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Sleep is perhaps the neglected stepsister in the health
conversation of today.
Often, we hear about exercise and being physically active.
And we hear about healthy eating and having a good diet.
But very few of us actually hear about the importance of sleep
in general for our health.
And it turns out that insufficient sleep
will compromise your ability to manage your body
weight with dieting.
One study, for example, found that in individuals
who weren't getting sufficient sleep, if they were getting
less than six hours of sleep a night,
70% of all of the weight that they lost
came from lean muscle mass and not fat.
Now, why would your body do this?
Fat is a highly energy-rich substance.
When you are under-slept, your body
will deliberately become stingy in giving up its fat.
It will start to metabolize things such as muscle,
which is protein.
In other words, when you're not getting sufficient sleep,
and you're trying to diet, then you actually
lose what you want to keep, which is muscle.
And you hold on to what you want to lose, which is fat.
So it may be that you're putting all of this diligent hard work
into dieting.
You're managing your cravings.
You're fighting that battle.
But if you're not getting sufficient sleep,
then you may be just unraveling all of that hard work
every night and compromising all of that hard work
that you're doing during the day.
When we're not getting sufficient sleep,
it's not only our appetite hormones
that become dysregulated, but we've also discovered changes
within the brain itself.
Several years ago, we did a study.
And we took healthy individuals.
And we gave them a full night of sleep,
and then we brought them back.
And we sleep deprived them for a night.
And the next day, we put them inside an MRI scanner.
And we showed them a whole range of different foods from things
that were very healthy to things that
were devilishly pleasurable and desirable but very unhealthy.
And we measured the brain's response
as it was viewing these images.
And what we found is that when those individuals were
under-slept, when they were sleep-deprived,
the brain was responding in a different way
to those highly desirable, highly pleasurable,
addictive foods.
Specifically, what we found is that there
is a deep emotional center in the brain called the amygdala.
And one of the things that the amygdala does
is regulate our positive and negative emotions.
And we found that when those individuals hadn't been getting
sleep, the amygdala, this hedonic center,
was lighting up far more brightly in response
to those very pleasurable, very unhealthy foods.
And we also found that another part of the brain
called the prefrontal cortex that sits directly
above your eyes, which helps try to regulate
these impulses, these desires of when you walk past
in the supermarket, the sort of the ice cream refrigerator,
and you think, oh, I would really like a pint of this
and a pint of that.
But you think, no, I'm trying to be good.
I'm trying to stay on this diet.
I'm going to walk past it.
That's your prefrontal cortex telling you the logic
and controlling that deep hedonic brain center.
But that part of the brain was impaired by a lack of sleep.
So we lost the impulse control site within the brain.
And instead, we got this ramping up
of the hedonic site within the brain.
So now we're giving way to our pleasurable desires.
And that's another reason why we start
to eat in more unhealthy, more impulsive ways
when we're not getting sufficient sleep.
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Now let's speak about the relationship between sleep
and your body weight and the control of your appetite
and your hunger.
And to do that, I want to introduce
two different appetite-regulating hormones.
They are called leptin and ghrelin.
Leptin is the hormone that signals satisfaction with food.
And leptin tells your brain and your body
you're no longer hungry.
You can stop eating.
It gives you a feeling that you've
been satisfied by your food and that you're full.
Ghrelin does the opposite.
Ghrelin is what we think of as the hormone of hunger.
When we have high concentrations of ghrelin,
we typically want to eat more.
And even if you eat a full meal, if ghrelin levels remain high,
you won't feel satisfied with that food.
You'll still want to eat more.
And more than likely, you will eat more.
You'll eat to excess.
And what studies have taught us is that a lack of sleep
can change the balance of these appetite-regulating hormones
in deleterious ways that can push us
towards a path of weight gain or even obesity.
A collection of studies have taken otherwise healthy adults
of normal weight, and then they've
put them under two different conditions.
Either they've been giving them plentiful
sleep for several nights, or they restrict their sleep
to maybe just four or five hours a night for several nights.
And then at the end of that experimental phase,
they will actually measure the levels of leptin and ghrelin
that are circulating in their bloodstream.
And what they discovered was essentially a double whammy
effect.
They found that levels of leptin, the hormone that
normally says "Don't worry, you're not hungry,
you're satisfied with your food,"
in those people who had been sleep-restricted,
their levels of leptin had gone down.
If that wasn't bad enough, what they also found
was that levels of ghrelin, the hunger hormone,
had actually gone in the opposite direction.
They had actually increased.
Overall, the hunger levels that those individuals reported
was higher as well.
There was another thing that they
identified in those studies.
Those under-slept people, despite eating
more of every food group, they seemed
to eat much more of the heavy-hitting,
stodgy carbohydrates and simple sugars.
So in other words, when you are under-slept,
you're going to start reaching for things such as pizza
and pasta and bread and ice creams and desserts
rather than a handful of leafy greens or some healthy fish
as a consequence.
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Beyond simply appetite regulating hormones or even
reproductive hormones, there's another set of hormonal changes
that are skewed by way of insufficient sleep.
And these are the metabolic hormones, particularly
things that help control our blood sugar,
in other words, our blood glucose levels.
Now, the way in which blood glucose and its regulation
typically works is that when we eat a meal,
our blood sugar levels will start to rise.
But it's actually quite dangerous for the body
to have high levels of blood sugar, high levels of glucose,
for long periods of time.
And in fact, if we have chronically high levels
of blood sugar, that can set us on a path towards type 2
diabetes.
So what we always want to do when
we see a spike in our blood sugar levels
is have a body system that is very well
adept at very quickly bringing back down those glucose levels.
How does the body do this?
Well, one of the mechanisms is that when the body signals
or receives the message of high blood sugar,
it releases a hormone called insulin.
And that insulin then starts to circulate all over the body.
The body needs to release the appropriate amount of insulin
to say to the cells in the body it's time to sort
of almost metaphorically pull your straws out and start
sucking in that glucose from the bloodstream
so that we don't get this monsoon of blood sugar
swilling around within our blood.
The second thing is that, however,
those cells in the body need to be listening
for the signal of insulin.
Even if the body is releasing the appropriate amount
of insulin into the bloodstream, if those cells aren't listening
to the insulin, then those cells won't open up,
lowering that blood sugar.
And what we found is that a lack of sleep
disrupts both sides of that metabolic blood sugar equation.
And this is a causal set of studies where you take people
who have no signs of diabetes.
And you limit them to maybe just four or five hours of sleep
a night for four or five nights, and then you
give them a very sugary glucose drink that
will raise their blood sugar a standard amount.
And firstly, what they found is that when those individuals had
not been getting sufficient sleep,
the body wasn't releasing enough insulin.
If that wasn't bad enough, the cells in the body
had also become ignorant, or they'd
stop listening to the signal of what little insulin had
actually been released.
So on both ends of the blood sugar regulation equation,
a lack of sleep was impairing that capacity
to regulate blood sugar.
And as a result, it reduced the regulation, the absorption,
of glucose by about 40% in those healthy individuals.
If those individuals had been checked by their doctor
at that moment, their doctor would
have classified those individuals
as being in a prediabetic state.
So, in other words, short sleep duration for just one week
will have your doctor, your GP, reaching for that prescription
because they would register you as being
right on the cusp of suffering from type 2 diabetes, which is
a desperately serious disorder.
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Beyond changes in our appetite hormones
or even changes in how our brain operates,
we're also starting to understand that a lack of sleep
can change the gut microbiome.
The gut microbiome is this incredible forest
of flora and fauna bacteria as it
were that helps regulate a healthy constitution
within our intestinal tract, within our gut.
And what we've been finding is that in people
who report getting insufficient sleep,
there is a change in the balance of the gut microbiome.
It shifts over more towards a bias of fermented species.
And it shifts away from more of the bacterial-based species.
And the reason that we think that that's not optimal
is that if we look at individuals
who have health conditions, things such as diabetes
or people who are overweight, they have exactly
that same abnormal profile of a gut
microbiome to that which we see in individuals who aren't
getting sufficient sleep.
One of the reasons that we think that the microbiome undergoes
deleterious changes when we're not sleeping
is due to a hormone called cortisol.
Everyone needs cortisol.
It's part of a healthy biology.
But if we have too much cortisol,
it starts to act like a chronic stress-related hormone.
And that has manifold consequences
that have been well proven by science such as changes
in your cardiovascular disease risk, changes in diabetes,
relationships with depression and mental illness.
But one of the other things that cortisol will do
is shift the microbiome in this deleterious, imbalanced
direction.
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So that's the impact of sleep on food-related behaviors,
the selection of your foods and the amount of the type of food.
But now let's change that association.
Let's reverse it.
Can the food that you're eating during the day
or in the evening impact the quantity
and the quality of your sleep at night?
So first what we found is that diets that are high in sugar
and low in fiber are typically worse for your sleep at night.
And as a result, you will have less deep sleep.
And it's more likely that you will wake up during the night.
One of the reasons for this is that sugar, particularly
if you're eating it throughout the day and especially
in the evening, will increase your metabolic rate
and particularly your temperature.
It's not just the different types of food
that you're eating that can impact your sleep at night.
It's also the timing of your food intake.
The general rule is don't go to bed desperately hungry.
And don't go to bed too full and for most people, trying
to stop eating, say, two or three hours before bed.
If you need a little bit of a snack
before bed just to take the edge off your hunger, that's OK.
But make sure it's not a snack that
has high concentrations of sugar in it.
And give your body the chance-- give it
an hour or a couple of hours to try to digest that food.
And therefore, you'll give yourself
the chance for better, restful sleep at night.
So it's a bidirectional relationship
when it comes to sleep, food, and diet.