Why Do Some People Gain Weight When Others Don't?
Do you have that friend — the one who can eat endless hot fudge sundaes and never gain weight?
Or do you
sometimes feel that even if you worked out three hours a day and ate
nothing but celery sticks, you couldn't lose weight?
gain or lose weight, it has to be due to an energy imbalance,"
according to Jeff Horowitz, assistant professor of kinesiology, who
recently received a five-year, $2.1 million grant from the National
Institutes of Health to look at what may be causing different people to
gain or lose weight when they appear to eat and exercise the same
losing weight for most people is far from simple, the regulation of
body weight boils down to simple math: calories eaten minus calories
burned equals weight gained, Horowitz said.
gain weight at different rates despite eating the same number of
calories, there must be a difference in how much energy is expended.
Horowitz's study, participants will spend two weeks in the hospital
with their diet and physical activity closely monitored. Volunteers
will get 2,000 calories more than they need each day while Horowitz's
team studies how quickly they gain weight and body fat.
weeks, volunteers will go on a calorie-restricted diet, and the
researchers will look at how quickly the extra weight and body fat come
aim of their study is to uncover what about the person's biology and
metabolism differs to make some prone to gain a lot of weight and
others more resistant.
inspiration for this project came when Horowitz was conducting a study
on low-carb diets. It was important to that specific research project
that volunteers maintain a steady weight. This worked for most
participants, but there were a few people who seemed to lose weight no
matter how many additional calories were added to their diets.
Horowitz's collaborators, Ariel Barkan, a professor of internal
medicine and of neurosurgery at the U-M Medical School, noted that he'd
seen a similar reaction in a rodent study, with the same diet causing
some to gain much more weight than others, despite similar activity
levels. It turned out that animals with high levels of growth hormone
were resistant to gaining weight.
returned to his study data, which included growth hormone samples from
his volunteers, and found that there was a strong connection between
those who had high growth hormone levels and those who had lost weight.
hormone spikes and falls a few times throughout the day. Those who lost
some weight on the diet that should have kept their weight stable had
higher spikes, not just consistently high hormone levels.
To test the
connection, Horowitz will use volunteers with growth hormone levels on
the low side of normal. Some of these participants will receive a
constant level boost of growth hormone during their two weeks of
indulgence, while others will get additional growth hormone following
the body's usualpattern of daily spikes.
As part of
the study, Horowitz will take muscle biopsy samples to measure muscle
protein synthesis, which burns a lot of energy. Horowitz hypothesizes
that one way growth hormone may help make people more resistant to
gaining weight is by increasing the activity of bodily processes like
this that expend a lot of energy throughout the day.
researchers see that giving additional growth hormone alters weight
gain, that could mean that it is an effective treatment for people who
struggle with obesity.
The bad news
is, there's a linear decline in growth hormone as we age, so if
Horowitz's theory is right, this could be one reason we gain weight as
we get older — it's part of our body chemistry. Gaining weight
reduces growth hormone, too, so you can get caught in a vicious cycle.
The good news
is, exercise boosts growth hormone, so those with milder weight control
issues might simply find that enough physical activity to generate more
growth hormone could help manage weight — separate from the
calories the exercise burns.
For more information on the University of Michigan Health System, visit www.med.umich.edu.