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.
"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.
It is published in PloS One.
The 'Protein Leverage' Effect
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.
Figuring Out Protein Needs
"Aiming at 15%-25% of total energy intake as protein seems about right for a moderately active person," Gosby says. "The take-home message is to avoid foods high in fat and simple sugars, as recommended in current dietary guidelines. These foods dilute the proportion of protein in the diet." And that can encourage people to overeat, take in too many calories, and gain weight.
So how to figure out if you're eating a diet that typically includes 15% protein?
If you eat 2,000 calories a day to maintain weight, a 15% protein diet would include 300 calories as protein, Gosby says. That translates to about 75 grams of protein. One gram has 4 calories.
Her suggested menu to keep protein at 15%:
- A bowl of cereal, piece of fruit, toast, banana, and orange juice. That provides 48 calories of protein or 12 grams, total.
- For lunch, a slice of ham and cheese with salad on a roll, yogurt, and a piece of fruit. That provides 28 grams of protein or 112 calories.
- For dinner, a piece of chicken, vegetables, mashed potato, and ice cream with fruit -- one scoop. That provides 148 calories, or 37 grams of protein.
If you skip the yogurt and eat a chocolate bar and eat cake instead of fruit with your ice cream, then add two soft drinks, your protein intake will stay at about 300 calories, she says. "But your total energy intake will have increased by approximately 600 calories."
Diekman offers this guide: Six servings of whole grains give you 18 of your 75 grams of protein, while 3 cups of dairy give you 24 grams.
One co-author of Gosby's reports receipt of a fee from the Rosemary Conley Diet and Fitness Company for lectures and articles.