Time Restricted Eating Put To The Test

“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.
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