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Many people think that being healthy is all about diet and exercise. But the truth is it's very difficult to lose weight and keep it off if you don't practice another key lifestyle habit: getting good sleep. Being in a state of constant tiredness makes it that much harder to eat well or be motivated to exercise. Lack of sleep can also lead to weight gain, which contributes to obesity in adults and children as well as serious health conditions, such as sleep apnea.

Many things happen in your body while you sleep. Several types of hormones are released, including growth hormones, testosterone and cortisol, the primary stress hormone. Insulin is also released at night, which affects the amount and regulation of sugar in your bloodstream.

Not getting enough sleep — especially deep, restful sleep called slow wave sleep (nonrapid eye movement sleep) — also affects your "hunger hormones," leptin and ghrelin. Leptin, produced mainly in the fat cells, helps your body monitor energy needs, and high levels of leptin usually suppress hunger. Ghrelin is a hormone produced mainly in the stomach, but also in the brain. It promotes hunger and encourages the desire to eat.

As you might have guessed, ghrelin is at its peak when you are low on sleep. Have you ever noticed that bagels and muffins are harder to resist on mornings you wake up feeling exhausted? Or maybe when you're tired, you're a bottomless pit, snacking all day long but never truly feeling satiated. That may be hormones such as ghrelin at play.

It's also important to note that fragmented sleep has the same effect as too little sleep. If you don't get enough deep, restful sleep, your hunger hormones are likely to be activated, which can lead to weight gain. So it might be time to put away your smartphone or any other nighttime disruptors and focus on getting better quality sleep.