In my last video, I featured a study that found that

curtailing sleep can cut your rate of body fat loss in half,

while exacerbating the loss of lean mass.

To get better insight into what was going on, researchers took fat

and muscle biopsies from people after a night of sleep loss.

In terms of genes that were turned on and off,

molecular signatures were discovered suggesting

muscle breakdown and fat buildup.

That was after an all-nighter, though,

and in the weight-loss study the sleep-restricted groups

ended up getting little more than 5 hours a night.

What about a more realistic scenario like sleeping

just like one hour less a night?

Overweight adults were randomized to 8 weeks

of a calorie restricted diet or the same diet

combined with just 5 days a week of one hour a night less sleep.

The sleep restricted group achieved the one hour a day less sleep

on weekdays but ended up sleeping an hour more on the weekend days.

So overall, they just cut about 3 hours of sleep out of their week.

Would just those few hours a week make any weight loss difference?

On the scale, no, but in the normal sleep group,

80% of the weight loss was fat,

whereas in the group just missing a few hours of sleep a week

it was the opposite— 80% of the loss was lean.

This shows that a few hours of “catch up sleep” on the weekends

is insufficient, and may in fact be contributing to the problem

based on “social jetlag” effect I explored in a previous video.

A comparable study was designed for kids,

but the sleeping periods only lasted a week.

Eight- to eleven-year olds were randomized to either

increase or decrease their time in bed by 1.5 hours per night

for a week and then switch the following week.

They ate an average of 134 calories more on the days they slept less

and gained in that week about half a pound

compared to the sleep-more week.

The question then becomes would sleeping more facilitate weight loss?

When it comes to body fat, can we just, sleep it off?

The benefit of interventional studies is that you can demonstrate

cause and effect, but observational studies can allow you

to more easily track people and their behaviors

over a longer time span.

For example, researchers followed a group of

mostly overweight individuals who started out to averaging

less than six hours of sleep a night for more than five years.

During that time, about half maintained that schedule

but the other half increased their sleep duration up to

seven or eight hours a night and ended up gaining 5 pounds less fat.

A study entitled “Sleeping habits predict the magnitude of fat loss”

(among those cutting calories)

found that every extra hour of sleep

at night was associated with an extra 1-and-a-half pounds

of weight loss over a period of about 3 to 6 months.

That's not the same as randomizing people to extra sleep, though.

Maybe they were sleeping more because they were exercising more

and that's the real reason they lost more weight?

Getting people to bump their sleep from about 5.5 hours up to 7

can lead to an overall decrease in appetite within two weeks,

particularly for sugary and salty foods.

A four-week study getting habitually short sleepers to sleep

about an extra hour a night led them to consume about

two fewer spoonful's worth of sugar a day compared to

the control group but this didn't translate

into any changes in body composition.

A twelve-week study, on the other hand,

randomizing overweight and obese individuals

to a weight loss intervention with or without a sleep component

found that the sleep group lost weight significantly faster.

A national cross-sectional survey suggested lower obesity rates

among kids in households that regularly ate dinner together

as a family, got adequate sleep, and limited screen times,

and so Harvard researchers decided to try to...

put those behaviors to the test.

A six-month randomized trial to improve household routines

for obesity prevention among young children resulted in a lower BMI.

Normally it's hard to tease out the effects

of multi-component interventions, but in this case

exhortations to limit overall TV watching didn't work,

and the families were already eating together 6 days a week

and so that didn't change much either.

The only thing they were able to get the kids

to significantly alter was their sleep,

and so the improved weight outcomes may be attributed

at least in part to the ¾ hour average increase in nightly sleep.

Overall, most sleep improvement interventions

tended to show improved weight loss.

I was intrigued to look up the one study that didn't.

The nice thing about systematic reviews

(as opposed to so-called “narrative” reviews)

is that they exhaustively include mention of every study

that meets some prespecified criteria.

This keeps reviewers from cherry-picking,

but it can also lead to the inclusion of some strange studies.

In this case, a randomized controlled trial of didgeridoo playing,

the indigenous Australian wind instrument.

Those randomized to the didgeridoo to improve their sleep quality

did not lose any weight,

but they also failed to improve the quality of their sleep

(or, likely, that of their neighbors).