Cereal protein biofortification at the interface of nutrition, yield and sustainability.

Protein malnutrition remains a major global health challenge, particularly in regions where cereal grains dominate daily diets and access to diverse protein sources is limited. Cereals such as rice, wheat and maize provide most of the world's calories, yet their grain proteins are often low in essential amino acids and poorly balanced for human nutrition. Improving both the quantity and quality of cereal protein therefore represents a critical opportunity to enhance human health while reducing reliance on environmentally intensive animal-based foods. In this Review, we synthesize recent advances in understanding how grain protein content and composition are regulated in cereals, and why protein enhancement has historically been constrained by trade-offs with starch accumulation and yield. We discuss how domestication and modern breeding reshaped carbon and nitrogen allocation in cereal grains, creating a starch-dominant optimum that limits protein concentration. Drawing on genetic studies from rice, maize and wheat, we highlight emerging strategies that improve nitrogen acquisition, amino acid transport, storage protein composition and endosperm buffering capacity, enabling partial decoupling of protein accumulation from yield penalties. Finally, we place cereal protein biofortification within a broader nutritional and environmental context. Enhancing protein density and amino acid balance in staple cereals can improve dietary adequacy for vulnerable populations while lowering greenhouse gas emissions per unit of nutrition. Together, these insights position cereal protein biofortification as a scalable and equitable pathway towards healthier diets and more sustainable food systems under global climate and population pressures.