Nutrition, Metabolism, and Energy Balance

Chapter 24: Nutrition, Metabolism, and Energy Balance

Introduction to Nutrients

  • Nutrient Definition: Substances in food necessary for growth, maintenance, repair.

  • Categories of Nutrients: Five categories exist, including:

    • Macronutrients (provide energy):

    • Carbohydrates

    • Lipids

    • Proteins

    • Micronutrients (required in small amounts):

    • Vitamins

    • Minerals

  • Essential Nutrients: Molecules that must be obtained through the diet because the body cannot synthesize them in adequate amounts.

  • Water: Also essential, contributes to the volume of food content.

Energy Value of Nutrients

  • Nutrients provide energy measured in kilocalories (kcal).

    • 1 kcal is the amount of heat required to raise the temperature of 1 kg of water by 1°C.

    • Energy Content:

    • Carbohydrates: 4 kcal/g

    • Proteins: 4 kcal/g

    • Lipids: 9 kcal/g

  • USDA MyPlate Guidelines: Recommends balanced portions of food groups:

    • Fruits

    • Vegetables

    • Grains

    • Protein

    • Dairy

Carbohydrates
Dietary Sources

  • Mainly from plants.

    • Sugars: Mono- and disaccharides (e.g., fruits, sugarcane, honey, lactose).

    • Starch: Polysaccharides found in grains and vegetables.

    • Fiber Types:

    • Insoluble Fiber: Cellulose; aids in stool bulk.

    • Soluble Fiber: e.g., pectin; can reduce blood cholesterol.

Uses in the Body

  • Glucose: Primary molecule used by cells for ATP production.

    • Conversion: Fructose and galactose are converted to glucose by the liver.

    • Energy Dependence: Neurons and red blood cells primarily depend on glucose.

    • Excess Glucose Storage: Converts to glycogen or fat for later use.

Dietary Requirements

  • Recommended intake: 45-65% of total calories.

  • Emphasize complex carbohydrates (whole grains, vegetables).

  • Consequences of high intake of refined sugars: obesity, nutritional deficiencies.

Lipids
Dietary Sources

  • Mainly found in triglycerides (neutral fats).

  • Categories:

    • Saturated fats: animal sources, some tropical plants.

    • Trans fats: hydrogenated oils (margarine).

    • Unsaturated fats: plant oils (olive, nuts).

  • Cholesterol: Found in animal products; liver can synthesize cholesterol.

  • Essential Fatty Acids:

    • Linoleic acid (omega-6)

    • Linolenic acid (omega-3)

Uses in the Body

  • Adipose tissue: Provides cushioning, insulation, and energy storage.

  • Phospholipids: Essential for myelin sheaths and membranes.

  • Cholesterol: Stabilizes cell membranes; precursor to bile salts and steroid hormones.

  • Triglycerides: Major energy source for muscle and liver cells; aid in absorption of fat-soluble vitamins.

Dietary Requirements

  • Fats: 20-35% of total caloric intake.

    • Limit saturated fats to 10% or less.

    • Cholesterol intake: As low as possible for individuals with cardiovascular diseases.

Proteins
Dietary Sources

  • Complete Proteins: Animal products (meat, eggs, dairy) and soybeans.

  • Incomplete Proteins: Found in legumes, nuts, grains, and vegetables.

    • Combining cereal grains and legumes provides all essential amino acids.

Uses in the Body

  • Structural: Keratin (skin), collagen (connective tissue), muscle proteins.

  • Functional: Enzymes and hormones control body activities.

  • Amino Acids Use: Depends on several factors: the all-or-none rule, caloric intake adequacy, hormonal controls.

Nitrogen Balance

  • Balance States:

    • Positive nitrogen balance: synthesis exceeds breakdown (common in growing children).

    • Negative nitrogen balance: breakdown exceeds synthesis (during stress, starvation).

Dietary Requirements

  • Protein Needs: 0.8 g/kg body weight; accounts for age, size, and metabolic rate.

Vitamins
Overview

  • Definition: Organic compounds essential in minute amounts; act as catalysts for metabolic processes, primarily as coenzymes.

  • Most vitamins must be obtained through diet, except for Vitamins D, B, K (synthesized in the body).

Types

  • Water-soluble Vitamins: (B complex, C)

    • Absorbed with water; no significant storage; excess excreted.

  • Fat-soluble Vitamins: (A, D, E, K)

    • Stored in body; excess intake may cause health issues.

Antioxidants and Mega Doses

  • Vitamins A, C, E, and selenium act as antioxidants.

  • Mega doses of fat-soluble vitamins can lead to toxicity.

Table 24.2: Vitamins Summary

  • Includes major dietary sources, functions, and deficiency symptoms for each vitamin.

Minerals
Overview

  • Required Minerals: Calcium, phosphorus, potassium, sulfur, sodium, chlorine, magnesium, and trace amounts of others.

  • Functions: Structural (bone hardness), electrochemical (electrolyte balance), and enzymatic roles.

Major Dietary Sources

  • Plant foods, dairy, meats, and the importance of balanced mineral intake.

Table 24.3: Minerals Summary

  • Detailed descriptions of essential minerals, their dietary sources, functions in the body, and deficiency symptoms.

Metabolism
Overview

  • Metabolism: Sum of all biochemical reactions involving nutrient use; consists of anabolism and catabolism.

Anabolism vs. Catabolism

  • Anabolism: Building larger molecules from smaller ones.

    • Example: Synthesis of proteins from amino acids.

  • Catabolism: Breaking down complex structures to simpler ones (e.g., hydrolysis of proteins).

Stages of Energy Processing

  1. Digestion and absorption in the gastrointestinal tract.

  2. Cytoplasmic metabolism (either anabolic or catabolic pathways).

  3. Mitochondrial metabolism leading to complete breakdown and ATP production.

Phosphorylation

  • Mechanisms: Transfer of high-energy phosphates.

    • Substrate-level phosphorylation and oxidative phosphorylation.

Oxidation-Reduction Reactions

  • Redox Reactions: Critical in energy transfer; involve electron transfer.

    • Coenzymes like NADH and FADH2 are key players.

Carbohydrate Metabolism

  • Central role in ATP production; involves processes such as glycolysis and the citric acid cycle.

Glycolysis Overview

  • Occurs in the cytosol; converts glucose to pyruvate.

    • Three major phases: sugar activation, cleavage, oxidation.

Citric Acid Cycle and Oxidative Phosphorylation

  • Detailed processes of the citric acid cycle; how acetyl CoA enters; ATP yield from oxidative phosphorylation.

Lipid Metabolism

  • Triglyceride oxidation for energy; processes like lipogenesis and lipolysis.

Lipogenesis and Lipolysis

  • Lipogenesis: Synthesis of triglyceride when energy is in excess.

  • Lipolysis: Breakdown of triglycerides into glycerol and fatty acids for energy utilization.

Amino Acid Metabolism

  • Details on protein synthesis and degradation processes.

Degradation of Amino Acids

  • Steps including transamination and oxidative deamination.

Energy Balance

  • Important concepts of energy intake vs. output; implications on health.

Regulation of Food Intake

  • Biological controls of hunger and satiety, including the role of hormones such as insulin and glucagon.

Obesity and Health Risks

  • Definitions, statistics, health implications associated with obesity, current figures in the U.S.

Homeostatic Imbalances

  • Discusses various metabolic conditions and imbalances, such as diabetes, hyperthyroidism, and metabolic syndrome.