By Marie Spano, M.S., R.D., Contributing Editor
Protein is a key trend that continues to gain steam. It’s essential for building and repairing all body tissues, and may help with weight loss and maintenance. And plant-based proteins can both fulfill consumers’ protein needs and allay eco-friendly consciences.
Proteins can provide 22 amino acids, but only eight are essential. Without adequate intake of the eight essential amino acids, the body will break down muscle tissue to meet its protein needs. A protein that contains all eight essential amino acids is considered a complete protein. All animal proteins are complete, whereas only some plant sources are complete. Nutritionally speaking, though, plant proteins can meet our protein needs while providing additional health benefits.
Protein efficiency ratio (PER) and, more commonly, protein digestibility-corrected amino acid score (PDCAAS) are used to compare protein source,. PER is determined by feeding growing young animals a test protein for 28 days and measuring weight gain. However, PER can vary among different species or even within a given species, and this measure does not take into account the protein required for tissue maintenance (“CRC Desk Reference for Nutrition," 2nd Edition, 2006). In addition, PER overestimates the value of some animal proteins and underestimates the value of some vegetable proteins for human growth (Food Technology, 1994; 48:74-77).
PDCAAS is an internationally used measure that takes into account the protein’s ability to supply the essential-amino-acid requirements of humans corrected for its digestibility (the amount of protein that is absorbed) and its ability to supply the FAO/WHO amino acid requirements for 2 to 5 year olds. The PDCAAS is calculated based on the essential amino acid present in the lowest quantity; the highest PDCAAS score is 1.0 (Protein Quality Evaluation, FAO Food and Nutrition Paper 51, 1991; Protein and Amino Acid Requirements in Human Nutrition, Report of a Joint WHO/FAO/UNU Expert Consultation, Geneva, Switzerland, 2007).
Soy protein concentrate and soy protein isolate are complete proteins with a PDCAAS of 0.99 and 0.92, respectively. In addition to providing all eight essential amino acids, soy is packed with phytochemicals (Journal of Agricultural and Food Chemistry, 2010; 58:8,199-8,133).
According to Michelle Braun, nutrition science specialist, Solae, St. Louis, soy protein offers the unique health advantage “of helping reduce the risk of heart disease, by lowering total and LDL-cholesterol levels, when 25 grams per day is consumed as part of a diet low in saturated fat and cholesterol." In addition, soy protein, when taken after a bout of resistance training, can effectively stimulate the process of muscle protein synthesis (Current Opinions in Clinical Nutrition and Metabolic Care, 2009; 12:66-71).