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.
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.
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.