NTR 108 Exam 1: Principles of Nutrition, Digestion, Carbohydrates, and Lipids

Principles of Nutrition

Essential vs. Nonessential Nutrients

Nutrition is the study of how food and its components nourish the body and influence health. Nutrients are classified based on whether the body can synthesize them in sufficient amounts.

• Essential Nutrients: Nutrients that must be obtained from the diet because the body cannot make them or cannot make enough of them. Examples include vitamins, minerals, essential fatty acids, and essential amino acids.

• Nonessential Nutrients: Nutrients that the body can synthesize in adequate amounts. Examples include some amino acids (e.g., alanine), cholesterol.

Example: Linoleic acid (an omega-6 fatty acid) is essential, while cholesterol is nonessential because the liver can produce it.

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 (e.g., colon, breast)

Example: Diets high in saturated fat and low in fiber are associated with increased risk of heart disease.

Types of Research Studies

Nutrition science relies on various research designs to investigate diet-health relationships.

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

• Intervention (Experimental) Studies: Researchers assign participants to different treatments to test effects.

• Randomized Controlled Trials (RCTs): Participants are randomly assigned to groups; considered the gold standard.

Example: A cohort study following dietary patterns and heart disease incidence over time.

Serving Sizes for ChooseMyPlate

ChooseMyPlate is a visual guide for healthy eating, emphasizing balanced portions from all food groups.

• Vegetables: 2.5 cups/day (for a 2,000 calorie diet)

• Fruits: 2 cups/day

• Grains: 6 ounces/day (at least half whole grains)

• Protein Foods: 5.5 ounces/day

• Dairy: 3 cups/day

Example: 1 cup of raw or cooked vegetables counts as one serving.

Single Blind vs. Double Blind Research Studies

Blinding reduces bias in research studies.

• Single Blind: Participants do not know which group they are in, but researchers do.

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

Example: In a double-blind drug trial, both the patient and the administering doctor are unaware of whether the patient receives the drug or placebo.

Placebo

A placebo is an inactive substance or treatment given to a control group in research to assess the effect of the actual intervention.

• Purpose: To control for psychological effects and ensure observed outcomes are due to the intervention.

Assessment of Nutritional Status

Evaluating nutritional status involves multiple methods:

• Anthropometric: Measurements of body size and composition (e.g., BMI, waist circumference).

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

• Clinical: Physical examination for signs of deficiency or excess.

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

Nutrients that Provide Energy

Only certain nutrients supply energy (calories) to the body.

• Carbohydrates: 4 kcal/gram

• Proteins: 4 kcal/gram

• Fats (Lipids): 9 kcal/gram

• Alcohol: 7 kcal/gram (not a nutrient, but provides energy)

Dietary Guidelines for Americans 2025-2030

The Dietary Guidelines provide science-based advice for healthy eating patterns.

• Emphasize fruits, vegetables, whole grains, lean proteins, and low-fat dairy.

• Limit added sugars, saturated fats, and sodium.

• Encourage physical activity and healthy body weight.

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: Secretes acid and enzymes; protein digestion begins.

• Small Intestine: Main site of digestion and absorption.

• Large Intestine: Absorbs water and electrolytes; forms feces.

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

Peristalsis

Peristalsis is the coordinated, rhythmic contraction of smooth muscles that propels food through the GI tract.

Sphincters

Sphincters are circular muscles that regulate the passage of food between sections of the GI tract.

• Examples: Lower esophageal sphincter (prevents acid reflux), pyloric sphincter (controls stomach emptying).

Hormonal Control of Digestion

Several hormones regulate digestive processes:

• Gastrin: Stimulates gastric acid secretion.

• Secretin: Stimulates bicarbonate release from pancreas.

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

Disorders of the GI Tract

• Gastroesophageal Reflux Disease (GERD): Acid from the stomach flows back into the esophagus.

• Peptic Ulcers: Sores in the stomach or duodenum lining.

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

• Constipation and Diarrhea: Disruptions in normal bowel movements.

Carbohydrates

Types of Carbohydrates

Carbohydrates are classified by their chemical structure:

• Monosaccharides: Single sugar units (e.g., glucose, fructose, galactose).

• Disaccharides: Two monosaccharides linked (e.g., sucrose, lactose, maltose).

• Polysaccharides: Long chains of monosaccharides (e.g., starch, glycogen, fiber).

Function of Carbohydrates

• Primary energy source for the body, especially the brain and red blood cells.

• Protein sparing effect: prevents breakdown of body proteins for energy.

Digestion of Carbohydrates

• Begins in the mouth with salivary amylase.

• Continues in the small intestine with pancreatic amylase.

• Disaccharidases in the intestinal lining break down disaccharides to monosaccharides for absorption.

Glycogen

Glycogen is the storage form of glucose in animals, found mainly in the liver and muscles.

• Liver glycogen maintains blood glucose levels.

• Muscle glycogen provides energy during exercise.

Normal Blood Glucose Regulation

Blood glucose is tightly regulated by hormones:

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

• Glucagon: Raises blood glucose by stimulating glycogen breakdown.

Ketosis

Ketosis occurs when carbohydrate intake is very low, leading to increased production of ketone bodies from fat breakdown.

• Ketones can be used as an alternative energy source by the brain and muscles.

Risk Factors of Type 2 Diabetes

• Obesity

• Physical inactivity

• Family history

• Older age

• Ethnicity (higher risk in some populations)

Treatment of Type 1 and Type 2 Diabetes

• Type 1 Diabetes: Requires insulin therapy, dietary management, and physical activity.

• Type 2 Diabetes: Managed with diet, exercise, oral medications, and sometimes insulin.

Dangers of Excessive Sugar Intake

• Increased risk of obesity

• Dental caries (cavities)

• Potential increased risk of type 2 diabetes and heart disease

Recommendations of Carbohydrate and Fiber Intake

• Carbohydrates: 45-65% of total daily calories

• Fiber: 25g/day for women, 38g/day for men (adults under 50)

Lipids

Fat Recommendations

• 20-35% of total daily calories from fat

• Limit saturated fat to less than 10% of calories

• Minimize trans fat intake

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

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

• Trans Fats: Artificially produced; found in some processed foods.

Unsaturated vs. Saturated Fat Characteristics

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

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

Monounsaturated Fat

• One double bond in the fatty acid chain.

• Sources: olive oil, canola oil, avocados, nuts.

Polyunsaturated Fat

• Two or more double bonds in the fatty acid chain.

• Sources: soybean oil, corn oil, fatty fish, walnuts.

Omega-3 Fatty Acids

• Type of polyunsaturated fat with the first double bond at the third carbon from the omega end.

• Sources: fatty fish (salmon, mackerel), flaxseed, walnuts.

• Benefits: reduce inflammation, support heart and brain health.

Triglyceride and Phospholipid Structure

• Triglyceride: Glycerol backbone + 3 fatty acids.

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

Triglyceride Structure Equation:

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

Digestion of Fat

• Begins in the small intestine with bile emulsification.

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

• Absorbed into intestinal cells and reassembled into triglycerides.

Lipoproteins

Lipoproteins transport lipids in the blood.

• Chylomicrons: Carry dietary fat from intestine to tissues.

• VLDL (Very Low-Density Lipoprotein): Transports triglycerides from liver to tissues.

• LDL (Low-Density Lipoprotein): Delivers cholesterol to cells; high levels increase heart disease risk.

• HDL (High-Density Lipoprotein): Removes cholesterol from cells and returns it to the liver; high levels are protective.

HDL and LDL

• HDL ("good" cholesterol): High levels reduce heart disease risk.

• LDL ("bad" cholesterol): High levels increase heart disease risk.

Risk Factors for Heart Disease

• High LDL cholesterol

• Low HDL cholesterol

• High blood pressure

• Smoking

• Obesity

• Physical inactivity

• Diabetes

Prevention of Heart Disease

• Eat a diet low in saturated and trans fats

• Increase intake of fruits, vegetables, and whole grains

• Exercise regularly

• Maintain a healthy weight

• Avoid smoking