Best Protein Sources for Building Muscle: Complete vs. Incomplete Proteins

When I started lifting seriously, I thought protein was protein. Chicken, beans, peanut butter—all the same, right? Then I learned about amino acid profiles, leucine content, and protein quality. It turns out not all proteins are created equal, even if the gram count looks similar on paper.

Here's what you need to know about choosing protein sources for optimal muscle building.

What Makes a Protein "Complete"?

Proteins are made of amino acids—20 in total, with 9 being "essential," meaning your body can't make them. You have to get them from food.

Complete proteins contain all 9 essential amino acids in adequate amounts. Most animal proteins are complete.

Incomplete proteins are missing or low in one or more essential amino acids. Most plant proteins fall into this category.

For muscle building, you need all the essential amino acids, especially leucine, which triggers muscle protein synthesis more than any other amino acid.

The Protein Quality Hierarchy

Not all proteins stimulate muscle growth equally. Here's a rough ranking based on amino acid profile, leucine content, and digestibility:

Tier 1: Optimal

• Whey protein (highest leucine, fast-digesting)
• Eggs (excellent bioavailability, complete profile)
• Lean beef (high-quality, iron and creatine bonus)
• Chicken breast (lean, complete, versatile)
• Fish (complete, omega-3 bonus from fatty fish)
• Greek yogurt (complete, convenient)

Tier 2: Very Good

• Cottage cheese (slow-digesting casein)
• Turkey
• Pork tenderloin
• Milk
• Casein protein

Tier 3: Good

• Legumes + grain combinations (complete when combined)
• Tofu and tempeh (soy is relatively complete for a plant)
• Edamame
• Seitan (high protein, but not complete)

Tier 4: Supplementary

• Nuts and nut butters (incomplete, high fat)
• Seeds
• Most vegetables (very low protein content)

The Leucine Factor

Leucine is the key amino acid for triggering muscle protein synthesis. To maximally stimulate muscle growth, you need about 2.5-3g of leucine per meal.

Leucine content per 30g protein:

• Whey protein: ~3.5g
• Eggs: ~2.5g
• Beef: ~2.4g
• Chicken: ~2.3g
• Milk: ~2.2g
• Soy: ~2.0g
• Beans: ~1.8g

This is why whey protein is popular post-workout—it's the highest leucine source available.

Plant-Based Protein: Making It Work

Can you build muscle on a vegetarian or vegan diet? Absolutely. But it requires more planning.

Challenges with plant proteins:

• Lower leucine content per gram of protein
• Often incomplete (missing essential amino acids)
• Lower digestibility (you absorb less of what you eat)
• Higher volume needed to hit protein targets

Solutions:

Combine sources: Rice and beans together form a complete protein. You don't need to eat them in the same meal—just within the same day.

Eat more total protein: Because plant proteins are less efficient, aim for the higher end of recommendations (1.0-1.2g/lb bodyweight).

Include soy: Tofu, tempeh, and edamame are relatively complete and have decent leucine content.

Consider plant protein powder: Pea protein + rice protein blends have good amino acid profiles.

Protein Digestibility and Bioavailability

How much protein you eat isn't the same as how much your body actually absorbs and uses.

DIAAS scores (higher is better):

• Eggs: 1.13
• Milk: 1.14
• Beef: 1.11
• Chicken: 1.08
• Soy: 0.90
• Peas: 0.82
• Beans: 0.63
• Wheat: 0.45

Animal proteins generally score higher because of better amino acid profiles and digestibility. This doesn't mean plant proteins don't work—they just require eating more to compensate.

Practical Recommendations

For most people: Include a variety of protein sources. Don't stress about optimizing every meal, but prioritize at least 2-3 servings of high-quality protein (chicken, eggs, fish, beef, dairy) daily.

For vegetarians: Eggs and dairy can provide high-quality complete proteins. Include them regularly.

For vegans: Combine protein sources (legumes + grains), include soy regularly, consider eating slightly more total protein, and potentially use a quality plant protein blend supplement.

My Go-To Protein Sources

Here's what makes up most of my protein intake:

Daily staples:

• Eggs (breakfast)
• Chicken breast (lunch or dinner)
• Greek yogurt (snack)
• Whey protein (convenience/post-workout)

Regular rotations:

• Salmon (2-3x per week)
• Lean beef (2-3x per week)
• Cottage cheese (before bed sometimes)

Occasional:

• Turkey, pork, shrimp, other fish

This gives me variety, hits all my amino acid needs, and stays within budget.

Don't Overcomplicate It

While protein quality matters, don't stress about optimizing every gram. If you're eating 0.7-1.0g protein per pound of bodyweight from a variety of sources, you're almost certainly getting everything you need.

The hierarchy matters most when:

• You're eating minimal protein (every gram counts)
• You're plant-based (need to be strategic about sources)
• You're an advanced athlete trying to optimize everything

For most people, eating enough total protein from varied sources is 90% of the game.

The Bottom Line

All protein sources can contribute to muscle building, but quality varies. Animal proteins generally have better amino acid profiles and digestibility. Plant-based athletes can absolutely succeed but need to be more strategic. Focus on getting adequate total protein from a variety of sources, and you'll be well-covered.