Over the past decade or so an alarming amount of research has started to reveal the strong
links between poor sleep and weight gain.
Studies such as ‘The Nurses Health Study’ and ‘The Wisconsin Sleep Cohort Study’ have
demonstrated that a shorter average sleep time (i.e. less than 7 hours) is linked with as
much as a 60% increased risk of obesity.
But how is that possible? How can something as seemingly innocuous as a loss of sleep cause you to gain weight?
To explore this link, more detailed studies have been done to find possible mechanisms that
explain how a lack of sleep and weight gain are related.
5 of those are covered below.
Sleep & Appetite
A lack of sleep has a profound effect on your hormones, and in particular two hormones that are critical for weight loss – ghrelin and leptin.
- Ghrelin is a hormone that stimulates your appetite.
- Leptin is hormone that tells the brain when you’re full.
So basically, your feelings of hunger and fullness are largely regulated by these two hormones.
When you’re not getting the sleep you need, levels of ghrelin rise and levels of leptin fall.
So you have both an increased appetite, and your body takes longer to tell you it’s full.
This is a powerful double whammy that can derail any weight loss plan.
An imbalance of these two hormones can increase your appetite by as much as 50%.
And what makes this even worse is that when you’re sleep deprived, you have an increased craving for calorie dense, high carb and high fat foods.
So not only is your appetite stronger, and your fullness response is impaired…
…you also have a brain trying to convince you to eat more of the foods that are completely
wrong for weight loss.
It’s a pretty strong chemical barrier for anyone trying to lose weight.
Sleep & Fat Mobilization
A University of Chicago study found that how much sleep you’re getting effects whether your body uses fat or lean tissue for energy.
The study put a group on a controlled calorie diet, and then studied how their weight loss changed when they got 8.5 hours in bed at night versus just 5.5
What they found was that the amount of weight lost didn’t really change – that is, the amount of sleep didn’t impact on the amount of weight lost.
What it did impact on was the amount of FAT lost.
When they were getting adequate sleep, around 50% of the weight loss came from fat stores.
But when they were only getting 5.5 hours of sleep a night, this went down to just 25%.
So when you get enough sleep your body is much, MUCH more likely to burn fat than if you’re sleep deprived.
It would seem that the body burns lean tissue ahead of fat when you’re sleep deprived, presumably to conserve energy.
Sleep & Basal Metabolic Rate
One of the more interesting findings over the past decade with relation to sleep has been it’s impact on our Basal Metabolic Rate (BMR). The BMR is how many calories your body burns when you’re resting and sleeping. On average it accounts for about 60% of the calories you burn each day.
What scientists have discovered is that your body’s BMR is not as steady as you’d think and can actually be affected by a lack of sleep. When you aren’t getting enough sleep you’re awake for more hours each day than your body would like.
So your body goes into ‘energy conservation mode’ – it figures that you need to spread your calories out over more waking hours, and it slows down the rate you burn those calories to compensate.
Now this is bad news if you’re trying to lose weight.
The goal of a weight loss program is to burn more calories than you eat. But if your body is fighting against you by slowing down the rate you burn those calories at rest, you’re going to have to exercise even harder to make up the difference.
Let’s do some simple math to illustrate.
Let’s say you’re trying to maintain your current weight and you’ve calculated that eating 1800 calories a day will achieve that. Of those 1800 calories roughly 60% or 1080 calories are burned at rest (BMR).
Now lets say you start working night shift, you start getting less sleep than you need your body responds by slowing down your BMR by 10%. This now means you’re burning 108 calories fewer each day without even realizing it (1080 ÷ 10).
108 calories might not sound like much, but if you sleep poorly for 30 days this would add up to roughly an extra pound of fat gained.
So you go from thinking you’ve got your weight under control, to all of a sudden having an extra pound of fat just in one month – and you’ve got no idea how it happened.
Sleep & Cortisol
Also known as the stress hormone, at normal levels cortisol plays an important role in the body. It increases your blood pressure and blood glucose levels when you’re under stress and need a quick burst of energy.
It’s a survival mechanism developed over many millennia of evolution. Unfortunately, lack of sleep causes higher levels of cortisol than is healthy.
This in turn means higher blood sugar levels, a reduced ability of insulin to deal with those blood sugar levels as well as a craving for high carb foods to provide more glucose for fuel during this ‘stressful’ time.
Over the long run the end result is a greater chance of you gaining weight.
And to make matters worse there’s also research showing that increased cortisol levels hinder your ability to sleep.
So you can fall into a vicious cycle where your stress levels causes you to sleep less, which keeps your cortisol level raised which reduces your ability to sleep which keeps cortisol levels high and so on.
Sleep & Blood Glucose Regulation
Studies have shown that even a couple of sleep deprived days can cause a reduction in glucose tolerance, down to levels that would be considered close to those of someone who is a diabetic.
What’s most interesting about some of these studies is that they’ve been done on groups of young, healthy individuals with no prior demonstration of any issues with glucose metabolism or insulin resistance.
The fact that just a couple of nights of shortened sleep can cause such dramatic swings shows how crucial sleep is for maintaining a healthy balance in your body.
So what happens when your body can’t regulated blood glucose effectively?
In the short run it leads your body to release more and more insulin to deal with the excess blood sugar.
In the long run this can lead to insulin resistance which in turn is linked to obesity and diabetes.
Sleep & Exercise Motivation
An important part of any weight management program is consistent exercise & activity.
Exercise can play an important role in losing weight and maybe an even more important role
in maintaining any weight loss you’re able to achieve.
Anyone who has tried to lose weight understands that maintaining the motivation to exercise
can be a real challenge as the weeks and months roll by. This is especially true where
regular exercise is not yet a habit or something you do regularly as part of your daily routine.
Studies into sleep have demonstrated a strong link between sleep and exercise motivation.
Get less sleep and your motivation to exercise drops dramatically.
Now the good part about the link between sleep and exercise is that it’s bi-directional.
So if you can get better sleep you’re going to be more motivated to exercise. And if you’re
exercising more consistently, your sleep is going to improve.
Sleep also plays an important role in what is known as Non Exercise Activity Thermogenesis
These are the activities you do each day as you go about your life – walking, cleaning,
gardening, playing with kids, picking up toddlers etc.
As much as 15 – 20% of your daily calorie expenditure comes from NEAT. For most people
NEAT accounts for more calories burned each day than intentional exercise so it plays an
important role in weight management.
Now if you’re sleep deprived then you’re going to feel sluggish and less energetic. This
means the amount of incidental movement you do throughout the day will be reduced, as will the amount of calories you burn, making weight loss just that little bit more challenging.
So get more sleep, get better quality sleep and your activity levels will improve as will your
ability to manage your weight.
Sleep & Food Choices
A study out of Cornell recently discovered that humans on average make just over 200 foodrelated decisions each day. And other studies have estimated that we make as many as
30,000 decisions each day in total.
This leads to a phenomenon known as decision fatigue, where our ability to make good food
choices drops over the day as we’re forced to make more and more decisions.
This decision fatigue is only worsened when you throw in some sleep deprivation, which
explains why it’s much more common for us to make poor food choices late in the day than it
is in the early morning when we’re feeling a little more refreshed.
Two examples of situations where fatigue related to poor sleep can have an impact are when
we’re doing our grocery shopping late in the day or where we are having an evening meal at
If we’re tired because of poor sleep and our decision fatigue is high as well because it’s late
in the day, then we’re more likely to succumb to food temptations and make the sort of food
choices that take us further away from our health goals rather than closer to them.
We’re also more likely to make poor food choices at work (especially if we’ve forgotten to
pack our lunch). And in general across the day our decisions with regards to portion control
can mean we eat more than we originally intended to.
By getting better sleep your brain will be better equipped to make those healthier decisions
just when you need them most.
Sleep & Late Night Binges
Above we talked about the impact decision fatigue combined with sleep loss can have on your ability to make healthy choices at the right time.
There’s one period of the day that seems to come up for many people as the time when they’re most vulnerable to poor food decisions. Late in the evening.
It’s very common for people to talk about having an awesome day in terms of making healthy choices that is then completely derailed by a late night binge.
This situation can be made even worse when you’re sleep deprived. Sleep plays a role in these binges in two important ways.
1) As we’ve talked about previously, when we’re sleep deprived we have trouble controlling our appetite due to hormone issues. We also have trouble making the right decision at the right time. Combine those two together and it’s understandable that the urge to eat late at night can be tough to ignore.
2) When we’re sleeping poorly it often means we’re up later than we should be. This then leads to a situation where the time between our last main meal and when we go to bed is longer than normal. This in turn increases the chances that hunger is going to take hold.
So not only can sleep help you reduce your cravings and make good decisions late at night, the simple act of being in bed for an extra 60 – 90 minutes each day reduces your chances of succumbing to one of those late night binges.
Sleep & Weight Loss Summary
So let’s quickly summarize what you’ve just gone through.
1) Poor sleep messes with the hormones that regulate your appetite.
The result? You’re driven to eat more, it takes longer to feel full and you crave unhealthy, calorie rich foods that are high in fat and sugar.
2) Poor sleep reduces your ability to use fat as an energy source, making it harder for you to reduce your body fat levels.
3) Your metabolism slows down which means you need to engage in more intentional exercise just to maintain your current weight
4) Your cortisol levels rise. This causes higher blood glucose levels and a craving for high carb foods making it tougher to lose weight. And to make matters worse, high cortisol levels lead to poor sleep so a vicious cycle is created – poor sleep…leads to high cortisol…leads to poor sleep…leads to high cortisol…leads to (you get the point).
5) Your ability to regulate blood glucose is reduced, leading to insulin resistance and weight gain.
6) Sleep lowers your motivation to exercise.
This makes it much harder to develop a consistent routine with your exercise which in turn makes weight loss and weight management a greater challenge.
7) Poor sleep affects your ability to make good food choices.
If you’re tired and also suffering from decision fatigue at the end of the day, it’s much harder to make the healthier decision which often involves more work in terms of preparing a meal.
8) Sleep affects your ability to avoid late night snacking.
The period right before bed tends to be when we’re most vulnerable to succumbing to the urge to binge eat unhealthy foods. We tend to succumb far more easily and more often when we are sleep deprived.
Also just the simple fact that we’re awake for more hours in the day increases the odds that you’re going to be hungry late at night when the chances of you making poor food choices are at their greatest.
Sleep More And Lose Weight
It may seem over simplistic, but the truth is it’s going to be much easier for you to lose weight or maintain your current weight if you’re sleeping well.
Good sleep helps gets your body and your brain working for you instead of making it tougher to hit those targets.
Set yourself the goal of prioritizing your sleep for just 21 days and see for yourself what the impact can be. You’ll be amazed at how much easier things become when you’re well rested.