Elements of Nutrition

Essential Nutrients

Nutrition is the study of how food and its components nourish the body and influence health. Essential nutrients are substances the body cannot synthesize in sufficient quantities and must be obtained from the diet.

• Macronutrients: Nutrients required in large amounts, including carbohydrates, proteins, fats, and water.

• Micronutrients: Nutrients needed in smaller quantities, such as vitamins and minerals.

• Organic Nutrients: Compounds containing carbon, such as carbohydrates (C6H12O6), proteins, fats, and vitamins.

• Inorganic Nutrients: Do not contain carbon; examples include water (H2O) and minerals.

Key Functions:

• Carbohydrates: The body's preferred energy source.

• Proteins: Build and maintain tissues; form enzymes and hormones.

• Fats: Serve as energy sources and support cell structure.

• Water: Regulates metabolism, transports nutrients, and maintains temperature; does not provide energy.

• Vitamins and Minerals: Regulate metabolism and support physiological functions.

Energy Content of Macronutrients:

• Carbohydrates: 4 kcal/g

• Proteins: 4 kcal/g

• Fats: 9 kcal/g

Example Calculation:

• To calculate total energy: multiply grams of carbohydrates and proteins by 4, and fats by 9.

Obtaining Nutrients

Obtaining nutrients involves consuming a well-balanced diet or, when necessary, supplements. A balanced diet provides all essential nutrients, phytochemicals, and fiber, supporting overall health and enjoyment of food.

• Supplements may be useful for individuals with dietary restrictions or increased needs (e.g., pregnant women).

• Diet Quality Concerns: Excess intake of added sugars, sodium, and saturated fats; insufficient fiber, vitamins, and minerals; inadequate fruits, vegetables, and whole grains.

Body Weight and Obesity

• Overweight: Body Mass Index (BMI) 25–29.9; affects over 70% of adults in the U.S.

• Obesity: BMI ≥ 30.

The Human Body & Digestion

Gastrointestinal (GI) Tract

The GI tract is a series of organs responsible for digesting food, absorbing nutrients, and eliminating waste.

• Main Organs (in order): Mouth → Esophagus → Stomach → Small Intestine → Large Intestine (Colon) → Rectum → Anus

• Accessory Organs: Salivary glands, pancreas, liver, gallbladder

Functions of the GI Tract:

• Digestion of macronutrients

• Absorption of nutrients

• Physical and immunological barrier

• Communication with the nervous system

Types of Digestion

• Mechanical Digestion: Physical breakdown of food (e.g., chewing, peristalsis, segmentation, pendular movement).

• Chemical Digestion: Enzymatic breakdown of food molecules into absorbable units.

Key Digestive Processes and Structures

• Mouth: Saliva moistens food; amylase begins carbohydrate digestion; mucus lubricates food; epiglottis prevents food from entering the airway.

• Esophagus: Connects mouth to stomach; peristalsis moves food; gastroesophageal sphincter prevents reflux (heartburn).

• Stomach: Secretes hydrochloric acid (HCl) for defense and digestion; gastrin stimulates digestive activity; pepsin digests proteins; pyloric sphincter regulates passage to small intestine.

• Small Intestine: Main site of nutrient absorption; circular folds and villi increase surface area.

• Large Intestine (Colon): Reabsorbs water; forms and eliminates feces.

• Ileocecal Sphincter: Connects small and large intestines.

• Rectum and Anus: Control elimination of waste; anus has involuntary and voluntary control.

Accessory Organs

• Liver: Produces bile for fat digestion.

• Gallbladder: Stores and concentrates bile.

• Pancreas: Produces digestive enzymes, insulin, and bicarbonate ions to neutralize stomach acid.

Hormones, Enzymes, and Bile

• Hormones: Chemical messengers that regulate digestive processes (e.g., secretin triggers bicarbonate release in response to acidic chyme).

• Enzymes: Biological catalysts that speed up chemical reactions in digestion.

• Bile: Emulsifies fats, breaking large fat globules into smaller droplets for enzyme action; produced by the liver, stored in the gallbladder, acts in the small intestine.

Major Digestive Enzymes and Their Functions

Absorption of Nutrients

Nutrient absorption occurs primarily in the small intestine through several mechanisms:

• Passive Diffusion: Movement from high to low concentration; no energy required.

• Facilitated Diffusion: Movement from high to low concentration with the help of a carrier protein; no energy required.

• Active Transport: Movement from low to high concentration; requires energy and a carrier protein.

• Endocytosis: Whole molecules are engulfed by the cell membrane.

Transport Systems:

• Circulatory System: Transports water-soluble nutrients via blood to tissues.

• Lymphatic System: Transports fat-soluble nutrients via lymph fluid to the heart, where they enter the bloodstream.

Storage:

• Excess glucose is stored as glycogen in the liver and muscles.

• Excess glycogen is converted to fat and stored in adipose tissue.

Summary Table: Essential Nutrients and Their Functions

Additional info:

• Phytochemicals are non-nutrient compounds in plant foods that have health-promoting properties.

• Fiber is a type of carbohydrate that aids in digestive health but is not digested for energy.

• Enzymes are specific to the macronutrient they digest (e.g., amylases for carbohydrates, proteases for proteins, lipases for fats).