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By Mark Messina, PhD, MS
Concentrated sources of soy protein, commonly referred to as soy protein products (SPPs), are widely used by the food industry for their functional properties, such as enhancing moisture content and increasing shelf life.1-4 These concentrated sources of protein, which include isolated soy protein (ISP), soy protein concentrate (SPC) and soy flour (also textured soy protein or textured vegetable protein), are also used to increase the protein content of a wide variety of products such as energy bars and breakfast cereals. These protein sources form the basis for creating a variety of meat analogues, such as soy burgers, which have become increasingly popular as more people opt to consume plant-based meals. By definition, ISP, SPC and soy flour are approximately 90%, 65% and 50% protein, respectively (See Table 1)
Despite surveys indicating consumer interest in increasing protein intake, in recent years, there has been some resistance against consuming foods that contain SPPs. This resistance has occurred at the individual level as well as the institutional setting. There is no question that the SPPs are viewed very differently than traditional Asian soyfoods, such as tofu and miso. In some cases, institutions have balked at using products to which soy protein has been added on the grounds that these soy protein-enhanced products are inconsistent with the public’s desire to consume “clean label” foods. Since the SPPs began being added to meat products in the 1960s/1970s as a cost-saving measure (the cost of beef increased dramatically in the early 1970s), it is not surprising that products to which soy protein were added were initially viewed as inferior. However, that perception of these products is without scientific merit.
To some extent, differentiating the traditional soyfoods from the SPPs makes nutritional sense. Virtually all nutritionists and dietitians recommend emphasizing the consumption of whole foods and minimizing the intake of highly refined products. However, more often than not, refinement refers to the effect of processing on the carbohydrate content of a food. As a result of processing, there are clear differences in nutrient and non-nutrient content between the traditional soyfoods and the SPPs. For example, many of the SPPs are devoid of fat and fiber, and some are very low in isoflavones. SPPs are, as the name suggests, primarily sources of protein.
Today, soy protein can be found in many products of questionable nutritional value. However, the value of the products to which soy protein has been added needs to be separated from the value of the SPPs. Concerns about the use of SPPs in institutional settings are not new. Forty years ago, it was claimed that adding soy protein to meat lowered the protein quality of the soy-enhanced product.5 However, that impression was based on rodent assays which are now known to undervalue legume proteins such as soy. Current assays show that the quality of soy protein is similar to or higher than the quality of meat protein.6,7Thus, not only is protein quality not compromised when SPPs are added to meat, from a functional perspective, the organoleptic properties are likely enhanced as a result.
While it is difficult to say precisely what constitutes a “clean label,” the interest in eating this way is increasingly tied to concerns about the environmental impact of the foods we eat. Therefore, it is ironic that at a time when the impact of dietary choices on the environment are beginning to influence consumer purchases, soy protein-enhanced meat products are actually perceived as being less environmentally friendly. It is well established that soybeans are an especially efficient means of producing protein8 and life-cycle assessments show that the SPPs are also an environmentally efficient means of delivering protein even though they require additional processing in comparison to the whole soybean.1
Soy protein is one of the eight foods responsible for 90% of all food allergic reactions in the United States.9 As such, product labels require that the presence of soy protein be indicated. The widespread use of SPPs does require that soy allergic-individuals be especially observant. However, the eight foods that require being labeled are not equally allergenic. In fact, surveys suggest that only about 1/2,500 adults have a doctor-diagnosed soy allergy.10 Therefore, relatively few people will be inconvenienced by the use of SPPs.
It is hard to identify all of the objections to the use of SPPs but lack of long term safety data should not be one. Several long-term trials that have intervened with far more soy protein than would likely be consumed via soy protein-enhanced products have not revealed any significant adverse effects.11,12Notably, soy infant formula produces normal growth and development according to the American Academy of Pediatrics.13 Infants using soy infant formula consume far more soy protein on a body weight basis than could realistically be consumed via the consumption of foods containing soy protein.
In conclusion, SPPs are widely used by the food industry for their functional attributes. When used primarily to increase protein content, protein quality is definitely not compromised nor are any environmental advantages sacrificed.
1. Thrane M, Paulsen PV, Orcutt MW, Krieger TM. Soy protein: Impacts, production, and applications. In: Nadathur SR, Wanasundara JPD, Scanlin L, eds. Sustainable Protein Sources. United Kingdom: Academic Press; 2017:23-46.
2. Singh P, Kumar R, Sabapathy SN, Bawa AS. Functional and edible uses of soy protein products. Comprehensive Rev Food Sci Food Safety. 2008;7:14-28.
3. Endres JG. Soy protein products: Characteristics, nutritional aspects, and utilization. Champaign, IL: AOCS Press; 2001.
4. Maningat CC, DeMeritt J, G.K, Chinnaswamy R, Bassi SD. Properties and applications of texturized wheat gluten. Am Assoc Cereal Chem. 1999;44:650-5.
5. Murphy WB. Some things you might not know about the foods served to children. Nutr Today. 1972;7:34-5.
6. Hughes GJ, Ryan DJ, Mukherjea R, Schasteen CS. Protein digestibility-corrected amino acid scores (PDCAAS) for soy protein isolates and concentrate: Criteria for evaluation. J Agric Food Chem. 2011;59:12707-12.
7. Rutherfurd SM, Fanning AC, Miller BJ, Moughan PJ. Protein digestibility-corrected amino acid scores and digestible indispensable amino acid scores differentially describe protein quality in growing male rats. J Nutr. 2015;145:372-9.
8. González AD, Frostell B, Carlsson-Kanyama A. Protein efficiency per unit energy and per unit greenhouse gas emissions: Potential contribution of diet choices to climate change mitigation. Food Policy. 2011;36:562-70.
9. Bousquet J, Bjorksten B, Bruijnzeel-Koomen CA, et al. Scientific criteria and the selection of allergenic foods for product labelling. Allergy. 1998;53:3-21.
10. Vierk KA, Koehler KM, Fein SB, Street DA. Prevalence of self-reported food allergy in American adults and use of food labels. J Allergy Clin Immunol. 2007;119:1504-10.
11. Hodis HN, Mack WJ, Kono N, et al. Isoflavone soy protein supplementation and atherosclerosis progression in healthy postmenopausal women: a randomized controlled trial. Stroke. 2011;42:3168-75.
12. Kok L, Kreijkamp-Kaspers S, Grobbee DE, Lampe JW, van der Schouw YT. A randomized, placebo-controlled trial on the effects of soy protein containing isoflavones on quality of life in postmenopausal women. Menopause. 2005;12:56-62.
13. Bhatia J, Greer F. Use of soy protein-based formulas in infant feeding. Pediatrics. 2008;121:1062-8.
Mark Messina, PhD, MS, is the co-owner of Nutrition Matters, Inc., a nutrition consulting company, and is an adjunct professor at Loma Linda University. His research focuses on the health effects of soyfoods and soybean components. He is chairman of The Soy Connection Editorial Board and executive director of the Soy Nutrition Institute.
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