Eating
at 'wrong
time' affects body weight, circadian rhythms
UT Southwestern
Medical Center
A new high-precision
feeding system for lab mice reinforces the idea that the time of day food is
eaten is more critical to weight loss than the amount of calories ingested.
Mice on a reduced
calorie plan that ate only during their normal feeding/active cycle were the
only ones among five groups to lose weight, despite consuming the same amount
as another group fed during their rest time in daylight, according to the study
at UT Southwestern Medical Center.
"Translated into
human behavior, these studies suggest that dieting will only be effective if
calories are consumed during the daytime when we are awake and active. They
further suggest that eating at the wrong time at night will not lead to weight
loss even when dieting," said Dr. Joseph S. Takahashi, Chairman of
Neuroscience at UT Southwestern's Peter O'Donnell Jr. Brain Institute and
Investigator with the Howard Hughes Medical Institute.
Using high-tech sensors and automated feeding equipment, scientists developed the feeding system to help answer the difficult question of why calorie-restricted diets improve longevity. They say the new set of tools has already offered fresh insights.
Among the findings
published in Cell Metabolism, scientists documented how mice on a
diet reduced their eating to a very short time period and were unexpectedly
active during the day -- the normal rest period for the nocturnal animals.
These data reveal previously unknown relationships among feeding, metabolism,
and behavior.
"It has been
known for decades that caloric restriction prolongs lifespan in animals, but
these types of studies are very difficult to conduct because they required
manual feeding of subjects over many years. Therefore, shortcuts were taken in
order to deal with practical matters such as the normal Monday-to-Friday work
week," said Dr. Takahashi, holder of the Loyd B. Sands Distinguished Chair
in Neuroscience.
Besides affecting
weight, scientists believe the timing of food consumption affects one's
circadian rhythms and may be the route by which dietary habits impact lifespan.
The study reinforced this notion by testing the day/night cycles of mice under
different feeding schedules.
Two groups of mice
that were fed at the wrong times during their normal light-dark cycle -- those
with a 30 percent calorie reduction and others with unlimited food access
during the day -- remained active at night, suggesting they might have chronic
sleep deprivation.
This is an especially
important factor for scientists to consider for future research, given that
many calorie-reduction studies involve only daytime feeding, which is the wrong
time for otherwise nocturnal mice. Without accounting for the timing of food
intake, research that examines the effects of calorie reduction on lifespan may
be skewed by hidden factors such as lack of sleep and desynchronized circadian
rhythms.
Dr. Takahashi said the
automated system developed for this latest study helped his team address this
issue and other confounding variables that have inhibited previous research,
including the varied amounts of food given and how quickly it is consumed.
"Despite the
importance of these factors, manipulating when and how much food is available
for extended periods has been difficult in past research. This automated
system, which can be scaled up for large and very long longevity studies,
provides the means to address open questions about what mechanisms extend
lifespan in mammals, and whether it is actually the calorie reduction
or the time at which food is consumed that extends lifespan," Dr.
Takahashi said.
