Protein in a child's plate: how protein quality affects growth, brain and obesity risks

Protein is more than just a “building block” for muscles. For children, it is a source of essential amino acids, a predictor of normal growth, cognitive development, and immunity. But as a new review in Nutrients shows, in childhood, it’s not just how much protein matters, but also what kind: its digestibility, amino acid profile, and source (animal or plant) can change the trajectory of health for years to come. The authors systematically collected 2020-2025 data on the “biological value” of proteins for children and adolescents - from infants to 18 years old - and provided a practical framework for parents, doctors, and those who write nutrition recommendations.

The key conclusion is simple, but inconvenient for universal advice: animal proteins often have a full composition of essential amino acids and are absorbed better; plant proteins can also ensure normal growth, but require a well-thought-out combination of products and, often, vitamin and mineral support (primarily B12, iron, iodine, zinc, long-chain omega-3). And one more subtle point: excessive protein consumption in children is associated with accelerated weight gain and an increased risk of obesity later. Balance is the key.

Background of the study

The growth and development of a child depend not only on the amount of protein in the diet, but also on its quality - the completeness of essential amino acids, digestibility and the food matrix in which this protein comes. In childhood, protein is not just a "building material"; through signaling pathways (for example, mTORC1, sensitive to leucine) it regulates linear growth, bone mineralization, muscle mass formation, immune function and brain maturation. Deficiency of essential amino acids in "critical windows" (especially in the first 1000 days: pregnancy + 0-2 years) is associated with stunting/wasting, delayed cognitive development and greater vulnerability to infections. At the other extreme, excess protein in babies (often due to dairy products and formula) is associated with accelerated fat gain and an increased risk of obesity later: here, not maximalism, but a "safety corridor" is appropriate.

At the same time, the landscape of children’s nutrition is changing. In high-income countries, there is growing interest in plant-based diets and a reduction in red meat for environmental and ethical reasons; families are increasingly asking for animal protein “equivalents” for children. In low-resource countries, there remains a “hidden hunger” for iron, zinc, vitamin B12, iodine – nutrients that usually go hand in hand with animal protein sources and affect growth and neurodevelopment. Universal advice on “more/less protein for everyone” does not work here: vulnerable groups (infants, preschoolers, children with chronic diseases) require a targeted approach.

The methodological field is also ambiguous. The “quality” of protein in children has traditionally been assessed using PDCAAS, but this metric averages digestibility and weakly takes into account anti-nutritional factors (phytates, tannins), technological processing, and age-related features of digestion. The more modern DIAAS more accurately reflects the availability of amino acids at the ileum level and is better suited for children's diets and real dishes (mixtures of legumes and cereals, fermented products). The culinary context is also important: soaking, fermentation, and gentle heat treatment increase the bioavailability of plant protein; aggressive heating and ultra-processing, on the contrary, can reduce it.

The practical task for pediatricians and parents is to collect a complete amino acid profile and maintain energy/micronutrient balance:

• for plant-based diets - consciously combine sources (legumes + cereals) and control critical nutrients (B12, iron, zinc, iodine, DHA/EPA), sometimes with supplementation;
• in the omni diet - rely on eggs, dairy products, fish and lean meat as “simple” carriers of a complete profile, without overloading babies with protein;
• in conditions of illness/recovery - individualize needs (during infections and rehabilitation, the need for protein is temporarily higher; in case of CKD - on the contrary, restrictions are possible).

Finally, there are research gaps: there are few randomized trials comparing protein sources for “hard” childhood outcomes (length-for-age z-score, body composition, cognitive tests), there is a lack of standardized biomarkers of amino acid status in children, and the DIAAS databases for real-world meals are still being filled. At the policy level, this means that recommendations for complementary foods and school meals will need to be updated to take into account protein quality, not just grams per kilogram, and to do so differently for resource-rich and resource-poor countries.

What exactly is important in the "quality" of protein

• Completeness of amino acids: It is critical for children to receive all 9 essential amino acids (IAA); if the “limiting” ones (such as lysine or methionine) are deficient, growth and muscle synthesis suffer.
• Digestibility and assessment methods: the classic PDCAAS often overestimates protein quality and does not take into account anti-nutritional factors (phytates, tannins, etc.), while DIAAS more accurately reflects the real availability of amino acids at the ileum level.
• Processing: Fermentation, soaking, and heat treatment may increase the digestibility of plant proteins, but harsh heating oxidizes methionine/cysteine and reduces bioavailability.

The review provides a visual table: egg and whey are the “gold standard” (BV≈100 and above), soy has a “complete” profile, but lower methionine; lentils are rich in lysine, poor in sulfur-containing amino acids - it is better to combine them with cereals.

Protein and age - a story about "windows of opportunity". In the first 1000 days (pregnancy + first 2 years), imbalances in protein and essential amino acids correlate not only with "statics" - low height/weight - but also with cognitive outcomes and the risk of chronic diseases later. During infections and recovery, the need for protein briefly increases by 20-30% (with diarrhea - up to 50%). In children with chronic diseases (CKD, oncology, after transplantation), the needs are individualized and often higher or, with the risk of uremia, on the contrary, are limited.

What does this mean for families in practice?

• Toddlers and preschoolers: avoid hyperprotein "adult" diets - excess protein at an early age is associated with a higher risk of obesity later. Adjust the diet to the FAO/WHO/EFSA recommendations by age (the charts in the review show how the norms gradually decrease from infants to adolescents).
• Plant-based diets: possible and safe with proper planning: combine legumes + grains to cover lysine/methionine, monitor B12, iron, iodine, DHA/EPA; vegan children are more likely to need supplements.
• Animal sources: eggs/dairy/fish provide a “complete” profile and micronutrients, eggs and dairy have an additional role of leucine/glutamine in activating mTORC1 (growth, bone mineralization).
• Combined approach: the omni-diet remains the most “simple” way to meet needs; with plant-based nutrition, more attention is paid to the quality and diversity of sources.

In a global context, the picture is more contrasting. In resource-poor countries, attempts to “cut animal products for the sake of ecology” in vulnerable groups (infants, young children) can increase hidden hunger: there, animal sources are often irreplaceable for protein, zinc and bioavailable iron. Blanket bans during the period of complementary feeding are both scientifically untenable and ethically questionable. At the same time, interest in “alternative proteins” (microalgae, insects, cultured meat) is growing, but the authors call for a sober assessment of nutrition and safety - from allergenicity to real bioavailability - before including them in mass policies.

Scientific nuances worth paying attention to

• Protein and target of mTORC1: sufficient amino acids (including leucine) switch the child's body to anabolism - growth, protein synthesis, mineralization; deficiency - suppresses mTORC1, activates autophagy and inhibits growth.
• Microbiota and puberty: in schoolchildren, a more "animal-protein" microbial profile was associated with earlier menarche/voice mutation; plant-protein - with later periods. The cause-and-effect relationship is not proven, but the signal is interesting.
• Quality metrics: The authors support the transition from PDCAAS to DIAAS and the expansion of panels of methods (dual isotope tracing, IAAO, nutriproteomics) - otherwise we underestimate the impact of fiber/anti-nutritional factors and "mixed" meals.

Conclusion

There is no universal answer for children: “plant-only for everyone” or “more animal-based for everyone.” The right vector is a targeted strategy: in wealthy countries, attention to balance and prevention of excess at an early age; in countries with deficits, protection of access to high-quality protein sources in complementary foods; in families on a plant-based diet, smart combination and competent supplementation. At the research and policy level, updating protein assessment scales (DIAAS), strengthening digestibility databases and transferring this to recommendations for children's nutrition.

Source: Escobedo-Monge MF et al. The Biological Value of Proteins for Pediatric Growth and Development: A Narrative Review. Nutrients (2025). https://doi.org/10.3390/nu17132221