Is Sleep Essential For Optimal Body Composition?


By Greg Nuckols Simply Shredded

“Insufficient sleep undermines dietary efforts to reduce adiposity”

The title of the study says it all. If there’s one subject I tend to get preachy about, it’s sleep. It’s not exciting like a new exercise protocol or as sexy as some new diet trend, so it doesn’t get the coverage it deserves. But it is absolutely crucial that you get a full night of sleep. Today we’re talking about how sleep can help make you sexy. Putting aside the considerable health implications of neglecting sleep, we’re starting off on a topic more immediately relevant to most of you – body composition – losing fat while holding onto muscle.

So, without further ado, let’s dive in.

The study at hand was conducted to ascertain whether amount of sleep would affect results while dieting. It built upon previous studies showing hormonal disturbances with lack of sleep, and increases in appetite.

So the authors wanted to know whether those changes would actually manifest themselves in meaningful body composition changes when on a controlled, low calorie diet.

The subjects were 10 overweight (average BMI 27.4) but otherwise healthy people, mostly in their late 30s or early 40s. They were excluded from the study if they were heavy drinkers, smokers, had jacked up sleep habits, had any major abnormalities on a physical, or were habitual heavy caffeine users. In short, they were pretty average, middle aged folks.

The study procedure
For 14 days, participants had to stay in bed for either 8.5 or 5.5 hours per night. At least 3 months later, participants swapped conditions. Food intake was restricted to 90% of resting metabolic rate. Doubly labeled water was used to assess energy expenditure (I won’t go too far afield explaining how it works, but rest assured that doubly labelled water is a VERY good method for assessing energy expenditure accurately).

Meals were standardized and weighed to ensure calorie intake was controlled for as tightly as possible. In short, it was a very well-controlled study.

The results
Amount of time the participants actually slept increased or decreased as it was supposed to. Those in bed 8.5 hours per night slept, on average, 7hrs and 25min per night (pretty close to their habitual average before the study of 7.7 hrs/day), and those who were in be 5.5 hours per night slept, on average, 5hrs and 14min. Energy consumption was darn near identical – about 1450 calories per day. Daily caloric expenditure was also nearly identical – about 2140 calories per day. That essentially a 700 calorie daily deficit, which is quite reasonable. Macronutrient breakdown was 48% carbohydrate, 34% fat, and 18% protein. Both groups lost about 3kg (6.6lbs) during the study, BUT…

The 8.5 hour group lost about 50/50 fat and lean mass.

The 5.5 hour group lost 20/80 fat and lean mass. That’s not a typo. Only 1/5 of the weight lost was actually fat. 0.6kg of the 3.0kg total. That’s substantial.

So, in more concrete numbers, the 8.5 hour group lost 2.33x 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. If most of us are aiming for body REcomposition (more muscle and less fat), would this be the definition of body DEcomposition?

It doesn’t get much better for the poor sleep deprived subjects from there, either….

  • Hunger was higher. This was accompanied by greater increases in acylated ghrelin – a hormone that promotes hunger.
  • Respiratory quotient was higher. That means that for each calorie burned, more of the energy came from carbohydrate, and less of it came from fat.

Well, for one, the participants were sedentary. That makes it a little harder to generalize results since resistance exercise helps you retain more muscle while dieting. Also, at least in the eyes of most people reading this, protein intake was laughably low (about 65g/day). It should be noted that lean mass also includes water. So of the 3kg lost, only about 1.2-1.7kg (2.7-3.8 pounds) of that should come from tissue loss (your body theoretically gets about 3500 calories from a pound of fat, and 2500 from a pound of muscle, so with an overall deficit of 9660 calories on average, some of those 6.6 pounds almost certainly came from water).
With that in mind, let’s do a little rough math.

Let’s say both groups lost about 50/50 water/tissue – a fair enough assumption. The 8.5 hour group lost 1.4kg of fat, which means .1kg left over for lean tissue loss (93% fat lost, 7% lean – not too shabby!). The 5.5 hour group lost .6kg of fat, which means .9kg left over for lean tissue loss (40% fat lost, and 60% lean mass. A little better than 20/80, but still pretty dismal). I’ll admit, that’s just a rough estimate, but it probably gives a little clearer picture of what was actually lost by both groups. The 8.5 hour group probably lost almost all fat and kept their lean tissue quite well, in spite of a 1450 calorie diet, low protein, and no exercise.
The 5.5 hour group, no matter how you slice it or dice it, lost a considerable amount of lean tissue, whether that be from muscle, bone, or organs.

Breaking it down
I understand if you’re a little skeptical about how well this would translate to you if you’re eating enough protein and you’re lifting. Sure, you’d probably do a better job of holding onto lean mass than the 5.5 hour group in this study, BUT we’re probably just talking about the degree to which you stop the bleeding. Maybe instead of 40/60 it would be 60/40 fat/lean. That’s still not painting a rosy picture. Mechanistically, I have a hard time seeing how improved diet and exercise would mitigate ALL the lean mass loss that comes from losing sleep. There are some well-documented hormonal changes (I’ll talk about those in a later post), a higher RQ means less fat is burned proportional to total energy expenditure so that energy HAS to come from stored glycogen or protein, and acylated ghrelin does some nasty stuff on it’s own.
To quote the authors, “Acylated ghrelin has been shown to reduce energy expenditure, stimulate hunger and food intake, promote retention of fat, and increase hepatic glucose production to support the availability of fuel to glucose-dependent tissues.”

The Takeaway

It’s as simple as that. Let’s take it out of the realm of “sleep helps with recovery,” and let’s forget for a moment about the health consequences or fogginess that come from not sleeping. We have concrete evidence that sleep is essential for optimal body composition. Lack of sleep directly makes it harder to burn fat and increases your risk of losing lean mass. If it’s worth it to you to prioritize training and prioritize nutrition (as seems to be the case for almost everyone), make a point of also prioritizing sleep.

Good sleep will magnify the effectiveness of the other two, and bad sleep will be a huge obstacle to your physique goals.



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