Debunking the “soy boy”: What the science says about plant proteins

The Soy Nutrition Institute Global is calling for people to consume more plant proteins at a time when the 2025–2030 Dietary Guidelines for Americans encourage reducing saturated fat intake while increasing protein intake. High-protein calls may lead to increased meat consumption, raising non-communicable disease risks, especially if plant proteins are not well understood.

Michelle Braun, Ph.D., director of Nutrition Research, tells Nutrition Insight why people should consume more soy, including processed versions, and what drives unfounded fears about soy products.

Braun points out that soy stands out among plant proteins because the body can digest it well while providing the essential amino acids required by children and adults. Yet, its consumption remains relatively low.

“Instead, refined grain products and mixed grain-based dishes currently account for most plant protein intake among US adults, even though they are not considered high-quality plant protein sources.”

Additionally, soy is well-studied and offers various benefits, including supporting daily human needs as a high-quality protein that can support muscle and strength.

“Short-term studies suggest that some animal proteins, like whey — which has a higher content of a specific amino acid, leucine — can stimulate muscle protein synthesis more than proteins such as soy or casein.” 

“However, based on a meta-analysis of multiple studies testing protein supplementation in combination with resistance exercise training over the longer term, soy protein supplementation leads to similar improvements in strength and lean body mass as animal sources, including whey protein,” she points out.

Plant-based proteins have been called out for being an incomplete source of amino acids. However, research demonstrates this is not true. Lentils, quinoa, kidney beans, and soy are examples that offer lysine and leucine, for instance.

Soy protein offers complete amino acids and supports muscle health, making it a key plant-based protein for adults and children (Image credits: Soy Nutrition Institute Global).Previously on Nutrition Insight, Braun told us that focusing solely on protein quantity may neglect dietary diversity, fiber, and the nutrients plants can also provide. At the same time, plant-based meal kit provider Purple Carrot called out the influence of meat and dairy groups that may be sidelining plant protein.

Processed food fears

According to Braun, focusing on a food’s processing level can distract from understanding its nutritional value, as shown by the Nutrition Facts panel on the packaging.

“What matters most for health is the nutrient content of a food and how it fits into the overall diet. Foods that fall into the same processing category can have very different effects on health because all foods are complex mixtures of nutrients and other bioactive compounds.” 

“As a result, labeling foods as ‘healthy’ or ‘unhealthy’ based solely on how much they are processed oversimplifies a much more nuanced issue. Foods with similar levels of processing can differ widely in nutrient quality,” she says.

Certain non-nutritive ingredients shown to harm health should be directly addressed, but at the same time, more highly processed foods can offer more real health benefits than less processed options, says Braun. “These foods should not be dismissed simply because of how they are made.”

“In soymilk, for example, the benefits to risk factors, including blood pressure and lipids (cholesterol), exist in spite of soymilk being classified as ‘highly’ or ‘ultra-processed.’ Analysis shows that in adults, both sweetened and unsweetened soymilk lowers blood lipids and blood pressure without affecting markers of inflammation.”

Call for consuming more plant-based protein

According to Braun, for plant protein to be treated as a central rather than a complementary part of future dietary guidance, more awareness, familiarity, and comfort with it are required in daily diets.

Highly processed soy foods, such as soymilk and meat alternatives, can provide health benefits while helping meet daily protein recommendations.“Plant-based proteins can be incorporated into healthy dietary patterns in many ways and across different eating occasions. For example, plant proteins can be in convenient, on-the-go options, such as protein bars or meal replacements that deliver high-quality protein along with other nutrients.”

“There are other simple snack formats like edamame (dried or steamed), where 100 g of edamame provides about 10 g of complete, high-quality protein with less than 1 g of saturated fat,” she adds. 

Braun advises choosing plant-based meat replacements in novel or popular formats when dining out or shopping to boost fiber intake while limiting saturated fat. These formats are familiar and can fit more easily into daily diets.

“A daily serving can be part of an overall healthful diet, where higher intakes can aid in reaching the new protein recommendations. These products can be fortified with nutrients that are sometimes limited in plant-based diets, such as iron, zinc, iodine, selenium, and vitamin B12.” 

“Plant proteins like soy can be easily incorporated into customary family recipes. Ingredients such as tofu or textured vegetable protein can be blended with other protein sources to boost protein quantity without sacrificing taste or tradition,” she suggests.