Tuesday, January 29, 2008

Sleep Yourself Slim: The Impact of Sleep Loss on Hormones, Appetite, and Weight

Hi Jean,

You mentioned even sleep being an important factor in Christa's regimen. Any articles you can link to explain the benefits or even consequences of its deficiency (I'm legend for sleeping only when dead tired). Thanks in advance JJ!


I hate sleep; I’m always eager to pop out of bed and start. Start anything: writing, making omelets, whatever. Though, sometimes, I wake up on a Saturday, get excited about wakefulness, and realize that it’s only 5:30am. I feel good enough to wake up and get going. But with only 6 hours of sleep, I convince myself to close my eyes, and think about anything relaxing that is not sleep. Then I usually wake up a couple of hours later. After 7.7 hours of sleep, I am really ready to start my day. But why all the fuss about sleep?

It’s important!

First, there is conclusive research that constant, inadequate sleep puts you at risk of obesity and diabetes. Specifically, sleep loss messes with 1) how your body uses glucose (sugar/carbs) and secretes insulin 2) increases appetite; and 3) decreases energy burned during a 24 hour period.

Don’t Mess with Insulin

Insulin resistance

Insulin resistance is a problem that starts to rear its ugly head in the early stages of Type 2 diabetes. Despite the fact that the body (pancreas) is still making and releasing insulin, a person still cannot get rid of the sugar in her blood fast enough. This lingering sugar is very harmful to blood vessels, nerves, and eyes; it's also bad for the kidneys, since extra sugar is eliminated through the urine. As a result, your body has to make more and more insulin to get the glucose (sugar) out of your blood and into fat (usually) or muscle cells. Eventually, your pancreas says

“Screw it, I work hard to clean up the blood and my insulin doesn’t work anymore.”

In the advanced stages of diabetes, when your pancreas gives up, you have to start injecting insulin to use clean up carbs.

Listen up college students, shift-workers, and parents of small children, MANY studies show that a couple days of less than 4 hours of sleep per night causes insulin resistance (1). In essence, your body starts acting more like a diabetic’s body, and your pancreas has to work too hard. As a result, many researchers think that chronic loss of sleep may contribute to the development of type 2 diabetes and the metabolic syndrome (which are both also linked to obesity and overweight).

Increased Desire to Eat High Carbohydrate Foods

In conjunction with insulin resistance, sleep loss also induces cravings for high-carbohydrate foods (1,2). As such, the problem detailed above is made worse because the pancreas has to secrete even more insulin to take care the gummy bear binge.

Increased Cortisol

Sleep deprivation also increases the stress hormone cortisol, which is associated with obesity, high blood sugar, and lowered immunity (disease-fighting ability). Furthermore, cortisol acts as a stimulus to BREAK DOWN MUSCLE, in order to raise the blood sugar.

The result of 2-3 restless nights is 1) greater intake of high-carb foods; 2) increased cortisol levels, which results in muscle destruction; and 3) a large spike in insulin to cope with excess blood sugar and insulin resistance. These hormonal imbalances, when you are feeling lethargic and snacky, can lead to significant weight gain.

I Can’t Eat Enough

Cortisol and insulin aren't the only hormones affected by poor sleep. A number of hormones that directly influence appetite are also manipulated.

Lower Leptin

Scientists used to think that fat was an inert place to store extra energy. Now researchers recognize fat tissue as a powerful hormone-releasing organ that influences diet and activity behaviors. Leptin is a hormone secreted from the fat tissue itself. The more fat you have (extra energy in your body) the more leptin is secreted, generally. Leptin is a hormone that tells your body:

“You’re too fat, stop eating and burn more energy (Calories)”

As a result, appetite diminishes and the body naturally burns more calories, mostly through non-exercise activities (1,2).

But if a person doesn't get enough sleep, leptin levels decrease. Low leptin levels tell the body that energy levels are low. As a result, appetite increases!

Increased Ghrelin

It is easy to think of ghrelin as a hormone that is exactly the opposite of leptin. Increased ghrelin tells your body:

“You are not getting enough energy; eat more and move less!”

As a result, you eat more and move less! As little as 2-3 days of sleep deprivation (4 hours per night) is sever enough to significantly increase the ghrelin in your blood. Combined, the ghrelin and leptin changes after a couple of days of crappy sleep is enough to make you overeat, no question. Research strongly supports this conclusion (1,2,3)!

Increased Time to Eat

Let’s say you’re the kind of person who likes to eat every 2-3 hours. And let’s also assume you’re sleep deprived. Your body is giving you signals that you don’t have enough energy and you are craving high-carb junk food. A sleep loss of 3-4 hours hours would translate into at least one extra meal of poor-quality food, combined with little motivation to move and burn off the extra Calories. In addition, both population and lab-based studies (3) show that people actually eat more, on average, the less they sleep!

Don’t Ask Me to Move; I’m Tired!

Low Leptin; Decreased Energy Expenditure

Low leptin and high ghrelin levels are shown to reduce Non-Exercise-Activity-Thermogenesis (NEAT) HUH? Well, NEAT is basically any movement you do that is not planned exercise. Most of the daily Calorie-burn is used to keep the body tickin'; NEAT is second and exercise is third. So if NEAT activities subside significantly, the result can be more detrimental than skipping the gym! For instance, when you are tired at 3:00pm, do you feel like playing with your little niece or getting up to go talk to a co-worker? It’s unlikely, and you’ve just given up some NEAT calorie-burn!

Lower Thyroid Stimulating Hormone (TSH)

TSH is the hormone that stimulates, well, your thyroid, which then releases the thyroid hormones T3 and T4. These hormones are STRONGLY related to your metabolism. Sleep deprivation causes a lowering of TSH. In short, the thyroid gland will not be stimulated as much; T3 and T4 will not be fully made/released. Do not pass go; do not drop 20 lbs! Capisci?

Faster Metabolism in Second Half of Sleep

Ghrelin levels lower in the second half of sleep-night (2). Remember that lower ghrelin means less appetite and more movement! If you wake up too early, this ghrelin drop will not happen and you may wake up hungrier than you should be, in addition to all the other obesigenic fun already described. Furthermore, REM (dream) sleep is greater during the second half of the night. REM sleep is very important for a number of other reasons (long-term memory, etc), but you also burn more calories during REM that during the deeper sleep that predominated the earlier sleep cycles. So pass the 800 TC sheets and silence the cell phone!

Obesity Sleep Apnea

Sleep apnea is a chronic sleep-disturbing condition where an afflicted person actually stops breathing repeatedly throughout the night. This condition is highly detrimental for a variety of reasons and really screws with all the hormones mentioned above. Obesity very strongly correlates with sleep apnea, which results in a positive feedback loop in the person with sleep apnea. For instance, a woman gains a lot of weight, is diagnosed with sleep apnea and never has quality sleep; her hormones go wild, and she becomes even more obese. Folks, this is just one more reason to eat your veggies!

Baby Fat

A really interesting study done by Gunderson et al (4) also shows that women who sleep less after giving birth (less than 5 hours a day as opposed to 7 or more hours) are more than twice as likely to retain an extra 13 pounds one year after giving birth! The women (over half of a large sample) who managed to collect at least 7 hours throughout the day and night were more likely to return to their pre-baby weights within a year.

Sleep All Day?

Interestingly enough, too much sleep is also associated with obesity and other chronic diseases (1)! So what’s perfect? It really depends. Everyone is different and some lucky people (though VERY few) only need 5-6 hours/night to be fully functional. For the rest of us, one study showed the lowest risk of disease and obesity at 7.7 hours/night (3). That means if you set aside 8 hours and count sheep, then you should be good to go!


1. Knuston et al. The metabolic consequences of sleep deprivation. Sleep Medicine Review. 2007;11:163-78.

2. Tahen et al. Short Sleep Duration is Associated with Reduced Leptin, Elevated Ghrelin, and Increased Body Mass Index. Plos Medicine. 2004;1:e62.

3. Spiegel et al. Sleep loss: a novel risk factor for insulin resistance and Type 2 diabetes. Journal of Applied Physiology. 2005;99:2008-19.

4. Gunderson et al. Association of Few Hours of Sleep at 6 Months Postpartum with Substantial Weight Retention at 1 Year Postpartum. American Journal of Edidemiology. 2007; DOI: 10.1093/aje/kwm298

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