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Beauty Sleep: The Importance of Sleep on Body Composition

Throughout college, sleep was public enemy number one in my eyes. I used to envision a world where you could take a pill that made it so you wouldn’t have to sleep and had the ability to accomplish whatever you wanted with full 24-hour days. With this mindset, I wouldn’t sleep for more than 4-6 hours per night as sleeping upwards of 25% of my life away was terrifying to me. I saw sleep as an inefficiency that was slowing down the evolution of humanity. In my imagined world, sleep had no benefits and this magic pill would erase any deleterious effects that come with a lack of sleep. Obviously, this is not our reality and fortunately for me, I chose to enter a career path where I learned rather quickly the negative effects of not sleeping. Many of you have probably experienced symptoms such as anger, memory-loss, and slow reaction times when you don’t get enough rest. However, there is a lot more going on internally that could negatively impact any body-recomposition goals you have.

In 2010, a study was conducted that placed 10 overweight participants in a caloric restriction for 14 days while six of them spent an average of 8.5 hours sleeping per night and the remaining four spent 5.5 hours sleeping per night. After three months, participants swapped conditions. Caloric consumption and energy expenditure were nearly identical between the groups, leading to a similar weight lost of 6.6lbs for each group. This isn’t a surprising outcome, as previous articles demonstrate how weight loss is derived from energy balance. What is surprising, is where this weight loss is coming from betwixt the groups. The 8.5-hour group lost 50% fat mass and 50% lean mass. The 5.5-hour group lost 20% fat mass and 80% lean mass. This means the 8.5-hour group lost about 2.3x more fat than the 5.5-hour group, and the 5.5-hour group lost 1.6x more lean mass than the 8.5-hour group. In terms of body-recomposition goals, the 5.5-hour group experienced the exact opposite of what you want to happen. This study shows that if you are dieting (in a period of caloric restriction), sleep is vital to maintaining lean body mass and preventing “skinny-fat”. This study also reported higher rates of hunger for participants when their sleep was restricted. This is caused by the hunger hormone ghrelin, which is proven to increase with lack of sleep. Dieting is challenging enough, don’t create another hurdle by not getting proper sleep.

Not only is lack of sleep detrimental to those dieting, it is also counterproductive for those trying to gain muscle through resistance training. Sleep deprivation reduces two primary anabolic (the synthesis of complex molecules in living organisms) hormones, testosterone and IGF-1. Both are important for hypertrophy and permitting the body to properly conduct muscle protein synthesis. Sleep deprivation isn’t just anti-anabolic, it is also catabolic (the breakdown of complex molecules in living organisms). Lack of sleep leads to rising cortisol levels. Cortisol blocks protein synthesis and activates pathways that lead to muscle protein breakdown. Much like with dieting and fat-loss, if you are trying to build lean muscle mass, not sleeping is just going to be one more obstacle for you to tackle along your journey.

The takeaway from this blog? Sleep. How much you should sleep greatly varies from person to person, but my recommendation would be that if you need an alarm clock, you probably aren’t getting enough sleep. I know a lot of us are worried about missing a meeting or being late for work, so I don’t expect you to delete your alarm apps on your phone today. However, a good habit to get into for you may be to not set alarms on the weekends. Once you get comfortable with waking up naturally and figure out how many hours are ideal for you, try it on the weekdays (but leave a last-minute desperation alarm just in case).

Links to studies:

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