September 28, 2005
SIUC scientists test theory on lab rats Once disparaged, eggs may help control appetite
CARBONDALE, Ill. -- Egg white — no yolk! — may have some fat-fighting ability.
In a study that ended last fall, nutritionists at Southern Illinois University Carbondale fed high-fat, high-sugar meals that also included dried egg white to both fat rats and lean rats over nine weeks.
"The egg protein prevented the fat rats from getting fat," said D. Allan Higginbotham, an assistant professor of animal science, food and nutrition in SIUC's College of Agricultural Sciences.
"At the end of the study, they had the same body fat as the lean rats."
Higginbotham, who is also a registered dietician, has long wondered about the relationship between our weight and the food we eat.
"What I'm interested in is how our bodies control how much we eat and what happens to interrupt that control and cause us to get fat," he said.
"It's been known for several years that if you take rats and feed them a concentration of protein just below their requirement, they will overeat. Theoretically, they're compensating for the reduced protein.
"Part of my dissertation was to determine if that reduced protein changed their natural ability to control their food intake. We showed that instead it changed their sensitivity to leptin (a hormone made by fat cells that regulates food intake). With lower protein, they became less sensitive and therefore ate more."
The results of his doctoral research, which he completed in 2001, suggested a logical next step.
"I thought if we could find out whether different proteins cause different amounts of intake, we would be closer to finding out how protein controls the amount we eat," he said.
With funding from the U.S. Poultry & Egg Association and a small seed grant from the Council on Food and Agricultural Research, Higginbotham and colleagues William J. Banz and M. Javed Iqbal (who has since moved on) designed a study that called for feeding fat and lean rats a high-energy diet mixed with egg, milk or soy protein and keeping track of how much they ate.
"Not much work has been done comparing the appetite-suppressing effect of different protein types, and most of what has been done focused on milk or soy," Higginbotham said.
"Little has been done with egg protein, although it has been shown to be more effective than other proteins at suppressing food intake."
While genetically obese rats have been a staple in lab experiments for years, a new kind of fat rat would make the study's findings particularly useful.
"Other fat rats have a specific, defined, genetic mutation — a single gene that is messed up to cause them to get fat," Higginbotham said.
"This rat was bred from rats that naturally get fat, probably as a result of lots of genes that come into play — which is more like human obesity."
The lean rats, too, came from a line of rats that seldom gained weight no matter what they ate.
"In both the fat and lean rats, there's some variability in how fat or how lean each one becomes — once again, more like humans," Higginbotham said.
The SIUC researchers looked first at how rats on the different diets would do in the short run. In order to make sure the rats were hungry, the researchers didn't give them an evening meal.
The next morning's breakfast consisted of a liquid egg, milk or soy protein solution appetizer, followed 10 minutes later by a dish of high-fat, high-sugar rat food. Twenty-four hours later the researchers measured what the rats ate, finding that fat rats given the egg protein appetizer ate the same amount as the lean rats and less than their counterparts on milk or soy.
For the nine-week trial, the researchers took the high-fat, high-sugar rat chow and added egg, milk or soy protein to it, depending on which rats they were feeding. At the end of the nine weeks, fat rats on the egg-enhanced diet ate the same amount as the lean rats on that diet, and both fat and lean rats ate less than those rats given the food with milk protein. The egg-eating fat rats weighed less than those milk-fed rats, too.
"The milk protein caused the rats to get fat — even the lean ones," Higginbotham said.
The fat rats on soy ate more than both kinds of egg-fed rats, and they weighed more than the fat rats on the egg diet. In addition, the soy-fed rats had more body fat than the egg-fed rats.
"There were some other effects, however," Higginbotham said.
"The soy-fed rats had lower blood glucose, which may be an early indicator of resistance to developing diabetes."
The researchers presented their findings in April at the Federation of American Societies for Experimental Biology professional meeting in San Diego, Calif. They will be submitting an article based on this work to professional journals soon.
As for the next step, Higginbotham said the team is tinkering with the diet again.
"The high-sugar, high-fat diet was supposed to simulate an average American's diet," he said.
"This time, we're going to reduce the carbohydrates to try to simulate a fad, low-carb diet. These diets are very popular for weight loss, but the mechanism by which they work is still unknown. Understanding that mechanism is important to making recommendations to people who need to lose weight or want to avoid lifelong weight gain."
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