Protein

What Is Protein?

Protein is one of the three primary macronutrients, alongside carbohydrates and fat. It is composed of chains of amino acids linked together by peptide bonds. The human body uses approximately 20 amino acids to build proteins, of which 9 are considered essential because the body cannot synthesize them and must obtain them from food.

Protein provides 4 kilocalories per gram and plays a structural and functional role in virtually every biological process, including muscle contraction, enzyme catalysis, hormone production, immune defense, and oxygen transport.

Recommended Intake

The Recommended Dietary Allowance (RDA) for protein is 0.8 grams per kilogram of body weight per day for sedentary adults. However, higher intakes are recommended for specific populations:

• Endurance athletes: 1.2–1.4 g/kg/day
• Strength-training athletes: 1.6–2.2 g/kg/day
• Older adults (65+): 1.0–1.2 g/kg/day to preserve muscle mass
• Pregnant women: an additional 25 g/day above baseline

Food Sources

Protein is found in both animal and plant foods. Animal sources such as meat, poultry, fish, eggs, and dairy are typically complete proteins, meaning they supply all essential amino acids. Plant sources such as legumes, tofu, tempeh, nuts, and seeds are often lower in one or more essential amino acids but can be combined to meet needs.

• Chicken breast (100 g cooked): ~31 g protein
• Lentils (1 cup cooked): ~18 g protein
• Greek yogurt (170 g): ~17 g protein
• Eggs (2 large): ~12 g protein