Complete vs. Incomplete Protein
Proteins are made of amino acids, nine of which are "essential" — meaning your body can't make them and must get them from food. A complete protein contains all nine essential amino acids in adequate proportions. Animal proteins (meat, fish, dairy, eggs) are complete. Most plant proteins are "incomplete," meaning they're low in one or more essential amino acids.
This doesn't mean plant proteins are inadequate for health — it means you need to consume a variety of plant proteins to ensure you get all essential amino acids. The classic example is rice and beans: rice is low in lysine, beans are low in methionine, but together they provide a complete amino acid profile.
Cost Per Gram of Protein: Rankings
| Food Source | Protein per serving | Cost/serving | Cost per gram protein |
|---|---|---|---|
| Eggs (large, grocery store) | 6g per egg | ~$0.15/egg | ~$0.025/g |
| Canned tuna (chunk light) | 25g per can | ~$0.75/can | ~$0.030/g |
| Whey protein powder | 25g per scoop | ~$0.75/scoop | ~$0.030/g |
| Canned chicken breast | 26g per can | ~$1.50/can | ~$0.058/g |
| Chicken breast (fresh, bulk) | 31g per 4 oz | ~$1.50 per serving | ~$0.048/g |
| Greek yogurt (non-fat, store brand) | 17g per cup | ~$0.80/cup | ~$0.047/g |
| Canned chickpeas/black beans | 7g per 1/2 cup | ~$0.25/serving | ~$0.036/g |
| Lentils (dry, cooked) | 9g per 1/2 cup cooked | ~$0.20/serving | ~$0.022/g |
| Tofu (firm) | 10g per 3 oz | ~$0.50/serving | ~$0.050/g |
PDCAAS: Measuring Protein Quality
The Protein Digestibility-Corrected Amino Acid Score (PDCAAS) is the FDA's standard for measuring protein quality. It accounts for both amino acid completeness and digestibility. Scores range from 0 to 1.0:
- Score 1.0: Whey, eggs, casein, soy, quinoa
- Score 0.9–0.95: Beef, chicken, fish, dairy
- Score 0.5–0.7: Legumes, grains (individually)
Soy protein is notable as the only plant protein that scores 1.0 on PDCAAS — making it a complete, high-quality protein source equivalent to animal proteins.
Practical Budget Protein Strategy
For maximum protein per dollar:
- Eggs: Most affordable complete protein. Versatile, nutrient-dense, and fast to prepare.
- Canned tuna and canned chicken: Shelf-stable, no preparation, excellent protein density.
- Lentils and canned beans: Cheapest protein available, with the bonus of fiber. Pair with a grain for complete amino acids.
- Plain Greek yogurt (store brand): Doubles as a snack with good protein density; also provides calcium and probiotics.
- Whey protein: Excellent cost-per-gram when bought in bulk (5 lb bags); useful for hitting protein targets without a lot of food volume.
Protein Combining for Plant-Based Diets
You don't need to combine complete proteins at every meal — your body maintains an amino acid pool that averages across your daily intake. However, consistently eating a variety of plant proteins (legumes + grains, nuts/seeds + legumes) across the day ensures you meet all essential amino acid needs. Soy, quinoa, buckwheat, and hemp seeds are complete plant proteins that don't require combining.