Physiology of Nutrition

Introduction

• Nutrition is essential for maintaining health, supporting growth, and preventing disease.
• Both undernutrition and overnutrition can impair normal body functions and increase the risk of chronic diseases.
• A balanced diet supplies adequate energy and essential nutrients for normal physiological activities.
• Good nutrition promotes growth and development, tissue repair, maintenance of organ function, and preservation of immune competence.
• Adequate nutrient intake enhances resistance to infections and improves recovery from illness and injury.

Dietary requirements:

• A balanced diet should provide appropriate amounts of carbohydrates, fats, proteins, dietary fiber, vitamins, minerals, and water.
• Dietary composition should be adjusted according to age, physical activity, physiological state, and underlying health conditions.
• Total energy requirement depends on body size, metabolic rate, and the level of physical activity.
• Carbohydrates and fats are the principal sources of dietary energy.
• Healthy fats are essential components of cell membranes and contribute to intracellular signaling, hormone synthesis, and absorption of fat-soluble vitamins.
• Excessive restriction of dietary fat is not advisable because essential fatty acids are required for normal cellular structure and function.
• Protein requirement in healthy adults is approximately 0.8 grams per kilogram of body weight per day.
• Protein needs increase during childhood, adolescence, pregnancy, lactation, recovery from illness, major surgery, and intense physical training.
• Dietary proteins should supply all essential amino acids needed for tissue growth, repair, enzyme synthesis, and immune function.
• Vitamins and minerals do not provide energy but are indispensable for enzyme activity, metabolism, growth, bone health, and normal physiological processes.
• Adequate dietary fiber supports gastrointestinal function, promotes bowel regularity, and contributes to long-term metabolic health.
• Advancing age is generally associated with reduced energy requirements; therefore, calorie intake should decrease while dietary fiber and nutrient density should increase.

Essential Nutrients

• Essential nutrients include carbohydrates, proteins, fats, vitamins, minerals, and water.
• These nutrients are required for energy production, growth, tissue repair, metabolism, and maintenance of normal physiological functions.
• A balanced diet should provide all essential nutrients in adequate amounts.

Carbohydrates

• Carbohydrates are the primary source of energy for the body, particularly for the brain and red blood cells.
• Complete oxidation of 1 gram of carbohydrate yields approximately 4 kilocalories of energy.
• Excess carbohydrate intake beyond energy requirements is converted into fat and stored in adipose tissue.

Types of Carbohydrates

Monosaccharides

• Monosaccharides are the simplest carbohydrates and require no further digestion before absorption.
• Hexoses contain six carbon atoms and include glucose, fructose, and galactose.
• Pentoses contain five carbon atoms and include ribose, an important component of nucleic acids.

Disaccharides

• Disaccharides consist of two monosaccharide molecules joined by glycosidic bonds.
• Sucrose is composed of glucose and fructose.
• Lactose consists of glucose and galactose, whereas maltose contains two glucose molecules.
• Lactase deficiency results in lactose intolerance, causing abdominal discomfort, bloating, flatulence, and osmotic diarrhea after ingestion of milk products.

Polysaccharides

• Polysaccharides are complex carbohydrates composed of numerous glucose molecules.
• Starch is the principal storage carbohydrate in plants and is an important dietary source of energy.
• Glycogen is the storage carbohydrate in animals and is stored mainly in the liver and skeletal muscles.
• Dietary fiber is classified as soluble or insoluble and is not digested by human gastrointestinal enzymes.

Sources and Functions of Carbohydrates

• Soluble fiber delays gastric emptying, slows glucose absorption, and helps lower blood cholesterol by binding bile acids.
• Regular intake of soluble fiber contributes to improved glycemic control and reduced cardiovascular risk.
• Insoluble fiber increases stool bulk, accelerates intestinal transit, and promotes regular bowel movements.
• Adequate fiber intake helps prevent constipation and supports normal colonic function.
• A diet rich in whole grains, fruits, vegetables, and legumes provides sufficient dietary fiber and contributes to long-term metabolic and gastrointestinal health.

Lipids

Types of Lipids

• Triglycerides are the principal dietary lipids and consist of one glycerol molecule linked to three fatty acids.
• Dietary lipids also contain smaller amounts of cholesterol and phospholipids.
• Triglycerides differ according to fatty acid chain length, degree of saturation, and the presence of essential fatty acids.

Table 161.1: Sources and functions of carbohydrates.

Carbohydrate Type	Common Sources	Major Physiological Function
Glucose	Sugar, cereals, fruits, vegetables, honey	Primary energy source for body tissues
Fructose	Fruits, honey	Metabolized mainly in the liver to glucose intermediates
Galactose	Milk and dairy products	Converted to glucose in the liver
Sucrose, Lactose, Maltose	Sugarcane, milk, germinating grains	Digested into monosaccharides for energy production
Starch	Rice, wheat, potatoes, maize, cassava	Major dietary polysaccharide supplying glucose
Soluble fiber	Fruits, legumes, oats, whole grains	Slows glucose absorption and lowers cholesterol absorption
Insoluble fiber	Vegetables, wheat bran	Increases stool bulk and promotes regular bowel movements

Degree of Saturation

• Saturated fatty acids contain no carbon–carbon double bonds, and each carbon atom is fully saturated with hydrogen.
• Monounsaturated fatty acids contain one carbon–carbon double bond.
• Polyunsaturated fatty acids contain two or more double bonds.
• Highly unsaturated fatty acids contain multiple double bonds and include many biologically important omega-3 and omega-6 fatty acids.
• Replacing saturated fats with unsaturated fats, particularly polyunsaturated fats, improves blood lipid profile and reduces cardiovascular risk.
• Monounsaturated and polyunsaturated fatty acids also help maintain normal cell membrane fluidity.

Length of the Carbon Chain

• Fatty acids usually contain an even number of carbon atoms.
• They are classified as short-chain, medium-chain, long-chain, or very-long-chain fatty acids according to the number of carbon atoms.
• Long-chain fatty acids are the predominant form present in the human diet and body tissues.

Presence of Essential Fatty Acids

• Essential fatty acids cannot be synthesized in sufficient amounts by the human body and must be obtained from the diet.
• The principal essential fatty acids are linoleic acid and alpha-linolenic acid.
• Arachidonic acid is considered conditionally essential because it can be synthesized from linoleic acid under normal physiological conditions.
• Essential fatty acids are required for normal growth, maintenance of cell membranes, neurological development, and skin integrity.
• They are precursors of eicosanoids, including prostaglandins, thromboxanes, and leukotrienes, which regulate inflammation, vascular tone, platelet function, and immune responses.

Cholesterol

• Cholesterol is a sterol synthesized mainly in the liver from acetyl coenzyme A.
• It is also obtained from foods of animal origin.
• Cholesterol is an essential structural component of cell membranes and helps maintain membrane stability.
• It serves as the precursor for steroid hormones, bile acids, and vitamin D.
• Although physiologically essential, excessive circulating low-density lipoprotein cholesterol increases the risk of atherosclerotic cardiovascular disease.

Functions of Dietary Fats

• Fats are the most energy-dense dietary nutrients, providing approximately 9 kilocalories per gram.
• They supply concentrated energy for normal metabolism and prolonged physical activity.
• Lipids are essential components of cell membranes and maintain membrane integrity and fluidity.
• Dietary fats facilitate intestinal absorption of the fat-soluble vitamins A, D, E, and K.
• They improve the taste, texture, and palatability of food.
• Fat delays gastric emptying, promoting prolonged satiety after meals.
• Essential fatty acids are required for synthesis of eicosanoids, including prostaglandins, thromboxanes, and leukotrienes.
• Cholesterol provides the substrate for synthesis of steroid hormones and bile acids.
• Subcutaneous fat acts as thermal insulation and helps maintain normal body temperature.
• Brown adipose tissue, especially in infants, generates heat through non-shivering thermogenesis.
• During prolonged fasting, fatty acids are converted into ketone bodies, providing an alternative energy source for many tissues.
• Adipose tissue cushions internal organs and protects them from mechanical injury.

Daily Requirements and Sources

• Dietary fat should contribute approximately 20–35 percent of total daily energy intake, depending on age, health status, and physical activity.
• The diet should provide adequate amounts of essential fatty acids while limiting excessive intake of saturated and trans fats.
• Triglycerides are the principal dietary lipids and are present in both plant and animal foods.
• Cholesterol is found only in foods of animal origin, including egg yolk, meat, and organ meats.
• Saturated fats are abundant in butter, full-fat dairy products, fatty meats, coconut oil, and palm oil.
• Unsaturated fats are found in vegetable oils, nuts, seeds, soybeans, and fish oils, which are rich in omega-3 fatty acids.
• After intestinal absorption, lipids circulate in blood as lipoproteins.
• Chylomicrons transport dietary triglycerides from the intestine to tissues.
• Very-low-density lipoproteins transport triglycerides synthesized by the liver.
• Low-density lipoproteins deliver cholesterol to peripheral tissues.
• High-density lipoproteins remove excess cholesterol from tissues and transport it to the liver for metabolism and excretion.

Diseases Associated with Excess Fat

• Excess intake of dietary fat and calories contributes to obesity, increasing the risk of several chronic diseases.
• Obesity is associated with atherosclerosis, coronary artery disease, stroke, hypertension, type 2 diabetes mellitus, and certain cancers.
• Desirable total serum cholesterol is generally less than 200 milligrams per deciliter, while higher values increase cardiovascular risk.
• Most circulating cholesterol is synthesized by the liver, with a smaller proportion obtained from the diet.
• Elevated low-density lipoproteins, very-low-density lipoproteins, and triglycerides increase cardiovascular risk, whereas high-density lipoproteins are protective.
• Regular physical activity, weight control, and diets rich in vegetables, fruits, whole grains, and fish improve the lipid profile.
• Reducing saturated and trans fats while increasing unsaturated fats, especially polyunsaturated fats, helps lower cardiovascular risk.
• Alcohol should not be recommended to improve high-density lipoprotein levels because its potential harms outweigh any cardiovascular benefit.

Proteins

Structure of Proteins

• Proteins are large biological molecules composed of amino acids linked by peptide bonds.
• They contain approximately 16 percent nitrogen, allowing estimation of protein content from nitrogen measurements using a conversion factor of 6.25.
• Every amino acid contains an amino group, a carboxyl group, a hydrogen atom, and a variable side chain that determines its chemical properties.
• Proteins possess an amino terminal and a carboxyl terminal, which define the orientation of the amino acid chain.

Classification of Amino Acids

• About 20 standard amino acids are used for protein synthesis in humans.
• Amino acids are classified as essential or nonessential according to whether they must be obtained from the diet.
• Essential amino acids cannot be synthesized in adequate amounts by the body and are therefore required in food.

Functions of Proteins

• Proteins are the principal structural components of cells, tissues, and organs.
• They are essential for normal growth, tissue maintenance, and repair throughout life.
• Structural proteins contribute to the integrity of muscles, connective tissues, skin, and bones.
• Proteins form numerous enzymes that catalyze biochemical reactions essential for metabolism.
• Many hormones, including peptide hormones, are proteins or peptides.
• Hemoglobin and several plasma proteins are synthesized from amino acids.
• Plasma proteins and hemoglobin contribute to acid–base balance by acting as physiological buffers.
• Transport proteins carry hormones, lipids, vitamins, and metal ions throughout the body.
• Albumin maintains plasma oncotic pressure, helping regulate fluid movement across capillary walls and preventing excessive edema.
• Immunoglobulins are proteins that provide humoral immunity by recognizing and neutralizing pathogens.
• Storage proteins, such as ferritin, store essential substances including iron for future use.
• Many cell surface receptors are proteins that mediate cellular communication and signal transduction.
• Several proteins, including fibrinogen and prothrombin, are essential components of the blood coagulation system.
• Contractile proteins, such as actin and myosin, enable muscle contraction and movement.
• Under prolonged starvation or severe energy deficiency, proteins may be broken down to provide substrates for energy production, although this is not their primary physiological role.
• Adequate dietary protein is therefore essential for maintaining normal body structure, physiological function, immunity, and metabolic homeostasis.

Table 161.2: Essential and non-essential amino acids.

Essential Amino Acids*	Nonessential Amino Acids
Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, Valine	Alanine, Asparagine, Aspartate, Glutamate, Glutamine, Glycine, Proline, Serine, Tyrosine, Cysteine

Daily Requirement and Sources

• The recommended daily protein intake for healthy adults is approximately 0.8–1.0 grams per kilogram of body weight.
• Protein requirements increase during infancy, childhood, adolescence, pregnancy, lactation, illness, and recovery.
• Good dietary sources include meat, fish, eggs, milk, legumes, beans, nuts, and cereals.
• Animal proteins are generally complete proteins, containing all essential amino acids.
• Most plant proteins are incomplete individually but can provide complete nutrition when appropriately combined.
• Severe protein deficiency contributes to protein-energy malnutrition, including kwashiorkor and marasmus.

Vitamins

• Vitamins are organic micronutrients required in small amounts for normal growth, metabolism, and maintenance of physiological functions.
• They do not provide energy but act as coenzymes or cofactors in numerous enzymatic reactions.
• Vitamins participate in energy metabolism, tissue repair, immune function, and normal cellular activity.
• Antioxidant vitamins, including beta-carotene and vitamins C and E, help protect cells from oxidative damage caused by free radicals.
• Vitamins are classified as water-soluble or fat-soluble according to their absorption and storage characteristics.
• Clinical manifestations of vitamin deficiency depend on the specific vitamin affected and its physiological role.
• Multiple vitamin deficiencies commonly occur in generalized malnutrition, producing overlapping clinical features.
• Plasma vitamin concentrations may not always accurately reflect intracellular vitamin status, although reduced plasma levels often indicate early deficiency.
• Vitamin deficiency may result from inadequate dietary intake, impaired intestinal absorption, defective metabolism, increased physiological requirements, or excessive losses.
• Requirements increase during periods of rapid growth, pregnancy, lactation, chronic illness, and recovery from major disease or surgery.

Table 161.3: Types of vitamins.

Vitamin Group	Major Vitamins
Water-soluble vitamins	Vitamin C and the B-complex vitamins: B1 (thiamine), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), B6 (pyridoxine), B7 (biotin), B9 (folate), and B12 (cobalamin)
Fat-soluble vitamins	Vitamin A (retinoids), Vitamin D (calciferols), Vitamin E (tocopherols), and Vitamin K (phylloquinones and menaquinones)

Vitamin A

• Vitamin A exists in three biologically important forms: retinol, retinal, and retinoic acid.
• Retinol is the storage and transport form, retinal functions in vision, and retinoic acid regulates gene expression and cell differentiation.
• Beta-carotene is a provitamin A carotenoid that is converted to vitamin A in the intestinal mucosa and liver.

Sources of Vitamin A

• Rich animal sources include liver, fish liver oils, egg yolk, whole milk, butter, and dairy products.
• Plant sources include carrots, spinach, sweet potato, pumpkin, broccoli, mango, papaya, and other dark green or orange-colored fruits and vegetables.
• Plant foods supply carotenoids, which serve as precursors of vitamin A.

Daily Requirement

• The recommended dietary intake for adults is approximately 700 micrograms of retinol activity equivalents daily for women and 900 micrograms for men.
• Requirements increase during pregnancy and are highest during lactation to support infant growth and development.

Functions of Vitamin A

Vitamin A is essential for normal vision, epithelial integrity, immunity, growth, reproduction, and skeletal development.

Role in Vision

• Retinal combines with opsin to form rhodopsin, the visual pigment of rod cells.
• Rhodopsin is essential for vision in dim light and for normal dark adaptation.
• Vitamin A deficiency reduces rhodopsin regeneration, causing night blindness, which is often the earliest clinical manifestation.
• Cone photoreceptors also require retinal for normal color vision.

Epithelial Cell Function

• Vitamin A maintains the structure and function of epithelial cells lining the respiratory, gastrointestinal, urinary, and reproductive tracts.
• It promotes mucus secretion and prevents excessive keratinization of epithelial surfaces.
• Deficiency increases susceptibility to infections because epithelial barriers become damaged.

On Bone and Teeth Formation

• Vitamin A regulates cell proliferation and differentiation during growth.
• It supports normal bone remodeling by maintaining balanced osteoblast and osteoclast activity.
• Severe deficiency during childhood may impair normal skeletal growth and development.

On Reproduction

• Vitamin A is required for normal spermatogenesis and healthy reproductive function.
• It supports normal embryonic development and fetal growth during pregnancy.

On Immunity

• Beta-carotene acts as an antioxidant by reducing oxidative damage caused by free radicals.
• Vitamin A supports both innate and adaptive immunity by maintaining epithelial barriers and promoting normal lymphocyte function.
• Adequate vitamin A intake improves resistance to infections and supports normal wound healing.

Vitamin A Dysfunctions

Vitamin A Deficiency

• Vitamin A deficiency initially causes night blindness due to impaired rhodopsin regeneration and defective dark adaptation.
• Progressive deficiency produces xerophthalmia, conjunctival dryness, Bitot spots, corneal dryness, and keratomalacia, which may lead to irreversible blindness.
• Deficiency also impairs epithelial integrity, immune function, and normal growth.

Vitamin A Toxicity

• Excessive vitamin A intake causes hypervitaminosis A, presenting with headache, nausea, vomiting, dry skin, hair loss, bone pain, and liver toxicity.
• Chronic toxicity may produce raised intracranial pressure, skeletal abnormalities, and teratogenic effects during pregnancy.

Vitamin D

• Vitamin D is a fat-soluble vitamin that regulates calcium and phosphate balance and maintains normal bone health.
• The two major forms are vitamin D2 (ergocalciferol) from plant sources and vitamin D3 (cholecalciferol) from animal sources and skin synthesis.
• Vitamin D3 is synthesized in the skin from 7-dehydrocholesterol following exposure to ultraviolet B radiation.
• Vitamin D is converted in the liver to 25-hydroxyvitamin D and then in the kidneys to calcitriol (1,25-dihydroxyvitamin D), the biologically active form.

Sources and Daily Requirement

• Rich dietary sources include fish liver oils, fatty fish, egg yolk, fortified milk, butter, and cheese.
• Sensible sunlight exposure is an important natural source of vitamin D.
• The recommended dietary intake is 600 International Units (15 micrograms) daily for most adults and 400 International Units (10 micrograms) for infants.
• Requirements increase during pregnancy, lactation, older age, and conditions associated with reduced sunlight exposure.

Functions of Vitamin D

• Vitamin D enhances intestinal absorption of calcium and phosphate and promotes normal bone mineralization.
• It also supports muscle function, neuromuscular coordination, and immune regulation.

Vitamin D Dysfunctions

• Vitamin D deficiency causes rickets in children, osteomalacia in adults, muscle weakness, and an increased risk of fractures.
• Premature infants and exclusively breastfed infants without supplementation are particularly susceptible to deficiency because breast milk contains limited vitamin D.
• Excessive vitamin D intake causes hypervitaminosis D, resulting in hypercalcemia, anorexia, nausea, constipation, polyuria, dehydration, and weakness.
• Chronic toxicity may lead to kidney stones and abnormal calcium deposition in soft tissues, including the kidneys, blood vessels, lungs, heart, and gastric mucosa.

Vitamin E

• Vitamin E is a fat-soluble vitamin that primarily functions as a powerful antioxidant.
• It consists of eight naturally occurring compounds, including four tocopherols and four tocotrienols.
• Alpha-tocopherol is the principal biologically active form in humans and is preferentially retained in the body.

Sources of Vitamin E

• Rich sources include vegetable oils such as sunflower, soybean, safflower, corn, and wheat germ oil.
• Nuts, seeds, whole grains, green leafy vegetables, eggs, and avocados also provide significant amounts.
• Food processing and prolonged storage may reduce vitamin E content.
• The recommended dietary intake for adults is approximately 15 milligrams of alpha-tocopherol daily.
• Requirements are slightly higher during pregnancy and lactation.

Functions of Vitamin E

• Vitamin E protects polyunsaturated fatty acids within cell membranes from oxidative damage.
• It neutralizes free radicals and limits lipid peroxidation, thereby preserving membrane stability.
• It maintains the structural integrity and survival of red blood cells.
• It supports normal immune function by enhancing lymphocyte activity.
• It contributes to neuromuscular function and protects nervous tissue from oxidative injury.
• Vitamin E works synergistically with vitamin C and selenium in antioxidant defense.
• It may reduce oxidative stress associated with chronic inflammatory conditions, although supplementation does not consistently prevent cardiovascular disease or cancer.

Effects of Deficiency

• Vitamin E deficiency is uncommon in healthy individuals because it is widely available in foods.
• It usually occurs in disorders causing fat malabsorption or inherited defects of vitamin E transport.
• Deficiency increases susceptibility of red blood cells to oxidative injury, producing hemolytic anemia.
• Neurological manifestations include peripheral neuropathy, ataxia, muscle weakness, and impaired vibration sense.
• Premature infants are particularly susceptible because of limited body stores and immature antioxidant defenses.
• Severe deficiency may produce retinal dysfunction and reduced immune responses.

Vitamin K

• Vitamin K is a fat-soluble vitamin essential for normal blood coagulation and bone metabolism.
• The major forms are phylloquinone (vitamin K1) from plants and menaquinones (vitamin K2) produced by intestinal bacteria and obtained from some animal and fermented foods.

Source and Daily Requirement

• Green leafy vegetables, broccoli, cabbage, spinach, kale, and vegetable oils are excellent dietary sources.
• Smaller amounts are present in meat, eggs, dairy products, and fermented foods.
• Normal intestinal microbiota also synthesize menaquinones that contribute to vitamin K status.
• Adults generally require about 90–120 micrograms of vitamin K daily.
• Body stores are limited, making regular dietary intake important.

Functions

• Vitamin K acts as a cofactor for gamma-carboxylation of glutamate residues in specific proteins.
• This modification activates coagulation factors II, VII, IX, and X, and proteins C and S.
• It is also required for activation of osteocalcin and other proteins involved in bone mineralization.
• Adequate vitamin K supports normal hemostasis and skeletal health.

Deficiency

• Deficiency results in impaired coagulation and prolonged bleeding.
• Newborn infants are particularly susceptible because of low hepatic stores, limited placental transfer, and immature intestinal microbiota.
• Prolonged antibiotic therapy, fat malabsorption, and chronic liver disease increase the risk of deficiency.
• Vitamin K deficiency is prevented in newborns by routine prophylactic administration after birth.

Vitamin C

• Vitamin C, also known as ascorbic acid, is a water-soluble vitamin required for numerous metabolic processes.
• Humans cannot synthesize vitamin C because they lack the enzyme required for its final biosynthetic step.
• Therefore, regular dietary intake is essential.
• Vitamin C is absorbed mainly in the jejunum and ileum by sodium-dependent transport mechanisms.
• Excess amounts are excreted in urine because body storage is limited.

Dietary Sources and Daily Requirements

• Citrus fruits, guava, amla, kiwi, strawberries, papaya, tomatoes, bell peppers, broccoli, cabbage, and green leafy vegetables are excellent sources.
• Fresh fruits and vegetables provide the highest concentrations.
• Vitamin C is destroyed by prolonged cooking, exposure to air, and excessive heat.
• The recommended dietary intake for adults is 75 milligrams daily for women and 90 milligrams daily for men.
• Requirements increase during pregnancy, lactation, smoking, severe infections, and wound healing.

Functions

• Vitamin C is essential for hydroxylation of proline and lysine during collagen synthesis.
• It maintains the strength of connective tissues, blood vessels, skin, cartilage, bones, teeth, and ligaments.
• It promotes normal wound healing by supporting collagen formation.
• It enhances intestinal absorption of iron by converting ferric iron to the more absorbable ferrous form.
• It facilitates normal iron utilization and helps reduce the risk of iron deficiency anemia.
• Vitamin C functions as a potent antioxidant by scavenging reactive oxygen species.
• It regenerates oxidized vitamin E and strengthens the body’s antioxidant defense system.
• It participates in synthesis of carnitine, supporting mitochondrial fatty acid transport and energy production.
• It contributes to synthesis of neurotransmitters, including norepinephrine.
• Vitamin C supports immune cell function, epithelial barrier integrity, and host defense against infections.
• It participates in folate metabolism by maintaining folate in its biologically active reduced form.
• It also contributes to cholesterol metabolism and several detoxification reactions in the liver.

Deficiency of Vitamin C

• Vitamin C deficiency causes scurvy, resulting from defective collagen synthesis.
• Early manifestations include fatigue, weakness, irritability, and poor appetite.
• Fragile capillaries lead to petechiae, bruising, bleeding gums, and mucosal hemorrhages.
• Wounds heal slowly because collagen formation is impaired.
• Bone growth is reduced in children, and fractures occur more easily.
• Teeth may loosen because periodontal connective tissue becomes weak.
• Iron absorption decreases, increasing the risk of microcytic iron deficiency anemia.
• Severe untreated deficiency may result in extensive hemorrhage, poor tissue repair, and increased susceptibility to infections.

Thiamine (Vitamin B1)

• Thiamine is a water-soluble vitamin essential for energy production and normal nervous system function.
• It is rapidly depleted because body stores are limited and regular dietary intake is required.
• Tissues with high metabolic activity, such as the brain, heart, and skeletal muscles, have the greatest thiamine requirement.

Sources and Daily Requirements

• Rich plant sources include whole grains, unpolished rice, wheat bran, legumes, peas, beans, nuts, and seeds.
• Animal sources include liver, pork, meat, eggs, milk, and fortified cereals.
• Milling and excessive polishing of grains markedly reduce thiamine content.
• The recommended dietary intake for adults is approximately 1.1–1.2 milligrams daily.
• Requirements increase during pregnancy, lactation, rapid growth, fever, and diets rich in carbohydrates.

Functions of Thiamine

• Thiamine is converted to thiamine pyrophosphate, the active coenzyme form.
• It plays a central role in carbohydrate metabolism and cellular energy production.
• Thiamine pyrophosphate is an essential coenzyme for pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, and branched-chain alpha-ketoacid dehydrogenase.
• It is also required for transketolase activity in the pentose phosphate pathway.
• Adequate thiamine supports adenosine triphosphate production and normal mitochondrial function.
• It is essential for normal nerve impulse conduction and maintenance of neuronal integrity.
• The heart depends on adequate thiamine because of its continuous requirement for aerobic energy production.

Thiamine Deficiency (Beriberi)

• Thiamine deficiency results in beriberi, which primarily affects the cardiovascular and nervous systems.
• Deficiency reduces oxidative metabolism, causing accumulation of pyruvate and lactate with impaired energy production.
• Individuals with chronic alcohol use disorder are at increased risk because of poor intake, reduced intestinal absorption, impaired utilization, and decreased hepatic storage.

Wet Beriberi

• Wet beriberi predominantly affects the cardiovascular system.
• Peripheral vasodilation increases cardiac workload and may lead to high-output heart failure.
• Clinical features include tachycardia, cardiomegaly, warm extremities, edema, and breathlessness.

Dry Beriberi

• Dry beriberi primarily affects the peripheral nervous system.
• Patients develop symmetrical peripheral neuropathy with numbness, tingling, burning sensations, muscle weakness, and loss of tendon reflexes.
• Severe motor involvement may produce foot drop or wrist drop because of muscle weakness.

Wernicke–Korsakoff Syndrome

• Severe thiamine deficiency, particularly in chronic alcohol use disorder, may cause Wernicke encephalopathy.
• Typical features include confusion, ophthalmoplegia, nystagmus, and gait ataxia.
• Untreated disease may progress to Korsakoff syndrome, characterized by profound memory impairment and confabulation.
• Prompt administration of thiamine before glucose therapy is essential in susceptible patients to prevent neurological deterioration.

Infantile Deficiency

• Infants of mothers with severe thiamine deficiency may develop infantile beriberi.
• Clinical manifestations include poor feeding, vomiting, tachycardia, heart failure, aphonia, convulsions, and respiratory distress.
• Early diagnosis and thiamine replacement usually produce rapid clinical improvement.

Riboflavin (Vitamin B2)

• Riboflavin is a water-soluble vitamin that is essential for cellular energy production and normal growth.
• It is the precursor of the coenzymes flavin adenine dinucleotide and flavin mononucleotide, which participate in numerous oxidation–reduction reactions.
• These coenzymes are components of many flavoproteins involved in cellular metabolism.

Sources and Daily Requirements

• Rich sources include milk, yogurt, eggs, liver, lean meat, fish, whole grains, legumes, mushrooms, almonds, and green leafy vegetables.
• Riboflavin is sensitive to light, and prolonged exposure reduces its concentration in foods.
• Adults require approximately 1.1–1.3 milligrams of riboflavin daily.
• Requirements increase during pregnancy, lactation, and periods of rapid growth.

Function of Riboflavin

• Riboflavin is essential for oxidative phosphorylation and efficient production of adenosine triphosphate.
• It supports carbohydrate, lipid, and protein metabolism.
• It facilitates the conversion of vitamin B6 and folate into their biologically active coenzyme forms.
• It contributes to normal cell growth, tissue repair, and maintenance of healthy skin and mucous membranes.
• Riboflavin also supports normal vision and antioxidant defense through its role in glutathione metabolism.

Effect of Deficiency

• Riboflavin deficiency causes angular cheilitis, fissuring at the corners of the mouth, glossitis, seborrheic dermatitis, and inflammation of oral mucosa.
• Ocular manifestations include conjunctival irritation, photophobia, excessive tearing, and corneal vascularization.
• Deficiency commonly occurs with generalized malnutrition or multiple vitamin deficiencies.

Niacin (Nicotinic Acid)

• Niacin includes nicotinic acid and nicotinamide, both of which are converted into active coenzymes.
• The body can synthesize limited amounts of niacin from the essential amino acid tryptophan, provided adequate vitamin B6 is available.

Sources and Daily Requirements

• Good sources include liver, poultry, fish, lean meat, peanuts, legumes, whole grains, mushrooms, and fortified cereals.
• Milk and eggs contain relatively little niacin but are rich in tryptophan, which contributes to endogenous niacin synthesis.
• Adults require approximately 14–16 milligrams of niacin equivalents daily.
• Requirements increase during pregnancy and lactation.

Functions of Niacin

• Niacin forms the coenzymes nicotinamide adenine dinucleotide and nicotinamide adenine dinucleotide phosphate.
• These coenzymes participate in numerous oxidation–reduction reactions essential for energy metabolism.
• They support metabolism of carbohydrates, fats, proteins, and alcohol.
• Nicotinamide adenine dinucleotide phosphate is essential for fatty acid synthesis, cholesterol synthesis, antioxidant defense, and biosynthetic reactions.
• Pharmacological doses of nicotinic acid can reduce triglyceride and low-density lipoprotein cholesterol concentrations, but routine use is limited because of adverse effects.

Effects of Deficiency

• Niacin deficiency causes pellagra.
• Classical manifestations include dermatitis, diarrhea, and dementia.
• The skin lesions occur mainly on sun-exposed areas and become hyperpigmented, rough, and scaly.
• Untreated severe deficiency may progress to confusion, neurological impairment, and death.

Pyridoxine (Vitamin B6)

• Vitamin B6 includes pyridoxine, pyridoxal, and pyridoxamine.
• The active coenzyme form is pyridoxal phosphate.
• Skeletal muscle stores a substantial proportion of body vitamin B6.

Dietary Sources

• Rich sources include whole grains, legumes, potatoes, bananas, nuts, poultry, fish, liver, eggs, and fortified cereals.
• The recommended dietary intake for adults is approximately 1.3–1.7 milligrams daily.

Functions of Vitamin B6

• Pyridoxal phosphate is an essential coenzyme in amino acid metabolism, including transamination, deamination, and decarboxylation reactions.
• It is required for synthesis of important neurotransmitters, including gamma-aminobutyric acid, dopamine, serotonin, norepinephrine, and histamine.
• Vitamin B6 is necessary for heme synthesis and normal hemoglobin production.
• It supports glycogen breakdown through its role in glycogen phosphorylase activity.
• It participates in homocysteine metabolism by facilitating conversion of homocysteine to cysteine.
• Vitamin B6 is required for conversion of tryptophan into niacin.
• Deficiency increases urinary excretion of xanthurenic acid, which may be detected after a tryptophan load and indicates impaired tryptophan metabolism.
• It also contributes to normal immune function and lipid metabolism.

Deficiency of Pyridoxine

• Vitamin B6 deficiency may occur because of malnutrition, chronic alcohol use disorder, malabsorption, chronic kidney disease, or prolonged treatment with drugs such as isoniazid.
• Clinical manifestations include microcytic or sideroblastic anemia, cheilosis, glossitis, peripheral neuropathy, depression, irritability, and impaired immunity.
• Infants with severe deficiency may develop seizures because of reduced synthesis of gamma-aminobutyric acid.
• Excessive long-term supplementation with high doses of vitamin B6 can also cause sensory neuropathy.

Pantothenic Acid

• Pantothenic acid is a water-soluble vitamin required for normal cellular metabolism.
• Its biologically active form is coenzyme A, which is essential for numerous metabolic reactions.
• Coenzyme A participates in the formation and utilization of acetyl coenzyme A, a key intermediate in energy metabolism.

Functions

• Coenzyme A is essential for metabolism of carbohydrates, lipids, and proteins.
• It combines with oxaloacetate to form citrate, initiating the citric acid cycle.
• It is required for synthesis of acetylcholine, cholesterol, steroid hormones, and ketone bodies.
• It participates in fatty acid synthesis, elongation, and oxidation.
• Pantothenic acid also supports normal energy production and cellular growth.

Sources and Daily Requirements

• Pantothenic acid is widely distributed in foods, making dietary deficiency uncommon.
• Rich sources include liver, kidney, meat, poultry, fish, eggs, whole grains, legumes, mushrooms, milk, and yogurt.
• Adults require approximately 5 milligrams daily.
• Requirements increase during pregnancy and lactation.

Effects of Deficiency

• Deficiency is rare because pantothenic acid is widely available in foods.
• It may occur in severe malnutrition or prolonged inadequate nutrition.
• Clinical features include fatigue, irritability, numbness, paresthesia, and burning feet syndrome.

Folic Acid

• Folic acid is a water-soluble vitamin essential for DNA synthesis, cell division, and normal erythropoiesis.
• The biologically active form is tetrahydrofolate, which transfers one-carbon units during metabolic reactions.

Dietary Sources

• Major sources include green leafy vegetables, legumes, citrus fruits, liver, beans, peas, and fortified cereals.

Daily Requirement

• Adults require approximately 400 micrograms of dietary folate equivalents daily.
• Pregnancy increases the requirement to 600 micrograms daily.

Functions

• Folate is required for synthesis of purines, thymidylate, and nucleic acids.
• It promotes normal maturation of red blood cells by supporting DNA synthesis.
• Folate is essential for rapid cell division during fetal growth.
• Adequate supplementation before conception and during early pregnancy markedly reduces the risk of neural tube defects.

Deficiency

• Folate deficiency causes megaloblastic anemia with enlarged, immature red blood cells.
• Deficiency may result from poor diet, malabsorption, alcoholism, pregnancy, or drugs that inhibit folate metabolism.
• Increased urinary formiminoglutamate excretion after a histidine load supports the diagnosis of folate deficiency.

Vitamin B12

• Vitamin B12 is a water-soluble vitamin required for DNA synthesis, neurological function, and red blood cell maturation.
• It is stored mainly in the liver, and body stores are usually sufficient for several years.

Dietary Sources

• Vitamin B12 is naturally present in liver, meat, fish, eggs, milk, and other animal-derived foods.
• Individuals following a strict vegan diet are at increased risk of deficiency without supplementation.

Absorption

• Absorption requires intrinsic factor, which is secreted by gastric parietal cells.
• The vitamin–intrinsic factor complex is absorbed in the terminal ileum.

Functions

• Vitamin B12 supports normal DNA synthesis and maturation of erythrocytes.
• It is required for myelin maintenance and normal neurological function.
• It participates in methionine synthesis and metabolism of methylmalonic acid.

Deficiency

• Vitamin B12 deficiency causes megaloblastic anemia, peripheral neuropathy, impaired vibration sense, and cognitive dysfunction.
• Pernicious anemia results from autoimmune loss of intrinsic factor, leading to impaired vitamin B12 absorption.
• Deficiency may also occur after gastrectomy, chronic gastritis, terminal ileal disease, or prolonged malabsorption.
• Increased methylmalonic acid concentration is a sensitive biochemical marker of vitamin B12 deficiency.

Minerals and Electrolytes

• Minerals are essential micronutrients required for normal growth, metabolism, tissue maintenance, and physiological functions.
• More than 20 minerals are essential for human health and are obtained through a balanced diet.
• Animal foods generally provide minerals with higher bioavailability than many plant foods.
• In cereals and legumes, minerals are concentrated mainly in the outer layers; therefore, excessive refining reduces mineral content.
• Mineral deficiency may result from inadequate intake, impaired absorption, increased physiological requirements, excessive losses, or chronic diseases.

Calcium and Phosphorus

• Calcium and phosphorus are the principal minerals responsible for the formation and maintenance of bones and teeth.
• Milk, yogurt, cheese, and other dairy products are excellent sources of calcium.
• Phosphorus is abundant in meat, fish, eggs, dairy products, legumes, nuts, and whole grains.
• Approximately 99 percent of body calcium and 85 percent of body phosphorus are stored in the skeleton.
• Calcium is essential for muscle contraction, nerve impulse transmission, blood coagulation, hormone secretion, and activation of several enzymes.
• Phosphorus forms an integral part of adenosine triphosphate, nucleic acids, phospholipids, and intracellular signaling molecules.
• Phosphate groups regulate enzyme activity through phosphorylation and play a major role in cellular metabolism.

Iron

• Iron is an essential trace element required for oxygen transport and cellular respiration.
• An adult body contains approximately 3–4 grams of iron.
• Most body iron is present in hemoglobin, while the remainder is found in myoglobin, ferritin, hemosiderin, transferrin, and cytochromes.
• Rich dietary sources include liver, lean meat, fish, poultry, legumes, green leafy vegetables, and fortified cereals.
• Cooking in iron utensils can modestly increase the iron content of food.
• Vitamin C enhances absorption of non-heme iron, whereas phytates and tannins reduce its absorption.
• Iron is essential for hemoglobin synthesis, oxygen transport, electron transport, immune function, and DNA synthesis.
• Adult men require approximately 8 milligrams of iron daily, while premenopausal women require about 18 milligrams because of menstrual losses.
• Requirements increase further during pregnancy.
• Iron deficiency is the most common nutritional deficiency worldwide.
• Deficiency produces microcytic hypochromic anemia, resulting in fatigue, pallor, reduced exercise tolerance, impaired cognition, and decreased work capacity.

Iodine

• Iodine is an essential component of thyroid hormones.
• Seafood, dairy products, eggs, and iodized salt are the principal dietary sources.
• Adults require approximately 150 micrograms of iodine daily.
• Requirements increase during pregnancy and lactation.
• Adequate iodine intake is necessary for normal growth, metabolism, and neurological development.
• Deficiency causes goiter, hypothyroidism, and impaired neurodevelopment in fetuses and children.

Zinc

• Zinc is an essential trace element involved in numerous enzymatic and cellular processes.
• The body contains approximately 2–3 grams of zinc, mainly in muscles and bones.
• Good dietary sources include meat, seafood, poultry, dairy products, legumes, nuts, and whole grains.
• Zinc absorption from plant foods may be reduced by phytates.
• Zinc serves as a cofactor for hundreds of enzymes involved in protein synthesis, nucleic acid metabolism, antioxidant defense, and cell division.
• It is essential for normal growth, sexual maturation, immune function, wound healing, and maintenance of taste and smell.
• Adults generally require 8–11 milligrams of zinc daily, with increased needs during pregnancy and lactation.
• Zinc deficiency causes growth retardation, delayed sexual maturation, impaired wound healing, loss of appetite, diminished taste and smell, dermatitis, and increased susceptibility to infections.
• An inherited disorder, acrodermatitis enteropathica, causes impaired intestinal zinc absorption and severe zinc deficiency unless treated.

Selenium

• Selenium is an essential trace element required in very small amounts for normal physiological function.
• Dietary selenium content depends largely on the selenium concentration of the soil where food is produced.
• Good sources include seafood, meat, eggs, dairy products, whole grains, nuts, and cereals.
• Selenium is a component of glutathione peroxidase and other selenoproteins that protect cells from oxidative damage.
• The recommended daily intake for adults is approximately 55 micrograms.
• Selenium deficiency may occur with prolonged parenteral nutrition, severe malabsorption, or low dietary intake.
• Deficiency is associated with Keshan disease, impaired immunity, thyroid dysfunction, and increased oxidative stress.

Recommended Dietary Allowances

• Recommended dietary allowances represent the average daily intake of nutrients needed to meet the nutritional requirements of nearly all healthy individuals in a specific population.
• These recommendations vary according to age, sex, body size, physical activity, pregnancy, lactation, and certain physiological conditions.
• Nutrient requirements may also change during illness, recovery, or chronic disease.
• Recommended dietary allowances are used to plan balanced diets, assess nutritional adequacy, and develop public health nutrition programs.

Balanced Diet

• A balanced diet supplies sufficient energy and all essential nutrients in appropriate proportions to maintain health and normal body functions.
• It should provide adequate carbohydrates, proteins, fats, vitamins, minerals, dietary fiber, and water.
• Total energy intake should match an individual’s age, body weight, sex, and level of physical activity.
• Protein intake should meet recommended requirements to support growth, tissue repair, and maintenance.
• Whole grains, cereals, and legumes provide energy, protein, and dietary fiber.
• A combination of cereals and pulses improves the overall quality of dietary protein by supplying complementary amino acids.
• Adults should consume at least 400 grams of fruits and vegetables daily to ensure adequate intake of vitamins, minerals, fiber, and antioxidants.
• Milk and dairy products provide calcium, high-quality protein, and several essential vitamins.
• Children, adolescents, pregnant women, and lactating women have increased nutritional requirements and benefit from additional nutrient-dense foods, including eggs, fish, meat, or well-planned plant-based alternatives.

Disorders of Nutrition

Malnutrition

• Malnutrition refers to an imbalance between nutrient intake and the body’s nutritional requirements.
• It may result from inadequate food intake, poor dietary quality, impaired absorption, chronic infections, parasitic diseases, poverty, poor sanitation, or limited access to healthcare.
• Children are particularly vulnerable because of rapid growth and increased nutrient requirements.
• Protein-energy malnutrition includes marasmus and kwashiorkor, which differ in their predominant nutritional deficiency and clinical features.

Kwashiorkor

• Kwashiorkor occurs primarily because of severe dietary protein deficiency despite relatively adequate calorie intake.
• Clinical features include edema, fatty liver, muscle wasting, growth retardation, skin and hair changes, impaired immunity, and increased susceptibility to infections.
• Early recognition and timely nutritional rehabilitation are essential to reduce complications and mortality.

Table 161.4: Recommended dietary allowance (RDA) for Indians as finalized by ICMR, 1990.

Population Group	Energy	Protein	Key Micronutrient Recommendations
Adult men (moderate activity)	2875 kilocalories/day	60 grams/day	Calcium: 400 milligrams, Iron: 28 milligrams, Vitamin A: 600 micrograms, Vitamin C: 40 milligrams, Folate: 100 micrograms, Vitamin B12: 1 microgram
Adult women (moderate activity)	2225 kilocalories/day	50 grams/day	Calcium: 400 milligrams, Iron: 30 milligrams, Vitamin A: 600 micrograms, Vitamin C: 40 milligrams
Pregnancy	2525 kilocalories/day	65 grams/day	Higher requirements for calcium (1000 milligrams), iron (38 milligrams), and folate (400 micrograms)
Lactation	2775 kilocalories/day	75 grams/day	Increased needs for calcium (1000 milligrams), vitamin A (950 micrograms), vitamin C (80 milligrams), and vitamin B12 (1.5 micrograms)
Infants, children, and adolescents	Requirements increase progressively with age, body weight, growth rate, and pubertal development to support normal growth and tissue maturation.

Clinical Features

• The most prominent clinical feature is pitting edema, which begins in the feet and gradually becomes generalized because of reduced plasma albumin and decreased oncotic pressure.
• Children develop marked muscle wasting despite the presence of edema.
• Fatty liver causes hepatomegaly and abdominal distension due to impaired lipoprotein synthesis.
• Other manifestations include anemia, poor appetite, diarrhea, malabsorption, skin and hair changes, growth retardation, weakness, and apathy.
• Severe protein deficiency also impairs immune function, increasing susceptibility to infections.

Biochemical Changes

• Plasma concentrations of albumin, transferrin, and retinol-binding protein are reduced.
• Hormonal changes include elevated cortisol and growth hormone concentrations with impaired protein synthesis.

Treatment

• Treatment requires gradual nutritional rehabilitation using energy-rich, protein-rich foods with careful correction of fluid and electrolyte imbalances.
• Micronutrient supplementation, including vitamins and minerals, is essential during recovery.
• Severe infections should be treated promptly with appropriate antibiotics, and intestinal parasitic infestations should be managed when present.
• Severe anemia may require iron therapy after stabilization or blood transfusion when clinically indicated.
• Continued nutritional counseling and regular follow-up help prevent recurrence and promote normal growth.

Marasmus

• Marasmus is a severe form of protein-energy malnutrition caused by prolonged deficiency of both calories and protein.
• It commonly affects infants and young children with inadequate food intake.
• Affected children have marked wasting of skeletal muscles and subcutaneous fat, producing a severely emaciated appearance.
• Body weight is usually less than 60 percent of the expected weight for age.
• Edema is absent, distinguishing marasmus from kwashiorkor.
• Skin becomes thin and loose, but significant skin and hair changes are usually minimal.
• Treatment consists of gradual nutritional rehabilitation with balanced energy, protein, vitamins, minerals, adequate hydration, and management of associated infections.

Obesity

• Obesity is a chronic disease characterized by excessive accumulation of body fat resulting from long-term positive energy balance.
• Genetic, environmental, behavioral, hormonal, and socioeconomic factors contribute to its development.
• Obesity increases the risk of type 2 diabetes mellitus, hypertension, coronary artery disease, obstructive sleep apnea, osteoarthritis, fatty liver disease, and several cancers.
• In obesity, both the size and number of adipocytes may increase during growth, while weight loss mainly reduces adipocyte size in adults.
• Prevention through a balanced diet, regular physical activity, adequate sleep, and healthy lifestyle habits is more effective than treating established obesity.
• Early intervention reduces long-term metabolic and cardiovascular complications and improves overall health outcomes.

Etiopathogenesis

• Obesity is a chronic metabolic disease resulting from prolonged positive energy balance, where energy intake exceeds energy expenditure.
• Its development involves interactions between genetic susceptibility, environmental influences, dietary habits, physical inactivity, and behavioral factors.
• Easy access to energy-dense foods and sedentary lifestyles are major contributors to the global rise in obesity.
• Secondary obesity may occur because of endocrine disorders such as hypothyroidism, Cushing syndrome, and certain genetic disorders or medications.

Neural Mechanisms

• Food intake is regulated by complex interactions between the central nervous system, peripheral hormones, and gastrointestinal signals.
• The hypothalamus is the principal brain region controlling hunger, satiety, and energy homeostasis.
• The lateral hypothalamic area stimulates feeding behavior and promotes food intake.
• The ventromedial hypothalamic nucleus functions as a satiety center and suppresses feeding after adequate nutrient intake.
• Normal body weight is maintained through balanced activity of these hypothalamic centers.
• Peripheral hormones, including leptin, insulin, ghrelin, peptide YY, and glucagon-like peptide-1, continuously provide information regarding energy stores and nutritional status.
• Leptin released from adipose tissue suppresses appetite, whereas ghrelin released from the stomach stimulates hunger.
• The limbic system, particularly the amygdala and nucleus accumbens, regulates the reward, motivation, and emotional aspects of eating.
• Cortical areas integrate sensory, emotional, and cognitive influences, allowing voluntary control of feeding behavior.
• Stress, anxiety, sleep deprivation, and environmental cues can override physiological satiety mechanisms and promote overeating.

Measurement and Grades of Obesity

• Body mass index is the most widely used screening tool for assessing obesity in adults.
• Body mass index is calculated as body weight in kilograms divided by the square of height in meters.
• According to the World Health Organization, body mass index values are classified as:
  • Underweight: less than 18.5 kilograms per square meter
  • Normal: 18.5–24.9 kilograms per square meter
  • Overweight: 25.0–29.9 kilograms per square meter
  • Obesity Class I: 30.0–34.9 kilograms per square meter
  • Obesity Class II: 35.0–39.9 kilograms per square meter
  • Obesity Class III: 40 kilograms per square meter or higher
• For Asian populations, lower body mass index cut-off values are often used because metabolic risk develops at lower levels of adiposity.
• Waist circumference and waist-to-height ratio provide additional information about central obesity and cardiometabolic risk.
• Measurement of skinfold thickness, bioelectrical impedance analysis, and dual-energy X-ray absorptiometry can estimate body fat more accurately in selected individuals.

Physiological Basis of Management

• Long-term weight control requires restoration of energy balance by reducing caloric intake and increasing energy expenditure.
• A balanced diet with appropriate portion control and nutrient-dense foods is the foundation of treatment.
• Regular physical activity increases energy expenditure, preserves lean body mass, and improves insulin sensitivity.
• Behavioral modification, including self-monitoring, healthy eating habits, adequate sleep, and stress management, enhances long-term success.
• Family support and structured lifestyle interventions improve adherence to weight management programs.
• Pharmacological therapy or bariatric surgery may be considered for selected individuals with severe obesity or obesity-related complications when lifestyle measures alone are insufficient.
• Early intervention is important because sustained weight reduction lowers the risk of type 2 diabetes mellitus, cardiovascular disease, hypertension, and other obesity-related complications.