Scientists at UCLA’s Neuropsychiatric Institute have made
the unexpected discovery that lean people may have higher levels of
a hunger-stimulating hormone than obese people do.
According to their research, which was published online last
month in the Proceedings of the National Academy of Sciences,
people with normal body weight experience had an unexpectedly
intense burst of ghrelin ““ a hormone that makes people feel
hungry ““ in the middle of the night, while obese people do
not.
Julio Licinio, professor of psychiatry and medicine at the David
Geffen School of Medicine at UCLA and co-author of the study, said
he was surprised at the results.
“People have always suspected some sort of hormone
imbalance (with obesity),” said Licinio, who is also director
of the pharmacogenomics laboratory and UCLA Pharmacogenetics and
Pharmacogenomics Research Group.
“But we were expecting the opposite ““ higher levels
of ghrelin in obese people,” he said.
Stomach cells, as well as the pituitary gland, the kidney and
the hypothalamus secrete ghrelin into the blood, where it rises and
falls predictably during the day, stimulating hunger before meals
and helping to decrease it after one has eaten.
Ma-Li Wong, co-author of the study and director of the General
Clinical Research Center at UCLA, says scientists now need to focus
on how and if the absence of a nighttime surge of ghrelin is
related to obesity.
“The study seems to indicate that obese people have a
disrupted hormone,” Wong said, “but it is difficult to
understand if this is a consequence of being obese.”
“It could change the way obesity is treated “¦ if we
could understand well what is the role of ghrelin at night and why
obese people don’t have as much as they should,” Wong
added.
There are currently two medications for treating obesity ““
one that prevents food from being absorbed by the body and the
other that acts as an antidepressant ““ but Licinio says
neither is very effective. “There is no magic bullet right
now,” Licinio said.
Instead, the main treatment for obesity is stimulating changes
in behavior through a combination of adjusting the diet, reducing
calorie intake and exercising.
“One recommendation is to stay away from processed foods
high in calories,” Licinio said. He reminds people that it is
not just what they eat but how much they eat. He also recommends
small amounts of exercise spread over the course of the day instead
of intense exercise followed by hours of sedentary behavior.
“When you are stationary for long periods of time your
metabolism shuts down and makes it hard to lose weight,”
Licinio said.
In the study, doctors took blood samples from five lean men and
five obese men every seven minutes over a 24-hour period,
collecting over 200 samples from each. They discovered that the
lean people’s ghrelin levels skyrocketed between the hours of
midnight and 6 a.m., surpassing all of the normal pre-mealtime
ghrelin peaks. But ghrelin levels stayed constant during the night
for the obese men.
For Licinio this finding implies that obesity changes the
biological mechanisms that regulate a person’s food
intake.
“The most powerful ghrelin surge was missing in the obese
men, suggesting that their regulatory system has gone awry or is no
longer able to listen to its own cues,” Licinio said in a
recent UCLA press release.
Ghrelin is one of many metabolism-regulating hormones that seem
to be offset by obesity. Licinio and his colleagues also tested the
subjects’ blood samples for two other such hormones, leptin
and adiponectin, which are secreted by fat cells. Leptin,
“the fullness hormone,” has the opposite effect from
ghrelin, and adiponectin helps regulate metabolism.
The obese men in the study showed higher levels of leptin and
lower levels of adiponectin, confirming earlier results found by
Licinio and other researchers. These results are also
counterintuitive, as one would expect obese people to have lower
levels of leptin ““ the fullness hormone ““ not
higher.
All 10 participants in the study were Mexican American males in
good physical and mental health between the ages of 21 and 25. All
slept during the night and ate meals designed to maintain their
current weights, and none had recent weight gain or loss or had
taken any medications, hormones or dietary supplements within 30
days before the study.
Both Licinio and Wong agree that further testing needs to be
done to replicate the results with a larger number of people of
different ages and ethnicities before scientists can draw any
definite conclusions. The results from a study with women are still
being processed.
Co-authors for the study also include Bulent Yildiz and Marc
Suchard of UCLA and Samuel McCann of Louisiana State
University.