Years of horrific insomnia will give you a world-class appreciation of sleep. Take it from me: sleep touches everything.

But we’re gathered here today to discuss sleep and weight loss. Science has taught us that getting enough sleep is one of the select few things with an impact on weight loss to write home about.

Why is this?

Let’s play devil’s advocate. Let’s assume you didn’t sleep well last night.

Look at this tangle of thorns.

You Won’t Feel Full

The hormone that makes you feel full is called leptin. Very important hormone. Feeling “full” is, more or less, feeling leptin. If your body is in good working order, the more leptin in your blood, the fuller you will feel.

But inadequate sleep causes your body to make less leptin. And with less leptin, you’ll feel…less full.

In other words, more hungry.

You’ll Be Extra Hungry

The opposite of leptin is ghrelin, the “hunger” hormone. Ghrelin makes you feel hungry. The more ghrelin in your blood, the hungrier you will feel. Ghrelin is the yin to leptin’s yang. Hungry and full. Full and hungry. Leptin and ghrelin.

And inadequate sleep causes your body to make more ghrelin.

And more ghrelin means…more hunger.

So inadequate sleep means you’ll have less leptin to make you feel full, and more ghrelin to make you feel hungry. On average, this nasty one-two punch (less leptin, more ghrelin) will cause you to eat more food—and gain more fat.

A 2010 study found that, compared to eight hours of sleep, young men on just four hours of sleep ate an average of 559 more calories a day. That’s an extra Big Mac. A 2013 study found that just five days of sleep restriction led to nearly two pounds of weight gain.

It gets worse.

You WILL Crave Junk Food

Not only is Tired You hungrier and less full, but according to a 2013 study in Nature, Tired You has a special hankering for “weight-gain promoting high-calorie foods.” In this study, they found that lack of sleep not only makes people crave more food in general, but specifically makes people crave junk food.

A well-controlled 2016 study may shed light here. This study found that sleep-deprived people have more endocannabinoids in their blood. If you noticed the first seven letters of “cannabis” lurking in that word, you’re on the right track: endocannabinoids bind to the same brain receptors as the THC of marijuana.

On a chemical level, being sleep-deprived may be like having the munchies.

When I’m tired and stressed, I’ll eat just about anything—as long as it’s not healthy.

You WILL Have Less Willpower

Willpower can be scientifically measured. (Entire careers hinge on this.) Willpower is basically the limited energy pool you use to do things you don’t really want to do. You know, the tough stuff. Like resisting junk food, entertaining in-laws, and sticking to New Year’s resolutions at 4pm on a Wednesday.

Willpower is general-purpose; you burn willpower doing hard tasks, and the more willpower you burn on one hard task, the less willpower you have for another hard task right after—even if that other task is a totally different "hard." This is why plans of going to the gym (physical) can be so unpalatable after a long day at the office (mental, mostly).

A broad range of studies (sources: 1, 2, 3, 4) have found that when people don’t sleep enough, they have less willpower the next day.

If this is true, can you really blame Tired You for gaining weight? It was practically inevitable. On top of feeling less full and more hungry, Tired You really craves junk food—and has less willpower to resist it.

Can you image imagine a more fattening scenario?

This is why a 2008 meta-analysis of 634,511 people found a “consistent increased risk of obesity amongst short sleepers [less than five hours per night].” And it's why a 2014 meta-analysis concluded that “short sleep duration was significantly associated with incidence of obesity.”

It's why the twin who sleeps less is significantly more likely to be overweight (which proves this sleep-weight thing is not just genetic), and why a 2009 study of 537 Canadians found that sleeping under six hours a night was the single greatest risk factor for being overweight. (Even more than dietary factors.)

Did a lack of sleep make America fat?

If sleep played a real role in the rather recent American Obesity Epidemic, then Americans would be sleeping less today than they slept in the recent past.

Sure enough, between the 1960s and 2000—when obesity rates took off like the Apollo 11 space shuttle—average US sleep time dropped from about 8.5 hours per night in the '60s to just 7 hours per night today.

That's nearly 20% less sleep.

And polls (this one and that one) suggest that since the year 2000, we’ve been sleeping even less. And since then, we’ve gotten even fatter.

Coincidence?

How to Sleep More

The evidence is overwhelming. You need to sleep enough.

But what’s enough? We’re all different, and there’s no golden number. Experts generally recommend between seven and nine hours of sleep a night. But rather than fixating on a number (the root of my insomnia), you should probably just try to feel rested most days.

If you don’t feel rested most days, then getting more sleep is one of the best things you can possibly do for weight loss (among other things).

So how do you get more sleep?

It depends. If you fall asleep easily, the answer is also easy: just go to bed earlier. Get some rough idea of how much sleep you need to feel rested, subtract that from the time you plan to wake up, and add 30 minutes for good measure.

Problem solved.

(Don’t think you have time to sleep more? This is mostly nonsense. Think of this: you’re wasting time being sleep-deprived and less efficient all day. You could accomplish more, in less time, if you were more rested. Prioritize sleep. Manage your time. You can do it.)

On the other hand, if your problem is falling asleep or staying asleep, then you’re like me.

I’m sorry.

I saw psychologists, psychiatrists, hypnotists, acupuncturists, and witch doctors.

I tried the best remedies of medicine and quackery. I swallowed every sleep drug known to man, experimented with various Eastern religions, and performed obscure rituals. I read books, perused websites from the nosebleed pages of search results, and thought about my sleeping problem very, very hard (which definitely didn’t help).

Alas, the magic bullet eluded me. The lead bullet may have tempted me. But saner heads prevailed, and, over the years, I managed a glacial crawl from deplorable depths to something resembling a semi-adequate sleeping pattern.

So without further adieu, according to science and research and years of treacherous trial and error, here (in no particular order) are thirteen sleep tips worth remembering:

Go to bed and wake up at consistent times.

Our circadian rhythms adapt to the time we’re typically asleep, so try to give your body what it’s expecting. Aim to sleep and wake at regular times. (Whatever those are.)

Reduce artificial light at night.

Staring at bright screens tricks your body into thinking it’s daytime; sleep circadian rhythms are regulated in the eyes. Make it a rule not to look at bright screens (cell phones, laptops, TVs, etc.) in the hour before bed. Instead of staring at a screen, read a book or meditate (or something).

If this is too much, at least download free software called f.lux. At night, this software reduces the blue light your screen emits. Blue light is the spectra of light with the worst impact on our circadian rhythms.

Move around during the day.

Physical activity improves sleep quality (and many other things). Evolution drives everything, and we evolved to sleep after moving around a few hours a day. Not sitting for 98% of them.

Get morning sunlight.

Morning sunlight can help reset your biological clock. Get sunlight (morning, or otherwise). We didn’t evolve indoors.

Attention, Skin-Cancer Police: Vitamin D deficiency from lack of sunlight is also a serious health problem. (And far more common than skin cancer.)

Avoid caffeine after noon.

Caffeine keeps you awake, and lingers in your system. The half-life of caffeine (how long it takes to clear half the caffeine you ingest) is almost six hours.

Within two hours of bedtime, avoid nicotine, big meals, and intense exercise.

All of these can mess up your sleep. All of these have messed up my sleep. (Big meals may lull you into sleepy comas, but can disrupt your sleep with dead-of-night bathroom trips.)

Sleep in a cool room.

Don’t let the notorious Hot Bedroom spoil your zzzzzzs.

Only use your bed for sleep (and romance).

Train your brain to link bed with sleep—not Netflix, texting, and tossing and turning. (If you can't sleep, get out of bed and do something else.)

Wear an eye mask and/or ear plugs.

Eye masks and ear plugs are a great antidote to obnoxious pre-alarm sun and traffic noise. I never travel without them.

Make a to-do list for the next day.

Thinking about upcoming duties can keep you up, and writing them down can help you relax. Making a list eases the subconscious burden of remembering.

Use relaxation techniques to fall asleep faster.

Deep breathing, listening to relaxing soundtracks, and progressive muscle relaxation can help people fall asleep faster.

(That last one means tensing and then relaxing all the muscles in your body, starting at the head or toes and working down or up. Some people swear by this. It has never worked for me.)

Get more organized.

This applies to your living space, your work desk, your car, and your life. Among many other benefits, an organized mind is less likely to race at night.

Do cognitive behavioral therapy (CBT).

CBT effectively treats many mental disorders, including insomnia. (For instance, CBT is better at treating depression than antidepressants.)

A big part of CBT is changing destructive thought patterns. Here's a sleep example: I might repeat to myself: "If I'm lying awake in bed and dwelling on my sleeping troubles, then I'll think about what I'm grateful for."

The key is replacing bad thoughts (I can't fall asleep), with more helpful ones.

Learn about CBT.

These tips aren't mind-blowing. Most are sort of commonsensical. But work on one or two, and you can improve your sleep.

And if you sleep better, you’ll feel better. You'll feel more full, less hungry, and less tempted by junk food.

And you'll have the willpower to make your dreams come true.