UNDERSTANDING SOY’S IMPACT ON THE GLOBAL FOOD SUPPLY

By Mark Messina, PhD, MS

When a typical consumer thinks about the role of soybeans in the food supply, foods like tofu and soy burgers may come to mind. While traditional soy foods such as tofu, and more modern options such as soy burgers, are important components of many diets worldwide, they represent only a small fraction of soybeans’ overall contribution to the U.S. and global food supply.

The significant role of soybeans can be attributed to their sheer volume of production, versatility, and unique macronutrient composition. Relative to other legumes, a soybean is much higher in fat — most beans are <5% fat on a caloric basis whereas soybeans derive >40% of their calories from this macronutrient — and are higher in protein — most beans are about 25% protein, whereas soybeans are about 35% protein (some varieties are even higher) on a caloric basis.² Higher oil and protein content make the soybean especially well positioned for meeting the world’s protein and energy needs.²

Based on a percentage of total production, the leading soybean producing countries are Brazil (40%), the U.S. (28%), Argentina (12%), and China (5%).³ Approximately 400 million metric tons of soybeans are produced annually, which is equivalent to 882 billion pounds or about 106 pounds per person — enough to meet the annual caloric needs of everyone in the world for about one-third of the year — assuming a daily energy requirement of 2,000 kcal and ~2,000 kcal per pound of raw soybeans.³ However, most of the world’s soybeans are consumed by livestock, not humans. According to the American Soybean Association, 90% of U.S. soybeans produced are used as a protein source for animal feed.⁵

After harvesting, estimates are that more than half of all U.S. soybeans are crushed so the oil can be separated from the meal (protein);⁶ 97% of the separated U.S. soybean meal goes to feed livestock and poultry.⁵ The protein used for human consumption and the oil extracted from the bean enter the food supply in myriad ways. Until just two decades ago, nearly all of the soybean oil produced was consumed by humans, but increasingly, the oil is also being used for biofuels, another way in which soybeans contribute to society.⁷

In addition to being consumed directly, soybean oil also serves as a source of several common ingredients and bioactives.

Soybean Oil

Soybean oil and palm oil are the two leading edible oils consumed worldwide⁸ whereas soybean oil, by far, is the leading edible oil in the U.S., accounting for over 40% of total consumption.⁹ In 2011, based on economic food disappearance data, Blasbalg et al.¹⁰ estimated that soybean oil accounted for over 7% of U.S. caloric intake and for more than 40% of the intake of both essential fatty acids, the omega-6 polyunsaturated fatty acid linoleic acid and the omega-3 polyunsaturated fatty acid alpha-linolenic acid. The high polyunsaturated fat content of soybean oil accounts for its ability to lower blood cholesterol levels when replacing dietary saturated fat, an attribute that was formally recognized by the U.S. Food and Drug Administration (FDA) in 2017 in the form of a qualified health claim for reducing risk of heart disease. The claim states: “Supportive but inconclusive scientific evidence suggests that eating about 1½ tablespoons (19.5 grams) of soybean oil daily may reduce the risk of coronary heart disease.”¹¹

Despite being so ubiquitous in the U.S. food supply, many consumers may not appreciate its importance and widespread use or even recognize they are consuming it because soybean oil is typically marketed as “vegetable oil”. This point is illustrated by a recently conducted survey of U.S. consumers which revealed that vegetable oil is much more highly rated than soybean oil.¹² Soybean oil may suffer reputationally because it is often found in relatively highly processed foods, often of low nutrient quality.¹³ However, it is important not to attribute the health effects of these foods to the presence of soybean oil. Regardless of the type of fat contained in these products, many of them are high in calories and sodium, low in fiber and/or protein, and hyperpalatable.

Lecithin

Crude soybean lecithin is obtained as a by-product of soybean oil processing. Soybean lecithin typically contains 18% phosphatidylcholine, 14% phosphatidylethanolamine, 9% phosphatidylinositol, 5% phosphatidic acid, 2% minor phospholipids, 11% glycolipids, 5% complex sugars, and 37% neutral oil.¹⁴ Phospholipids, which are found in all plant and animal cell membranes arranged as lipid bilayers, usually have two hydrophobic fatty acyl chains and a polar hydrophilic head group. For this reason, lecithin is classified as an amphiphilic compound — a molecule with both water-loving (hydrophilic) and fat/oil-loving (hydrophobic) parts. Consequently, lecithin is widely used by the food industry as an emulsifier to stabilize foods (think of mayonnaise) by bringing water and oil together. The percent distributions of lecithin products among the various sectors are margarine, 25-30%; baking chocolate and ice cream, 25-30%; technical products, 10-20%; cosmetics, 3-5%; and pharmaceuticals, 3%.¹⁴

From a health perspective, much of the lecithin-related research involves cardiovascular disease, in large part, because of its potential to lower LDL-cholesterol and raise HDL-cholesterol; the latter because of its effect on lecithin cholesterol acyltransferase and the role of this enzyme in reverse cholesterol transport.¹⁵ However, because of its widespread use and the dominant phospholipid being phosphatidylcholine, lecithin is also an important source of the essential nutrient choline. Consequently, lecithin may favorably affect cognitive performance. To this point, an analysis of the UK Biobank found that moderate choline intake was associated with a reduced risk of dementia, Alzheimer’s disease (AD), and mild cognitive impairment (MCI).¹⁶ Among the 125,594 participants (55.8% female) with a mean age of 56.1 y (range: 40-70 years) at baseline and a median follow-up of 11.8 y, 1,103 cases of dementia (including 385 AD and 87 cases of MCI) were recorded. The protective associations of choline against dementia and AD gradually dissipated with higher intakes although the hazards ratios were still below 1.0, whereas for MCI, risk was reduced by about half when comparing fourth and first intake quartiles.

Phytosterols

Phytosterols are phytosteroids, similar to cholesterol, that serve as structural components of biological membranes of plants. They encompass both plant sterols and stanols. More than 200 plant sterols and related compounds have been identified.¹⁷ Recognition of the hypocholesterolemic effect led to the marketing of foods such as phytosterol-fortified margarines.¹⁸ More than 20 years ago, it was shown that in male college students, consuming phytosterol-supplemented ground beef lowered plasma total cholesterol and LDL-cholesterol concentrations from baseline by 9.3% and 14.6%, respectively.¹⁹ No significant changes were found in the control group.

A recently published meta-analysis of randomized controlled trials found that phytosterols reduce levels of total cholesterol, LDL-cholesterol, triglycerides, C-reaction protein (a marker of inflammation), and systolic and diastolic blood pressure.²⁰ However, the authors acknowledged that more research is needed before reaching definitive conclusions. There is also interest in the role of beta-sitosterol, the primary soybean phytosterol,²¹ in reducing risk of prostate cancer and as a treatment for enlarged prostate.²² In the U.S. alone, in 2020, consumers spent $24,827,065 on supplements containing beta-sitosterol.²²

Soy Protein and Soy Protein Ingredients

Soy protein is well recognized as a high-quality protein as determined by both the protein digestibility corrected amino acid score²³ and the digestible indispensable amino acid score,²⁴ but the form or matrix in which that protein is provided influences the quality of the protein. Quality is affected because the matrix influences digestibility — one of the two factors determining score — and processing can cause subtle changes in amino acid profile — the other factor determining score.²⁵ Components such as fiber, which can be removed during processing, can inhibit protein digestion.²⁶ In addition, processing may more effectively inactivate compounds such as protease inhibitors, which can potentially inhibit protein digestion.²⁷

There are limited data on the protein quality of the protein provided by whole soybeans²⁸ and traditional soy foods such as tofu and soymilk,²⁹ and modern soy foods such as soy burgers.³⁰ In contrast, there is a wealth of information about the quality of soy protein when delivered in the form of concentrated sources of soy protein or soy protein ingredients, ^2,31 the main ones being soy protein isolate, soy protein concentrate, and soy flour. These products are ≥90%, 65–90%, and 50–65% protein, respectively.

Soy protein ingredients are widely used by the food industry to boost the protein content of commonly consumed products and when added to foods in smaller amounts for their functional properties, solubility, water absorption, viscosity, emulsification, texture, and antioxidation.³² According to Mintel, estimates from a few years ago were that 40% of all meat and seafood products contain soy ingredients.³³

Soy protein isolate is available as a supplement like proteins such as whey, casein, and pea protein. Although whey protein receives most attention as a protein source for building muscle and increasing strength in response to resistance exercise, soy protein isolate is equally efficacious. Soy protein isolate has a neutral flavor and is found in a variety of beverages, nutritional bars, snacks, and cereals.

Soy protein isolate is often a component of soy-based meat alternatives, although that role also falls to soy protein concentrate. Soy protein concentrate is used extensively to provide meat-like texture and as a water or fat-binding ingredient in processed meat and plant-based meat alternatives. In some low-income countries, soy flour has been used quite effectively in combination with foods such as cassava to make porridge that is both acceptable in taste and texture and richer in high-quality protein.31 Adding 15% soy flour to gluten-free bread improves bread quality, sensory characteristics, and nutritional properties of bread.³⁴

Soy flour can be further processed through extrusion to textured vegetable protein (TVP). TVP is used extensively as a meat substitute or in combination with meat in home recipes and food manufacturing. Incorporation of 10-40% TVP into beef patties was seen by researchers as a promising strategy for improving orosensory properties and even nutritional attributes.³⁵

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