Please don't misunderstand me - sleep is NOT the magic pill to losing weight, BUT it does have a huge impact on your fat loss efforts.
You see, in a study aptly named "insufficient sleep undermines dietary efforts to reduce adiposity", they ran some tests.
Essentially, they took a group of overweight people, gave them the same amount of food and the same activity levels (mostly sedentary, and we'll get to that in a moment).
The only difference was, one group spent 8.5 hours in bed, and the other group spent 5.5 hours in bed (actual sleep times were about 7hrs 25mins and 5hrs 15mins respectively).
By the end of the study, BOTH groups lost about 3kg in weight (makes sense since the calorie deficit was similar across all participants).
BUT...
The group who slept only 5.5 hours lost 80% of that 3kg from muscle tissue and only 20% of it from fat mass.
The 8.5 hour sleep group however lost about 50% of the weight from muscle tissue and 50% from fat mass.
If you're in a calorie deficit, you can always expect to lose both muscle tissue and fat mass, but the ratio between the two is what makes all the difference.
In simple numbers, the 5.5 hour group lost about 0.6kg of fat, whereas the 8.5 hour group lost about 1.5kg of fat - that's nearly 3 times the amount!
Not to mention that losing muscle tissue is NOT something you should be striving for as it'll hinder your ability to burn more fat going forwards!
So, if body recomposition is your goal (losing body fat and gaining a bit of muscle), then SLEEP is your best friend!
Remember, these guys were on the same diet and activity levels, the only difference was the amount of sleep they were getting.
If you still think sleep isn't important for fat loss, I don't know what else I can do to convince you!
This also highlights why tracking just bodyweight is an absolute waste of time.
You could be destroying your muscle tissue and keeping hold of most of your fat, yet still think you're making progress because the number on the scales is going down.
Please, track measurements and body fat %, NOT just weight.
To make things worse, the 5.5 hour group also experienced more hunger, so if you're in the real world this would likely lead to more snacking and poorer food choices further hindering your fat loss efforts.
Now, as I mentioned earlier, the participants in the study were mainly sedentary - there was no real exercise protocol in place.
Since we know that resistance training will also affect the ratio between fat and muscle breakdown (in favour of more fat being used and muscle tissue retained) in a calorie deficit, it's fair to say that both groups would likely have had better ratios if they'd been training properly too.
It's unlikely that you could stop ALL muscle tissue being lost, but the ratios would be even better for the 8.5 hour group!
Going back to your fat loss efforts, it becomes clear that the key take homes here are:
- You need to be in a calorie deficit to lose weight
- You need adequate sleep to ensure more of that weight is coming from fat rather than lean tissue
- You should be resistance training to further tip the scales in your favour in terms of where that "weight" is coming from
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