Nutrition

Fundamentals of Nutrients and Nutritional Classes

• Definition of Nutrients: Nutrients are specific biochemical substances used by the body for various vital functions, including growth, development, activity, reproduction, lactation, health maintenance, and recovery from illness or injury.

• Classification by Necessity (Essentiality):

  • Essential Nutrients: These are substances that the body cannot synthesize on its own or makes in insufficient amounts to meet physiological needs. Consequently, they must be acquired through the diet or through supplementation.

• Classification by Body Function and Quantity:

  • Macronutrients: Nutrients that supply energy and provide the building blocks for tissue construction. These include carbohydrates, fats, and proteins.

  • Micronutrients: Nutrients required in smaller amounts to regulate and control various body processes. These include vitamins and minerals.

• The Six Classes of Nutrients:

  • Energy-Supplying Nutrients: Carbohydrates, Proteins, and Lipids (fats).

  • Regulatory Nutrients: Vitamins, Minerals, and Water.

Energy Balance and Metabolic Rate

• The Concept of Energy: Energy is obtained from the food consumed and is measured in kilocalories (often simply referred to as calories).

• Caloric Sources: Only three nutrients provide energy/calories: carbohydrates, proteins, and fats.

• Total Daily Energy Expenditure (TDEE): This represents the sum of all calories used for:

  • Performing physical activity.

  • Maintaining metabolism.

  • Digesting, absorbing, and metabolizing food.

• Total Daily Energy Intake: This is the sum of total calories for every food item consumed.

• Weight Stability: Variations between daily intake and expenditure determine weight status. A balance leads to stable weight, while differences result in weight loss or weight gain.

• Basal Metabolic Rate (BMR):

  • Definition: The number of calories required to fuel involuntary body activities at rest after a $12\text{-hour}$ fast. It represents the energy needed to sustain the basic metabolic activities of cells and tissues.

  • Sex Differences: Males typically have a higher BMR than females due to their larger muscle mass.

  • Factors Increasing BMR: Growth phases, infections, fever, emotional tension, exposure to extreme environmental temperatures, and elevated levels of specific hormones.

  • Factors Decreasing BMR: Aging, prolonged fasting, and sleep.

Body Mass Index (BMI) and Weight Status

• BMI Definition: A ratio calculated as weight in kilograms divided by height in meters squared ($\text{kg/m}^2$).

• Clinical Utility:

  • Provides an estimate of body fat.

  • Serves as an initial assessment of nutritional status.

  • Estimates relative risk for diseases associated with high body fat, such as heart disease, type 2 diabetes, hypertension, and certain cancers.

• Limitations: BMI calculation may be inaccurate for specific groups of people.

• Box 37-1: BMI-for-Age Percentiles (Children and Teens):

  • Underweight: Less than $5\text{th}$ percentile.

  • Healthy Weight: $5\text{th}$ percentile to less than the $85\text{th}$ percentile.

  • Overweight: $85\text{th}$ percentile to less than the $95\text{th}$ percentile.

  • Obese: $95\text{th}$ percentile or greater.

Body Fat Distribution and Disease Risk

• Central Abdominal Obesity: The location of body fat is a reliable indicator of disease risk. Fat deposited in the central abdominal area poses a significantly greater risk.

• Waist Circumference Thresholds: A waist measurement indicating increased risk for type 2 diabetes, hypertension, and cardiovascular disease (CVD) is defined as:

  • Men: $40\text{ inches}$ ($102\text{ cm}$) or more.

  • Women: $35\text{ inches}$ ($88\text{ cm}$) or more.

• Waist-to-Hip Ratio (WHR): A specific tool used to identify central obesity.

• Table 37-1: Overweight and Obesity Classification by BMI and Waist Circumference:

  • Normal Weight (BMI $18.5 - 24.9$): Low risk regardless of waist circumference.

  • Overweight (BMI $25.0 - 29.9$): Increased risk if waist is $\leq 35\text{ in}$ (women) or < 40\text{ in} (men); High risk if waist is > 35\text{ in} (women) or > 40\text{ in} (men).

  • Obesity Class I (BMI $30.0 - 34.9$): High risk if waist is \leq 35/ < 40\text{ in}; Very high risk if waist is higher.

  • Obesity Class II (BMI $35.0 - 39.9$): Very high risk regardless of waist circumference.

  • Extreme Obesity Class III (BMI $40.0+$): Extremely high risk regardless of waist circumference.

Carbohydrates: The Primary Fuel

• Composition: Organic compounds made of carbon, hydrogen, and oxygen.

• Sources: Primarily plants (sugars and starches). Lactose (milk sugar) is the only animal-derived carbohydrate source.

• Economic Correlation: Carbohydrates are the most abundant and least expensive calorie source globally. Intake often decreases as household income increases.

• Classification: Simple or complex sugars.

• Metabolism and Storage:

  • Carbs are more easily and quickly digested than fats or proteins.

  • Calculated as $90\%$ of carbohydrate intake being ingested.

  • Converted to glucose for transport in the blood. Tissues like the nervous system rely almost exclusively on glucose for energy.

  • Transported from the GI tract through the portal vein to the liver. The liver stores glucose and regulates its release into the bloodstream.

  • Cellular oxidation of glucose produces energy, carbon dioxide ($CO_2$), and water ($H_2O$).

• Recommendations: Carbohydrates should constitute $45\%$ to $60\%$ of total daily calories for adults.

Protein: The Building Blocks

• Structure: Required for every living cell and the formation of all body structures. Proteins are created by combining various of the $22$ known amino acids.

• Types of Protein:

  • Complete Proteins: Contain sufficient essential amino acids to support growth. Generally found in animal proteins.

  • Incomplete Proteins: Deficient in one or more essential amino acids. Generally found in plant proteins.

  • Exceptions: Soy and quinoa are plant-based complete proteins.

  • Vegetarian Considerations: Vegetarians can combine different plant proteins to form a complete protein.

• Metabolism:

  • Pancreatic enzymes in the small intestine break protein into amino acids.

  • Amino acids are absorbed and sent to the liver to be recombined into new proteins or released for tissue use.

  • Anabolism: The continuous replacement of tissue.

  • Catabolism: The continuous breakdown of tissue.

• Recommendations: The Recommended Dietary Allowance (RDA) for adults is $0.8\text{ g/kg}$ of body weight, or about $10\%$ to $35\%$ of total caloric intake.

Lipids (Fats)

• Characteristics: Insoluble in water and blood; composed of carbon, hydrogen, and oxygen. $95\%$ of dietary lipids are in the form of triglycerides.

• Fatty Acid Types:

  • Saturated Fatty Acids: Tend to raise cholesterol levels. Most animal fats are saturated.

  • Unsaturated Fatty Acids: Tend to lower cholesterol levels. Most vegetable fats are unsaturated.

• Digestion and Transport:

  • Digestion occurs primarily in the small intestine.

  • Bile, secreted by the liver and stored in the gallbladder, emulsifies fat.

  • Pancreatic enzymes then break down the emulsified fat.

  • Fats are absorbed into lymphatic circulation before being transported to the liver.

• Energy Density: The most concentrated source of energy in the human diet.

• Recommendations: Limit saturated fats to less than $10\%$ of daily calories; keep trans fats as low as possible.

Vitamins and Minerals

• Vitamins:

  • Organic compounds needed in small amounts that do not provide calories but are essential for the metabolism of macronutrients.

  • Water-Soluble: Vitamin C and B-complex vitamins. These are not stored in the body.

  • Fat-Soluble: Vitamins A, D, E, and K. These are absorbed through the intestinal wall into the bloodstream.

  • Note: Fresh foods generally have higher vitamin content than processed foods.

• Minerals:

  • Inorganic elements found in body fluids and tissues that remain as ash after digestion.

  • Macrominerals (Required in larger amounts): Calcium, phosphorus (phosphates), sulfur (sulfate), sodium, chloride, potassium, and magnesium.

  • Microminerals (Trace elements): Iron, zinc, manganese, chromium, copper, molybdenum, selenium, fluoride, and iodine.

Water and Fluid Balance

• Body Composition: Water accounts for $50\%$ to $60\%$ of total adult body weight.

• Fluid Compartments:

  • Intracellular Fluid (ICF): Two-thirds of body water is contained within cells.

  • Extracellular Fluid (ECF): The remaining one-third includes plasma and interstitial fluid.

• Functions: Provides the medium for all chemical reactions; acts as a solvent; aids in digestion, absorption, circulation, and excretion.

Factors Influencing Nutrition and Dietary Guidelines

• Selection Tools: Dietary Guidelines for Americans, Dietary Reference Intakes (DRIs), Recommended Dietary Allowance (RDA), MyPlate food guide, and Food labeling.

• Physiologic Factors: Stage of development, state of health, medications, and sex assigned at birth.

• Social Determinants of Health (SDOH):

  • Economic stability.

  • Health care access and quality.

  • Social and community context.

  • Education access and quality.

  • Neighborhood and built environment.

• Other Influences: Culture, religion, food ideology, meaning of food, learned aversions, and alcohol use disorder.

• Developmental Considerations:

  • Infancy, Adolescence, Pregnancy, Lactation: These stages significantly increase nutritional needs.

  • Adulthood: Nutritional needs level off; fewer calories are required because BMR decreases.

• Food Intake Deviations:

  • Anorexia: Decreased intake due to lack of appetite.

  • Obesity: Increased intake leading to a BMI $\geq 30$.

Nutritional Assessment and Nursing Care

• Components of Assessment:

  • History: Dietary, medical, and socioeconomic data.

  • Dietary Data Methods: $24\text{-hour}$ recall, food diaries/calorie counts, food frequency records, and diet histories.

  • Physical Assessment: Anthropometric data (measurements) and clinical data.

  • Biochemical Data: Lab tests for protein status and vitamin/mineral/trace element levels.

• Nursing Interventions:

  • Teaching nutritional information and monitoring status.

  • Stimulating appetite and assisting with eating.

  • Providing oral nutrition and long-term support.

• Therapeutic Diets:

  • Pathology-Specific: Consistent carbohydrate (diabetes), Fat or sodium restricted, High or low fiber, Renal diet.

  • Modified Consistency: Clear liquid, Pureed, Mechanically altered.

Enteral and Parenteral Nutritional Support

• Short-Term Enteral Support: Delivery via Nasogastric (NG) or Nasointestinal (NI) routes.

  • Confirmation Methods for NG Tubes: Radiographic examination (Gold Standard), assessment of aspirate pH, measurement of tube length/markings, and carbon dioxide monitoring.

• Long-Term Enteral Support: Placement of enterostomal tubes.

  • Gastrostomy: Opening into the stomach ($PEG$ or surgical). It is the preferred route for comatose patients.

  • Jejunostomy: Opening into the jejunum.

• Enteral Feeding Management: Monitor for tolerance (Gastric Residual Volume - GRV), focus on patient safety, prevent complications, and provide education.

• Parenteral Nutrition (PN):

  • Highly concentrated, hypertonic intravenous solution containing amino acids, carbohydrates, and lipids.

  • Administered via a central venous access device ($CVAD$).

• Complications of Total Parenteral Nutrition (TPN):

  • Insertion-related problems.

  • Infection and sepsis.

  • Metabolic alterations and hyperlipidemia.

  • Fluid, electrolyte, and acid-base imbalances.

  • Phlebitis.

  • Liver and gallbladder disease.