Protein
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Understanding Protein: Structure, Function, and Dietary Importance
Protein Structure and Composition
Amino Acids and Peptide Bonds
Proteins are polymers composed of amino acids linked by peptide bonds. These amino acids can be arranged into primary, secondary, tertiary, and quaternary structures, but from a nutritional perspective, the primary sequence is most important2. The primary structure is determined by the DNA sequence of the gene encoding the protein3. There are 20 canonical amino acids encoded in DNA, plus five others that play significant roles in the body2.
Essential and Non-Essential Amino Acids
Of the 20 amino acids, nine are considered nutritionally indispensable (essential) because the human body cannot synthesize their carbon skeletons. These essential amino acids include leucine, valine, isoleucine, histidine, lysine, methionine, threonine, tryptophan, and phenylalanine2. Additionally, cysteine and tyrosine are synthesized from methionine and phenylalanine, respectively. Some amino acids, such as glutamine, glutamate, glycine, proline, and arginine, may be conditionally indispensable under specific physiological or pathological conditions2.
Dietary Protein Intake and Human Health
Recommended Dietary Allowance (RDA)
The RDA for protein for a healthy adult with minimal physical activity is 0.8 grams per kilogram of body weight per day. However, to meet functional needs such as promoting skeletal-muscle protein accretion and physical strength, higher intakes are recommended: 1.0, 1.3, and 1.6 grams per kilogram of body weight per day for individuals with minimal, moderate, and intense physical activity, respectively1. Long-term consumption of protein at 2 grams per kilogram of body weight per day is considered safe for healthy adults, with a tolerable upper limit of 3.5 grams per kilogram per day for well-adapted individuals1.
Health Implications of Protein Undernutrition
Protein undernutrition can lead to severe health issues, including stunting, anemia, physical weakness, edema, vascular dysfunction, and impaired immunity1. Therefore, adequate consumption of high-quality proteins is essential for optimal growth, development, and overall health.
Sources of Dietary Protein
Animal vs. Plant Proteins
Animal proteins are considered complete proteins as they contain all essential amino acids. However, they often come with concerns about saturated fat content7. On the other hand, plant proteins, while generally lacking one or more essential amino acids, can provide similar benefits when consumed in proper combinations7. Plant proteins are also seen as a sustainable alternative to animal proteins, especially in the context of a growing global population4 8.
Emerging Protein Sources
In addition to traditional animal and plant proteins, emerging sources such as insects, yeast, and microalgae are being explored for their nutritional and sustainability benefits8 10. These sources offer potential solutions to meet the increasing demand for protein while addressing environmental and social concerns.
Protein Function in the Body
Roles of Proteins
Proteins play a variety of roles in the body, including structural (cytoskeleton), mechanical (muscle), biochemical (enzymes), and cell signaling (hormones) functions3 9. They are involved in the synthesis of specific non-protein products such as nitric oxide, polyamines, creatine, glutathione, nucleotides, glucosamine, hormones, and neurotransmitters2. The diversity in protein function is due to the vast array of possible amino acid sequences and conformations9.
Conclusion
Proteins are indispensable macronutrients essential for numerous physiological functions and overall health. Understanding the structure, dietary sources, and recommended intake of proteins can help in making informed dietary choices. Both animal and plant proteins have their unique benefits and challenges, and emerging protein sources offer promising alternatives for sustainable nutrition. Adequate and balanced protein intake is crucial for maintaining health and preventing protein undernutrition-related issues.
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Most relevant research papers on this topic
Dietary protein intake and human health.
Adequate consumption of high-quality proteins from animal products is essential for optimal growth, development, and health in adults.
Highly CitedProtein.
Nine essential amino acids are essential for adult humans, while glutamine, glutamate, glycine, proline, and arginine may be conditionally indispensable for specific conditions.
Very Rigorous JournalProtein
Proteins play various roles in cells and are essential for maintaining health, playing structural, mechanical, biochemical, and cell signaling roles.
Plant proteins as high-quality nutritional source for human diet
Plant proteins offer a diverse, high-quality nutritional source for human diet, with potential for reducing animal protein dependence and meeting environmental and social needs.
Literature ReviewHighly CitedProtein Assembly by Design.
Artificial protein assemblies, using diverse design strategies, have been developed with unprecedented structures and functions, leading to novel protein-based materials with unique properties.
Highly CitedAMINO ACID COMPOSITION OF SIMPLE PROTEINS
This paper presents a complete analysis of a single preparation of a protein, P-lactoglobulin, by the same group of workers, providing valuable data for understanding protein composition and structure.
Highly CitedProtein - Which is Best?
A proper combination of animal and vegetable proteins can provide similar benefits to animal sources, with casein protein supplementation providing the greatest benefit for increased protein synthesis for prolonged duration.
Highly CitedPerspectives on Future Protein Production
Diversifying protein production, including animal, plant, and emerging sources, is crucial for ensuring a healthy diet and addressing global population growth and urbanization challenges.
Characterization Of Cellular Proteins
Cellular proteins are diverse, versatile components of living organisms, varying in size, shape, charge, stability, solubility, and other physical-chemical properties, and performing various cellular functions.
Food Proteins: Technological, Nutritional, and Sustainability Attributes of Traditional and Emerging Proteins.
Cultured meat and insect-derived proteins show potential for nutritional, technological, and environmental sustainability in food production, with potential for future food applications.
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