Basic Nutrition and Dietary Reference Intakes (DRIs)

Key Definitions and Concepts

• RDA (Recommended Dietary Allowance): The average daily intake level sufficient to meet the nutrient requirements of nearly all (97–98%) healthy individuals in a particular life stage and gender group.

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

• EAR (Estimated Average Requirement): The intake level estimated to meet the needs of 50% of individuals in a group.

• TUL (Tolerable Upper 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 associated with reduced risk of chronic disease while providing adequate intakes of essential nutrients.

• AMDR Values:

  • Carbohydrate: 45–65% of total calories

  • Protein: 10–35% of total calories

  • Fat: 20–35% of total calories

Nutrition-Related Causes of Death

• Heart disease, cancer, stroke, and diabetes are leading causes of death in the US linked to nutrition.

Nutrition Assessment

• Anthropometric: Measurement of body size, weight, and proportions (e.g., BMI, waist circumference).

• Biochemical: Laboratory analysis of blood, urine, or tissue samples.

• Clinical: Physical examination for signs of nutrient deficiencies or excesses.

• Dietary: Assessment of food and nutrient intake (e.g., 24-hour recall, food frequency questionnaire).

Types of Nutrition Studies

• Epidemiological Study: Observes associations between diet and health in populations; cannot establish causation.

• Controlled Trial: Experimental study where participants are assigned to intervention or control groups to test effects of dietary changes.

• Control Group: Used to compare outcomes and isolate the effect of the intervention.

Diet-Planning Principles

• Adequacy, Balance, Calorie Control, Moderation, Variety, Nutrient Density are key principles for planning a healthy diet.

USDA Food Pattern (MyPlate)

• Food Groups: Fruits, Vegetables, Grains, Protein Foods, Dairy

• Examples: Grains (bread, rice), Protein (meat, beans), Dairy (milk, cheese), Fruits (apples, berries), Vegetables (carrots, spinach)

Daily Value (DV) on Food Labels

• Represents the percentage of a nutrient in a serving of food, based on a 2,000-calorie diet.

Digestion, Absorption, and Transport

Digestive Enzymes and Organs

• Salivary glands: Produce amylase (carbohydrate digestion)

• Stomach: Produces pepsin (protein digestion), gastric lipase (fat digestion)

• Pancreas: Produces pancreatic amylase, proteases, and lipase

• Small intestine: Brush border enzymes (e.g., maltase, sucrase, lactase)

Sphincters of the Digestive System

• Upper esophageal sphincter (mouth to esophagus)

• Lower esophageal (cardiac) sphincter (esophagus to stomach)

• Pyloric sphincter (stomach to small intestine)

• Ileocecal valve (small to large intestine)

• Anal sphincters (rectum to outside)

Digestive Hormones

• Gastrin: Stimulates gastric acid secretion

• Secretin: Stimulates bicarbonate release from pancreas

• Cholecystokinin (CCK): Stimulates bile release from gallbladder and enzyme secretion from pancreas

Influence of Bacteria, Hormones, and Nerves

• Gut microbiota aid in digestion and immune function.

• Nervous system regulates peristalsis and enzyme secretion.

Principles of Digestion

• Most digestion and absorption occur in the small intestine.

• Stomach is highly acidic (low pH); small intestine is more alkaline (higher pH).

Transport of Monosaccharides

• Glucose and galactose: Active transport

• Fructose: Facilitated diffusion

Digestive Disorders

• Celiac Disease: Autoimmune reaction to gluten; requires gluten-free diet.

• GERD (Gastroesophageal Reflux Disease): Acid reflux; dietary modifications include avoiding spicy/fatty foods, eating smaller meals.

Carbohydrates

Types and Functions

• Storage in plants: Starch

• Storage in animals: Glycogen

• Disaccharides: Sucrose (glucose + fructose), Lactose (glucose + galactose), Maltose (glucose + glucose)

• Fermentable fibers: Can be digested by gut bacteria, producing short-chain fatty acids

• Soluble/viscous fibers: Dissolve in water, slow digestion, help lower cholesterol

• Insoluble fibers: Do not dissolve in water, promote bowel regularity

Blood Sugar Regulation

• Insulin: Produced by pancreas; lowers blood glucose by promoting uptake into cells

Whole Grains vs. Refined Grains

• Whole grains retain bran and germ, providing more fiber and nutrients than refined grains.

Lipids

Types and Health Implications

• Saturated fat: Should be less than 10% of total calories

• Trans fats: Major contributors are processed foods; increase heart disease risk

• Essential fatty acids: Linoleic acid (omega-6) and alpha-linolenic acid (omega-3); found in vegetable oils, nuts, seeds, fish

• Storage form in body: Triglycerides

• Fat digestion: Mostly occurs in small intestine

• Cholesterol: LDL ("bad") increases heart disease risk; HDL ("good") is protective

Proteins

Structure and Function

• Primary structure: Sequence of amino acids

• Secondary structure: Local folding (alpha-helix, beta-sheet)

• Tertiary structure: 3D folding of a single polypeptide

• Quaternary structure: Association of multiple polypeptides

• Essential amino acids: Must be obtained from diet

• Nonessential amino acids: Can be synthesized by the body

• Conditionally essential: Required in certain conditions

• Denaturation: Loss of structure due to heat, acid, etc.

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

Energy Metabolism

Metabolic Pathways

• Metabolism: All chemical reactions in the body

• Anabolic: Building up (e.g., protein synthesis); promoted by insulin

• Catabolic: Breaking down (e.g., glycolysis); promoted by glucagon, epinephrine

• Glycolysis: Breakdown of glucose to pyruvate

• TCA (Krebs) cycle: Central pathway for energy production

• Cori cycle: Converts lactate to glucose in the liver

• Electron Transport Chain (ETC): Produces most ATP

• Key substrate: Acetyl CoA

• ATP: Direct energy source for cells

• Pyruvate: 3 carbons; Acetyl CoA: 2 carbons

• Liver: Most metabolically active organ

• Anaerobic conditions: Glycolysis and lactate production are upregulated

Alcohol

Metabolism and Health

• Alcohol dehydrogenase: Main enzyme for alcohol metabolism; produced in the liver

• Standard drinks: 5 oz wine, 12 oz beer, 1.5 oz spirits

• Moderate drinking: Up to 1 drink/day for women, 2 for men

• Most alcohol metabolized in: Liver

Energy Balance and Weight Management

Energy Balance

• 1 pound of fat: Approximately 3,500 kcal

• Satiation: Feeling of fullness during a meal; Satiety: Feeling of fullness after a meal

• Foods promoting satiation: Protein-rich foods

• Foods promoting satiety: High-fiber foods

• Subcutaneous fat: Under the skin; Visceral fat: Around organs (more harmful)

• Ghrelin: Promotes hunger; produced in stomach

• Leptin: Reduces hunger; produced in adipose tissue

Weight Management

• Over two-thirds of US adults are overweight or obese; about one-third are obese.

• Healthy weight promoted by high-fiber, nutrient-dense foods; limit added sugars and saturated fats.

• BMI Classification:

  • Underweight: <18.5

  • Normal: 18.5–24.9

  • Overweight: 25–29.9

  • Obese: ≥30

Vitamins

Water-Soluble Vitamins

• Absorbed in small intestine, transported via blood

• Roles: e.g., B vitamins in energy metabolism, vitamin C as antioxidant

• Deficiency diseases: e.g., scurvy (vitamin C), beriberi (thiamin), pellagra (niacin)

• Food sources: fruits, vegetables, grains, dairy

• Folate (natural) vs. folic acid (synthetic): Folic acid is more bioavailable

• Riboflavin and niacin used as FAD and NAD/NADP in metabolism

• Antioxidant vitamins: C, some B vitamins

• Best to consume vitamins from food rather than supplements

Fat-Soluble Vitamins

• Vitamins A, D, E, K

• Absorbed with dietary fat, transported via lymph

• Roles:

  • Vitamin A: vision, immune function, cell growth

  • Vitamin D: calcium absorption, bone health

  • Vitamin E: antioxidant

  • Vitamin K: blood clotting, bone health

• Toxicity: A and D have clear toxicity symptoms (e.g., hypervitaminosis A: liver damage; excess D: hypercalcemia)

• Deficiency: A (night blindness), D (rickets/osteomalacia)

• Vitamin K and some B vitamins produced by intestinal bacteria

• Antioxidants: A (as beta-carotene), E

• Provitamin A: beta-carotene (found in carrots, sweet potatoes)

• Food sources:

  • Vitamin D: fatty fish, fortified milk

  • Pre-formed A: liver, dairy

  • K: leafy greens

  • E: nuts, seeds, vegetable oils

• Vitamin D activation: skin (precursor formed), then liver and kidney

Water and Major Minerals

Water

• Major roles: solvent, transport, temperature regulation, lubrication

• Hydrolysis: chemical reaction splitting molecules by adding water

• Body is ~60% water; water is the most needed nutrient

• Fluid compartments:

  • Extracellular: outside cells

  • Intracellular: inside cells

  • Interstitial: between cells

  • Intravascular: in blood vessels

• Fluid balance and blood pressure regulated by kidneys, hormones (ADH, aldosterone, renin-angiotensin system)

• Daily water requirement: varies, but ~2–3 liters/day for adults

• Sources: beverages, food, metabolic water

• All fluids except alcohol count toward intake

• Well-hydrated urine: pale yellow

• Tips to increase intake: carry a water bottle, flavor water with fruit, set reminders

Major Minerals

• Major vs. Trace: Major needed in larger amounts (>100 mg/day); trace in smaller amounts

• Major minerals: Sodium, potassium, calcium, phosphorus, magnesium

• Bioavailability factors: Presence of binders (phytates, oxalates), nutrient interactions, age, health status

• Functions, sources, symptoms:

• Minerals in bone health: Calcium, phosphorus, magnesium are critical for bone structure; deficiency increases osteoporosis risk.