Soy in Human Nutrition: Where Does the Research Stand in 2019?

The health benefits of consuming soy have been studied for over 50 years. In fact, among plant sources of protein, it is perhaps the most widely researched plant protein source in the world. Research has established its benefits for weight management, muscle health and more. Despite this large and growing body of evidence, the health implications of consuming soy in human nutrition continue to be debated as public opinion and understanding of nutrition evolve.

Soybeans are a complex food and often found in the food supply as an ingredient. The soybean is a legume in the same family as sugar snap peas or green beans. However, unlike these legumes, consumers encounter soybeans in the food supply in a wide range of food and beverage products. Soybeans can be consumed whole as edamame; however, people typically consume soy in the form of an ingredient added to a variety of food products or as traditional soy foods, such as tofu or soymilk.¹

Consumers are familiar with how sweet corn from a field ends up on their plate, but how a soybean arrives at the table in sauces, sides, snacks, beverages and center-of-plate dishes may be less understood. Creating food products from soybeans requires different processes to capitalize on the lipids, protein, carbohydrates and other components of the bean. The path of the soy value chain can be hard to follow for the everyday consumer, or even the soybean purchaser, which leads to confusion and misinformation.

This report details recent research and input from industry experts to discuss the known, scientifically supported health impacts of consuming soy. It also examines how new scientific findings are changing the perception of soy foods in the United States and abroad. Addressing common concerns about soy nutrition starts with building a common understanding of soybean components.

Soybeans and Food

• Whole soybeans — can be roasted, flavored and cooked.
• Soybean meal — an ingredient that includes all components of the soybean, except oil. Can be further processed into ingredients used for specific purposes.
  • Soy flour — toasted and ground.
    • Soy flour is made by toasting and grinding the meal. It is a source of protein, isoflavones, folate, iron and
    • Soy flour can be used as a protein-providing substitute for other flours to make items like cookies, breadsand more.
  • Textured soy protein — dehydrated soy flour.
    • TSP usually refers to products made from defatted and dehydrated soy flour, although the term also applies to textured soy protein concentrates and spun soy fiber. When hydrated, TSP absorbs flavors well and has a chewy, meatlike texture. It is available in powder form as well as chunks, slices and
    • TSP is often found in foods such as meats but used to cook with in vegan diets.
  • Soy protein powder — protein isolated from the soybean.
    • Soy protein powder as an ingredient can be used in recipes or for formulation of a variety of foods. It is available as soy protein concentrateor as soy protein isolate, depending on the purity of the protein product.
      • The general standard for soy protein products (Codex Alimentarius STAN 175-1989) is as follows:
        • Soy protein flour is a minimum of 50% to a maximum of 65% protein.
        • Soy protein concentrate is a minimum of 65% to a maximum of 90% protein.
        • Soy protein isolate is a minimum of 90% protein.
      • The starting material of isolated soy protein is the defatted flakes that remain after the oil is extracted. In the processing, most other portions are removed, leaving a highly concentrated source of protein.
      • As an ingredient, isolated soy protein is used in a variety of products where high-quality protein is desired, from infant formula to beverages for children, weight-managing adults or muscle-maintaining athletes.
      • Similar to isolate, soy protein concentrate has many uses and can boost the protein in nutrition bars, meats and meat analogues.
    • Soybean Oil
      • Liquid oil — vegetable oil extracted from the seeds of the soybean.
        • Foods: salad and cooking oils.
      • Hydrogenated — processed to improve shelf stability and preservation of an item.
        • Foods: shortening, margarine, packaged snacks.
      • Soy lecithin — extruded and dried.
        • Used as an emulsifier or stabilizer in processed foods.

 

Background

Soy in Asian Diets

Soy has been enjoyed around the world for many centuries, especially in Asia.

Traditional Asian soy foods can be broken down into two categories: fermented and unfermented. Fermented foods include miso, soy sauce and tempeh; unfermented foods include edamame, soy milk and tofu.

There has been considerable research interest in examining the relationship between soy intake and Asian cancer prevalence rates, which for many cancers tend to be lower than in the West.¹⁰There are also new health outcomes of interest that appeal to consumers in this region, such as research suggesting soyfoods may decrease wrinkles.

Consumer awareness and understanding of the health benefits of soy foods differ around the world as familiarity with many different types of soy products varies from region to region.

Soy Research

Because much research has been conducted to better understand the health benefits to humans from the consumption of soy, consumer interests have shifted over time. Michelle Braun, PhD, global protein and scientific affairs lead for DuPont, believes this is a positive thing because it demonstrates soy research has been far ahead in research compared to other food ingredients. “There is so much work that was conducted compared to protein sources, animal or plant,” she says. Braun adds advances in research methodology have been a positive step forward for soy research.

She echoes this by sharing the focus of soy nutrition has broadened and changed over the years, leading to wider consumer interest. “The health outcomes we are investigating have changed and are more aligned with current consumer needs,” Braun says. “Some consumers are choosing foods to support near-term health goals, such as feeling of fullness, weight management or lean muscle mass gains. Others choose foods to include in their diet for health concerns that are longer term, such as heart health or metabolic syndrome.”

Braun adds early studies often researched cancer and heart disease. These topics are still significant, but soy research has expanded. Braun says, “Topics like satiety, weight management and muscle health [are important]. These are some of the areas where we have new research to support consumer interests.”

Health Benefits from Soy Foods — Considerations for 2019 and Beyond

The health benefits associated with soy consumption are abundant, as are the studies that demonstrate these effects. From well-established benefits, like health, to emerging areas of research, the positive implications of adding soy to any diet are becoming more evident to consumers around the globe.

To some, questions about soy start with how it should be consumed. Recent trends, such as incorporating soy through plant-based diets and body building workouts, provide new avenues for soy inclusion.

Braun says that while people have traditionally consumed soy as tofu, soy milk and miso, today soy can be found in many mainstream, plant-based foods in the supermarket.

According to Innova Market Insights, global new product launches containing soy protein grew 9% annually from 2014-2018. Globally in 2018, over 7,000 new products were launched containing soy protein. Among the fastest growing categories for new launches containing soy protein included sports nutrition (nutrition bars and beverages), snacks and energy bars, meat substitutes and dairy alternatives.

Soy’s versatility drives its inclusion in so many foods today. Soy foods are packed with plenty of nutrients including B vitamins, fiber, potassium and magnesium, and also offer high-quality protein. Soy is considered a complete protein, containing all nine essential amino acids which the human body cannot make and must be obtained from the diet.

Consumers make food choices based on taste, price, nutrition andother trends. Exploring new consumer trends through research is important in helping consumers make healthy decisions.

Heart Health

Soy foods have long been recognized for their high protein and lower saturated fat content²⁰, but over the last 20 years,an impressive amount of research has evaluated the role these foods may have in reducing chronic disease risk.¹

According to the World Health Organization,cardiovascular diseases are the No. 1 cause of death globally.¹⁹Consuming soy protein as part of a diet low in cholesterol and saturated fat has been found to reduce the risk of heart disease. Diets containing soy protein can have a favorable impact on blood lipids, lowering low-density lipoprotein cholesterol, total cholesterol and triglycerides without lowering cardio-protective, high-density lipoprotein cholesterol.²²

Plant-Based Diets and Weight Management

In the consumer space, the conversation around soy has changed. “Recently, the trend for plant-based eating and its associated benefits has become a driving trend for new and existing product positioning,” Braun says.

Around the world, plant-based diets are becoming increasingly popular. The United States Department of Agriculture MyPlate initiative defines a healthy plate as one-halfplate of plant foods (non-starchy vegetables and fruits), one-quarter whole grains or unprocessed starchy food and one-quarter lean protein.⁵Recent research has shown that plant-based diets may also reduce the number of medications needed to treat chronic diseases and lower ischemic heart disease mortality rates.⁸

“There has certainly been a lot of innovation when it comes to plant-based diets in the meat alternative category,” Linda Funk says, executive director of The Soyfoods Council. “You’ll find a lot of soy protein in the products, and I think it’s important for farmers, consumers and manufacturers to understand why soy is a preferred plant protein[1]and a powerhouse of nutrients.”

Soy has been a part of vegan diets for years but now has become part of the larger movement toward plant-based diets. “Soy is the original plant-based protein,” Braunsays. “It enables the development of great-tasting alternatives that deliver protein nutrition. She offers soy milk as an example, which can be formulated to include the same amount of protein as dairy milk — 8 grams. Braun continues, “Some other plant-based milks have little to no protein, and what protein is present is often of lower quality.”

Further, research shows that protein intake, especially from high-quality sources such as soy, increases satiety. A 2015 study published in the Journal of Nutrition measured appetite and subsequent food intake, aiming to determine how a high-protein beef lunch compares to a high-protein soy lunch in terms of satiety. When comparing those two high-quality protein sources, the study found the type of protein consumed elicited veryfew differences in effect on appetite, satiety and food intake in healthy adults.¹⁵

Soy’s support of weight management goes beyond short-term satiety effects. Feeling fuller longer is important for a sense of well-being and helps people adhere to diets that support their weight loss or management goals. Higher-protein diets, especially those containing high-quality protein, have been shown to be effective at curbing food intake and promoting weight management. The evidence suggests that high-protein diets tend to preserve more lean body mass than high-carbohydrate diets during weight loss. Soy protein has been found to be as effective as other high-quality proteins at increasing satiety and promoting weight management while offering the additional advantage of promoting heart health.

The evidence is clear that higher-protein diets help preserve fat-free mass (FFM) or muscle during weight loss. Several studies have demonstrated soy protein is as effective as dairy and mixed protein sources for the retention of FFM during weight loss in adults. In fact, a daily supplement of soy protein reduces the gain in total abdominal fat and subcutaneous abdominal fat compared with a daily isocaloric casein placebo in post menopausal women.¹⁶An additional study using a similar approach found results of reduced abdominal fat among women supplemented with 20 grams of isolated soy protein.¹⁷While soy protein is on par with other high-quality proteins in producing satiety and promoting weight loss, it offers the unique advantage that it may help reduce coronary heart disease risk as part of a diet low in saturated fat and cholesterol. Several meta-analyses, summarizing dozens of human studies of soy protein, have been published since 2005 affirming that soy protein may reduce cholesterol.¹⁸

Body Composition

Protein supplements are a growing category around the world, and soy is a key ingredient in these products. Soy protein is often used in products to support weight loss or lean tissue gain goals. “One trend that emerged about a decade ago was the growing consumer interest in protein, fueled by its association with effective weight loss,” Braun says. As an ingredient, isolated soy protein is used in a variety of products where high-quality protein is desired, including products targeting weight-managing adults or muscle-building athletes.

Funk mentions that dairy has historically been the accepted standard for building muscle, but recent studies have shown that soy similarly supports muscle gain and recovery in active individuals.

A 2018 meta-analysis of nine randomized control trials compared the longer-term effects of soy proteins versus animal proteins on muscle mass and strength in combination with resistance exercise. The results indicate that soy protein supplementation produces similar gains in strength and muscle mass compared to animal protein.¹³

When it comes to trained athletes, a 2016 study in the Asian Journal of Sports Medicine investigated the effects of isolated soy protein in muscle recovery in well-trained athletes and the findings suggest soy protein is effective in mitigating the negative effects of exercise-induced muscle damage for sports such as long-distance running, plyometrics or resistance activities.⁶

No matter what diet or supplement choices people may make, Funk reminds people that the quantity and quality of protein, along with the timing of intake, is of great importance to athletes to ensure they are receiving the highest benefit from their protein sources.

Scientific Conclusions for Common Soy Food Perceptions

Though nutrition research has improved and expanded in its focus and methods, some deep-seated beliefs remain among consumers. Influential studies and up-to-date research can substantiate the benefits of consuming soy.

Soy Allergies

According to the Food Allergy Research & Education group, soybean allergies are one of the more common food allergies, especially among babies and children, and about 0.4% of children are allergic to soy.³The majority of children with soy allergy will outgrow the allergy by age 10.⁴Certainly, an allergy to soy could start a lifelong battle with soy foods, though research shows fewer adults have a soy sensitivity. The incidence of soy allergy is actually much lower than other common food allergens.

Women and Breast Cancer — Estrogen

Over the years, isoflavones, naturally occurring components in soy, and their structural similarity to estrogen have raised concern that soy foods might have adverse effects in some individuals.¹Although isoflavones are classified as phytoestrogens, research has shown they differ from the hormone estrogen at the molecular and clinical levels.²

Clinical studies show that even large amounts of soy do not adversely affect markers of breast cancer risk. Furthermore, observational studies involving more than 11,000 breast cancer survivors show that consuming soy after a diagnosis of breast cancer may reduce recurrence and mortality.²

Population studies in the Asia-Pacific region show soy food intake is associated with a decrease in breast cancer risk. However, several lines of evidence support the hypothesis that consumption must occur early in life for soy to reduce risk. In fact, these studies have found consuming one or more servings of soyfood per week during childhood and/or adolescence may reduce risk.²¹

Soy Oils and Trans Fats

Soy food processing is the most recent discussion about the impact of soy foods. The Soyfoods Council serves a key role in this conversation, working as a facilitator for mainstream soy-based foods in the global marketplace.

Funk says soy is surrounded by confusion in the U.S. She adds most people in the U.S., especially in the Midwest, did not grow up eating traditional soy foods. Although they likely consumed soy in other ways, mostly through soy oils, those consumers can easily misunderstand what is not familiar to them.

Many people do not know soybean oil is by far the most widely used cooking oil in the world. Soy oil production worldwide is three times that of its closest competitors — sunflower oil and butter.⁹

Research substantiates soybean oil as a healthy cooking option; however, the negative association of trans fats in other kinds of vegetable oils has affected the consumer perspective of soybeans. A 2015 study, published in Toxicological Research, analyzed and tested trans-fat content in six vegetable oils. The study showed soybean oil did not have a detectable amount of trans fat content.¹¹Soy oil contains a high percentage of polyunsaturated fatty acids and is rich in linoleic acid, the two essential fatty acids required by the body.⁹

Conclusion

As the global population expands and consumers look to incorporate more protein in their diets, research continues to explore the value of soy as a healthy, sustainable source of protein to meet future protein demand. As the research stands, soybeans in their many forms meet various consumer needs: heart-healthy oil, a plant-centered diet, weight loss or maintenance, muscle-building or overall diet quality.