Nutrients required in large amounts, providing energy (calories) and structural components for the body, including carbohydrates, proteins, and lipids.
These are the 'big three' nutrients that fuel the body and build its tissues, unlike micronutrients which are needed in smaller quantities and do not provide energy.
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Micronutrients
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Nutrients required in small amounts (milligrams or micrograms) that do not provide energy but are essential for metabolic processes, including vitamins and minerals.
While not providing calories, micronutrients are crucial cofactors for enzymes and play vital roles in nearly all bodily functions, making their deficiency impactful.
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Essential Nutrient
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A nutrient that the body cannot synthesize on its own or cannot synthesize in sufficient quantities, and therefore must be obtained from the diet to prevent deficiency.
For example, Vitamin C is an essential nutrient because humans cannot produce it, unlike many other animals, leading to scurvy if not consumed.
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Carbohydrates
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Organic compounds composed of carbon, hydrogen, and oxygen, serving as the body's primary source of energy, particularly for the brain and muscles, classified into simple and complex forms.
Their quick breakdown into glucose makes them the preferred fuel source for high-intensity activities and brain function.
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Protein
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Complex organic macromolecules made up of amino acids linked by peptide bonds, essential for building, repairing, and maintaining body tissues, as well as producing enzymes and hormones.
Proteins are unique among macronutrients for containing nitrogen, which is critical for their diverse structural and functional roles in the body.
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Lipids
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A diverse group of organic compounds including fats, oils, and cholesterol, characterized by their insolubility in water and serving as concentrated energy storage, insulation, and protective cushioning for organs.
Beyond energy, lipids are vital for the absorption of fat-soluble vitamins and the synthesis of hormones, making them far more than just stored energy.
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Fiber
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A type of carbohydrate found in plant foods that the human digestive enzymes cannot break down, promoting digestive health by adding bulk to stool and helping regulate blood glucose and cholesterol levels.
Though indigestible, fiber is crucial for gut motility and fermentation by beneficial gut bacteria, contributing significantly to overall health.
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Mechanical Digestion
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The physical breakdown of food into smaller pieces, primarily through chewing in the mouth and churning in the stomach, increasing its surface area for subsequent enzymatic action.
This initial physical process is crucial because it creates smaller particles that digestive enzymes can more efficiently access and chemically break down.
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Chemical Digestion
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The enzymatic breakdown of complex food molecules into their simpler, absorbable units, such as carbohydrates into monosaccharides, proteins into amino acids, and fats into fatty acids and glycerol.
This process relies on specific enzymes, like amylase, proteases, and lipases, to chemically alter the food's structure, allowing nutrient absorption.
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Peristalsis
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The wave-like muscular contractions that propel food through the digestive tract, starting from the esophagus and continuing through the intestines, an involuntary action.
Peristalsis ensures that food moves unidirectionally through the GI tract, even against gravity, facilitating efficient digestion and absorption.
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Villi and Microvilli
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Finger-like projections (villi) and microscopic folds on their surface (microvilli) lining the small intestine, dramatically increasing the surface area for nutrient absorption.
This extensive folded structure, often called the 'brush border', is key to the small intestine's efficiency in absorbing nearly all digested nutrients.
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Bile
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A digestive fluid produced by the liver and stored in the gallbladder, which emulsifies fats in the small intestine, breaking large fat globules into smaller ones to facilitate digestion by lipases.
Bile acts like a detergent, increasing the surface area of fats for lipase enzymes to work on, an essential step for fat digestion and absorption.
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Absorption
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The process by which digested nutrients pass from the lumen of the gastrointestinal tract through the intestinal wall and into the bloodstream or lymphatic system for distribution throughout the body.
This is the final stage of nutrient uptake, where the body actually acquires the usable components from food, primarily occurring in the small intestine.
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Recommended Dietary Allowance (RDA)
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The average daily dietary nutrient intake level sufficient to meet the nutrient requirements of nearly all (97-98%) healthy individuals in a particular life stage and gender group.
The RDA is a target for individual intake, designed to prevent deficiency diseases and promote overall health for the vast majority of the population.
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Adequate Intake (AI)
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A recommended average daily nutrient intake level based on observed or experimentally determined approximations of nutrient intake by a group of healthy people, used when an RDA cannot be determined due to insufficient scientific evidence.
The AI is a 'best estimate' when robust data for an RDA is lacking, often used for nutrients like Vitamin K or fluoride.
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Tolerable Upper Intake Level (UL)
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The highest average daily nutrient intake level that is likely to pose no risk of adverse health effects to almost all individuals in the general population.
Exceeding the UL increases the risk of toxicity, particularly for fat-soluble vitamins and certain minerals that can accumulate in the body.
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Nutrient Density
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A measure of the nutrients provided per calorie of food, where foods with high nutrient density provide a significant amount of vitamins, minerals, and other beneficial substances with relatively few calories.
Prioritizing nutrient-dense foods (e.g., vegetables, fruits) helps meet nutrient needs without consuming excess energy, which is crucial for weight management and overall health.
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Energy Balance
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The relationship between the energy consumed from food and beverages (energy intake) and the energy expended through metabolic processes and physical activity (energy output).
Maintaining a stable body weight requires a state of neutral energy balance, where energy intake equals energy output.
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Basal Metabolic Rate (BMR)
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The minimum amount of energy required to maintain vital bodily functions (such as breathing, circulation, and cell production) while at rest, in a fasting state, and in a neutral temperature environment.
The BMR accounts for the largest portion (60-75%) of total daily energy expenditure for most people, representing the energy cost of simply being alive.
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Thermic Effect of Food (TEF)
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The energy expended by the body to digest, absorb, transport, metabolize, and store nutrients from food, typically accounting for about 5-10% of total energy expenditure.
Proteins have a higher TEF than carbohydrates or fats, meaning more energy is used to process them after consumption.
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Total Energy Expenditure (TEE)
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The sum of all energy expended by the body over a 24-hour period, including basal metabolic rate, thermic effect of food, and energy expended during physical activity.
Understanding TEE is fundamental for managing body weight, as it dictates how many calories an individual needs to consume to maintain, gain, or lose weight.
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Fat-soluble Vitamins
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Vitamins (A, D, E, K) that dissolve in fat and are stored in the body's fatty tissues and liver, meaning they can accumulate to toxic levels if consumed in excessive amounts.
Because they are stored, consistent excessive intake of fat-soluble vitamins, often from supplements, poses a higher risk of toxicity compared to water-soluble vitamins.
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Water-soluble Vitamins
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Vitamins (B vitamins and C) that dissolve in water and are not significantly stored in the body, meaning they must be regularly consumed and excess amounts are typically excreted in urine.
Their limited storage means daily intake is generally more critical for water-soluble vitamins, but also makes toxicity less common.
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Vitamin A Deficiency (Xerophthalmia)
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A condition resulting from inadequate intake of Vitamin A, leading to impaired vision, especially night blindness, and in severe cases can cause permanent blindness due to damage to the cornea.
Vitamin A is crucial for the visual cycle and maintaining epithelial tissues, making its deficiency a leading cause of preventable childhood blindness globally.
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Vitamin C Deficiency (Scurvy)
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A disease caused by prolonged lack of Vitamin C, characterized by fatigue, swollen and bleeding gums, poor wound healing, joint pain, and small red-blue spots on the skin due to impaired collagen synthesis.
Vitamin C is essential for collagen formation, a protein vital for connective tissues, explaining the widespread symptoms affecting skin, gums, and blood vessels.
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Vitamin D Deficiency (Rickets/Osteomalacia)
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A condition caused by insufficient Vitamin D, leading to impaired bone mineralization; in children, it manifests as rickets (soft, weak, deformed bones), and in adults, as osteomalacia (softening of bones, muscle weakness).
Vitamin D is crucial for calcium absorption and bone health, and its deficiency can result from inadequate dietary intake, insufficient sun exposure, or impaired metabolism.
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Iron Deficiency Anemia
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A common type of anemia resulting from insufficient iron to produce adequate hemoglobin, leading to symptoms like fatigue, weakness, pale skin, and shortness of breath due to reduced oxygen transport.
Iron is a critical component of hemoglobin in red blood cells, which carries oxygen throughout the body, making its deficiency a significant health concern, especially for women and children.
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Pellagra
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A disease caused by severe niacin (Vitamin B3) deficiency, characterized by the '4 D's': dermatitis, diarrhea, dementia, and eventually death if untreated.
Pellagra was historically associated with diets heavily reliant on corn, which is low in bioavailable niacin, highlighting the importance of dietary diversity.
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Ghrelin
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A hormone primarily produced by the stomach that stimulates appetite, often referred to as the 'hunger hormone,' with levels typically rising before meals and decreasing after eating.
Ghrelin plays a short-term role in appetite regulation, signaling to the brain when the body needs more energy.
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Leptin
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A hormone primarily produced by adipose (fat) tissue that signals satiety and helps regulate long-term energy balance by inhibiting hunger and increasing energy expenditure.
Leptin acts as a long-term signal of energy stores, communicating to the brain about the body's fat reserves and influencing overall energy intake.