You may know from experience that not sleeping enough makes you more likely to opt for that greasy piece of pizza or go back for a second scoop of ice cream. You know what I’m talking about. But did you know that sleep deprivation is also scientifically linked to weight gain?
Whether you’re maintaining a healthy weight or trying to lose weight, ignoring the importance of sleep in the mix may be more detrimental to your weight goals than you might have thought.
Let’s take a look at how sleep and weight loss (or gain) are related, and how you should consider sleep as an essential component of any weight loss plan.
The questions at the heart of the issue are:
- Just how much sleep do you need to be getting to make sure sleep is helping you manage your weight rather than working against you?
- What happens if you regularly don’t get enough sleep? How big of an uphill battle against weight gain are you fighting?
Let’s find out.
The biochemical link between sleep deprivation and weight gain
According to the National Sleep Foundation, staying up late, sleeping in every day, and eating after 8 pm are risk factors for weight gain.  This is, in part, due to the fact that sleep deprivation can reduce energy levels. However, sleep deprivation also alters the body’s chemistry — that is, it affects the interactions between neurotransmitters, hormones, and other chemicals that the brain and body uses to communicate.
The science shows that how much you sleep every night is an important regulator of body weight and metabolism. That’s because sleep controls the levels of two important hormones, leptin and ghrelin, which control your appetite in different ways.
Leptin and ghrelin are two molecules that play a crucial role in weight loss and weight gain. Let’s explore each in more detail.
Leptin: The hormone that tells the brain to stop eating
The hormone leptin is produced primarily by the body’s fat cells, although it is also produced in smaller amounts in the stomach. Leptin is a signaling molecule that is sensed by receptors in the hypothalamus, a region of the brain that maintains balance in many aspects of our daily functioning, including energy homeostasis.
Energy homeostasis refers to the body’s natural ability to balance energy needs by controlling hunger and satiety.
The leptin system is implicated in the regulation of body weight. Leptin helps regulate energy balance over the long term, suppressing food intake and thereby causing weight loss. Scientists have found that genetically obese mice have mutations in the leptin gene that prevent the body from making the proper components for the leptin system.
Leptin’s effects on the body include decreased hunger, reduced food consumption, increased energy expenditure (e.g., higher body temperature, increased oxygen consumption, and a reduction in fat cells). However, it remains unknown how leptin exerts these effects on the metabolism.
Ghrelin: The hormone that makes you hungry
Ghrelin is an important hormone produced and released in the stomach, brain, and in smaller amounts elsewhere in the body. Ghrelin is a peptide, which means that it is a short chain of amino acids. The main function of ghrelin is to regulate hunger.
Like leptin, ghrelin is also involved in energy homeostasis, but its effects oppose that of leptin. While leptin promotes satiety, ghrelin’s main function is to regulate and, in fact, promote hunger.
In more specific terms, ghrelin increases hunger and therefore promotes food-seeking behavior by acting on feeding centers in the brain’s hypothalamus. Humans injected with the hormone ghrelin report feeling more hungry.
Ghrelin levels are elevated in humans after fasting. These findings indicate that ghrelin plays a direct role in weight gain by promoting hunger and food-seeking behaviors. Elevated levels of ghrelin can also play an important role in obesity.
Both leptin and ghrelin are involved in the regulation of energy homeostasis, and therefore play a role in weight loss and weight gain. Leptin helps to regulate satiety, while ghrelin promotes hunger. When these hormonal systems are disrupted, either due to genetics, sleep, stressors, or other factors, levels of ghrelin and leptin can become abnormal, causing weight loss or weight gain.
If the body produces too much ghrelin and not enough leptin, the hunger and satiety mechanisms of the body become disrupted, leading to elevated hunger and, by extension, weight gain.
The connection between leptin, ghrelin, and sleep
In the past two decades, scientists have learned more about the hormones leptin and ghrelin and how they are associated with energy balance as well as sleep. Specifically, a number of studies now support the idea that sleep affects your metabolism by changing the levels of leptin and ghrelin in your body. This research indicates that decreased sleep reduces levels of leptin and elevates levels of ghrelin.
The biochemical changes associated with sleep loss may be part of a larger picture influenced by other factors such as insulin resistance, increased calorie consumption, increased inflammation, or decreased physical activity (e.g., due to daytime sleepiness).
In fact, the evidence supports a strong link between nightly sleep duration and obesity.  In addition, sleep loss has also been associated with an elevated body mass index or BMI.  A meta-analysis of 18 research studies in over 604,000 people showed that, for people who slept less than five hours each night, each additional hour of sleep decreased their BMI by 0.35 kg/m2. 
Furthermore, chronic insomnia, which has been defined as over one month of ongoing insomnia,  is associated with obesity, and serves as a predictor of weight gain.  Scientists now know that chronic insomnia is associated with significantly decreased ghrelin, as well as corresponding reductions in Stage 2 and REM sleep, more time spent in Stage 1 sleep, and, of course, less sleep and decreased sleep efficiency overall. 
Of course, sleep deprivation can have a cascading effect that leads to weight gain. Beyond the molecular mechanisms at play here, people who do not sleep enough also may engage in stress-eating or have low energy and rely on caffeinated (and sometimes high-calorie) coffee or energy drinks. New research suggests that sleep can also alter gut bacteria, which can shape appetite as well. 
Unfortunately, weight gain can result in a downward spiral of persisting and magnifying sleep loss and decreased sleep quality. Weight gain can increase one’s risk for sleep apnea. Weight gain leads to fat accumulation in the throat area, and the added soft tissue in the back of the throat can obstruct the breathing passages during sleep, giving rise to sleep apnea, a sleep disorder marked by stops and starts in breathing throughout the night.
So, now that we’ve discussed the importance of sleep both in terms of molecular mechanisms underlying weight loss and more broad environmental factors, let’s talk about specific ways that getting sufficient sleep can help promote weight loss.
How does sleep help with weight loss?
Surprisingly, beyond the molecular link discussed above, sleep also plays several important roles that make it indispensable to healthy weight loss.
Sleep helps you deal with food cravings and make better healthy food choices
Sleep deprivation reduces activation in the brain’s frontal lobe, which is an area of the brain associated with decision-making and impulse control. This should come as no surprise given that sleep deprivation is well-known to affect decision making; in fact, being sleep deprived while driving has been shown to be just as dangerous as drunk driving. A person who has been awake for 18 hours straight drives similarly to a person with a blood-alcohol level of 0.05. If that person has been awake for 24 hours, their driving becomes more like someone whose BAC is 0.1, which is functionally equivalent to drunk driving. 
It’s not hard to imagine a similar decision-making phenomenon with food-related decisions. When you are tired, you’re more likely to throw caution to the wind and opt for high-carbohydrate, high-fat, and high-calorie foods. This is, in part, due to the fact that the brain’s reward centers are more stimulated by food when one is sleep-deprived. This means that after a night of not-so-great sleep, junk food may be harder to say “no” to.
A Mayo Clinic study found that people who only slept two-thirds of their normal time ate almost 600 extra calories each day. The extra calories add up over time, and could result in a weight gain of approximately a pound each week.
A study conducted by researchers at the University of Chicago found that sleep-deprived participants were unable to resist highly palatable, rewarding snacks such as cookies, candy, or chips. Participants were unable to say no to such snacks even after eating a meal just a couple of hours before offered junk foods.
This effect was highest during the late afternoon and early evening, when snacking has been linked to weight gain. The culprit for this inability to refrain from eating junk food was the chemical signal linked to pleasure and satisfaction gained from eating: the naturally-occurring compound 2-arachidonoylglycerol (2-AG). 2-AG is elevated in people with sleep loss, and levels of this compound are at their lowest during sleep.
Therefore, in sleep-deprived study participants, high levels of 2-AG represented a mechanism by which the participants opted for so-called “rewarding” foods such as candy, cookies, and chips. This tendency to seek rewarding foods is known as hedonic eating (or pleasure eating). Sleep-deprivation-related pleasure eating is therefore a significant cause of weight gain.
Poor sleep can decrease resting metabolic rate and lead to insulin resistance
Scientists have discovered that sleep deprivation can negatively affect your metabolism and serve as a stressor in your life. More specifically, accruing a sleep debt can be harmful for carbohydrate metabolism as well as hormonal function. Even a night of sleep deprivation can cause acute insulin resistance which is reversed after the sleep debt is fulfilled.
Lack of sleep can both increase stress hormone levels and cause the body’s cells to develop insulin resistance. The research shows that just one night of sleep deprivation could cause insulin resistance equivalent to six months on a high-fat diet. This, in turn, increases circulating blood sugar levels and significantly ups the risk of type 2 diabetes.
People who do not sleep enough also show increased concentrations of the stress hormone cortisol. These effects are similar to those observed in the normal aging process, which is why not sleeping enough may make age-related chronic disorders more severe.
Luckily, both elevated cortisol levels and insulin resistance resulting from sleep deprivation can be reversible if one makes up the sleep debt. However, if cortisol levels are too high for too long, this may cause weight gain, high blood pressure, affect sleep even more, impact mood, reduce energy levels, and put sleep-deprived people at risk for diabetes.
Sleep deprivation can make you too tired for exercise
Sleep loss can cause daytime sleepiness, which could reduce your motivation to exercise. For those who do have the energy to go to the gym, sleep loss can increase your risk of workout-related injuries, as a result of carelessness or being too tired to maintain proper form.
In fact, experts suggest that you skip your workout if you are sleep deprived, according to Self magazine. That’s another reason why you should make sure to get your zzz’s before you hit the gym. More on the relationship between physical fitness and sleep here.
Sleep loss reduces the amount of good bacteria in your gut
A 2016 study conducted by scientists from Sweden and Germany found that insufficient sleep can impact the gut microbiome, the community of microorganisms living in the gut. After two nights of sleep deprivation, participants exhibited a significant decrease in beneficial gut bacteria, a phenomenon that has been linked to both obesity and type 2 diabetes. Also, as discussed above, participants developed insulin resistance.
New research suggests that gut bacteria may be shaping one’s appetite and affecting their predilections for various food. Our gut produces hormones similar to leptin or ghrelin that can signal to our brain to start or stop eating. One particular molecule, called N-acyl-phosphatidylethanolamines, are produced by gut bacteria located in the small intestine after a meal. These molecules are quickly converted to N-acyl-ethanolamines (NAEs), which are fatty compounds known as powerful appetite suppressants.
Therefore, poor sleep affects your body’s ability to maintain a healthy gut microbiome. Sleep deprivation has been demonstrated to promote the growth of gut bacteria which alter hunger/satiety signaling and could thereby serve as yet another mechanism that promotes weight gain due to sleep loss.
Sleep and weight gain: the bottom line
Understanding the link between sleep and weight loss is essential for anyone seeking to lose weight. Sleep deprivation has a number of cascading effects on health, and can cause weight gain.
Sleep loss elevates levels of the hormone ghrelin, which promotes hunger, and also can cause insulin resistance and decrease resting metabolic rate. Plus, research shows that people who do not sleep enough tend to eat more calories, on average, than people who do.
Sleep loss can make people feel too tired or unmotivated to exercise, and can also increase one’s risk of injury during a workout.
Sleep, therefore, should be an essential tool for managing healthy weight loss (i.e., as a supplement to diet and exercise). To ignore the importance of quality sleep in one’s weight loss goals could completely derail any weight loss efforts.
Body Mass Index: Body Mass Index or BMI is a calculation based on height and weight that is used to measure body fat in adults.
Chronic Insomnia: Insomnia that occurs regularly for a period of over one month.
Energy homeostasis: A biological process involving the coordinated regulation of food intake and energy expenditure. Leptin and ghrelin are two major players in energy homeostasis as they regulate hunger and satiety.
Hypothalamus: A part of the brain involved in the maintenance of homeostasis, including the regulation of hunger and satiety (which is a specific type of homeostasis called energy homeostasis).
Leptin: A hormone secreted by fat cells that binds to receptors in the brain’s hypothalamus to signal the body to stop eating.
Ghrelin: A hormone secreted by the stomach that promotes hunger. Ghrelin levels are elevated in people with sleep deprivation.
Peptide: A short chain of amino acids.
Satiety: The feeling of being full, i.e., the opposite of hunger.
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