Protein Quality – Plant versus Meat Protein

Proteins are made of chains of amino acids, some of which can be made by the body, while others aren't (essential amino acids).

There are nine essential amino acids that have to be eaten and cannot be made by the body:

• Histidine

• Isoleucine

• Leucine

• Lysine

• Methionine

• Phenylalanine

• Threonine

• Tryptophan

• Valine

Plant-based proteins tend to be “incomplete” (poor amino acid profile) as they tend to have either no or low percentage of essential amino acid. Soy products and legumes are the closest to animal foods to be considered complete or of high quality. This does not consider the negative aspects of soy products, anti-nutrient issues of legumes and bioavailability of the protein/amino acids.

The branched-chain amino acids (BCAAs) are a group of three essential amino acids: leucine, isoleucine, and valine. BCAA supplementation is associated with building muscle, decreasing muscle fatigue and muscle soreness. For muscle health, the organ of longevity and metabolism, essential for glucose disposal and fatty acid oxidation, leucine is vitally important. Leucine stimulates the mammalian target of rapamycin (mTOR) complex which regulates cell growth, cell proliferation, cell motility, cell survival, protein synthesis, autophagy, and transcription and therefore generates muscle protein synthesis.

Muscle stimulation growth requires approximately 2.5 grams of leucine, which is included in about 30 grams of protein per meal. Let’s compare animal and plant protein (that is not leucine deficient).

To get 2.5 grams of leucine you could eat:

• 106 grams (3.7 ounces) of lean ground beef or

• 1.2-1.35 kg (7-8 cups) of quinoa or

• 120 grams (half a cup; 7.5 tablespoons; 22.5 teaspoons) of peanut butter

Plant protein tends to be low in leucine, lysine, and methionine. To compensate for this, if eating only plant protein (soy or wheat), you would have to eat 35 to 45 percent more of it, and this would result in excess calories and, ultimately, excess carbohydrates. This is also complicated by the bioavailability (digestibility) of plant proteins with plant foods digested less well compared with isolated proteins or animal proteins.

Digestible Indispensable Amino Acid Score (DIAAS), is a method of scoring protein quality. The Protein Digestibility-Corrected Amino Acid Score (PDCAAS) is another scale to evaluate protein quality and has been in use since the Food and Agriculture Organization, and the World Health Organization of the United Nations first published it in 1991 but does not evaluate and consider digestibility of each amino acid, just the protein.

As you can see, the plant protein quality is towards the lower end of the scale, and the animal proteins are at the upper end of the quality scale.

So yes, it is possible to get all the amino acids from plant-based protein, but it takes a lot of work and planning of meals.