I have been reading through this new study which compares a high versus medium protein diet and exercise. It seems to me that the title is misleading, "Moderate protein intake improves total and regional body composition and insulin sensitivity in overweight adults," because in almost every measure the high-protein diet performs better.
If you look at the research over the past few years, you see that scientists are slowing increasing the protein intake of diets with no ill effects. In fact, higher protein intake almost always leads to a wide variety of positive changes in patients with the metabolic syndrome.
The old bodybuilding rule of thumb is to get 1 gram of protein per pound of bodyweight. What I'm wondering is if this is the optimal protein level, whether a person is a bodybuilder or not. In the study mentioned above, the protein intake was 40% of calories - quite a departure from the normal low-fat nonsense. And this diet led to significant decreases in insulin, leptin, body fat, and on down the line. I would like to see further studies to study if high protein intakes can slow sarcopenia and other conditions that usually accompany aging.