The evidence-based recommendation for muscle building and maintenance is 1.6–2.2g of protein per kilogram of body weight per day, or approximately 0.7–1g per pound. For a 165 lb (75 kg) person, that works out to 120–165g per day — putting 150g squarely in the optimal zone.
Protein does three things nothing else can do at the gym. First, it provides the raw material (amino acids) for muscle repair after training. Second, it is more satiating per calorie than carbohydrates or fat, which helps with hunger management on any calorie target. Third, the thermic effect of protein is 20–30% — meaning your body burns 30 calories digesting every 100 calories of protein you eat, versus just 5–10 calories for carbs and fat.
Why not more — say 200g? Research shows muscle protein synthesis plateaus at approximately 1.8–2.2g/kg in most individuals. Eating beyond that adds calories without adding measurable muscle benefit. 150g is the sweet spot: above the minimum threshold for maximizing muscle protein synthesis, below the level where you are wasting money and digestion on excess protein.
The common mistake people make is front-loading protein in one or two large meals. Research from the Journal of Nutrition shows muscle protein synthesis is better stimulated by 4 meals of 30–40g than 2 meals of 75g each. Each meal in this plan is designed with that distribution in mind.
Quick reference — top protein-per-100g sources
Chicken breast31g
Lean sirloin steak31g
Canned tuna25g
Turkey breast29g
Salmon fillet25g
Lean ground beef26g
Cottage cheese11g
Greek yogurt10g
Eggs (per egg)6g