a role in this sleep loss-weight gain equation. In one of his experiments, a group of normal, healthy-weight individuals went through the study twice: once when sleep-deprived and once after a full night of sleep. After each condition, the individuals were placed inside an MRI scanner and shown different food types, and asked to rate how much they wanted each food item.
What they found is that the sleep-deprived brain changed markedly, shifting to a pattern of activity associated with what is called hedonic eating, or impulsive eating. Specifically, the prefrontal cortex, which is responsible for impulse control, was shut down by lack of sleep. As a result, the very primitive deep brain regions that drive excessive appetite become hyperactive and hyper-responsive to highly desirable, unhealthy food items, such as ice cream and donuts, rather than nuts or leafy greens.

He also reveals that staying awake across the night doesn't burn vastly more calories. You only burn about an extra 140 calories by staying awake all night relative to being asleep, yet you will eat more than twice that amount more in calories when sleep-deprived. Plus, you are less active when sleep-deprived, so you don't burn off those calories.

Worse still, Matt tells us that dieting becomes ineffective without sleep: 60% of the pounds you will lose come from lean body mass (such as muscle), and not fat. Specifically, when you are sleep-deprived, the body becomes especially stingy with fat, stubbornly refusing to give it up. In other words, you end up losing what you want to keep, which is muscle, keep what you want to lose, which is fat. Also, inadequate sleep increases levels of cortisol, which also makes your body store food as fats.

Matt concludes with an optimistic note by highlighting the fact that getting enough sleep is a scientifically proven way to help you regulate your appetite and a healthy body composition (a little bit less painful than going to the gym!?)

Please note that Matt is not a medical doctor, and none of the content in this podcast should be considered medical advice in any way, shape, or form, nor prescriptive in any way.

The good people at InsideTracker are the sponsors of this week's episode, and they are generously offering 25% off any one of their programs for anyone who uses the above link. InsideTracker is essentially a personalized biometric platform that analyzes your blood and your DNA to better understand what's happening inside of you and also offers suggestions regarding things that you can do to better try and adjust some of those numbers, optimize them, and, as a result, optimize you.

So, make your way over to InsideTracker, and take advantage of this incredible deal on this valuable and remarkably convenient service. And, as always, if you have thoughts or feedback you'd like to share, please reach out to Matt on Instagram.

Matt kicks off a two-part series all about sleep, eating, and weight gain.
He starts by introducing two appetite-regulating hormones: leptin and ghrelin. Matt explains how leptin sends a signal of fullness, to your brain. When leptin levels are high, your appetite is reduced, and you feel satisfied by the food you eat. Ghrelin does the exact opposite. It revs up your hunger, so when your ghrelin levels are high, you don’t feel satisfied by the food you ate, so you want to eat more.

Matt tells us that when you’re not getting enough sleep, the levels of these two hormones are affected in unfortunate ways, causing you to feel less full and more hungry. Specifically, sleep loss decreases leptin levels by 18%, yet increases ghrelin levels by 28%!
So when you are not getting enough sleep, the body losses the fullness signal AND suffers an increase in hunger levels. The combined consequences? Your appetite rockets up!

It’s also been discovered that levels of endocannabinoids --a class of cannabinoids we naturally produce ourselves -- increase sharply in response to a lack of sleep. As a result, your hunger levels increase even more (as you may know, cannabinoids are part of the reasons that cannabis gives you the munchies).

Adding up all of these effects, Matt describes how this lack of sleep causes people to consistently overeat. Usually somewhere between 250 to 400 extra calories each and every day!

Snacking also becomes a problem. For example, if you present a group of people with a large meal of over 1,000 calories, then give them the option to keep snacking, under-slept individuals will continue to snack, consuming an additional 200 to 300 calories relative to those who’ve been getting a full eight hours of sleep.

This all begs the question: is there a reason why your hunger goes into overdrive when you are under-slept? Matt explains one plausible theory from an evolutionary perspective, based on the fact that when animals are in a starvation state, the brain keeps them awake longer so they can forage further. Therefore, when the brain doesn’t get enough sleep, it thinks we may be in a state of starvation and increases our desire for food.

Finally, notes what's coming in part two: that insufficient sleep not only increases how much you eat but changes your food preferences, and changes how your bodies deposit the extra calories we take on as our hunger increases, relevant to body fat accumulation.

Please note that Matt is not a medical doctor, and none of the content in this podcast should be considered medical advice in any way, shape, or form, nor prescriptive in any way.

The good people at Athletic Greens are the sponsors of this week’s episode, and they are generously offering three benefits for anyone who uses the above link for their first order: 1) a discount on your order, 2) a one-year free supply of vitamin D, and 3) five free travel packs. Athletic Greens is a nutrition drink that combines a full complement of antioxidants, minerals, and biotics, together with essential vitamins. Matt’s been using it for several years now, first because he’s serious about his health and uses it as a full nutritional insurance policy, and second, because Matt did his research on the science and ingredients in Athletic Greens and thinks it’s science and scientific data that can be taken as ground truth.

So, make your way over to Athletic Greens, and take advantage of this incredible deal. And, as always, if you have thoughts you’d like to share, please reach out to Matt on

In today's episode, Matt unpacks the world of coffee, and caffeine in the first of a two-part series on caffeine. Matt describes the numerous health benefits associated with coffee, the fact that Matt has even changed his tune a little and advocates a morning cup for some. Matt may not have anything to do with caffeine itself, with more details on that in part 2. In part 1, Matt then takes a deep dive into the different ways in which caffeine negatively impacts your sleep, some of which you may be less familiar with.

The first is that caffeine makes it harder for you to fall asleep. Due to activation of the nervous system, caffeine can lead to that unpleasant experience of a racing mind that won't shut off in bed—almost a Rolodex of anxiety that leads to ruminating and therefore catastrophizing.

The second impact is that caffeine makes it more difficult for you to stay asleep soundly across the night. This is due, in part, to the fact that caffeine makes your sleep more unstable and fragile, so up more frequently at night. The consequence is something that scientists and doctors call sleep fragmentation, meaning that your overall sleep efficiency, or the consistent quality of your sleep, becomes significantly worse when you have caffeine on board.

The third feature that Matt points out centers on caffeine’s duration of action. Caffeine has a half-life of between five to six hours in the average adult. This means that, after five to six hours, 50% of that caffeine is still in your system. What this also means is that caffeine has a quarter-life of approximately 10 to 12 hours for a typical adult.

Here, Matt gives us some context: if you have a cup of coffee at 2 PM, a quarter or more of that caffeine could still be circulating in your brain at midnight. Meaning, if you have a cup of coffee at 2 PM, it may be the equivalent of getting into bed at midnight, and just before you turn the lights out, you swig a quarter of a cup of coffee and you hope for a good night of sleep.

Matt, however, points out that the 10 to 12 hours quarter-life of caffeine is for the average adult, but this varies significantly from one person to the next. He explains in detail why this is the case: based on differences in genetics, different people will have a more or less efficient version of an enzyme that clears caffeine from their system. Some people will have a version of that enzyme that allows them to remove the caffeine from their system very quickly, whereas other people will have a version of the enzyme that is much slower in its speed of clearing caffeine.

Please note that Matt is not a medical doctor, and none of the content in this podcast should be considered medical advice in any way, shape, or form, nor prescriptive in any way.The good people at InsideTracker are the sponsors of this week’s episode, and they are generously offering 25% off any one of their programs for anyone who uses the above link. InsideTracker is essentially a personalized biometric platform that analyzes your blood and your DNA to better understand what's happening inside of you and also offers suggestions regarding things that you can do to better try and adjust some of those numbers, optimize them, and, as a result, optimize you.

So, make your way over to InsideTracker, and take advantage of this incredible deal on this valuable and remarkably convenient service. And, as always, if you have thoughts or feedback you’d like to share, please reach out to Matt on Instagram.

As the great Roman poet, Ovid, once said, “There is more refreshment and stimulation in a nap, even of the briefest, than all the alcohol ever distilled.” But are naps always a good thing? Are we even designed to nap? And if you do nap, when should you do it, and for how long?

Today Matt explores the benefits and pitfalls of napping, how napping may fall in line with our pre-programmed sleep patterns as humans (a natural drop in alertness between 1 and 4pm each day), and what it means if you find yourself waking up from an accidental nap on the couch right before bed.

You’ll also hear about the NASA nap culture, sleep inertia (which can include a feeling of a “sleep hangover”), and Matt’s advice for how to use naps to your advantage. If done correctly, for most people not struggling with sleep or insomnia, naps can improve alertness, task performance, creativity, and even reduce blood pressure. However, there is a dark side to napping that Matt discusses in detail, and why that can be the case. So join Matt as he walks you through both the advantages and disadvantages of napping!

Please note that Matt is not a medical doctor and none of the content in this podcast should be considered as medical advice in any way, shape or form, nor prescriptive in any way.

The episode is sponsored by the wonderful folks over at Athletic Greens, who are providing a discount and free product if you use the link above. Athletic Greens is a comprehensive daily nutritional beverage containing 75 vitamins, minerals, and whole food-sourced ingredients, including a multivitamin, multimineral, probiotic.

So, head on over to Athletic Greens www.athleticgreens.com/mattwalker and get a free year supply of Vitamin D and 5 free travel packs today. Finally, if you have thoughts or feedback you’d like to share, please reach out on Instagram @drmattwalker.

Detailed Scientific Literature

Naps and overview (by the amazing Prof. Christopher Barnes)

The good and the bad of naps

Naps and Mortality

Naps, Brain function & Performance

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Episode 04: Chronotype: Part 1

Summary

Are you a morning type? Or are you an evening type? Perhaps you are neither of the two? Today’s episode is the first in a three-part series all about your chronotype, or your body’s natural biological preference to be awake and be asleep at a certain time.

Matt begins by explaining exactly what your chronotype is, then breaks down the three main “flavors” of chronotype (morning lark, night owl, or somewhere in-between). In addition, and listed in the show notes, below, he explains how to determine whether you are a night owl or a morning lark.

He will also describe how an individual’s sex falls into the equation and the difference between your chronotype and your circadian rhythm.

You’ll hear about the key ways in which evening types biologically differ from morning types, that your chronotype isn’t your own choice nor is it your own fault, but rather, there is a very strong genetic basis of why and how you are programmed in terms of being a morning or an evening type?

Today’s main takeaway is that when you or when society tries to force you to sleep in opposition to your biology, there can be unfortunate consequences. Stay tuned as we explore these in greater detail next time.

The episode is sponsored by the wonderful folks over at Athletic Greens, who are providing a discount and free product if you use the link above. Athletic Greens is a comprehensive daily nutritional beverage containing 75 vitamins, minerals, and whole food-sourced ingredients, including a multivitamin, multimineral, probiotic.

So, head on over to Athletic Greens www.athleticgreens.com/mattwalker and get a free year supply of Vitamin D and 5 free travel packs today. Finally, if you have thoughts or feedback you’d like to share, please reach out on Instagram @drmattwalker.

Basic Resources

Discover your chronotype: AutoMEQ: Automated Morningness-Eveningness Questionnaire (AutoMEQ)

Scientific Review: Biological Rhythm and Chronotype

Scientific Review: Chronotype and Mental Health: Recent Advances