Protein: Best Sources, RDA Value, Deficiency Diseases, and Its Crucial Role in Human Life
Introduction
Protein is one of the most essential macronutrients required for the growth, maintenance, and repair of tissues in the human body. Every cell in our body contains protein. It is not just a building block for muscles but also for enzymes, hormones, and immune molecules. Despite its importance, protein deficiency is still prevalent in many parts of the world, especially in developing nations.
This comprehensive guide explores the importance of protein in our daily lives, the best dietary sources of protein (both plant-based and animal-based), the recommended daily allowance (RDA), and the health complications that arise from protein deficiency.
What Is Protein?
Protein is a macronutrient made up of building blocks called amino acids. There are 20 different amino acids, 9 of which are considered essential, meaning the body cannot produce them on its own—they must come from the diet.
Proteins play a crucial role in:
• Muscle development and repair
Enzyme and hormone production
Immune function
• Transport and storage of nutrients
• Cellular communication
Types of Proteins
1. Complete Proteins
Complete proteins contain all nine essential amino acids in the right proportion. These are mainly found in animal-based sources.
Examples:
• Meat
• Fish
• Eggs
• Dairy
• Quinoa
• Soy
2. Incomplete Proteins
Incomplete proteins lack one or more essential amino acids. These are typically found in plant-based foods.
Examples:
• Grains
• Nuts
• Seeds
• Legumes
• Vegetables
Combining various incomplete proteins (e.g., rice and beans) can result in a complete protein profile, especially in vegetarian diets.
Crucial Roles of Protein in the Human Body
1. Muscle Building and Maintenance
Protein is vital for building and repairing muscle tissues. This is especially important after exercise, injury, or surgery.
2. Enzyme Production
Enzymes are biological catalysts that speed up chemical reactions in the body. Most enzymes are proteins, and they are essential for digestion, energy production, and cellular repair.
3. Hormone Regulation
Some hormones, like insulin and growth hormone, are proteins. These control numerous physiological processes, including metabolism and development.
4. Immune Function
Proteins help form antibodies and other immune molecules that defend the body against viruses, bacteria, and other pathogens.
5. Transportation of Nutrients
Certain proteins, such as hemoglobin, are responsible for transporting oxygen and other nutrients throughout the body.
6. Structural Support
Proteins like collagen and keratin form the structural framework of cells, tissues, and organs, supporting skin, hair, nails, and connective tissues.
Recommended Daily Allowance (RDA) for Protein
The RDA for protein varies based on age, sex, activity level, and health status.
Group RDA (grams/day)
• Adult men (19–50 years) 56 g
• Adult women (19–50 years) 46 g
• Pregnant women 71 g
• Children (4–13 years) 19–34 g depending on age
• Athletes/Bodybuilders 1.2 to 2.0 g/kg body weight/day
Note: For a sedentary adult, the general guideline is 0.8 g of protein per kg of body weight per day.
Best Sources of Protein
• Animal-Based Protein Sources
• These are considered complete proteins.
1. Eggs
• High-quality protein with all essential amino acids
• One egg provides about 6 grams of protein
2. Chicken Breast
• Lean source of protein
• One serving (100g) offers ~31 grams of protein
3. Fish (Tuna, Salmon, Sardines)
• Rich in protein and omega-3 fatty acids
• Tuna: ~25 g protein per 100g
4. Milk and Dairy Products (Yogurt, Cheese)
• Also rich in calcium
• Greek yogurt: ~10 g protein per 100g
5. Red Meat (Beef, Lamb)
• Nutrient-rich, especially in iron and B12
• Ground beef: ~26 g protein per 100g
Plant-Based Protein Sources
These can be complete or incomplete but are excellent for vegetarians and vegans.
1. Lentils and Legumes (Chickpeas, Beans)
Rich in fiber and plant protein
Lentils: ~9 g protein per 100g (cooked)
2. Tofu and Tempeh
Soy-based complete protein
Tofu: ~8 g per 100g
Tempeh: ~19 g per 100g
3. Nuts and Seeds (Almonds, Chia Seeds, Pumpkin Seeds)
• High in healthy fats and protein
• Almonds: ~6 g per 28g (1 oz)
4. Whole Grains (Quinoa, Brown Rice, Oats)
Quinoa is a complete protein
Quinoa: ~8 g per cup (cooked)
5. Spirulina
A blue-green algae, very protein-dense
Provides ~4 g per tablespoon
Protein Deficiency: Causes and Diseases
Causes of Protein Deficiency
• Poor dietary intake (especially in underdeveloped countries)
• Eating disorders (like anorexia nervosa)
• Chronic illnesses (e.g., cancer, kidney or liver disease)
• Digestive disorders (Crohn’s disease, celiac disease)
• Strict vegan diets without proper planning
Symptoms of Protein Deficiency
• Muscle wasting
• Fatigue
• Weak immunity
• Hair loss
Edema (swelling, especially in legs and feet)
• Delayed wound healing
• Growth retardation in children
Diseases Caused by Protein Deficiency
1. Kwashiorkor
A severe form of protein malnutrition, primarily seen in children
Symptoms: Edema, irritability, enlarged liver, thinning hair
2. Marasmus
Caused by overall calorie and protein deficiency
Symptoms: Severe wasting, muscle loss, fatigue, weight loss
3. Sarcopenia
Age-related loss of muscle mass, worsened by low protein intake in older adults
Protein in Special Diets and Lifestyles
1. Protein for Athletes
Athletes and bodybuilders require more protein to support muscle repair and growth. Whey protein supplements, BCAAs, and high-protein diets are commonly used.
2. Protein for Vegans and Vegetarians
A combination of legumes, grains, seeds, and soy can fulfill protein needs. Plant-based protein powders like pea or rice protein are also popular.
3. Protein in Weight Management
High-protein diets help in weight loss by increasing satiety and reducing overall calorie intake. Protein also boosts metabolism slightly due to the thermic effect of food (TEF).
How to Include More Protein in Your Diet
• Add eggs or Greek yogurt to your breakfast
• Include nuts and seeds as snacks
• Choose lean meat or tofu in meals
Add legumes to salads and soups
• Use protein powders if necessary (consult your healthcare provider)
Risks of Excess Protein Intake
• While protein is essential, excessive intake over a long time may pose risks:
• Kidney strain (especially in people with existing kidney conditions)
Dehydration
• Increased calcium loss (possible link to bone health)
• Nutrient imbalance (if over-relying on high-protein foods)
Tip: Stay within recommended guidelines unless advised otherwise by a healthcare provider.
Protein Myths and Facts
Myth Fact
“More protein means more muscle.” Only with resistance training and sufficient calories.
“Vegans can’t get enough protein.” With proper planning, plant-based diets can meet protein needs.
“Protein supplements are necessary.” Not always. Whole foods are usually sufficient for most people.
“High-protein diets damage kidneys.” True only for individuals with pre-existing kidney conditions.
Conclusion
Protein is a cornerstone of good health. From building muscles to supporting vital organs and immune functions, it plays numerous crucial roles. While animal-based sources provide complete proteins, plant-based diets can also meet protein needs through careful combinations and food diversity.
A balanced intake aligned with the RDA helps maintain muscle mass, metabolic health, and immunity. Being aware of deficiency signs and correcting them early can prevent long-term health complications.
By choosing high-quality protein sources and understanding your body’s needs, you can optimize your health and well-being through this powerhouse nutrient.
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Writer: Vandita Singh, Lucknow (GS India Nursing Group)