Diet and nutrition, immune system

1 Introduction to a balanced diet – types and importance of nutrients

The body is like a machine, and every machine needs fuel to run. Our body's fuel is food—but simply filling the stomach isn't enough; food must contain the right things in the right quantities. This is called nutrition—the process by which an organism absorbs food and uses it for growth, energy production, repair, and disease resistance. The useful elements present in food that help the body perform these functions are called nutrients.

Types of nutrients

Nutrients are broadly classified into two categories – those required in large quantities by the body are called macronutrients, and those required in very small quantities but are still essential are called micronutrients.

What is a balanced diet?

A balanced diet is one that contains all the nutrients—carbohydrates, proteins, fats, vitamins, minerals, water, and fiber—in the right proportions and in adequate amounts, according to a person's age, sex, physical activity, and health status. The approximate energy ratio for a normal adult is approximately 55–60% of total energy should come from carbohydrates, 10–15% from proteins, and 20–30% from fats.

2 Carbohydrates – Structure, Types, Sources and Physiological Role

Imagine the body as a car—carbohydrates are its gasoline. They are the body's most rapidly available source of energy. Chemically, carbohydrates are compounds composed of carbon (C), hydrogen (H), and oxygen (O), with the hydrogen to oxygen ratio typically being 2:1, similar to water.

Types of carbohydrates

• Simple sugars/monosaccharides — The smallest units, such as glucose, fructose, and galactose. These are absorbed directly into the bloodstream.
• Disaccharides – Made up of two monosaccharide units, such as sucrose, lactose, and maltose.
• Polysaccharides – Long chains of many monosaccharide units, such as starch (found in grains and tubers), glycogen (stored form in the body, in the liver and muscles), cellulose (plant cell walls and dietary fiber).

Physiological role

The primary function of carbohydrates is to provide energy—1 gram of carbohydrate provides approximately 4 kilocalories. The brain and red blood cells rely primarily on glucose for energy. Excess glucose is stored as glycogen in the liver and muscles, and excess glucose is converted into fat. Indigestible fibers like cellulose help maintain smooth intestinal peristalsis, preventing problems like constipation.

3 Proteins – structure, amino acids, sources and protein-energy malnutrition

If carbohydrates are the body's gasoline, then protein is its building material—like bricks and cement in a building. Every cell in the body, every muscle, every enzyme, and most hormones are made of protein. The word protein comes from the Greek word "proteos," meaning "first of all"—and the name is meaningful.

Structure – Amino Acids

Proteins are made up of long chains of amino acids (polypeptide chains). The human body uses a total of 20 types of amino acids to build proteins, nine of which the body cannot make on its own—these are called essential amino acids, which must be obtained from food. The body synthesizes the remaining amino acids on its own; these are called nonessential amino acids.

Physiological role

• Essential for body growth and formation of new cells – especially for children and pregnant women.
• Tissue repair – The process of wound healing depends on proteins.
• Enzymes and most hormones (such as insulin) are made from proteins.
• Antibodies, which are the foundation of the immune system, are themselves proteins – so protein deficiency directly weakens the immune system.
• 1 gram of protein also provides approximately 4 kilocalories of energy, although using protein for energy is a last resort.

Protein-Energy Malnutrition (PEM)

When diets are severely deficient in protein and/or total energy over a long period of time, protein-energy malnutrition (PEM) occurs, especially in young children. Its two major severe forms—kwashiorkor and marasmus—remain a major cause of child malnutrition in developing countries, including India.

4 Fats (lipids) – types, saturated-unsaturated fats and cholesterol

Fats (Lipids) are often given a bad rap, but the truth is that they are just as essential to the body as carbohydrates and proteins—just a balance of quantity and type is required. Fat is the body's most concentrated energy reserve—1 gram of fat provides approximately 9 kilocalories of energy, more than twice as much as carbohydrates and protein.

Types of fats

Essential Fatty Acids

Omega-3 and omega-6 fatty acids are called essential fatty acids because the body cannot make them on its own. Omega-3s are found primarily in fish (such as salmon), flaxseeds, and walnuts, and are important for brain development and heart health.

Cholesterol

Cholesterol is a fat-like substance essential for the formation of cell membranes, vitamin D, and certain hormones (such as testosterone and estrogen). The body makes its own cholesterol in the liver, so the need for additional cholesterol intake from food is limited. It is divided into two parts: LDL (Low-Density Lipoprotein, also known as 'bad cholesterol', which can build up and block blood vessels) and HDL (High-Density Lipoprotein, also known as 'good cholesterol', which carries excess cholesterol back to the liver).

5 Fat-soluble vitamins – A, D, E, K

Vitamins are organic compounds that the body needs in very small quantities, but without them many important biochemical functions of the body come to a standstill. They are divided into two categories based on their solubility – fat-soluble (A, D, E, K) and water-soluble (B-group and C). Fat-soluble vitamins can be stored in the liver and fat tissue in the body, hence their excess (overdose) can also be harmful.

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Vitamin D deficiency causes rickets – crooked legs and weak bones

Vitamin D deficiency – a particular concern in India

Interestingly, vitamin D deficiency is very common even in a sun-rich country like India, as most people don't spend enough time in the sun during the day, and the habit of keeping the skin completely covered is also a reason for this. Rickets causes children's bones to become soft and weak and crooked (especially the legs become bow-shaped), while in adults the same deficiency is called osteomalacia, in which the bones become weak and painful.

6 Water-soluble vitamins – B-group and vitamin C

Water-soluble vitamins are not stored in the body—excess amounts are excreted through urine. Therefore, their daily needs must be met through diet. This group includes the B group of vitamins (eight types) and vitamin C.

The special role of vitamin C

Vitamin C not only protects against scurvy, but it's also a powerful antioxidant, aiding in iron absorption and wound healing. It also strengthens the immune system by increasing white blood cell function—hence the recommendation to eat amla (Indian gooseberry) and lemon for colds.

Indian gooseberry (Phyllanthus emblica) is considered one of the richest natural sources of vitamin C—it provides many times more vitamin C than oranges.

7 Minerals – calcium, iron, iodine, zinc etc.

Minerals are inorganic nutrients that play a role in many functions in the body, from bones to the nervous system. They are divided into two sub-classes—macrominerals (such as calcium and phosphorus, which are needed in large quantities) and trace elements (such as iron, iodine, and zinc, which are needed in very small quantities).

Anaemia – India's biggest nutritional challenge

According to the National Family Health Survey (NFHS), iron deficiency anemia is a widespread problem among women and children in India. To address this, the Indian government has launched the Anemia Mukt Bharat campaign, under which iron-folic acid (IFA) supplements are regularly administered to children, adolescents, pregnant and lactating women.

8 Modern aspects of water, fibre and diet

Water

Water is often overlooked in the list of nutrients, even though the human body is composed of approximately 60-70% water. It participates in every vital function, including digestion, nutrient transport, body temperature regulation, and excretion. A typical adult requires approximately 2.5-3 liters of water per day.

Dietary Fibre

Fiber is the plant part that human digestive enzymes cannot digest, yet it is vital for digestive health. It regulates bowel movements, prevents constipation, helps control blood sugar and cholesterol levels, and also aids in weight management by providing a feeling of fullness. Whole grains, vegetables, fruits, and pulses are the main sources of fiber.

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🖼️ Food Pyramid — the proportion of different food groups in a balanced diet

Millets – The Renaissance

Millets like bajra, sorghum, ragi (mandua), kodo – once considered 'grains of the poor' – are now gaining global recognition for their nutritional value. On India's proposal, the United Nations declared the year 2023 as the International Year of Millets. Millets are high in fibre, low in glycemic index and rich in minerals like iron and calcium – making them especially suitable for diabetics and heart patients. Millets have traditionally been the most important food grain in Rajasthan, especially in desert areas where it yields well even with less water.

Probiotics

Probiotics are live, beneficial microorganisms (mainly bacteria) that, when consumed in adequate amounts, promote gut health. Yogurt, buttermilk, and idli-dosa batter (fermented foods) are natural sources of probiotics. They improve digestion by increasing the number of beneficial bacteria in the gut and also indirectly support the immune system, as the gut contains approximately 70% of the body's immune cells.

9 The overall picture of malnutrition and the nutrition plans of India and Rajasthan

Malnutrition doesn't just mean eating less—it has two opposite forms. Undernutrition is when the body doesn't get enough nutrients (e.g., PEM, anemia, vitamin deficiencies), while overnutrition is when excess calories are consumed, leading to obesity and lifestyle diseases. Today, India faces the 'double burden' of both types of malnutrition—undernutrition among children in rural and tribal areas on the one hand, and increasing obesity in urban areas on the other.

Key indicators to measure malnutrition

• Stunting — short height for age, a sign of long-term malnutrition.
• Wasting – low weight for height, indicating acute/recent malnutrition.
• Underweight – Low weight for age, both types of malnutrition.

India's major public nutrition programs

• Integrated Child Development Services Scheme (ICDS) – Supplementary nutrition, vaccination and health check-up to children up to 6 years of age, pregnant and lactating women through Anganwadi centres.
• Mid-Day Meal Scheme/PM Poshan – Cooked nutritious food for children in government schools, which reduces malnutrition and increases school attendance.
• POSHAN Abhiyaan – National convergence mission to reduce problems like stunting, wasting, anemia and low birth weight.
• Anemia Mukt Bharat Abhiyan – Iron-folic acid supplementation at every stage of life.

Special Nutrition Schemes of Rajasthan

The Rajasthan government has launched several special schemes keeping in view the geographical challenges of the state (desert, tribal remote areas):

10 Introduction to the Immune System – Innate Immunity

When a thorn pricks your body and the wound becomes inflamed, or when a cold causes a fever, an invisible army within your body is activated—this is our immune system. It's a complex network of cells, tissues, and organs that protects the body from harmful external elements—bacteria, viruses, fungi, and parasites (collectively called pathogens)—and the body's own abnormal cells (such as cancer cells).

Two main types of immunity

The immune system is divided into two broad categories—innate immunity, which is present from birth and is non-specific; and acquired immunity, which develops after exposure to a particular pathogen during life and is specific. These two systems work together—innate immunity is the first line of defense, while acquired immunity is a more targeted and memorable second line.

Levels of innate immunity

• Physical Barriers — The skin acts as an impenetrable wall; the mucous membranes of the respiratory and digestive tracts trap germs.
• Physiological Barriers — Stomach acid (HCl) kills most germs; an enzyme called lysozyme in tears and saliva breaks down bacterial cell walls.
• Cellular Barriers — White blood cells (WBCs) such as phagocytes (neutrophils, macrophages) engulf and engulf pathogens (phagocytosis); natural killer cells destroy infected and cancerous cells.
• Inflammatory Response – When there is an injury or infection, blood flow to the site increases, causing redness, swelling, warmth, and pain – this is the process of sending more protective cells to the site.

11 Acquired Immunity – B-cells and T-cells

While innate immunity responds to every pathogen in the same way, acquired/adaptive immunity acts like an intelligent army—it recognizes each pathogen and develops specific 'weapons' against it, and most importantly, it has a memory, allowing the body to respond much faster if the same pathogen attacks again in the future.

Lymphocytes – the main soldiers of acquired immunity

Lymphocytes, a special class of white blood cells, are at the heart of acquired immunity. There are two main types—B-lymphocytes and T-lymphocytes—both are formed from stem cells in the bone marrow, but T-cells migrate to the thymus gland to mature (hence the name T-cell, while B-cells derive their name from the bone marrow/bursa).

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🖼️ Layers of the immune system—functioning of helper T-cells, B-cells, plasma cells, and antibodies

primary and secondary immune response

When the body is first exposed to a pathogen, the primary response is slow, taking a few days for antibodies to form—this is when a person feels sick. However, the memory cells formed during this time remain in the body for years. If the same pathogen attacks again in the future, the secondary response is much faster and more powerful, neutralizing the pathogen before symptoms appear—this is the principle on which vaccination works (detailed in Topic 13).

12 Antibodies – Structure and types of immunoglobulins

An antibody, also called an immunoglobulin (Ig), is a special type of protein that plasma cells (derived from B-cells) produce in response to pathogens. This is often explained by the 'lock-and-key' principle—the structure of each antibody precisely matches the antigen on the surface of a particular pathogen.

structure of antibodies

A specific antibody is shaped like the letter 'Y' and is composed of four polypeptide chains—two heavy chains and two light chains—linked by disulfide bonds. It has two main parts—the Fab region (antigen-binding fragment), which is located at the two ends of the 'Y' and binds directly to the antigen; and the Fc region (crystallizable fragment), which is the stem of the 'Y' and serves to send signals to other immune cells.

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🖼️ Basic structure of an antibody—heavy and light chains, Fab and Fc regions

Five major types of immunoglobulins (Ig)

13 Vaccination – Principles, Types and India's Programme

The basic principle of vaccination is simple—to 'recognize' the actual pathogen without making it sick, so that memory cells are created. The first vaccine in history was developed in 1796 by Edward Jenner against smallpox, after he observed that cowpox-bearing cows were protected from smallpox.

Types of vaccines

• Inactivated/killed vaccine — made from a killed pathogen, such as the injectable polio vaccine (IPV).
• Live Attenuated Vaccine — Made from weakened live pathogens, such as measles, BCG (for tuberculosis).
• Subunit/Toxoid Vaccine — Made from only a part of the pathogen (such as a protein) or inactivated toxin, such as hepatitis B, tetanus.
• mRNA Vaccine — A newer technology that delivers instructions (mRNA) for making the pathogen's surface protein, which the body then reads and develops an immune response to — such as the Pfizer and Moderna vaccines for COVID-19.

India's Universal Immunization Programme (UIP)

The Government of India's UIP is one of the world's largest immunization programs, providing free vaccines to millions of children and pregnant women every year—including BCG, polio (OPV/IPV), DPT (diphtheria-pertussis-tetanus), measles-rubella (MR), hepatitis B, rotavirus, and pneumococcal vaccines. Special campaigns like Mission Indradhanush focus on reaching children who have missed routine vaccinations.

14 Immune system disorders – allergies, autoimmune diseases and immunodeficiencies

The immune system protects the body, but sometimes it causes problems itself—either by becoming overactive, weakened, or confused and attacking its own body.

Allergy

When the immune system mistakes a normally harmless substance (such as pollen, dust, certain foods) for a threat and overreacts, it's called an allergy. IgE antibodies play a key role, triggering mast cells to release histamine, which causes symptoms like sneezing, itching, and swelling.

Autoimmune Diseases

When the immune system mistakenly attacks the body's own healthy cells, mistaking them for "foreign enemies," it's called an autoimmune disease. Examples include type 1 diabetes (the body destroys its own insulin-producing pancreatic cells), rheumatoid arthritis (attacks the joints), and psoriasis (attacks the skin).

Immunodeficiency

When the immune system becomes weaker than normal, making a person susceptible to frequent and serious infections, it is called immunodeficiency. This can be congenital (primary, due to genetic factors) or acquired (secondary). HIV/AIDS is a prime example, in which the human immunodeficiency virus directly attacks helper T-cells (CD4+ cells) and gradually destroys the immune system, leaving the body unable to fight even common infections.