The best diet for weight loss with muscle maintenance is also the safest diet and one that can be followed for a lifetime. This type of diet:

Restricts calories by 300-500 daily, aiming for a 1-2 pound weekly weight loss but not so low that the body goes into starvation mode.
Encourages a fitness program to boost metabolism and health benefits.
Allows for a variety of foods to meet the body’s nutritional needs.
As far as the breakdown of carbs/protein/fat, a good range would be:
Carbs; 45-65%
Protein; 10-35%
Fat: 20-35%.

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