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In studies to evaluate the connection
between leptin and hunger, nutritionist
William Horn and chemist Nancy Keim
designed questionnaires to help
volunteers assess their hunger.
Here, the researchers review the
study data.
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If you're dieting and your leptin
levels go down, you may get a lot hungrier. So say
ARS researchers in Davis, California,
who are studying the effects of this hormone.
Their investigation at the ARS Western Human Nutrition Research Center is among
the first long-term analyses of blood (plasma) leptin levels in women who are
on a weight-loss regimen. ARS chemist Nancy L. Keim led the study. Keim hopes
that the leptin findings will "help obesity researchers and others who are
trying to determine whether leptin can be used effectively to help people shed
body fat."
Overweight and obesity are pervasive and costly health problems in the United
States. Finding ways to help prevent this overnutrition is a priority research
topic at the Davis research lab.
Nearly one-fourth of all Americans age 20 or older are obese, meaning that they
are 30 or more pounds over their ideal weight. Obesity is linked to 5 of the 10
leading causes of death. Nationwide costs of obesity are estimated at nearly
$100 billion. |
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Endocrinologist Peter Havel
checks a volunteer’s blood
pressure in a study of diets
high in fructose or glucose.
These sugars affect production
of leptin and insulin, hormones
that regulate appetite.
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Less Leptin, More
Hunger
Twelve overweight but otherwise healthy women, age 20 to 40, volunteered for
Keim's 15-week study. For the first 3 weeks, the volunteers ate a stabilization
diet, which determined how many calories they could consume every day without
either gaining or losing weight.
For the remaining 12 weeks, the women went on a low-fat, weight-loss regimen.
Each volunteer ate 500 fewer calories per day than she would have needed to
maintain her starting weight. Calories derived from fat never exceeded 22
percent of each day's total calories. The weight-loss phase of the study also
included a program of moderate exercise—walking, weight training, and
working out on an exercise bike or treadmill.
Meals prepared for the volunteers by the center's dietary staff featured tasty,
familiar fare. For breakfast there were foods such as orange juice, canned
peaches, pancakes and maple syrup; lunch might be a ham sandwich with jack
cheese on french bread, vegetable soup, and gingersnap cookies; and at dinner
there would be something like nonfat milk, steak with gravy, mashed potatoes,
broccoli florets, and canned pineapple. That day's menus also included an
evening snack of orange sherbet and graham crackers.
Keim found that during the first week of the weight-loss stint, volunteers'
plasma leptin levels dropped by an average of 54 percent. Levels remained low
throughout the rest of the study. What's more, the incidence of hunger—and
the desire to eat—doubled in response to the reducing diet. Says Keim,
"The volunteers who reported the greatest increase in hunger and desire to
eat—and biggest prospective estimates of how much they'd like to eat at
the next meal—were those with the largest drop in leptin."
Volunteers Evaluate Their Hunger
Once every 2 weeks, volunteers ranked their hunger by filling out a one-page
questionnaire several times during the day. Below each question was a short
horizontal line that served as a scale. To answer the question, "How
hungry do you feel right now?" volunteers put a small vertical tick mark
toward the left end of the scale if they were "not at all hungry" or
toward the far right if they were "extremely hungry."
"This scale is subjective, of course," Keim admits, "but it's
really the only way we have right now to assess appetite." To get a better
idea of how to use the questionnaire and estimate their hunger, volunteers
began working with the form during the stabilization-diet portion of the study.
Volunteers with higher leptin concentrations and smaller decreases in leptin
were less hungry while on the reducing diet. Decreases in body weight and body
fat didn't seem to play a role in the degree of hunger that the volunteers
reported.
Keim collaborated in the study with Peter J. Havel and Judith S. Stern of the
Department of Nutrition at the University of California at Davis. The work was
funded by ARS, the National Institutes of Health, and the Juvenile Diabetes
Foundation, International. The research is of interest to the diabetes
foundation because new information about the relationships among leptin,
insulin, and obesity may lead to better ways to prevent or treat diabetes. The
scientists published their findings in the American Journal of Clinical
Nutrition.
Fructose, Glucose Scrutinized
Now Keim, Havel, and Craig H. Warden, a genetics and pediatrics researcher at
U.C. Davis, are collaborating in another leptin investigation. The study should
help reveal how two kinds of sugars in our foods—glucose and
fructose—affect the body's production of leptin and insulin.
"When we eat or drink foods with glucose in them," explains Havel,
"the glucose triggers release of leptin and insulin. Both of those
hormones help regulate our appetite. However, when we eat or drink foods with
fructose in them—like soft drinks or some juice beverages—our bodies
may produce less leptin or insulin. As a result, we may still feel hungry after
eating. It's as if the fructose-containing foods are invisible to our bodies,
so our appetites aren't adjusted after eating them." In the new study,
Havel hopes to determine whether fructose is indeed "unrecognized by our
central nervous system."
Keim wants to find out if leptin helps boost metabolism, the rate at which we
burn calories. That happened in tests—done elsewhere—on laboratory
animals. Animals deficient in leptin burned more calories when they were given
additional leptin. And a study of leptin levels in young children showed that
those with higher leptin levels apparently burned more calories when they were
active.
Craig Warden will look for the effects of fructose on the activity of two
genes, UCP2 and UCP3. Both genes are thought to control how much
energy we expend, and thus, how many calories we burn.—By
Marcia
Wood, Agricultural Research Service Information Staff.
This research is part of Human Nutrition, an ARS National Program (#107)
described on the World Wide Web at http://www.nps.ars.usda.gov.
Nancy L. Keim is with the USDA-ARS
Western Human Nutrition Research
Center, One Shields Ave., Davis, CA 95616; phone (530) 752-4163,
fax (530) 754-4376.
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