Plant-based foods are gaining global attention as a potential solution to future protein shortages and as an alternative to animal-based diets. Among plant-based protein sources, soy stands out for its high nutritional quality, versatility in food processing, and widespread use in products such as soy milk, meat alternatives, and protein powders. At the same time, understanding how soy protein is produced—and its potential risks, including allergies and naturally occurring compounds like lectins—is essential for informed dietary choices.
What Are Plant-Based Foods?
Plant-based foods are products made primarily from plant-derived ingredients and do not contain animal-based materials such as meat or fish. Common examples include plant-based meat alternatives, soy-based meat substitutes, and plant-derived milks such as soy milk and almond milk.
These foods are widely consumed by people following vegan or vegetarian diets, but interest has expanded far beyond these groups. In recent years, plant-based foods have been increasingly discussed as a possible response to the global “protein crisis”—a projected shortage of high-quality protein sources as the world population continues to grow.
While many developed countries, including Japan, are experiencing population decline due to aging societies, global population numbers continue to rise. This trend raises concerns about the long-term availability of animal-based protein sources such as livestock and seafood, which require substantial land, water, and feed resources.
Soybeans: A Key Player in the Global Protein Crisis
oybeans have emerged as one of the most promising plant-based protein sources. Often referred to as “meat of the field,” soybeans are rich in high-quality protein and have an amino acid score of 100, indicating a well-balanced amino acid profile.
According to standard food composition data, dried yellow soybeans contain approximately:
31–33% protein
20–23% fat
Around 30% carbohydrates
In addition to their nutritional value, soy proteins are highly functional in food processing. They dissolve well in water, can be processed into liquids or pastes, and form gels when heated at sufficient concentrations. This makes soy particularly suitable for a wide range of food applications, including meat alternatives and dairy substitutes.
How Soy Is Used Globally, and Why Most of It Is Not Eaten Directly
Despite its nutritional value, soybeans are often described as “high-value crops but low-value foods.” In Japan, soy is widely consumed in traditional foods such as natto, tofu, miso, and soy sauce. However, this level of direct food use is relatively uncommon globally.
Worldwide annual soybean production is estimated at approximately 360 million metric tons. Of this amount:
Only about 0.3% is used directly for human food consumption in Japan.
Roughly 83% is processed into soybean oil.
The remaining byproduct, defatted soybean meal, accounts for about 250 million tons and is used primarily as animal feed.
Even in Japan, where soy-based foods are common, soy protein and soy peptide products account for less than 1% of total soybean production (excluding soybean oil).
A Key Consideration: Lectins in Soybeans
While soy offers many benefits, one important consideration is the presence of lectins, a type of glycoprotein found widely in plants, animals, microorganisms, and viruses.
Foods relatively high in lectins include:
Whole grains (such as brown rice and wheat)
Legumes
Seeds (including chia seeds)
Certain animal-derived foods
Lectins can cause gastrointestinal symptoms such as bloating, nausea, vomiting, and diarrhea when consumed in large amounts or in raw form. From a biological perspective, lectins are thought to function as a plant defense mechanism against predators.
Importantly, lectins are inactivated by proper cooking or fermentation. Heating soybeans in boiling water for 5–10 minutes or longer significantly reduces lectin activity.
Fermented soy foods such as natto are considered safe in this regard, as the production process includes a steaming step before fermentation, which effectively neutralizes lectins.
Soy Protein and Soy Peptides as Plant-Based Ingredients
Soy Protein
Soy protein is produced from defatted soybean meal by extracting protein with water, precipitating it with acid, neutralizing, sterilizing, and drying it. The resulting product—commonly labeled as soy protein isolate (SPI)—contains 90% or more protein.
Because of its excellent gel-forming, water-holding, and emulsifying properties, soy protein is widely used in:
Meat products and meat alternatives
Bakery products
Dairy alternatives
Protein supplements and powders
Textured soy protein, produced using high-temperature extrusion, is often marketed as soy meat or plant-based meat, as it develops a texture similar to animal meat when rehydrated.
Soy Peptides
Soy peptides are produced by enzymatically breaking down soy protein into smaller molecules using proteases. These peptides are more easily absorbed and are commonly used in:
High-absorption protein supplements
Functional foods
Medical or sports nutrition products
Soy Milk as a Dairy Alternative
Soy milk is one of the most established plant-based milks. Unsweetened soy milk contains roughly the same amount of protein as cow’s milk (around 3%) and has strong emulsifying and fermentation properties.
Because of this, soy milk is increasingly used as a base for:
Yogurt alternatives
Plant-based cheeses
Fermented beverages
Soy Allergy: What Consumers Should Know
One important concern with soy-based foods is soy allergy. In the United States, soy is classified as a major food allergen and must be clearly labeled under FDA regulations.
While soy allergy prevalence has traditionally been lower in Japan, recent data suggest an increase in allergies related to legumes and tree nuts globally. In Japan, soy accounts for approximately 1.3% of all reported food allergies, with higher prevalence among adults.
As plant-based foods become more common worldwide, continued monitoring of soy allergy trends is necessary.
Does Fermentation Reduce Soy Allergy Risk?
Fermentation may reduce the allergenic potential of soy. In the case of natto, soy proteins are partially broken down by enzymes such as nattokinase, which may lower allergenicity.
This hypothesis is supported indirectly by the large difference between reported cases of soy allergy and natto allergy. However, natto itself can cause allergic reactions through different mechanisms, and individuals with known sensitivities should exercise caution.
Key Takeaways
Soy-based plant foods offer a highly efficient and versatile source of protein with potential benefits for sustainability and nutrition. When properly processed—through cooking or fermentation—soy products are generally considered safe for most people. However, awareness of food allergies and moderation remain important, especially as plant-based diets continue to grow in popularity.
