January 18, 2011 – Article
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).
Soy is also versatile. Functional products can include soy flour, tofu, soy nuts or textured vegetable protein (soy is typically an ingredient), which comes in flakes, granules and chunks. “Soy protein can be formulated in a wide array of products, including nutrition bars, meal-replacement bars, ready-to-drink and dry-blended beverages, cereals, bakery products, veggie burgers, ice cream, and much more," notes Braun. “It can be formulated in combination with other proteins or as the sole protein source in a product."
Tree nuts and peanuts
Though tree nuts are loaded with healthy compounds, including antioxidants, phytosterols, vitamins, minerals, monounsaturated fatty acids and fiber, their protein quality is relatively poor. Almonds and pistachios are among the higher-protein tree nuts, with 6 grams per 1 oz. of raw nuts. The PDCAAS of tree nuts ranges from approximately 0.40 to 0.43.
Peanuts are also packed with vitamins and minerals, and they have more protein than tree nuts with a PDCAAS of 0.52.
Grain, legumes and seeds
Grains are a good source of fiber and several B vitamins, as well as iron, magnesium and selenium. However, grains score low on protein quality. The PDCAAS of whole wheat is 0.42, wheat gluten scores at 0.25 and rolled oats are 0.57 (“Reference Manual for U.S. Whey and Lactose Products"). There are, however, a few grains that are complete proteins, including buckwheat and quinoa.
Like all plant-based foods, beans are packed with good nutrition, including vitamins, minerals and fiber. The PDCAAS for lentils, canned garbanzo beans and black beans are 0.52, 0.69 and 0.75, respectively (“Reference Manual for U.S. Whey and Lactose Products").
Pea protein is being added to various food products, including baked goods, snacks, cereals, condiments, meats and beverages. “Pea protein extracted from the yellow pea is naturally low in anti-nutritional factors such as trypsin inhibitors, phytoestrogens and oligosaccharides," notes Harshal Kshirsagar, Ph.D., business development project coordinator, Roquette America, Inc., Lebanon, OH. The company’s pea protein undergoes a manufacturing process that further reduces and/or eliminates these anti-nutritional factors. He says the pea protein “has excellent digestibility (over 98%) coupled with a well-balanced amino-acid profile. The adult PDCAAS value is 0.93."
A newer source of protein―at least for human nutrition―is canola. Processor have developed methods to produce canola isolate with a balanced amino acid profile with adequate levels of all the essential amino acids (PDCAAS scores over 1.00.) The isolates are high in sulfur-containing amino acids (methionine and cysteine) compared to other vegetable proteins, have low levels of anti-nutritionals, and are free of phytoestrogens.
Canola proteins are poised for use in U.S. products. One canola protein company has completed the GRAS notification process with no objections, “somewhat clearing the way for other companies, such as ourselves," says David T. Balke, Ph.D., food applications specialist, BioExx Specialty Proteins Ltd., Toronto, Ontario. He says the company’s canola protein ingredients have self-affirmed GRAS and have “initiated convening a GRAS review panel so that we may start the FDA GRAS notification process."
Flax and hemp are both complete proteins. In addition to their protein, flaxseeds are also rich in dietary fiber (lignans), which may act as antioxidants, thereby helping decrease damage caused by free radicals. Also, flax contains the two essential fats, omega-6 linoleic acid and omega-3 alpha-linolenic acid (Molecular and Cellular Biochemistry, 2000; 209:89-96). Plus, flax is naturally gluten-free.
Both whole and ground flaxseeds have been formulated into several products, including pasta, breads, cereals, crackers, energy bars, pancake and waffle mixes, animal feed (which will boost the omega-3 content of eggs), snack foods, and instant oatmeal. But, “the Flax Council of Canada recommends routine consumption of ground flax over whole flaxseeds, because the smaller particles of ground flax allow for the absorption of more nutrients," notes Diane H. Morris, Ph.D., nutritionist and consultant, Flax Council of Canada, Winnipeg, Manitoba.
Hemp seed is rich in several vitamins and minerals and also contains a good bit of dietary fiber. In addition, the PDCAAS of whole hemp, hemp meal and dehulled hemp seed ranges from 0.49 to 0.66 (Journal of Agricultural and Food Chemistry, 2010; 58:11,801-11,807).
Though many plant-based proteins score lower than animal sources (eggs, whey and milk all have a PDCAAS of 1.00), several plant foods are good sources of quality protein or can be combined to boost the nutrition value, including the protein content (and essential amino acid mix). For instance, dry beans and rice are both incomplete proteins, but together they provide all of the essential amino acids. Likewise, adding chopped pistachios to a muffin or bread will increase the protein content and provide a different array of amino acids while adding flavor and texture.
Marie Spano, M.S., R.D., CSCS, CSSD, is a nutrition communications expert and food industry consultant. Marie writes for popular press magazines and trade publications, has given cooking demos on NBC, ABC, FOX and CBS affiliates and helps companies formulate healthy products. For more information, visit mariespano.com.