During the years 1976 through 1980, 15% of U.S. adults were obese.
Today, about 40% of adults are obese. Another 33% are overweight.
Coinciding with
this increase in weight are ever-rising rates of heart disease, diabetes,
cancer and health complications caused by obesity, such as hypertension. Even
Alzheimer’s disease may be partly attributable to obesity and physical
inactivity.
“The diet in the
U.S. and other nations has changed dramatically in the last 50 years or so,
with highly processed foods readily and cheaply available at any time of the
day or night,” Ali Güler, a professor of biology at the University of Virginia,
said. “Many of these foods are high in sugars, carbohydrates and calories,
which makes for an unhealthy diet when consumed regularly over many years.”
In a study published Thursday in the journal Current Biology, Güler and his
colleagues demonstrate that the pleasure center of the brain that produces the
chemical dopamine, and the brain’s separate biological clock that regulates
daily physiological rhythms, are linked, and that high-calorie foods — which
bring pleasure — disrupt normal feeding schedules, resulting in
overconsumption. Using mice as study models, the researchers mimicked the 24/7
availability of a high-fat diet, and showed that anytime snacking eventually
results in obesity and related health problems.
Güler’s team
found that mice fed a diet comparable to a wild diet in calories and fats
maintained normal eating and exercise schedules and proper weight. But mice fed
high-calorie diets laden with fats and sugars began “snacking” at all hours and
became obese.
Additionally,
so-called “knockout” mice that had their dopamine signaling disrupted — meaning
they didn’t seek the rewarding pleasure of the high-fat diet — maintained a
normal eating schedule and did not become obese, even when presented with the
24/7 availability of high-calorie feeds.
“We’ve shown
that dopamine signaling in the brain governs circadian biology and leads to
consumption of energy-dense foods between meals and during odd hours,” Güler
said.
Other studies
have shown, Güler said, that when mice feed on high-fat foods between meals or
during what should be normal resting hours, the excess calories are stored as
fat much more readily than the same number of calories consumed only during
normal feeding periods. This eventually results in obesity and obesity-related
diseases, such as diabetes.
Speaking of the
modern human diet, Güler said, “The calories of a full meal may now be packed
into a small volume, such as a brownie or a super-size soda. It is very easy
for people to over-consume calories and gain excessive weight, often resulting
in obesity and a lifetime of related health problems.
“Half of the
diseases that affect humans are worsened by obesity. And this results in the
need for more medical care and higher health care costs for individuals, and
society.”
Güler said the
human body, through thousands of years of evolution, is hard-wired to consume
as much food as possible as long as it’s available. He said this comes from a
long earlier history when people hunted or gathered food and had brief periods
of plenty, such as after a kill, and then potentially lengthy periods of
famine. Humans also were potential prey to large animals and so actively sought
food during the day, and sheltered and rested at night.
“We evolved
under pressures we no longer have,” Güler said. “It is natural for our bodies
as organisms to want to consume as much as possible, to store fat, because the
body doesn’t know when the next meal is coming.
“But, of course,
food is now abundant, and our next meal is as close as the kitchen, or the
nearest fast-food drive-through, or right here on our desk. Often, these foods
are high in fats, sugars, and therefore calories, and that’s why they taste
good. It’s easy to overconsume, and, over time, this takes a toll on our
health.”
Additionally,
Güler said, prior to the advent of our electricity-powered society, people
started the day at dawn, worked all day, often doing manual labor, and then
went to sleep with the setting of the sun. Human activity, therefore, was
synchronized to day and night. Today, we are working, playing, staying
connected — and eating — day and night. This, Guler said, affects our body
clocks, which were evolved to operate on a sleep-wake cycle timed to daytime
activity, moderate eating and nighttime rest.
“This
lights-on-all-the-time, eat-at-any-time lifestyle recasts eating patterns and
affects how the body utilizes energy,” he said. “It alters metabolism — as our
study shows — and leads to obesity, which causes disease. We’re learning that
when we eat is just as important as how much we eat. A calorie is not just a
calorie. Calories consumed between meals or at odd hours become stored as fat,
and that is the recipe for poor health.”
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