By Coach Alex Larcom, MPH, RD, LDN
I’m sure it doesn’t take much to convince anyone of the merits of sleep. No one likes to feel tired and sluggish after too few hours of shuteye. But sleep can affect more than just how tired you feel – it can also influence:
- Hunger and appetite
- Diet quality
- Exercise habits
- Athletic performance
But first, what happens when you sleep?
Sleep occurs in two parts, non-rapid eye movement (NREM) and rapid eye movement (REM) sleep.
NREM sleep makes up about 75% of sleep time and consists of four stages. Stages 1 and 2 are the beginnings of sleep, when you start breathing more irregularly and begin to disengage from your surroundings. Stages 3 and 4 are the parts of the sleep cycle where the most recovery occurs, as breathing slows, tissues are repaired, energy is restored, and important hormones are released.
REM sleep makes up the other 25% of sleep time, usually happening 90 minutes after you fall asleep and recurring every 90 minutes. During REM sleep, energy is provided to the brain and body, the brain is active – this is the part of sleep where dreaming happens – while the body becomes immobile as muscles are turned off.
Sleep and Appetite
Research suggests people who sleep less tend to take in more energy during the day. A 2016 review in the European Journal of Clinical Nutrition, which included 11 studies and 172 participants, found that energy intake increased by 385 calories following partial sleep deprivation. Another study found similar results in adolescents – in this study including 256 people ages 10-16, insufficient sleep was linked to sweets cravings and poorer diet quality.
This may be due to two important hunger controlling hormones that are influenced by sleep. These two hormones are leptin and ghrelin. Leptin is stored in fat cells, and low levels of it tell the body you are starving and need to eat more food. Ghrelin is produced by the stomach and stimulates your appetite. Ideally, you’d want to have higher leptin levels and lower ghrelin levels. However research has found that people who sleep less than 5 hours per night on average had lower levels of leptin and higher levels of ghrelin than people who sleep more.
Sleep and Diet Quality
Lack of sleep can increase cravings for less healthful food choices and impair parts of the brain related to self control and decision making.
Two studies conducted in 2013 used magnetic resonance imaging (MRI) to look at brain activity, and found two different ways that sleep may influence what you eat. In both studies, people were assessed after getting enough sleep and after a period of disrupted sleep and in both they were shown images of healthy and unhealthy foods while in the scanner. One study found that the part of the brain that tells us something is rewarding was more active when looking at unhealthy foods after sleeping poorly than it was after sleeping enough. In the other study people who didn’t get enough sleep showed less activity in the frontal lobe, or the part of the brain responsible for making decisions.
When you don’t get enough sleep, foods lower in diet quality look more appealing and at the same time the ability to make a healthier choice may be diminished.
The good news is, evidence suggests trying to get more sleep can have positive effects on diet and health. A review of seven studies that aimed to extend sleep found that getting more sleep (on average 21-177 minutes in these studies) was linked to improve insulin sensitivity, lower leptin levels, reduced appetite, reduced sweet and salty food cravings, lower sugar intake, and greater protein intake as a percentage of calories.
Sleep and Exercise
An abundance of evidence suggests physical activity and exercise are beneficial for sleep. Exercise has been linked to better sleep quality and faster onset of sleep. But does it work the other way around?
Limited evidence suggests it is possible, but more research is needed. Several studies included in a 2014 review exploring the bidirectional relationship between exercise and sleep showed a link between adequate sleep and higher levels of physical activity the following day, though those effects were very small and likely insignificant. A small study on women with insomnia found that shorter time to sleep was linked to shorter exercise duration the following day.
Despite this lack of evidence, I think it’s still worth mentioning. Less sleep often means lower energy levels the next day, which can make it harder to find motivation for a workout. This is especially true if you tend toward the morning classes (I can personally speak to this). The effects of sleep on the parts of the brain that impact decision making might make it more challenging to overcome a lack of motivation and feelings of sluggishness to get in a workout.
Sleep and Athletic Performance
In 2012, ESPN published a commentary article calling sleep the new “magic pill”. This claim was based on research at Stanford, which manipulated sleep habits of 11 basketball players and found that when they increased their sleep they sprinted faster, felt better, and saw improvement in three-point shooting and free throw percentages. This is because during deep sleep, the body releases growth hormones that stimulate the building and recovery of bone and muscle. A 2019 Washington Post article followed up on this claim, citing the benefits of sleep for reaction time and alertness, reducing injury and illness risk, and the link between sleep and career longevity in baseball players.
In CrossFit training, reaction time can be important. According to the Sleep Foundation, reaction time slows as sleep debt (or accumulated lack of sleep) builds. This could make a difference when you’re working on technical movements like Olympic lifts or gymnastics.
While sleep doesn’t affect the body’s physiological capabilities, lack of sleep can make exercise feel harder, which does impact performance. According to a study in Sports Medicine, sleep deprivation “does not affect cardiovascular and respiratory responses to exercise of varying intensity, or the aerobic and anaerobic performance capability of individuals.”
This doesn’t mean sleep doesn’t have a negative impact on performance. A review published in Current Sports Medicine Reports outlines several studies demonstrating that sleep can be detrimental to performance. These include studies showing a drop in endurance performance with no change in perceived exhaustion, shorter time to exhaustion during testing, decreased peak power efforts, and lower levels of muscle glycogen available prior to exercise.
Strategies to Improve Sleep
It’s not only important to get enough sleep, you need good quality, uninterrupted sleep too. Here are a few things you can do to promote productive, restful sleep:
- Sleep in a dark room
- Avoid blue light screens – like the TV, computer, and yes Instagram on your smartphone – 15-30 minutes before bed
- Sleep in a colder temperature
- Avoid caffeine 4-6 hours before bed
- Avoid drinking excess water before bed (getting up to use the bathroom will interrupt sleep)
Coping with Lack of Sleep
Sometimes, it is not possible to get 7-9 hours of sleep every night (shout out to new moms, graduate students, and healthcare workers on night shift to name a few). Coach Mariani shared some tips for counteracting a lack of sleep that has been successful with her clients. From her Fit & Fabulous Blog:
First, we establish a sleep ritual that allows them to be in the best position possible to make every second of sleep that they get restful and productive. What that ritual looks like differs from person to person, but it usually involves getting away from screens and work and doing something relaxing for at least half an hour before bedtime.
Second, we work on getting a little bit better each week. If a client starts out going to bed most nights at 1:00 am and gets four hours of sleep, we push that back by fifteen minutes a week until they are getting five hours, then six hours.
Third, we try to find improved efficiencies throughout their day so that they have more time for themselves and less need to be burning the candle at both ends. Once these strategies are in place, clients tend to have a much better quality of life as well as weight loss success.
Sleep is key to helping you stay on track with a good nutrition plan and making that plan work for you. Recovery nutrition is important, but without adequate sleep it won’t be enough. You can replenish protein and carbs after every workout, but if you’re not sleeping enough your body won’t recover and repair as well as it would with sufficient sleep. This can leave you fatigued and not able to perform your best, especially if overall diet quality suffers due to lack of sleep. It is important to get adequate sleep, especially if you are putting extra demands on your body with training. Everyone is different, but experts generally recommend that teens need 8 ½ to 9 ½ hours of sleep per night and adults need 7-9 hours to be well rested.