"How Circadian Rhythms Affect Blood Sugar Levels"
We've known for more than a half century now that our glucose tolerance declines
as the day goes on, meaning the ability of your body
to keep blood sugars under control.
If you hook yourself up to an IV and just drip sugar water into your vein
at a steady pace throughout the day, at about 8 pm your blood sugars
start to go up, even though you haven't eaten anything,
and the infusion rate didn't change.
The same amount of sugar is going into your system every minute,
but your ability to handle it deteriorates in the evening,
but bounces right back in the morning.
A meal eaten at 8 pm can cause twice the blood sugar response
as an identical meal eaten at 8 am. It's as if you ate twice as much!
Your body just isn't expecting you to be eating when it's dark outside.
Our species may have only discovered how to use fire
about a quarter million years ago. We just weren't built for 24-hour diners.
One of the tests for diabetes is called the glucose tolerance test
to see how fast your body can clear sugar from your bloodstream.
You swig down a cup of water
with about four and a half tablespoons of regular corn syrup mixed in,
and then have your blood sugar measured two hours later.
By that point your blood sugar should be under 140 mg/dL.
Between 140 and 199 is considered prediabetes,
and 200 and up is a sign of full-blown diabetes.
The circadian rhythm of glucose tolerance is so powerful that a person
can test normal in the morning but as a prediabetic later in the day.
Prediabetics who average 163 at 7 am,
test out as frank diabetics by 7 pm at over 200.
Choosing lower glycemic foods may help promote weight loss, but timing is critical.
Due to this circadian pattern of glucose tolerance,
a low glycemic food at night can cause a higher blood sugar spike
than a high glycemic food eaten in the morning.
We're so metabolically crippled at night, researchers found that eating a bowl
of All Bran at 8 pm caused as high a blood sugar spike
as eating Rice Krispies at 8 am.
High glycemic foods at night would seem to be the worst of both worlds.
So, if you're going to eat refined grains and sugary junk,
it might be less detrimental in the morning.
The drop in glucose tolerance over the day could therefore help explain
the weight loss benefits of frontloading calories
towards the beginning of the day.
Even just an earlier versus later lunch may make a difference.
People randomized to eat a large lunch at 4:30 pm
suffered a 46% greater blood sugar response
compared to the identical meal eaten just a few hours earlier at 1 pm.
And a meal at 7 am can cause 37% lower blood sugars
than an identical meal at 1 pm.
Now there doesn't seem to be any difference between a meal at 8 pm
and the same meal at midnight; they both seem to be too late.
But eating that late, at midnight, or even 11 pm
can so disrupt your circadian rhythm
that it can mess up your metabolism the next morning,
resulting in significantly higher blood sugars after breakfast,
compared to eating the same supper at 6 pm the evening before.
So these revelations of chronobiology bring the breakfast debate full circle.
Breakfast skipping not only generally fails to cause weight loss but worsens
overall daily blood sugar control in both diabetic and nondiabetic individuals.
See how the breakfast skippers have higher blood sugars
even while they're sleeping 20 hours later?
That may help explain why those who skip breakfast appear to be
at higher risk of developing type 2 diabetes in the first place.
Breakfast skippers also tend to have higher rates
of heart disease and atherosclerosis in general.
Is it just because breakfast skipping tends to cluster
with other unhealthy choices,
such as smoking and sicklier eating habits overall?
The link between breakfast skipping and heart disease—even premature death
in general—seems to survive attempts to control for these confounding factors.
But you don't know until you put it to the test.
Does skipping breakfast lead to higher cholesterol, for example?
Yes, a significant rise in LDL, bad cholesterol, in those randomized
to skip breakfast, about 10 points higher within just two weeks.
The Israeli 700/500/200 study found that the triglycerides of
the king-prince-pauper group
got significantly better— a 60-point drop—while those
on the pauper-prince-king group got significantly worse, a 26-point rise.
So, consuming more calories in the morning relative to the evening
may actually have a triple benefit:
more weight loss, better blood sugar control, and lower heart disease risk.
So if you're going to skip any meal,
whether practicing intermittent fasting or time-restricted feeding,
where you try to fit all your food into a certain daily time window, it would
be safer and more effective perhaps to skip dinner rather than breakfast.