Wrecking Your Diet, One Night At
a Time by Greg Nuckols
“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. This is probably going to turn into a 3-4 post series, so I want to start off
with something tangible that we can really sink our teeth into to get the ball
rolling.
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 (which I’ll cover in more detail in a later post),
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.
Participants
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’s 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.
Drawbacks
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.
If we wanted to go into the weeds of the effects sleep deprivation on cortisol,
and cortisol’s effects on water retention, there’s even the potential that the 5.5
hour group was holding onto a little more water, which means even more of
their lean mass loss would be muscle… but we’ll be charitable.
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.”
Literally the best case scenario with a shift in RQ is this: with adequate protein
intake and resistance training, you’re still able to hold onto your lean
mass. However, for every calorie you burn, more of it comes from stored
glycogen, and less of it comes from stored bodyfat. Less fat burned per calorie
burned means you’ll have to diet longer to get lean. More glycogen burned per
calorie means you’ll have less energy for your workouts. Elevated acylated
ghrelin means you’ll be hungrier. So, if you’re not sleeping enough and doing
everything else 100% right, the best possible scenario is that you have to
diet for longer, while having crappy workouts and being even hungrier all
the time. Sounds like more fun than a barrel of monkeys, right?
The Takeaway
Sleep.
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.