Oct. 12, 2011 -- Counting calories may not be enough to manage either your appetite or your weight, new research suggests.
Paying attention to the percent of calories from protein may be an important key, according to Alison Gosby, PhD, a postdoctoral researcher at the University of Sydney. Protein and weight control may go together, suggests her research. It echoes others' findings.
In her study, she found that men and women fed a 10% protein diet ate 12% more calories over four days than they did on a 15% protein diet.
"Any dietary intervention that results in dilution or restriction of protein in the diet will promote overeating in an environment where food is abundant," she tells WebMD.
While many experts believe that protein content in the diet plays an important role in determining how many calories we eat, and how hungry we are, the new study lends some solid numbers to that idea.
Gosby and other researchers believe that people have an especially strong appetite for protein.
When protein in the diet goes too low, ''We keep eating in an attempt to attain our target level of protein," Gosby says. This is known as the protein leverage effect. Some think low protein levels in the diet may help drive the obesity epidemic. From 1961 to 2000, other research shows, the U.S. diet declined from 14% protein to 12.5%.
Gosby asked lean men and women, average age 24, to eat diets with three different protein contents: 10%, 15%, and 25%. A diet that is made up of about 15% protein is often recommended.
The men and women ate each of the three diets for four days at the research center. They had unrestricted access to other food besides the fixed meals they were given. What they ate was recorded.
As the protein declined to 10%, the men and women tended to eat more carbohydrates and fat-containing food, boosting the risk for weight gain. But Gosby found that increasing the protein from 15% to 25% didn't seem to make any difference in total calories eaten.
The final analysis reported on 22 men and women, all very lean. Their average body mass index (BMI) was 21.8. A healthy BMI is from 18.5 to 24.9.
"This study provides a bit more support -- [but] it is a short-term study -- that consuming protein helps us feel full longer," says Connie Diekman, RD, director of university nutrition at Washington University in St. Louis. She reviewed the study findings for WebMD.
"So including some [protein] each time we eat can help us make better food choices and trim what we eat the next time we eat," she says.