Despite inconsistent results in the literature, high protein diets are being promoted for the management of metabolic syndrome parameters primarily due to their proposed favorable effects on weight loss. Therefore, lean and fa/fa Zucker rats were given normal and high protein diets with varying protein sources for 12 weeks. A high protein diet with a mixture of animal and plant protein sources was the most effective for improving metabolic syndrome parameters, specifically insulin resistance and hepatic steatosis. A high protein soy diet was the second most effective diet, while a high protein casein diet demonstrated no benefits compared to the other two high protein diets and minimal benefits compared to a normal protein casein diet. Interestingly, high protein diets did not affect body weight regardless of protein source. These findings suggest that the source of protein within a high protein diet is critical for improving metabolic syndrome parameters and that improvements can be observed independent of weight loss.