This is a story about the importance of good timing.
Two-thirds
of Americans are overweight or obese. This excess weight contributes to
a variety of health problems. Despite enormous effort over decades, the
problem has proved extremely difficult to solve. Biologist thinks we're missing a key variable: Instead of focusing so much
on what we eat, he says, we should pay more attention to when we eat.
A
researcher argues that eating
within a certain time window each day can help people lose weight and
may help prevent illnesses including diabetes, heart diseases and cancer. In animal studies, he and others have shown that limiting
food intake to a period of eight to 12 hours can boost cognitive and
physical performance, and may even lengthen life span. Known as
time-restricted feeding, or TRF, the approach is simple: Eat more or
less what you want, but don't consume anything before or after the
allotted time.
The researcher argues that humans' circadian rhythm is not
designed for a world with 24-7 access to food. "If you're eating all the
time, it messes up that pattern," he says. For many if not most
Americans, that pattern is deeply out of whack, and many of us eat from
early morning until late at night.
It
is not clear whether TRF works in humans the way it seems to work in
lab mice. For one, mice and humans have very different circadian
rhythms. Mice are nocturnal and sleep more than once a day. They also
live for only two or three years. "It may be that for a mouse, a 16-hour
fast is the equivalent of a two- or three-day fast for a human," says
a nutrition scientist who is doing research on TRF in humans.
In
addition, the researchers say, some of the benefits of TRF may stem
from decreased consumption due to the shortened eating window: It's not
really surprising that cutting out the after-dinner drink and the
late-night sundae is good for weight loss and overall health. And, in
fact, studies in humans and animals have found that TRF helps both mice
and people eat fewer calories.
The biologist first got interested in TRF
15 years ago, while studying the genetics of circadian rhythm. His
research on mice revealed that over the course of a day, hundreds of
liver genes turn on and off cyclically. The liver plays a central role
in metabolizing calories, and it turned out that most of these cyclic
genes were involved in eating and digestion. This led him to ask whether
mice - and humans, too - were programmed to eat according to a certain
circadian schedule. In 2008, he began examining how mice responded to
different feeding schedules; to his surprise, TRF had powerful health
benefits.
The researchers compared two groups of mice, both of
which consumed the same number of calories. One group was limited to an
eight-hour window, while the other could eat at any time. After four
months, the eight-hour mice weighed 28 percent less than the anytime
eaters. "When we saw the results, they were so unexpected," he says.
"Even I didn't believe it."
He
had his students independently repeated the experiment three times; all
of the results were similar. Using the same model - two groups eating an
equal number of calories, but on different feeding schedules - he found
that TRF mice had normal blood sugar levels, while the
unlimited-schedule animals developed Type 2 diabetes. Since then, he has
shown that TRF can reduce the risk of heart disease and cancer. In
addition, mice restricted to an eight- or nine-hour eating window could
run for twice as long as those that ate on a normal schedule.
"TRF
is an interesting and valuable idea, but it's not proven that it works
in humans," says nutrition researcher. "There is some evidence
to suggest that it might be useful for some things. But it's
extraordinarily complex to actually nail this down."
Overall, he
says, the evidence indicates that eating most of your food earlier in
the day is probably healthier than eating most of your food later in the
day. He also notes that there are many complexities to the issue,
including the fact that most people eat healthier food at breakfast
(oatmeal or cereal, for instance) than they do at dinner (hamburger,
fries and dessert).
Some evidence from research involving humans
indicates that TRF has benefits even when people don't eat any less. In a
study that is soon to be published, the team examined eight men with
pre-diabetes, a condition in which people are close to being diabetic
but not quite there. Researchers prepared all food in the study, and the
participants ate it under supervision. The men tried two schedules:
eating all their meals between 8 a.m. and 2 p.m., and between 8 a.m. and
8 p.m. Compared with the 12-hour schedule, the six-hour window
significantly lowered blood pressure and improved insulin sensitivity,
the ability to process glucose.
"We were really excited about the
results," Peterson says. "It was a small study, but it was done
extremely carefully." In a similar study, also not yet published, she
looked at 11 overweight people who followed the same two regimens.
Although those in the six-hour window did not increase the overall
number of calories they burned, they did increase the amount of fat they
burned and reduced levels of a key hunger hormone called ghrelin; these
metabolic changes might make it easier to lose weight and body fat.
"I
think that within 10 years we will have some really clear guidelines
for meal timing," the biologist says. "But we are in the early stages of this
research. There is a lot more work we need to do."
In 2015, he
looked at the eating patterns of 156 adults; more than half spread food
consumption over 15 hours or longer, while only 10 percent consistently
ate within a 12-hour window. He followed up with eight of these people,
who were overweight and typically ate for 14 hours or more a day. When
the subjects were limited to a 10-hour window for four months, with no
other restrictions - they could eat whatever they wanted - they lost
weight, slept better and had more energy.
Panda is now starting a
study that will eventually include thousands of adults worldwide. Using a
custom smartphone app that allows people to take photos of what they
eat and immediately send them to researchers, he will be able to more
accurately track which foods people eat. Using this data, he will
examine whether TRF can improve weight, blood sugar, blood pressure,
joint pain, sleep, anxiety and inflammation.
He says that mice and humans - and
probably most organisms - are not built to simultaneously ingest food
and metabolize it. "Everything cannot happen at once," he says. "The
body can't take in calories and break down calories at the same time."
He and other circadian scientists say that many if not most animals have
evolved to consume food according to the 24-hour solar cycle. For
humans, this rhythm involves eating during the day and sleeping after
sunset. With the advent of electric lights, refrigerators, microwaves
and 7-Elevens, millions if not billions of us have jettisoned this
pattern. But the circadian rhythm of our metabolism still expects us to
stop eating at sundown. This mismatch between modern society and
programmed biology can lead to myriad health problems, the researchers
say.
It is not clear exactly how TRF works, but it seems to
trigger several molecular changes. It increases the activity of
mitochondria, which provide energy to cells throughout the body; it
boosts levels of ketone bodies, molecules produced by the liver during
fasting, which are a powerful source of energy and are especially useful
to muscle and brain cells; it also raises production of brown fat, the
"good" fat that helps the body burn more energy. Together, these
mechanisms allow the body to generate more energy and metabolize
calories more efficiently than unscheduled eating.
TRF is just one
of several approaches that involve fasting. Scientists are also looking
at intermittent fasting, which typically involves eating every other
day, or eating for five days and then fasting for two.
A gerontologist, has focused on an approach in which people eat very
little for five days at a time, several times a year. Other researchers
are examining calorie restriction, which requires reducing calorie
intake below normal levels, for months, years or longer, in hopes of
triggering a variety of beneficial physiological responses. Studies of
animals and humans have found that these regimens can have benefits,
including weight loss, lower rates of cancer, diabetes and heart
disease, and, in some animal studies, significantly longer life span.
All
of these strategies have some similarities to TRF, he says, with one
major difference: They are much more difficult to follow. Whereas TRF
involves relatively minor adjustments in how most people already eat,
intermittent fasting and calorie restriction often require hunger and
discipline for long periods.
This, he says, is why TRF has
potential as a public health strategy. In a society where Big Gulps and
Big Macs are ubiquitous, unhealthy eating and obesity are very hard to
avoid. TRF, he contends, offers a simple, relatively manageable
alternative. "Just by changing when we eat, we can have an effect on
obesity and these related problems," Panda says. "This can really move
the needle."
He himself has adopted TRF and says he's seen
benefits: lower blood sugar, weight loss, better sleep and more energy.
He now uses a modified version, in which he eats breakfast at 7 a.m.,
skips lunch and has dinner with his family at around 7 p.m. In essence,
he has two long fasts a day, between meals and overnight. Others around
him have adopted the classic TRF regimen, including his 15-year-old
daughter, his mother and several graduate students in his lab. He says
his mother had pre-diabetes before starting the diet; since then, her
blood sugar has dropped significantly, to a healthy level.
So far,
TRF has not caught on widely. the scientist, is one of
the early adopters. Five to seven days a week, she limits her
consumption to a six- or seven-hour window, usually eating between 8
a.m. and 2 or 3 p.m. She says she has more energy, feels a bit calmer
and doesn't feel particularly hungry in the afternoon or evening.
"You have to adapt to it," she says. "When I first started trying this, I found 10 hours was hard. Now, six hours seems easy."
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