When we think of losing fat or building muscle, it’s easy to think of the big stuff - Calories, macronutrients, training frequency and volume, or even supplements.
But something many fail to take into account is sleep.
While sleep may not appear to directly play a role in how quickly you get lean, bulk up, or increase strength, an overwhelming body of research shows that actually, poor sleep could quite easily be having a hugely detrimental effect on your progress.
It might seem obvious that sleep is important, but people generally don’t bother to ask why.
According to the National heart, Lung, and Blood Institute, sleep is vital for growth and recovery, both in a mental and a physical sense. During sleep, your brain forms new pathways to help you learn and remember information, and also aids in healing your heart and blood vessels. Lack of sleep can severely affect how well we focus, as well as our attention span, and overworked neurons in our brains have an incredibly difficult time processing new information.
Sleeping & Fat Loss
We all know that calorie balance is the key factor in determining fat loss.
In order to lose weight (ideally body fat,) you need to consume fewer calories than you burn. So surely you can still lose fat when sleep deprived, providing you’re keeping an eye on calories?
Well, yes and no.
A study from the Current Opinion in Clinical Nutrition and Metabolic Care journal found that subjects who were sleep deprived experienced decreased insulin sensitivity, decreased glucose tolerance, increased levels of the stress hormone cortisol, increased levels of ghrelin, decreased levels of leptin, and increased hunger and appetite.
Again, while these factors in isolation won’t necessarily cause someone to gain fat, they certainly make losing fat a lot harder.
Increased ghrelin and decreased leptin will increase levels of hunger and cravings. Couple that with elevated cortisol levels, and it becomes very difficult to stay on track with a diet, and maintain a calorie deficit. The researchers concluded that -
“Laboratory studies and multiple epidemiological studies have linked short-sleep duration and poor-sleep quality to obesity risk.”
Another study, published in the Annals of Internal Medicine also made for very interesting reading.
Two groups of people were both given the same calorie intake, yet one group was allowed to sleep for 5.5 hours a night, and the other 8.5 hours.
Both groups lost weight, but after 14 days, the sleep deprived group had, on average, lost 55% less weight as fat, and 60% more weight as lean mass than the group who got a whole 8.5 hours, suggesting that sleep deprivation may cause a change in substrate usage, and lead to a lower percentage of weight being lost as fat.
Sleeping & Muscle Gain
Many of the same mechanisms that compromise fat loss due to a lack of sleep also have a negative effect on muscle mass and strength.
As well as the aforementioned increased cortisol, a 2011 study found lack of sleep resulted in a reduction in testosterone and Insulin-like Growth Factor 1. Participants also exhibited a decrease in the activity of protein synthesis pathways, and increases in the activity of degradation pathways, meaning they were at risk of losing muscle following exercise.
A more recent 2017 study, published in the Journal of Musculoskeletal and Neuronal Interactions noted a significant difference in muscle strength between those who slept between 7 and 8 hours per night, and those who averaged below 6.
Interestingly, they didn’t see any decreased muscle and strength adaptations from the guys who got 7-8 hours, and those who got more than 8, however.
So more sleep may not necessarily better, but too little is definitely detrimental.
What Does This Mean in the Real World?
The physiological changes that happen due to lack of sleep may not directly impact fat loss. For example, increased cortisol alone is unlikely to lead to an increase in fat gain, if calorie intake stays stable. Likewise, increased ghrelin and decreased leptin alone won’t make you gain fat. Wavering hormones (while not healthy,) won’t kick you out of a calorie deficit.
What will happen however, is that psychologically, dieting will become much harder.
Lack of sleep means a loss of focus, which makes it tougher for you to stay disciplined on your diet. Hunger signals are ramped up, and so you’re primed to binge, and give in to cravings.
When it comes to muscle gain though, it seems lack of sleep, or even poor quality sleep does have more of a direct effect on performance and progress.
Lowered motor ability and recovery capability mean your body simply can’t put as much effort into muscular repair and recovery as it would otherwise, because it has to worry more about maintaining basic day-to-day functions.
How Much Sleep Do We Need?
It’s always going to be individual, but the Journal of the National Sleep Foundation suggests young adults should get between 7 and 9 hours, and older adults between 7 and 8.
One or two lousy nights here and there are unlikely to make a difference in the grand scheme of things, though don’t be surprised if you’re in a fat loss phase and find your cravings are higher and energy lower the next day, or have to drag yourself through training, and don’t feel as alert and coordinated as normal.
7 to 9 hours seems like a good rule of thumb. Just as important though, is sleep quality.
Aim to turn your electronics off an hour or so before bed, avoid too much caffeine in the latter part of the day, and keep your room cool and dark.
Sleep might not seem as sexy as getting the ‘perfect’ fat loss diet, or as hardcore as beasting yourself in the gym, but it matters a lot in terms of hormone levels, energy, focus, coordination and recovery, so don’t think you can neglect it and still get optimal results.