Nutrition, Metabolism, & Energy Balance

Nutrition

Nutrition is the study of nutrients and how the body uses them for growth, maintenance, and repair. Nutrients are substances required by the body to sustain life and health.

• Macronutrients: Needed in large amounts; include carbohydrates, lipids, and proteins.

• Micronutrients: Needed in smaller amounts; include vitamins and minerals.

• Water: Essential for all physiological processes.

Body Water Content

The percentage of water in the human body varies by age and gender, and is crucial for physiological function.

• Adult male: ~60% water

• Adult female: ~55% water

• Children: ~65% water

• Infants: ~75% water

Importance: Loss of even one-tenth of body water can be fatal, while the body can survive significant loss of fat and protein.

Essential Nutrients

Essential nutrients are molecules that the body cannot synthesize rapidly enough to meet its needs and must be obtained from the diet.

• Essential amino acids: Required for protein synthesis; must be obtained from food.

• Essential fatty acids: Required for cell membrane structure and function; must be obtained from food.

Dietary Sources of Major Nutrients

Major nutrients are obtained from various dietary sources:

• Carbohydrates: Mostly from plants; exceptions include lactose (milk) and glycogen (meat).

• Lipids:

  • Saturated fats: Animal products

  • Unsaturated fats: Nuts, seeds, vegetable oils

  • Cholesterol: Egg yolk, meats, milk products

• Proteins:

  • Complete proteins: Contain all essential amino acids; mostly from animal products

  • Incomplete proteins: Legumes and beans; lack one or more essential amino acids

• Vitamins: Found in all major food groups; act as cofactors with enzymes

Essential Amino Acids

There are eight essential amino acids for adults and nine for infants (including arginine). These must be obtained from the diet.

• Tryptophan

• Methionine (Cysteine)

• Valine

• Threonine

• Phenylalanine (Tyrosine)

• Leucine

• Isoleucine

• Lysine

• Histidine (infants)

• Arginine (infants)

Vegetarian diets: Combining grains (corn, wheat) and legumes (beans) can provide all essential amino acids.

Vitamins

Vitamins are organic compounds required in small amounts for normal metabolism. They often function as coenzymes.

• Fat-soluble vitamins: A, D, E, K; absorbed with dietary lipids

• Water-soluble vitamins: B-complex, C

• Antioxidant vitamins: A, C, E; help neutralize free radicals

Minerals

Minerals are inorganic elements essential for body functions.

• Major minerals: Calcium, phosphorus, sodium, potassium, chlorine, sulfur, magnesium

• Trace minerals: Iron, zinc, fluorine, copper, iodine, selenium, cobalt, chromium, molybdenum, manganese

Sources include vegetables, legumes, milk, and some meats.

Summary Table: Categories of Nutrients

Key Definitions

• Nutrient: Substance used by the body for growth, maintenance, and repair.

• Macronutrient: Nutrient required in large amounts (carbohydrates, lipids, proteins).

• Micronutrient: Nutrient required in small amounts (vitamins, minerals).

• Essential nutrient: Must be obtained from the diet because the body cannot synthesize it fast enough.

Example Application

A balanced diet should include all macronutrients and micronutrients, as well as sufficient water, to support physiological functions and maintain health.

Additional info: These notes cover the introductory concepts of nutrition and essential nutrients, which are foundational for understanding metabolism and energy balance in Anatomy & Physiology.