Sleep is primarily a brain thing. Thousands of articles and many books have been written on sleep as it relates to brain function, brain waves, thinking, memory, mood, etc. The role of sleep in physical metabolic change, though, is what matters for those looking to lose weight. Simply put, sleep is the time that your body builds a new machine for burning calories. Exercise is nothing more than a stimulus for adaptation, a calculated assault on our body’s muscles, lungs, heart, and nerves. Our brain then says, hmmmmpphh, if we are going to have to keep doing this task, I’ve got to change a few things. The brain, then, as the master molecular organizer, sends out messages through the extensive network described above, to re-organize things so we can do the task. The changes the brain orders up are called anabolic changes. Seventy five percent of the changes we need to ultimately lose weight – and keep it off – will occur during sleep (the other twenty five during rest). I would go so far as to say that adequate and extra sleep are more important than diet or exercise when it comes to sustainable weight loss.
Structurally, your body is making molecules during sleep that follows exercise which will do the following useful things for you: strengthen your muscles, lower your blood pressure, neutralize inflammation, increase your metabolism, decrease damage caused by stress, give you energy, protect your heart, protect you from cancer, protect you from diabetes, mobilize your protective immune response so you get sick less, safeguard you from depression, injuries, and stroke, as well as make you smarter. (1-17)
Imagine a new flower you bring home from the Piggly Wiggly to brighten
up the kitchen. You water it because you want it to bloom, grow, and be
beautiful. Then you water it again, and again, and again – without leaving
adequate time in between for the flower to absorb the water, take in light, and
change. The flower needs the water, but
more importantly it needs the time in the sun following the water application
to restructure itself and bloom. The
water itself, like exercise, is there to induce
change. If we water again before the changes have occurred, the flower will
drown and die – and you will quit your exercise program.
The hook, I am betting for many readers, though, is that sleeping enough will also make you eat less. Right, eat less. Functional MRI scans of the brain have been studied that show people are far more interested in eating when they are sleep deprived. Moreover, sleep deprived subjects are more driven toward unhealthy foods when given the option. Sleep deprived subjects also have increased levels of ghrelin, the hormone that makes us feel hungry, and decreased levels of leptin, the hormone that makes us feel full. And it’s not just eloquent brain MRI studies and hormone level draws that have been done, subjects have been shown to actually eat more food and actually gain more weight when sleep deprived, and population based studies have shown increased BMIs in people with less sleep hours. (16, 18-33)
In short, sleep has been shown to correlate with a multitude of positive reorganizations in the human body following exercise, including increased exercise capacity, less metabolic disease, and decreased appetite.
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 “stress” here is a whole host of things, from external stressors that increase cortisol levels to store fat to direct reduction (chemically and literally) of something called oxidative stress which accelerates aging.