It’s a new year and we are all set to leave behind our old habits and turn over a new leaf. Perhaps your goal for this year is to eat healthier, exercise more often or save more money. But did you know that a whopping 80% of New Year’s resolutions fail by February? In the face of such damning statistics, how do you ensure your resolve does not fizzle out in a few weeks?

“Lead with sleep,” advises Dr. Josiane Broussard, Assistant Professor and Director of the Sleep and Metabolism Lab at Colorado State University. Research from her lab and several others shows that if you get enough sleep, you are also more likely to exercise and make healthy diet choices. On the other hand, lack of sleep is associated with weight gain, poor dietary choices, poor exercise performance and impulsive behaviors.

You snooze, you lose (weight): How sleep affects metabolism

Although we spend a third of our lives sleeping, why sleep is biologically important to an organism is still unclear. One theory is that sleep rejuvenates our immune and endocrine systems. This theory is plausible given that lack of sleep wreaks havoc on our metabolism.

Young woman is measuring blood sugar level and using mobile phone. Credit: AzmanL
Sleep deprivation can affect your insulin sensitivity, blood sugar control, metabolism, inflammatory processes and more. Credit: AzmanL.

Short sleep duration is associated with an increased risk of obesity and type 2 diabetes. One obvious explanation for the link between sleep loss and obesity is that you consume more food when you are awake. However, insufficient sleep can also cause insulin insensitivity and affect the way your body utilizes glucose. Under normal conditions, an increase in blood glucose levels (e.g., after a meal) stimulates the release of insulin which then signals our cells to soak up the elevated blood glucose. Insufficient sleep can cause blood glucose levels to remain elevated because cells do not respond as well to the insulin signal. Consistently high blood sugar levels increase the chances of developing diabetes.

A soon-to-be-published study from Dr. Broussard’s lab shows just how devastating even a single night of sleep deprivation can be. In their canine model, a single night of sleep deprivation reduced insulin sensitivity to a similar extent as in dogs that were fed a high-fat diet for six months!

“We don’t really understand why sleep loss leads to these metabolic impairments and increased risk of diabetes,” says Dr. Broussard. Trying to understand the biology of this phenomenon is a major focus of her lab. Her previous work has demonstrated that experimental sleep restriction in healthy men promotes lipid breakdown, resulting in an increase in free fatty acids in the blood. This increase in free fatty acids may be related to insulin insensitivity in human fat cells following two consecutive nights of sleep restriction.

Insufficient sleep can also alter the levels of the body’s hunger hormones – leptin and ghrelin. Leptin is the “satiety hormone” that regulates fat storage and acts on the brain to suppress hunger. Ghrelin is termed the “hunger hormone” because it stimulates appetite and increases food intake. Short sleep duration results in low serum leptin and high ghrelin. This may contribute to the high body mass index of sleep-deprived individuals, through lowered satiety signals and greater sensations of hunger.

Ghrelin and leptin - hormones regulating appetite. Leptin the satiety hormone. Ghrelin the hunger hormone. When ghrelin levels are high, we feel hungry. After we eat, ghrelin levels fall and we feel satisfied. Credit: ttsz.
Ghrelin and leptin – hormones regulating appetite. Leptin the satiety hormone. Ghrelin the hunger hormone. When ghrelin levels are high, we feel hungry. After we eat, ghrelin levels fall and we feel satisfied. Credit: ttsz.

Adding insult to injury is the fact that sleep duration can also affect how individuals on a calorie-restricted diet lose weight. In a 2010 study, normally sleeping adults on a caloric restriction diet for 14 days experienced healthy weight loss; most of their weight loss was due to loss of body fat (56% or roughly 3 pounds). Sleep-restricted individuals also lost weight, but they lost 60% more of this weight (or more than 5 pounds) through loss of fat-free lean mass as compared to normally sleeping adults. Sleep-restricted individuals only lost roughly 1 pound of body fat.

“Sleep curtailment decreased the fraction of weight lost as fat by 55% (1.4 vs. 0.6 kg with 8.5 vs. 5.5-h sleep opportunity, P=0.043) and increased the loss of fat-free body mass by 60% (1.5 vs. 2.4 kg, P=0.002). This was accompanied by markers of enhanced neuroendocrine adaptation to caloric restriction, increased hunger, and a shift in relative substrate utilization towards oxidation of less fat.” – Insufficient Sleep Undermines Dietary Efforts to Reduce Adiposity 

So, not only are you more likely to put on weight if you are sleep-deprived, but you break down more protein instead of fats (thus negatively impacting your health) if you restrict your calorie intake while being chronically sleep-deprived.

Interestingly, it’s not just how long you sleep but how well you sleep that dictates your metabolic well-being.  Disrupting sleep quality (by suppressing the deepest phase of non-rapid eye movement sleep) without altering sleep duration also reduces insulin sensitivity and increase diabetes risk.

Eating fewer calories when sleep restricted leads to greater loss of fat-free lean mass, i.e., your body breaks down proteins instead of fats. Picture credit: Motortion.
Eating fewer calories when sleep restricted leads to greater loss of fat-free lean mass, i.e., your body breaks down proteins instead of fats. Picture credit: Motortion.

The moody foodie: How sleep controls your food choices

Have you ever found yourself reaching for a bag of chips or a tub of ice-cream when you stay up late at night? That’s because sleep loss can dictate your food and dietary choices in addition to altering your body’s sensitivity to insulin and throwing your hunger hormones out of whack.

Healthy lean men who were totally sleep deprived for one night tended to choose bigger portion sizes on a computerized test the next day than men who slept for 8 hours the night before. Interestingly, the sleep deprived men also preferred larger portions of snack items (chips and candy) than meal items (rice, pasta, bread, pizza). Similar observations were made when food choices were compared between men who were only allowed to sleep for 4.5 hours each night for four consecutive nights versus those who were allowed to sleep for 8 hours each night. Sleep-restricted men gravitated toward consuming more carbohydrate-rich snacks than men who slept adequately. Additionally, levels of the hunger-stimulating hormone ghrelin remained elevated in the sleep-restricted group even after eating a meal.

Loss of sleep can lead you to make poor food choices, opting for snacks and carbohydrate-rich foods over healthy foods. Picture credit: Tookapic on Pixabay

Scientists are trying to understand why sleep loss leads people to make poor dietary choices. Is it because sleep loss causes enzyme and hormonal disturbances that stimulate appetite, or because sleep loss alters the food-related reward centers in our brain? And because biology is messy, the answer may be both.

A recently published study tried to parse the relative contributions of hormonal factors versus hedonism leading to overeating after sleep loss. Participants who slept adequately versus those who stayed awake for an entire night were asked to perform a value-based decision making task with snack food versus non-food rewards. Despite similar hunger levels the next day, sleep-deprived individuals were willing to pay more for food (but not for the non-food reward) than the well-rested individuals. The study also found increased activity in brain circuits connecting the hypothalamus (seat of the brain’s hunger center) and the amygdala (your “lizard brain” that guides your primal instincts and emotions) with sleep deprivation. Although ghrelin levels were higher following sleep deprivation, this did not correlate with increased food valuation. This indicates that over-activation of brain regions involved in food reward processing, rather than hormonal dysfunction, may be responsible for the poor food choices we make when sleep-deprived.

Young sporty woman exercising before jogging in park . She is stretching to warm up. Morning in park.
Sleep. Rise early. Get the longevity worm.

Work it off: How sleep dictates exercise performance

Perhaps you think you’ll shed the extra calories you consumed during your night out by exercising more the next day? But studies show that individuals who only slept for 4 hours on two consecutive nights were less active and engaged in less intense physical activity than people who slept the recommended 8 hours.

If you do not get adequate sleep, you are less likely to exercise and more likely to consume unhealthy foods to overcompensate for the lack of energy.

A slave of habit: How sleep affects self-control

Even if your New Year’s goals are non-health-related, like saving more money, chances are that a good night’s sleep will still benefit you.

For an action to become a habit, our brains have to learn to associate that action with an outcome. So every habit, good or bad, begins as purposeful goal-directed learning. If the outcome is rewarding, we tend to perform that action over and over again, thus reinforcing that behavior. For example, if you go shopping when you are stressed and the retail therapy makes you feel better, you will be motivated to shop every time you are stressed out. Over time, this behavior becomes automatic (i.e., a habit) and you continue to engage in it even if it doesn’t make you feel any better. To break the habit, your brain needs to engage in goal-directed learning again and associate stress-shopping with a bad outcome (having less money) so that you are not motivated to pursue it any more.

A study in healthy college students showed that a single night of total sleep deprivation promoted habitual behaviors over goal-directed learning. This may be because the extended period of wakefulness causes fatigue, not leaving you with enough cognitive reserves to engage in purposeful goal-directed behaviors. Ultimately, sleep deprivation makes you less sensitive to change in outcome valuation (i.e., discerning that something that was previously rewarding is now bad) and therefore more likely to engage in old habits.

Can we recover from the effects of sleep loss?

Okay, we get it. Not getting enough sleep is BAD! But life is not always a bed of roses (pun intended). Kids need to be taken care of, work needs to be caught up with and Netflix shows need to be binge-watched, so sleep gets sacrificed at times. But can we get back on track after a few sleepless nights?

Dr. Broussard’s research suggests that we may be able to recover from the effects of short-term sleep loss. Her study measured insulin sensitivity in healthy young men who slept for 8 hours on four consecutive nights and those who slept 4.5 hours for four nights followed by two nights of recovery sleep averaging 10 hours each. Sleep restriction significantly reduced insulin sensitivity. But, notably, two nights of recovery sleep after four nights of sleep restriction restored insulin sensitivity and diabetes risk to levels observed after normal sleep.

If you are thinking it’s time for a weekend sleep binge, however, you might want to reconsider. Although most of us sleep less on weekdays and sleep in on the weekends, Dr. Broussard cautions against weekend sleep patterns that can create a phenomenon known as “social jet lag”. Sleeping during the day on a Saturday or Sunday and eating later into the day and night will confuse the body’s biological clock and can lead to weight gain.

“Staying up later than normal and sleeping in on weekends is like traveling from New York to Los Angeles and back every weekend,” she warns. “This causes circadian misalignment wherein we tend to be awake and eating during our biological night but sleeping and fasting during our biological day [sleeping late into the morning]. So, although we can seemingly recover from the effects of less sleep acutely, what it means to live your whole life cycling between not getting enough sleep and trying to recover, we don’t really know.”

Setting up a regular sleep routine is part of good sleep hygiene that promotes long-term health. Picture credit: Toa Heftiba on Unsplash

Based on evidence emerging from scientific laboratories and in shift workers, we can start to piece together the effects of chronic sleep loss on long-term health. It has been proposed that disruption of the daily rhythms of our biological clocks may predispose certain individuals to Alzheimer’s disease. Chronic sleep loss such as that observed in night shift workers is also associated with increased risk of obesity, cardiovascular disorders and cancers.

Therefore, it is important to adopt good sleep hygiene for long-term health. Here are some sleep hygiene practices to ensure good quality sleep for the recommended 7-9 hours per night for adults:

1. Avoid bright lights and the blue screens of your electronic devices before bed. Keep your bedroom dark, quiet and cool.

2. Avoid stimulants such as caffeine and nicotine close to bedtime.

3. Avoid consuming alcohol close to bedtime. Although it may help you fall asleep faster, it can severely impair sleep quality.

4. Avoid heavy meals, fried, fatty and spicy foods close to bedtime as these can trigger indigestion.

5. Exercising for as little as 10 minutes a day can help promote good quality sleep, but avoid strenuous workouts close to bedtime.

6. Establish a relaxing bedtime routine. This could include brushing your teeth, taking a warm shower, reading a book or performing light stretches.