Nutrition Basics

Dietary Reference Intakes (DRIs)

The Dietary Reference Intakes (DRIs) are a set of nutrient reference values used to plan and assess diets for healthy people. They include several different types of recommendations:

• EAR (Estimated Average Requirement): The average daily nutrient intake level estimated to meet the requirement of half the healthy individuals in a particular life stage and gender group.

• RDA (Recommended Dietary Allowance): The average daily intake level sufficient to meet the nutrient requirement of nearly all (97–98%) healthy individuals.

• AI (Adequate Intake): Established when evidence is insufficient to develop an RDA; set at a level assumed to ensure nutritional adequacy.

• UL (Tolerable Upper Intake Level): The maximum daily intake unlikely to cause adverse health effects.

• AMDR (Acceptable Macronutrient Distribution Range): The range of intake for a particular energy source (carbohydrate, fat, protein) associated with reduced risk of chronic disease while providing adequate intakes of essential nutrients.

Example: The AMDR for carbohydrates is 45–65% of total daily calories; for fats, it is 20–35%.

Daily Values and Food Labels

Daily Values (DVs) are reference values used on Nutrition Facts labels to help consumers understand the nutrient content of a food in the context of a total daily diet.

• Nutrition Facts labels display information such as serving size, calories, and nutrient content per serving.

• Food-label claims include nutrient content claims (e.g., "low fat"), health claims (e.g., "may reduce the risk of heart disease"), and structure/function claims (e.g., "supports immune health").

MyPlate and Dietary Guidelines

MyPlate is a visual guide developed by the USDA to help Americans build healthy meals. It emphasizes the five food groups: fruits, vegetables, grains, protein, and dairy.

• Dietary Guidelines for Americans provide science-based advice on what to eat and drink to promote health, reduce risk of chronic disease, and meet nutrient needs.

• Nutrient density refers to foods that provide substantial amounts of vitamins, minerals, and other nutrients with relatively few calories.

Example: Choosing whole fruits over fruit juice increases nutrient density.

The Human Body & Digestion

Overview of Digestion

Digestion is the process by which food is broken down into absorbable units. It involves both mechanical and chemical processes.

• Order of the GI tract: Mouth → Esophagus → Stomach → Small Intestine → Large Intestine → Rectum → Anus

• Mechanical digestion: Physical breakdown of food (e.g., chewing, churning in the stomach).

• Chemical digestion: Enzymatic breakdown of food molecules (e.g., amylase in saliva, gastric acid in the stomach).

• Chyme: The semi-liquid mass of partially digested food that moves from the stomach to the small intestine.

• Peristalsis: Rhythmic contractions of the GI tract that propel food forward.

• Digestion → Absorption → Elimination: Food is digested, nutrients are absorbed (mainly in the small intestine), and waste is eliminated.

• Small intestine vs. large intestine: The small intestine is the primary site of nutrient absorption; the large intestine absorbs water and forms feces.

Transport Systems

• Lymphatic system: Transports fat-soluble nutrients and larger molecules (e.g., chylomicrons) from the intestine to the bloodstream.

• Circulatory system: Transports water-soluble nutrients directly from the intestine to the liver via the portal vein.

Digestive Hormones

• Gastrin: Stimulates secretion of gastric acid in the stomach.

• Secretin: Stimulates the pancreas to release bicarbonate-rich fluids to neutralize stomach acid in the small intestine.

• Cholecystokinin (CCK): Stimulates the release of bile from the gallbladder and digestive enzymes from the pancreas.

• Ghrelin: Stimulates appetite and increases food intake.

Carbohydrates

Types of Carbohydrates

Carbohydrates are organic compounds that serve as a major energy source. They are classified as simple or complex based on their chemical structure.

• Simple carbohydrates: Include monosaccharides (glucose, fructose) and disaccharides (sucrose, lactose, maltose).

• Complex carbohydrates: Include polysaccharides such as starch (plant storage form) and glycogen (animal storage form).

Fiber

• Soluble fiber: Dissolves in water, can help lower blood cholesterol and glucose levels (e.g., oats, beans).

• Insoluble fiber: Does not dissolve in water, promotes regular bowel movements (e.g., whole grains, vegetables).

Blood Glucose Regulation

• Insulin: Hormone produced by the pancreas that lowers blood glucose by facilitating cellular uptake.

• Glucagon: Hormone that raises blood glucose by stimulating the release of glucose from liver stores.

Diabetes

• Type 1 diabetes: Autoimmune destruction of insulin-producing cells; requires insulin therapy.

• Type 2 diabetes: Insulin resistance and relative insulin deficiency; often manageb d with diet, exercise, and medication.

Carbohydrate Recommendations

• AMDR for carbohydrates: 45–65% of total daily calories.

Lipids

Types of Lipids

Lipids are a diverse group of hydrophobic molecules, including fats, oils, and cholesterol. They are important for energy storage, cell structure, and hormone production.

• Saturated fats: No double bonds between carbon atoms; solid at room temperature (e.g., butter).

• Monounsaturated fats: One double bond; liquid at room temperature (e.g., olive oil).

• Polyunsaturated fats: Two or more double bonds (e.g., omega-3 and omega-6 fatty acids).

• Trans fats: Unsaturated fats with trans double bonds; associated with increased heart disease risk.

• Essential fatty acids: Fatty acids that must be obtained from the diet (e.g., linoleic and alpha-linolenic acid).

Cholesterol and Lipoproteins

• Cholesterol: A sterol important for cell membranes and hormone synthesis; found only in animal products.

• HDL (High-Density Lipoprotein): "Good" cholesterol; transports cholesterol from tissues to the liver for excretion.

• LDL (Low-Density Lipoprotein): "Bad" cholesterol; delivers cholesterol to tissues, associated with increased heart disease risk.

Digestion and Absorption of Lipids

• Bile: Produced by the liver, stored in the gallbladder; emulsifies fats in the small intestine.

• Pancreatic lipase: Enzyme that breaks down triglycerides into fatty acids and monoglycerides.

Lipid Recommendations and Functions

• AMDR for fat: 20–35% of total daily calories.

• Functions of fat: Energy storage, insulation, protection of organs, absorption of fat-soluble vitamins (A, D, E, K).

Comparisons and Classifications

Key Comparisons

• Lean vs. extra lean: Terms used on food labels to describe the fat content of meat and poultry. "Lean" contains less than 10g total fat, 4.5g saturated fat, and 95mg cholesterol per serving; "extra lean" contains less than 5g total fat, 2g saturated fat, and 95mg cholesterol.

• Saturated vs. unsaturated fats: Saturated fats have no double bonds; unsaturated fats have one or more double bonds.

Sample Table: Types of Carbohydrates

Sample Table: Types of Lipoproteins

Key Formulas

• AMDR for Carbohydrates:

• AMDR for Fat:

Example Exam Questions

• Definition: What is chyme?

• Comparison: How do HDL and LDL differ in function and health impact?

• Matching: Match the following: insulin, fiber, bile, HDL.

• Calculation: If a person eats 2,000 kcal/day, how many grams of carbohydrate should they consume to meet the AMDR?

Calculation Example:

• 45% of 2,000 kcal = 900 kcal; 65% = 1,300 kcal

• Carbohydrates provide 4 kcal/g

• Grams: g to g per day

Additional info: These notes synthesize and expand upon the main concepts highlighted in the provided study materials, offering definitions, examples, and tables for clarity and exam preparation.