Principles of Nutrition

Introduction to Nutrition Science

Nutrition is the science of food intake and how food nourishes the body. It encompasses the study of nutrients, their metabolism, and the impact of human behavior and environment on food choices and nourishment. Nutrition is interdisciplinary, involving chemistry, biology, physiology, psychology, and socioeconomics.

• Nutrition: The study of how food and its components affect health, growth, and disease prevention.

• Nutrients: Biochemical substances in food used for growth, development, activity, reproduction, health maintenance, and recovery from illness or injury.

• Essential nutrients: Nutrients not synthesized by the body or made in insufficient amounts; must be obtained from the diet.

• Macronutrients: Carbohydrates, proteins, and fats—supply energy and build tissue.

• Micronutrients: Vitamins and minerals—required in smaller amounts to regulate and control body processes.

• Nonessential nutrients: Synthesized by the body or not required for body functioning.

Example: Excess carbohydrates and protein can be converted to fat and stored as triglycerides.

Energy Balance and Metabolic Requirements

Energy in the Diet

Energy is required for all body functions and is derived from carbohydrates, proteins, and fats. Energy is measured in kilocalories (calories).

• Only carbohydrates, proteins, and fats provide energy (4, 4, and 9 kcal/g, respectively).

• Total daily energy expenditure includes calories used for physical activity, basal metabolism, and digestion/absorption/metabolism of food.

• Energy balance: Weight remains stable if energy intake equals expenditure; weight decreases if intake is less than expenditure, and increases if intake exceeds expenditure.

Formula:

Basal Metabolic Rate (BMR)

BMR is the energy required for involuntary activities of the body at rest after a 12-hour fast.

• Includes maintaining body temperature, muscle tone, secretions, GI motility, lung inflation, and heart contraction.

• Factors increasing BMR: Growth, infection, fever, emotional tension, extreme temperatures, elevated hormones (epinephrine, thyroid).

• Factors decreasing BMR: Aging, prolonged fasting, sleep.

Body Weight Standards and Assessment

Body Mass Index (BMI)

BMI is a ratio of weight to height and is used to estimate body fat and assess nutritional status.

Formula:

• BMI < 18.5: Underweight

• BMI 18.5–24.9: Healthy weight

• BMI 25–29.9: Overweight

• BMI 30–39.9: Obesity

• BMI ≥ 40: Extreme obesity

BMI may not be accurate for athletes, those with edema/dehydration, or older adults with muscle loss.

Body Fat Distribution

• Central (abdominal) obesity increases risk for cardiovascular disease and diabetes.

• Waist circumference: Risk increases at ≥40 inches (men), ≥35 inches (women).

• Waist-to-hip ratio (WHR): Females <0.8, Males <0.95 is desirable.

Macronutrients

Carbohydrates

Carbohydrates are organic compounds (carbon, hydrogen, oxygen) and are the main energy source for the body.

• Classified as simple (monosaccharides, disaccharides) or complex (polysaccharides).

• Digested and converted to glucose, which is used for energy or stored as glycogen or fat.

• Primary function: Supply energy (4 kcal/g).

• Recommended intake: 45–65% of total calories, focusing on complex carbohydrates (whole grains).

Example: Glycogenesis (glucose to glycogen), Glycogenolysis (glycogen to glucose).

Proteins

Proteins are made of amino acids and are essential for body structure and function.

• Complete proteins: Contain all essential amino acids (e.g., animal proteins, soy, quinoa).

• Incomplete proteins: Deficient in one or more essential amino acids (e.g., most plant proteins).

• Complementary proteins: Combining plant proteins to provide all essential amino acids.

• Protein metabolism: Catabolism (breakdown), Anabolism (synthesis), Nitrogen balance (intake vs. excretion).

• Primary function: Build and repair tissues; can be used for energy (4 kcal/g).

Example: Cereal with milk (complementary proteins).

Lipids (Fats)

Lipids are insoluble in water and provide the most concentrated energy source (9 kcal/g).

• Types: Triglycerides (95% of dietary fat), phospholipids, cholesterol.

• Saturated fats: Solid at room temperature, mainly animal sources, raise serum cholesterol.

• Unsaturated fats: Liquid at room temperature, mainly plant sources, lower serum cholesterol.

• Trans fats: Raise LDL, lower HDL; mostly from processed foods; associated with increased disease risk.

• Cholesterol: Found only in animal products; not essential in the diet.

Example: Limiting saturated and trans fats helps reduce cardiovascular risk.

Regulatory Nutrients

Vitamins

Vitamins are organic compounds required in small amounts for metabolism and regulation of body processes.

• Water-soluble: Vitamin C, B-complex (not stored, excess excreted in urine).

• Fat-soluble: Vitamins A, D, E, K (stored in liver/adipose tissue; excess can be toxic).

• Deficiency or excess can cause specific syndromes.

• Supplements may be needed for certain populations (e.g., dieters, vegans, older adults).

Minerals

Minerals are inorganic elements essential for structure and regulation.

• Major minerals (>5g in body): Calcium, phosphorus, sodium, potassium, magnesium, chloride, sulfur.

• Trace elements (<5g): Iron, zinc, manganese, copper, selenium, iodine, fluoride, etc.

• Not destroyed by cooking, but can be lost in water.

Water

Water is vital for all chemical reactions, temperature regulation, and as a solvent and lubricant.

• Accounts for 50–60% of adult body weight; higher in infants.

• Sources: Beverages, foods, metabolic water.

• Average adult intake: ~2,600 mL/day.

• Balance affected by intake/output changes (e.g., illness, age).

Digestion and Absorption

Overview of Digestion

Digestion is the process of breaking down food into absorbable components.

• Begins in the mouth, continues in the stomach and small intestine.

• Enzymes and secretions from the GI tract, liver, and pancreas aid digestion.

• Most absorption occurs in the small intestine.

Dietary Guidelines and Tools for Healthful Eating

Dietary Guidelines for Americans

Science-based recommendations to promote health, published every 5 years.

• Encourage healthy eating patterns, appropriate calorie intake, and nutrient adequacy.

• Key recommendations: Variety, nutrient density, limit added sugars, saturated fat, sodium, and alcohol.

Dietary Reference Intakes (DRIs)

Reference values for nutrient intake to maintain health and prevent deficiencies.

• RDA: Average daily intake sufficient for nearly all healthy people.

• AI: Used when RDA cannot be determined; based on observed intakes.

• UL: Highest daily intake unlikely to cause toxicity.

• EAR: Estimated to meet needs of half the population.

• CDRR: Intake reduction expected to reduce chronic disease risk (currently sodium only).

MyPlate Food Guide

Visual tool to help consumers make healthy food choices, based on the Dietary Guidelines.

• Illustrates five food groups: fruits, vegetables, grains, protein, dairy.

• Emphasizes portion control, variety, and physical activity.

Nutrition Labeling

Nutrition labels provide standardized information to help consumers make informed choices.

• Required information: Serving size, calories, total fat, saturated/trans fat, cholesterol, sodium, carbohydrates, fiber, sugars, protein, vitamin D, potassium, calcium, iron.

• Helps compare foods and monitor nutrient intake.

Factors Affecting Nutrition

Physiologic and Physical Factors

• Developmental stage: Infancy, childhood, adolescence, adulthood, pregnancy/lactation, older age—all have unique nutrient needs.

• Sex assigned at birth: Males generally require more calories/protein; females of childbearing age need more iron.

• State of health: Illness, trauma, chronic disease, and mental health can alter requirements.

• Alcohol use disorder: Increases nutrient needs, impairs absorption and metabolism.

• Medications: Can alter absorption, metabolism, or excretion of nutrients.

• Megadoses of supplements: Can cause imbalances and interact with medications.

Sociocultural and Psychosocial Factors

• Economic status: Affects ability to purchase nutritious foods.

• Culture and religion: Influence food choices, preparation, and dietary restrictions.

• Social determinants: Literacy, language, social support, access to food markets.

• Personal meaning of food: Emotional, social, and psychological associations.

Assessment of Nutritional Status

Nutritional Screening and Assessment

• Screening tools (e.g., Mini Nutritional Assessment) identify risk for malnutrition.

• Assessment includes dietary history, physical assessment, anthropometric data, and laboratory data.

Methods of Dietary Assessment

• 24-hour recall: Patient recalls all food/beverages consumed in the past 24 hours.

• Food diaries/calorie counts: Record intake over several days.

• Food frequency records: Assess how often certain foods/groups are consumed.

Anthropometric Data

• Height, weight, BMI, waist circumference.

• Used to assess growth in children and body composition in adults.

Clinical and Biochemical Data

• Physical signs of malnutrition (see table below).

• Laboratory tests: Hemoglobin, hematocrit, prealbumin, transferrin, blood urea nitrogen, serum creatinine, blood glucose, cholesterol, triglycerides, urine tests for protein metabolism.

Modified Consistency Diets

Enteral Nutrition

Short-Term and Long-Term Support

• Short-term (<4 weeks): Nasogastric (NG) or nasointestinal (NI) tubes.

• Long-term (>4–6 weeks): Gastrostomy (PEG) or jejunostomy tubes.

• Indications: Inability to meet nutritional needs orally, but with functional GI tract.

Verification of Tube Placement

• Radiographic examination (x-ray): Gold standard for initial placement.

• Measurement of tube length/marking, aspirate pH, and carbon dioxide monitoring for ongoing checks.

• Gastric pH ≤5.5 suggests correct gastric placement; pH ≥6 may indicate respiratory or intestinal placement.

Administration of Enteral Nutrition

• Feeding schedules: Bolus, intermittent, continuous, or cyclic feeding.

• Formulas: Standard (intact nutrients) or hydrolyzed (pre-digested nutrients).

• Feeding pumps regulate delivery; flush tubes regularly to prevent blockage.

• Monitor for tolerance: Absence of nausea, vomiting, diarrhea, constipation, abdominal pain, distention.

• Keep head of bed elevated 30–45° during and after feeding to prevent aspiration.

Factors Affecting Food Intake

• Decreased intake: Anorexia, illness, psychosocial factors, difficulty chewing/swallowing, GI problems, inadequate budget.

• Increased intake: Overweight/obesity, sedentary lifestyle, energy-dense foods, social/emotional factors.

Nursing Process for Nutrition

Assessment, Diagnosis, Planning, Implementation, and Monitoring

• Assessment: Screening, history, physical, anthropometric, and laboratory data.

• Diagnosis: Identify actual/potential nutrition problems (e.g., impaired nutritional status, impaired swallowing, overweight).

• Planning: Set individualized goals (e.g., maintain ideal body weight, eat adequate diet, follow modified diet as needed).

• Implementation: Collaborate with dietitian, provide education, assist with eating, administer enteral/parenteral nutrition as needed.

• Monitoring: Observe intake, appetite, tolerance, weight, and progress toward goals.

Food Safety

• Wash hands and surfaces frequently.

• Wash fruits and vegetables; do not wash meat, poultry, or eggs.

• Cook foods to safe temperatures; refrigerate perishable foods promptly.

• Prevent cross-contamination by separating raw and cooked foods.

Special Considerations Across the Life Span

• Infants: Rapid growth; breast milk or iron-fortified formula recommended; introduce solids at ~6 months.

• Toddlers/Preschoolers: Growth slows; appetite may decrease; develop food preferences.

• School-age children: Gradual growth; focus on health promotion and balanced intake.

• Adolescents: Rapid growth; increased needs for calories, protein, calcium, iron; risk for eating disorders.

• Adults: Growth ceases; caloric needs decrease with age; focus on maintenance and prevention.

• Pregnancy/Lactation: Increased needs for calories, protein, iron, folic acid; lactation requires even more calories.

• Older adults: Decreased BMR, physical activity, lean body mass; increased need for protein, calcium, B12, vitamin D; risk for malnutrition and dehydration.

Summary Table: Biochemical Data with Nutritional Implications

Additional info: These notes integrate and expand upon the provided material with academic context, definitions, and examples to ensure a comprehensive, self-contained study guide for college-level nutrition students.