Every body is different. As a result everyone has different macro nutrient needs. Some need more and others need less. Protein is the macro nutrient behind preserving lean mass. Protein helps the dieter maintain muscle while losing weight. There is no single rule as to how much protein an individual should be consuming. Rather there is a formula to figure this out.
To start have people find a body composition scale and measure their current body weight. We calculate this number in pounds and multiply it by .8 to find out daily protein requirements. This is the minimum amount of protein the dieter should eat in order to preserve their lean mass. For example if someone ways 200 lbs they should be eating a minimum of 160 grams of protein per day.
When following these steps, it is important you use a body composition scale and not a regular one. This way you will be able to monitor your lean mass. Monitoring lean mass tells you what adjustments to make to your daily protein intake. If your lean mass is going down, you likely need to add some protein to your diet. My favorite form to add is protein water. Simply because it has 20 grams of protein and 0 carbs. Oh and it tastes great!