Source:
medicalnewstoday.com
Living against the clock, working late night shifts or eating at inappropriate times can come with real health risks, metabolic syndrome, obesity, and diabetes among others. Now, researchers reporting in Current Biology, a Cell Press publication, have new evidence to explain why it matters not just what mice (or by extension, people) eat, but also when they eat it.
INSULIN
RISE AND FALL
Insulin (hormone
needed for utilization of sugar in body; treatment for diabetics) action
rises and falls according to a 24-hour circadian (pertaining to or occurring in 24-hour periods or cycles) rhythm,
the researchers found. What's more, mice unable to keep the time for one reason
or another get stuck in an insulin-resistant and obesity-prone mode.
"We
used to think some things were so important that they must be kept
constant," says Carl Johnson of Vanderbilt University. "But those
metabolic set points are changing as a function of the time of day."
Johnson's
team took careful measurements of insulin in mice at different hours to reveal
a regular pattern. Normal mice become insulin resistant during the day, when
the nocturnal animals are mostly sleeping. Mice made unable to keep the time
based on a genetic defect or constant exposure to light lost that rhythm. They
also gained more weight when fed on high-fat mouse chow.
That
responses to insulin would vary over the course of a day makes sense, even if
it isn't the way scientists or doctors have often thought about it.
"From the work of Claude Bernard in the
19th century, the concept of homeostasis as the maintenance of a constant
internal environment is deeply ingrained in our thinking about how organisms
work," the researchers write. But it's also wrong, Johnson argues, for the
simple reason that an animal's environment follows an obvious daily rhythm too.
Evolution will favor organisms that have an optimal response to that
environment, which is rhythmic.
And so it is that insulin action and blood
sugar metabolism are tied to the time of day and to the internal mechanisms
that keep track of that time. It's a challenging reality for us humans, living
as we do today in the comfort of our homes, where the lights come on at the
flip of a switch and the food is plentiful.
"Mediterranean diets in which the main
meal is eaten in the middle of the day are probably healthier," Johnson
says. It's probably best to eat a light supper and avoid snacking after dinner.
Diets that only limit when people eat surely
won't reverse the epidemic of obesity, he says, but they would probably help.
