The quality of a protein refers to its amino acid content. Specifically, how well will a protein source meet my needs for essential amino acids, the ones that my body cannot make itself.
When we eat the muscle, tissue, eggs or milk from another animal, it will have all of the amino acids we humans need—because we all have the same kind of tissues and protein needs. When we eat a plant protein, however, that is not the case. The plant does not need to make muscle cells or milk for the lactation of infants–so its amino acid composition will be different. A plant needs to make proteins for structure, enzyme functions and seed and nut production—so there will be some significant differences in amino acid content.
Milk and eggs are very high quality proteins because developing animals are capable of solely surviving and developing on the milk from their mothers. Eggs solely feed the development of the embryos of the poultry laying the eggs.
Ranking of the Protein Quality of Foods
From highest to lowest protein quality:
- Milk from any mammal, cheese, yogurt and other products made from that milk, including whey and whey powder; also lactose-free dairy products and lactose free yogurts. It includes the milk from cows, goats, yaks–and from any other mammal you can get milk from. (This category does not include soy milk, rice milk or almond milk–all of which are low quality protein sources.)
- Eggs from any land animal, usually from chicken and poultry, but also from fish and shellfish; any food made from eggs, like omelettes, custards, quiche, for example, and fish and shellfish eggs, such as caviar (sturgeon), salmon roe, trout roe, lobster roe, scallop roe.
- Protein from animals of the sea: fish, shellfish and mollusks, including salmon, cod, catfish, shrimp, lobster, scallops, mussels and clams, for example.
- Protein from land animals: cows, chickens, pigs, lamb and other poultry–the list is long, but it is beef in any form, chicken, pork, lamb, duck, Cornish hen, and turkey, as examples.
- Soybeans and products made from them, including tofu, miso, tempeh and soy milk and soy protein powder
- Beans other than soybeans and foods made from them, lentils and peas, hummus, kidney beans, fava beans, pinto beans, red beans, black-eyed peas, just to name a few.
- Nuts and seeds, including peanuts, almonds, walnuts, pecans, hazelnuts, peanut butter, almond butter, sesame seeds and tahini, sunflower seeds, pumpkin seeds, and many more. Almond milk is down here–quite low in protein amount and low in protein quality.
- Quinoa and other grains and foods made from them, including bread, tortillas, rice, noodles, and pasta to name the most common ones. Rice milk is way down here in the lower quality protein sources–it is no match for cow or goat milk.
- Starchy vegetables, then leafy vegetables–such as potatoes, corn, parsnips, sweet potato; leafy vegetables include artichoke, asparagus, carrots, cauliflower, collards, salad greens, sprouts, mushrooms, chard, tomatoes and turnips, to name some of them.
© 2012 Ann M. Del Tredici, MS, RD, CDE