A high-protein diet is often recommended by nutritionists to help build muscle and lose fat.
Such a diet may include tuna, salmon fillet, chicken breast, steak, peanuts, and green soybeans.
However, a recent study published in Cell Reports shows that eating too much protein reduces an important health benefit of weight loss: improvement in insulin sensitivity, which is critical to lowering diabetes risk.
Researchers from Washington University School of Medicine in St. Louis conducted the study. They recruited 34 women who were 50-65 years old.
All women had body mass indexes (BMI) of at least 30, indicating significant obesity. None of them had diabetes.
These participants were randomly assigned to 3 groups: one group ate a high-protein diet that helped lose weight; one group ate a weight-loss diet that included the recommended daily allowance of protein, and one group just maintained their body weight.
The whole study lasted 28 weeks. Researchers found that the women who ate recommended amount of protein showed a big improvement (25-30%) in their insulin sensitivity.
However, in women who ate high-protein diet, this metabolic benefit was gone.
Researchers suggest that the improvement in insulin sensitivity can help lower the risk of diabetes and cardiovascular disease.
Many women who try to lose weight hope to lose more fat tissue and less lean tissue. It is thought that high-protein food can help them achieve that.
The finding of the study shows that high-protein diet may help with the goal, but the cost is also big: the metabolic benefits from weight loss are eliminated.
This means even though people can lose weight, their physical health is not improved as much as that in people who ate regular-protein food.