If your appetite is wrecking your diet, protein might help, new research shows.
Protein may help patrol the space between you, the fridge/menu/vending machine, and belt-busting eating habits.
You needn't banish carbohydrates from your plate, researchers write in the American Journal of Clinical Nutrition.
Of course, there's a catch. Forget about slathering protein in fat-laden sauces. Mind your calories, too, and expect more studies to probe the matter.
Still interested? If so, here are the appetite experiment's details.
Step No. 1: Full Disclosure
Nineteen healthy adults from Seattle took part. They were about 41 years old, on average. Average BMI (body mass index) was 26. That's overweight but not obese.
First, they wrote down every morsel they ate for three days. Then, they checked in with a dietitian to make sure they didn't skimp or gorge on carbs.
Next, they got a heads-up from the researchers, who included University of Washington endocrinologist David Weigle, MD.
Weight loss isn't the study's point, Weigle's team told subjects. Those hoping for weight loss were dismissed.
Step No. 2: Head to the Kitchen
Participants got carry-out meals -- and a few ground rules -- from the researchers.
Rule No. 1: Only eat the food provided. Rule No. 2: Eat all of it.
For the first two weeks, half of all calories came from carbs, 15% from protein, and 35% from fat. Then, protein was doubled and fat was halved. Carbs held steady throughout the study.
Step No. 3: Eat as Much as You Like
Four weeks into the study, the rules changed. The higher-protein foods remained. But subjects no longer had to eat all of it.
The instructions were simple: Eat when you're hungry. Stop when you're full.
Subjects were also told not to try to change food intake, physical activity, or body weight.
Step No. 4: Weighing the Results
Weight didn't change during the study's first two phases. But participants reported feeling fuller on the higher-protein diet.
When they didn't have to eat all the higher-protein food, they ate about 441 calories less per day. As a result, they lost nearly 11 pounds, about 8 pounds of which was fat.
Read WebMD's "The Benefits of Protein"
Protein vs. Carbs
The effect could partly explain why people lose weight on low-carb diets associated with high proteins, suggest the researchers.
"Our results suggest that less emphasis should be placed on carbohydrate restriction without regard for ... increases in dietary fat," write Weigle and colleagues.
"Replacing a portion of dietary fat with protein may result in weight loss comparable with that reported with low-carbohydrate diets while minimizing the adverse long-term effects of increased dietary fat," they continue.
However, more studies are needed on dietary protein's effects on kidney function and calcium before high-protein diets can be widely recommended for weight loss, they write.
Read WebMD's "Top 10 Protein Foods"
Appetite-Related Hormones
Blood tests were done to check levels of two appetite-related hormones: leptin and ghrelin.
On the eat-any-amount, higher-protein diet, leptin fell and ghrelin rose.
That's the opposite of what might be expected, write the researchers. Ghrelin is thought to increase appetite, while Leptin is thought to decrease it. However, many cases of obesity are resistant to the hormone leptin.
Read WebMD's "Why Do Low-Carb Diets Cause Weight Loss?"
What About the Real World?
The participants didn't have to plan, shop, chop, or bake. But the foods weren't exotic or elaborate.
A sample high-protein breakfast was orange juice, egg white substitute, raisin bread with peanut butter and jam, and skim milk.
Lunch was a turkey sandwich with "light" cheese, fat-free mayo, and lettuce on whole-wheat bread, served with more skim milk.
Dinner was beef lasagna, green beans, and lettuce-and-tomato salad dressed in olive oil and wine vinegar. Snacks were canned mandarin oranges and pineapple.
See a health care provider for guidance on nutrition, weight, and activity issues.
By Miranda Hitti, reviewed by Brunilda Nazario, MD
SOURCE: Weigle, D. American Journal of Clinical Nutrition, July 2005; vol 82: pp 41-48.