NTR 108 Exam 1 Study Guide: Principles of Nutrition, Gastrointestinal Tract, Carbohydrates, and Lipids

Principles of Nutrition

Essential vs. Nonessential Nutrients

Understanding the difference between essential and nonessential nutrients is fundamental in nutrition science.

• Essential Nutrients: Nutrients that must be obtained from the diet because the body cannot synthesize them in sufficient quantities. Examples include vitamins, minerals, essential fatty acids, and essential amino acids.

• Nonessential Nutrients: Nutrients that the body can synthesize in adequate amounts; they are not required to be consumed in the diet. Examples include cholesterol and some amino acids (e.g., alanine).

• Key Point: Deficiency of essential nutrients leads to specific deficiency diseases.

Current Health Problems in the US with Strong Diet Connection

Many prevalent health issues in the United States are closely linked to dietary patterns.

• Obesity

• Type 2 Diabetes

• Cardiovascular Disease

• Hypertension

• Certain Cancers

• Osteoporosis

• Key Point: Diets high in saturated fat, added sugars, and sodium are major contributors.

Types of Research Studies

Nutrition science relies on various research designs to establish evidence.

• Observational Studies: Examine associations between dietary factors and health outcomes without intervention.

• Experimental Studies: Involve active intervention, such as clinical trials.

• Meta-Analyses and Systematic Reviews: Combine results from multiple studies for stronger evidence.

Single Blind vs. Double Blind Research Studies

• Single Blind: Participants do not know which group (treatment or control) they are in, but researchers do.

• Double Blind: Neither participants nor researchers know group assignments, reducing bias.

Placebo

• Definition: An inactive substance or treatment given to the control group in research to assess the effect of the actual intervention.

Assessment of Nutritional Status

Evaluating an individual's nutritional health involves several methods:

• Dietary Assessment: Food records, 24-hour recalls, food frequency questionnaires.

• Anthropometric Measurements: Height, weight, BMI, waist circumference.

• Biochemical Tests: Blood, urine, or tissue analysis for nutrient levels.

• Clinical Assessment: Physical signs of deficiency or excess.

Nutrients that Provide Energy

• Carbohydrates: 4 kcal/g

• Proteins: 4 kcal/g

• Fats (Lipids): 9 kcal/g

• Alcohol (not a nutrient): 7 kcal/g

Dietary Guidelines for Americans 2025-2030

• Emphasize: Fruits, vegetables, whole grains, lean proteins, and healthy fats.

• Limit: Added sugars, saturated fats, sodium, and alcoholic beverages.

• Promote: Physical activity and healthy eating patterns across the lifespan.

Serving Sizes for ChooseMyPlate

• Fruits: 1 cup fruit or 100% fruit juice, or ½ cup dried fruit

• Vegetables: 1 cup raw or cooked vegetables, or 2 cups leafy salad greens

• Grains: 1 slice bread, 1 cup ready-to-eat cereal, or ½ cup cooked rice/pasta

• Protein Foods: 1 ounce meat, poultry, or fish; 1 egg; 1 tablespoon peanut butter

• Dairy: 1 cup milk, yogurt, or 1.5 ounces natural cheese

Gastrointestinal Tract

Organs of the Gastrointestinal System and Functions

The gastrointestinal (GI) tract is responsible for digestion and absorption of nutrients.

• Mouth: Mechanical breakdown, saliva begins carbohydrate digestion.

• Esophagus: Transports food to stomach via peristalsis.

• Stomach: Mixes food, secretes acid and enzymes, begins protein digestion.

• Small Intestine: Main site for digestion and absorption; enzymes from pancreas and bile from liver aid digestion.

• Large Intestine (Colon): Absorbs water and electrolytes, forms feces.

• Accessory Organs: Liver (produces bile), Gallbladder (stores bile), Pancreas (secretes digestive enzymes and bicarbonate).

Peristalsis

• Definition: Coordinated, rhythmic contractions of smooth muscle that propel food through the GI tract.

Sphincters

• Definition: Circular muscles that regulate the passage of food between sections of the GI tract (e.g., lower esophageal sphincter, pyloric sphincter).

Hormonal Control of Digestion

• Gastrin: Stimulates gastric acid secretion in the stomach.

• Secretin: Stimulates pancreas to release bicarbonate into small intestine.

• Cholecystokinin (CCK): Stimulates gallbladder to release bile and pancreas to release enzymes.

Disorders of the GI Tract

• Gastroesophageal Reflux Disease (GERD): Acid reflux into esophagus.

• Peptic Ulcers: Sores in stomach or duodenal lining.

• Lactose Intolerance: Inability to digest lactose due to lactase deficiency.

• Constipation/Diarrhea: Altered bowel movements due to various causes.

Carbohydrates

Types of Carbohydrates

• Simple Carbohydrates: Monosaccharides (glucose, fructose, galactose) and disaccharides (sucrose, lactose, maltose).

• Complex Carbohydrates: Oligosaccharides and polysaccharides (starch, glycogen, fiber).

Function of Carbohydrates

• Primary Energy Source: Especially for the brain and red blood cells.

• Protein Sparing: Prevents breakdown of body proteins for energy.

• Regulation of Blood Glucose: Maintains normal blood sugar levels.

Digestion of Carbohydrates

• Begins in the mouth with salivary amylase.

• Continues in the small intestine with pancreatic amylase and brush border enzymes.

• End products: monosaccharides absorbed into the bloodstream.

Glycogen

• Definition: Storage form of glucose in animals, primarily in liver and muscle.

Normal Blood Glucose Regulation

• Insulin: Lowers blood glucose by promoting uptake into cells.

• Glucagon: Raises blood glucose by stimulating glycogen breakdown.

Ketosis

• Definition: Metabolic state resulting from insufficient carbohydrate intake, leading to increased ketone body production from fat breakdown.

Risk Factors of Type 2 Diabetes

• Obesity

• Physical inactivity

• Family history

• Unhealthy diet

Treatment of Type 1 and Type 2 Diabetes

• Type 1: Insulin therapy, carbohydrate counting, healthy diet, physical activity.

• Type 2: Lifestyle modification (diet, exercise), oral medications, sometimes insulin.

Dangers of Excessive Sugar Intake

• Increased risk of obesity, type 2 diabetes, dental caries, and cardiovascular disease.

Recommendations of Carbohydrate and Fiber Intake

• Carbohydrates: 45-65% of total daily calories (Dietary Guidelines for Americans).

• Fiber: 25 g/day for women, 38 g/day for men (Adequate Intake, AI).

Lipids

Fat Recommendations

• 20-35% of total daily calories from fat (Dietary Guidelines for Americans).

• Limit saturated fat to less than 10% of calories.

Functions of Fat

• Energy storage

• Insulation and protection of organs

• Absorption of fat-soluble vitamins (A, D, E, K)

• Cell membrane structure

Types of Fat and Food Sources

• Saturated Fat: Solid at room temperature; found in animal products (butter, cheese, red meat).

• Unsaturated Fat: Liquid at room temperature; found in plant oils, nuts, seeds, fish.

Unsaturated vs. Saturated Fat Characteristics

• Saturated Fats: No double bonds; increase LDL cholesterol.

• Unsaturated Fats: One or more double bonds; may decrease LDL cholesterol.

Monounsaturated Fat

• One double bond in the fatty acid chain; sources include olive oil, avocados, and nuts.

Polyunsaturated Fat

• Two or more double bonds; sources include soybean oil, corn oil, fatty fish.

Omega-3 Fatty Acids

• Essential polyunsaturated fats; sources include fatty fish (salmon, mackerel), flaxseed, walnuts.

• Benefits: anti-inflammatory, heart health.

Triglyceride and Phospholipid Structure

• Triglyceride: Glycerol backbone + 3 fatty acids.

• Phospholipid: Glycerol backbone + 2 fatty acids + phosphate group.

Triglyceride Structure Equation:

$\text{Triglyceride} = \text{Glycerol} + 3 \times \text{Fatty Acids}$

Phospholipid Structure Equation:

$\text{Phospholipid} = \text{Glycerol} + 2 \times \text{Fatty Acids} + \text{Phosphate Group}$

Digestion of Fat

• Begins in the small intestine with bile emulsification and pancreatic lipase action.

• End products: fatty acids, monoglycerides, absorbed into intestinal cells.

Lipoproteins

• Definition: Complexes that transport lipids in the blood.

• Types: Chylomicrons, VLDL, LDL, HDL.

HDL and LDL

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

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

Risk Factors for Heart Disease

• High LDL cholesterol

• Low HDL cholesterol

• High blood pressure

• Smoking

• Obesity

• Physical inactivity

• Unhealthy diet

Prevention of Heart Disease

• Eat a diet low in saturated and trans fats

• Increase intake of fruits, vegetables, whole grains, and omega-3 fatty acids

• Maintain a healthy weight

• Exercise regularly

• Avoid smoking