Research Review: Sleep, stress, and fat loss | Precision Nutrition

Research Review:
Sleep, stress, and fat loss

By Helen Kollias, Ph.D.


Some of my friends are having trouble losing weight.

I usually ask about their workouts and diets. They’re exercising regularly, and eating healthy.

Then I ask about how much they sleep they get, and if they are feeling stressed.

Turns out they sleep fewer than 4 hours a day and have stress oozing from their eyeballs. I suggest they sleep more, take yoga, and meditate. They snort with laughter.

Stress makes you a warrior! Sleep means quitting your job and becoming a hippie! I can’t sleep eight whole hours! I have Things To Do! I have to have a 50-child, 3-story-cake, 2-clown, 1-pony, birthday party for my 1 year old. What kind of parent would I be if I didn’t?

Sleep hygiene

I’ve been lucky enough to sleep well, but my family is littered with insomniacs. Some have underlying physiological issues, while most just have terrible sleep hygiene.

Sleep hygiene is a set of habits you have around sleep. You can’t just sit in bed watching your favorite program while drinking a big cup of coffee one minute and expect to nod off the next… or even in the next hour. You need to set up an environment to facilitate sleeping. You need to chase sleep.

Here is a list of good sleep hygiene practices.

  1. Don’t consume caffeine, cigarettes, and other stimulants (such as decongestants) late in the day. Many folks find that any caffeine after noon is a problem.
  2. Don’t drink alcohol in the evening. It sedates you at first, but then screws up your sleep rhythm, leading to worse sleep.
  3. Keep a regular sleep schedule. Go to bed and get up at roughly the same time.
  4. Exercise regularly, but not too close to bedtime. Save the tough, adrenaline-pumping workouts for earlier in the day.
  5. If you do nap, don’t do it for too long or too late in the afternoon.
  6. Actively address relaxation — don’t just expect it to happen. Build relaxation practices into your day.

I’ve found that I can strength train closer to bedtime without affecting my sleep, but after any type of metabolic training (circuit, soccer, basketball, intervals, or general aerobics) I need to give myself 4-6 hours to unwind.

Other practices I recommend:

  1. Turn of your computer, TV, cell phones, and any other devices with a screen at least an hour before bed.
  2. Don’t watch TV in bed. (FYI: TV kills your love life too.)
  3. Get up at the same time every day (including weekends).
  4. Take a warm bath before you go to bed.
  5. Keep your home a degree or two cooler at night.
  6. Keep your room really dark, or use a sleep mask to block out any light.

You think these recommendations are too restrictive and crazy? With a few exceptions (such as regular bathing), nearly all of these habits happened normally as a part of life up until about 100 years ago.

Dark. Check.

No TV. Check.

No Starbucks or Diet Coke. Check.

Go to sleep and get up at the same time. Check (sunset and sunrise).

Cooler home at night. Check. (Fire goes out.)

For more on sleep, check out All About Sleep.

Research question

Good sleep hygiene, obviously, includes reducing stress and screen time (i.e. computers, TV, etc.).

Stress and screen time are closely linked with sleep. After all, most people will say they don’t sleep well because they’re stressed, and/or because they’re doing other things before bed — usually playing on Facebook or video games, checking their work email, or watching telly. Too much stress and screen time usually leads to poor sleep.

This week’s review asks: Can you “sleep yourself skinny”? How do stress and screen time affect weight loss?

Elder CR, Gullion CM, Funk KL, Debar LL, Lindberg NM, Stevens VJ. Impact of sleep, screen time, depression and stress on weight change in the intensive weight loss phase of the LIFE study. Int J Obes (Lond). 2011 Mar 29.


Over 470 (n=472) obese volunteers with body mass indices (BMI) between 30-50 were in this study. Everybody was given a list of 8 targets for the 6 month “weight loss intervention”.

These targets were:

  1. Eat about 500 fewer calories per day than you currently are eating.
  2. Eat a healthy, low fat diet rich in fruits and vegetables.
  3. Exercise at a moderate intensity most days.
  4. Increase your activity until you’re exercising 30-60 min most days and at least 180 min/week.
  5. Record everything you eat and drink every day.
  6. Record your minutes of exercise every day.
  7. Set short-term goals and create action plans to reach your goals.
  8. Attend all group sessions.

The participants met weekly for 90 minutes in groups for 20-25. Group leaders did exercise and nutrition demonstrations, and taught skills such as problem solving, social support, relapse prevention planning, calorie awareness, and goal-setting.

This is one of a few studies I’ve seen that tries to get the volunteers involved in the process by using goal setting, action plans, and daily self records. Being involved in the process usually leads to better long term results. At some point these volunteers will be on their own. If they don’t have skills to deal with that, they will find it tough to succeed.


I’m not a fan of only measuring weight loss (instead of fat loss) in exercise and diet studies because as many of you know, your scale lies. Some days it tells you you’ve gained 5 pounds after being 100% compliant, while other days you’ve lost 5 pounds after eating bonbons and lying on the couch.

Only once in my life have I dropped a significant amount of weight, and that was nearly all muscle. I actually ended up with a higher percent body fat, even though I was lighter. Not so good. Usually I can drop 5% of body fat with no change in weight or even a slight increase.

The scale measures so much more than fat. It measures water, glycogen, muscle and even yesterday’s supper that hasn’t quite made it through you. Gee, most of those things go up and down way faster than fat.

Why do researchers use scales for these weight loss studies if weight isn’t a good way of measuring fat loss?

There are a few reasons. Some are practical, and some come down to what is accepted.

To measure body fat with accuracy you need time and someone well-trained. Actually, you need time, someone well-trained, and expensive equipment. Cheaper methods of assessing body fat, like skin folds, can be embarrassing for volunteers, which usually means fewer volunteers.

In comparison, to measure body weight, you need a scale.

Last — and this may sound a bit cynical — weight has been used for a long time to measure the effectiveness of diet and exercise programs, so researchers know that they’ll be able to publish studies using weight as the only measure. Why bother spending more money and time at the risk of getting fewer volunteers?

In this study, participants lost 6.3 kg (13.9 lb) of weight. (But had they measured body fat, researchers would likely have seen more actual fat pounds lost and muscle pounds gained.) That works out to about 0.26 kg or 0.58 lb per week.

Not very impressive. Using the PN weight loss calculator (using the average start weight of 104.1 kg, 24 weeks and selecting female) you’d expect to lose 14 kg. That’s more than double the weight participants lost in this study.

Sleep, stress and screen time: Factors in weight loss

Most weight loss plans focus on two things: exercise and nutrition. This study focused on sleep, stress and screen time.


Setting the bar pretty low, the researchers decided that losing 10 pounds (4.5 kg) in 6 months was “weight loss success”. (We can do a lot better than that here at PN. Check out what the men and women in our PN Coaching Program have been able to do!)

Based on that measure of “success”, the amount of sleep someone got was a pretty good predictor of weight loss. Using statistical analysis (logistic regression using quadratic trend) there was a significant correlation (p=0.035).

What does that mean? There seems to be an optimal amount of sleep (between 6 to 8 hours a day) that is related to weight loss success.

But there are two things you should keep in mind: First, this is only a relationship — not a cause — and second, sleeping more isn’t necessarily better.

We do know that sleep and weight loss are related. However, this study only looked at correlation, not causation. It could be that people who sleep more than 6 hours but less than 8 hours are physiologically more capable of losing weight. We can’t say that sleep is causing the weight loss, just that the two are related.

Before you decide to take a long nap to help you lose those last stubborn 10 pounds, more doesn’t necessarily mean better. Getting more than 8 hours of sleep a day actually reduces weight loss success. However, again, this may be correlated to other factors, such as depression (which can lead to overeating), general inactivity, etc.


All the volunteers answered a questionnaire (Perceived Stress Scale; PSS) to figure out their stress levels. The higher the score, the more stressed each volunteer felt they were, with 40 being the highest score.

After some statistical analysis the researchers found that a higher score in PSS predicted less weight loss. More starting stress predicted less weight loss, but just like the hours of sleep, we can’t say that more stress directly causes less weight loss. It could be that stressed people just happened to be genetically predisposed to being stressed and struggle with weight loss. Or perhaps people who are stressed are more likely to get takeout food as they burn the midnight oil at the office. This study just shows us a relationship; not the exact mechanism.

Screen time

I figured hours of screen time (TV and computer screens) was going to be a big factor in predicting weight loss, but this study showed no correlation. (However, other studies have found a strong connection between time spent sitting and fat loss — overall daily movement is still a significant factor.)

The researchers even looked at hours of screen time during work days compared to days off, to see if maybe one correlated to weight loss. Really, if you work all day in front of a computer and then spend all your off hours physically active, then screen time isn’t necessarily going to correlate to weight loss.

I was surprised that most people reported workday screen hours of only 1-5 hours per day. In an office job (aka sitting in front of a computer most of the day) I’d think you’d get to 7 hours of screen time at work, plus an hour or two at home.

Since the population was on average 55 years old, with 25% of the participants over 65 years old, it may be that either they have jobs that don’t require being in front of a computer or they’re retired. Either way this age group may not get enough screen time to affect weight loss, but that’s another study.

Weight loss: changes in stress

Losing weight had the added bonus of reducing stress scores — or is it that reducing stress caused more weight loss?

After 6 months on the program, the volunteers retook the PSS test. Researchers found that weight change and changes in stress scores were correlated (again no proof that one caused the other). More stress usually meant less weight lost. Volunteers who gained weight also had higher stress scores after the study. Weird thing, was volunteers who lost more than 20 kg had no change in stress scores.


There is an optimal amount of sleep related to weight loss and in this study it falls between 6-8 hours of sleep. Keep in mind that as you age you generally need less sleep and the average age for these volunteers was 55 years old. If you’re younger or working out, you’ll need more.

Less stress is also related to more weight loss. Decreased stress is related to decreased weight in this study. People who reduced stress while losing weight had better weight loss. Gee, reducing stress may be as important as reducing calories.

While this study didn’t prove that optimal sleep and no stress cause more weight loss, it’s something you can optimize. You can improve sleep hygiene, meditate and prioritize sleep and relaxation.

After all, think about it: Is more stress actually good for you? Is less sleep good for you? Is more screen time good for you? I think most of us would agree that the answer to all of those questions is no.

What’s the worst that can happen if you add a little more sleep? You miss watching a few hours of TV or lose the sleep deprivation competition at work.

Here’s a fun little talk from Adrianna Huffington about sleep. While the talk is for a female audience, I think it applies to everyone.

Maybe sleeping more will help you do more.

Bottom line

People who don’t sleep much, and people who are stressed out, lose less weight.

For good health and to help weight loss, get 6-8 hours of sleep — more if you’re working out (7-9 hours).

Actively pursue relaxation — make relaxation techniques part of your day. And quit watching the darn TeeVee before your eyes go square.

Eat, move, and live… better.

The health and fitness world can sometimes be a confusing place. But it doesn’t have to be.

Let us help you make sense of it all with this free special report.

In it you’ll learn the best eating, exercise, and lifestyle strategies — unique and personal — for you.

Click here to download the special report, for free.


Click here to view the information sources referenced in this article.