The body makes adaptations to survive. Don’t eat enough and the body will catabolize calorie-consuming lean body tissue to lower your metabolism. Lift weights and the body will build lean muscle and raise your metabolism. In order for that to occur sufficient protein must be consumed. To fight the resulting lower metabolism of a restrictive diet it makes sense to lift weights and consume adequate protein to keep your metabolism up.
From this study, More Protein Combined With Exercise May Lead to Weight Loss and Muscle Gain | McMaster University Research Snaps this quote:
“Weight loss regimes that involve a low-calorie diet result in a major loss in fat mass, but can also cause a loss in muscle mass.”