"Time-Restricted Eating Put to the Test"
The reason many blood tests are taken before eating after an overnight fast
is that meals can tip our system out of balance, bumping up certain biomarkers
for disease such as blood sugars, insulin, cholesterol, and triglycerides.
Yet, fewer than 1 in 10 Americans may even make it 12 hours without eating.
As evolutionarily unnatural as eating three meals a day is,
most of us are eating even more than that.
One study using a smartphone app to record more than 25,000 eating events
found that people tended to eat about every 3 hours
over an average span of about 15 hours a day.
Might it be beneficial to give our bodies a bigger break?
Time-restricted feeding is “defined as fasting for periods
of at least 12 hours but less than 24 hours.”
This involves trying to confine calorie intake to a set window of time,
typically 3–4 hours, 7–9 hours, or 10–12 hours a day,
resulting in a daily fast lasting 12 to 21 hours.
When mice are restricted to a daily feeding window they gain less weight
even when fed the exact same amount.
Rodents have such high metabolisms, though, that a single day of fasting
can starve away as much as 15% of their lean body mass.
This makes it difficult to extrapolate from mouse models.
You don’t know what happens in humans until you put it to the test.
The drop-out rates in time-restricted feeding trials certainly appear lower
than most prolonged forms of intermittent fasting
suggesting it’s more easily tolerable.
But does it work?
If you have people even just stop eating between 7 p.m. and 6 a.m.
for two weeks, they lose about a pound each week
compared to no time restriction.
Note no additional instructions or recommendations were given on the amount
or type of food consumed, no gadgets, calorie counting, or record keeping.
They were just told to limit their food intake
to the hours of 6 a.m. through 7 p.m., a simple intervention,
easy to understand and implement.
The next logical step was to try putting it to the test
for months instead of just weeks.
Obese men and women were asked to restrict eating
to the eight-hour window between 10 a.m. and 6 p.m.
Twelve weeks later they had lost seven pounds.
This deceptively simple intervention
may be operating from a number of different angles.
People tend to eat more food later in the day,
and higher fat foods later in the day.
By eliminating eating in the late evening hours, one removes
prime-time snacking on the couch, a high-risk time for overeating.
And indeed, during the no-eating-after-7-p.m. study
the subjects were inadvertently eating about 250 fewer calories a day.
Then, there are also the chronobiological benefits
of avoiding late-night eating.
I’m going to do a whole series of videos about the role
our circadian rhythms have in the obesity epidemic,
how the timing of meals can be critical,
and how we can match meal timing to our body clocks.
Just to give you a taste, the exact same number of calories at dinner
is significantly more fattening than the same number of calories
eaten at breakfast.
Calories in the morning cause less weight gain
than the same calories given in the evening.
A diet with a bigger breakfast causes more weight loss
than the same exact diet with a bigger dinner.
Nighttime snacks are more fattening than the same snacks in the daytime.
Thanks to our circadian rhythms, metabolic slowing,
hunger, carbohydrate intolerance, triglycerides,
and a propensity for weight gain are all things that go bump in the night.
What about the fasting component of the time-restricted feeding?
There’s already the double benefit of fewer calories
and avoiding night-time eating.
Does the fact that you’re fasting for 11 or 16 hours a day play any role,
considering the average person may only make it
about 9 hours a day without eating?
How would you design an experiment to test that?
What if you randomized people into two groups and forced both groups
to eat the same number of calories a day
and both to eat late into the evening,
but with one group fasting even longer—20 hours.
That’s exactly what researchers at the USDA and National Institute of Aging did.
Men and women were randomized to eat three meals a day
or to fit all those same calories into a
four-hour window between 5 p.m. and 9 p.m. and fast the rest of the day.
If the weight loss benefits from the other two time-restricted feeding
studies was due to the passive calorie restriction or avoidance
of late night eating, then presumably both these groups should end up the same,
because they’re both eating the same amount and they’re both eating late.
But that’s not what happened.
After eight weeks, the time- restricted feeding group
ended up with nearly five pounds less body fat.
About the same number of calories, but they lost more weight.
A similar study with an eight-hour window resulted in three pounds more fat loss.
So, there does seem to be something to giving your body
daily breaks from eating around the clock.
Because that four-hour window was at night, though, they suffered the chronobiological
consequences—significant elevations in blood pressures
and cholesterol levels— despite the weight loss.
The best of both worlds was demonstrated in 2018:
early time-restricted feeding, eating within a narrow window
earlier in the day, which we’ll cover next.