Clinical Biochemistry and Nutrition Notes

Nutrition

  • Nutrition is defined as the utilization of food by living organisms, promoting health and welfare.
  • The field of nutrition can be controversial due to public opinion and scientific debates.

Methodology in Nutrition

  • Most knowledge has been derived from animal studies, despite differences in biochemical composition between humans and animals (e.g., ascorbic acid synthesis).

Areas of Study in Human Nutrition

  1. Ideal Nutrition - Desirable for optimal health.
  2. Undernutrition - A major concern in developing countries.
  3. Overnutrition - A concern in developed countries.

Essential Understanding for Nutrition

  • Knowledge in chemistry and metabolism is essential, focusing on: carbohydrates, lipids, proteins, vitamins, and minerals.
  • Key topics include energy demand, dietary allowances (RDA), balanced diet, and nutritional disorders.

Nutrition and Energy Supply

  • Food acts as the body's fuel source and must be metabolized for energy production.
Calorific Values of Foodstuffs
  • Carbohydrates: 4 Cal/g (4.1 in calorimeter)
  • Fats: 9 Cal/g (9.4 in calorimeter)
  • Proteins: 4 Cal/g (5.4 in the body)
  • Alcohol: 7 Cal/g (7.1 in the body)
Units of Energy
  • Calorie: Heat needed to raise 1 gram of water by 1°C.
  • Kilocalorie (Cal): 1 Cal = 1000 calories
  • Joule: Another energy measurement; 1 Cal = 4.128 KJ.
Nutrient Roles
  • Vitamins and minerals have no calorific value but are crucial for bodily functions.
Respiratory Quotient (RQ)
  • RQ measures the ratio of CO2 produced to O2 consumed, varying by nutrient:
    • Carbohydrates: RQ = 1
    • Fats: RQ ≈ 0.7
    • Proteins: RQ ≈ 0.8
Energy Utilization
  • Energy is consumed to support three processes:
    1. Basal Metabolic Rate (BMR): Energy for basic functions at rest.
    2. Specific Dynamic Action (SDA): Energy after food ingestion.
    3. Physical Activity: Energy during movement.

Basal Metabolic Rate (BMR)

  • The minimum energy required for life functions at rest.
    • Normal BMR:
    • Adult Men: 35-38 Cal/m²/hr
    • Adult Women: 32-35 Cal/m²/hr
Factors Influencing BMR
  1. Surface Area: Larger surface area = higher BMR
  2. Sex: Males typically have a higher BMR
  3. Age: BMR decreases with age
  4. Physical Activity: Exercise increases BMR
  5. Hormones: Thyroid hormones increase BMR
  6. Environment: Cold climates increase BMR
  7. Starvation: BMR decreases during starvation
  8. Fever: BMR increases with fever
  9. Disease States: Some increase/decrease BMR
  10. Racial Variations: Different populations can have varying BMRs.
Significance of BMR
  • Crucial for calculating daily energy needs and assessing metabolic health.

Specific Dynamic Action (SDA)

  • Extra energy required to metabolize food beyond its caloric value:
    • SDA for Proteins: 30%
    • SDA for Fats: 5%
    • SDA for Carbohydrates: 10%

Energy Requirements

  • Energy needs vary by activity level:
    • Light work: 2200-2500 Cal/day
    • Moderate work: 2500-2900 Cal/day
    • Heavy work: 2900-3500 Cal/day
    • Very heavy work: 3500-4000 Cal/day.

Nutritional Importance of Carbohydrates

  • Major energy source (60-70% total caloric intake).
  • Spares proteins, required for brain function, and aids fat oxidation.

Fiber in Nutrition

  • Non-digestible carbohydrates critical for gut health, glucose tolerance, and cholesterol levels.
  • Two types:
    1. Soluble: Forms gels, seen in fruits/legumes.
    2. Insoluble: Absorbs water, found in grains/vegetables.
Beneficial Effects of Fiber
  1. Prevents constipation.
  2. Reduces toxins.
  3. May lower GIT cancer risk.
  4. Improves glucose tolerance.
  5. Lowers cholesterol absorption.
  6. Adds satiety without extra calories.

Nutritional Importance of Lipids

  • Provide essential fatty acids, concentrated energy, and fat-soluble vitamins (A, D, E, K).

Nutritional Importance of Proteins

  • Body's building blocks, giving essential amino acids and serving as energy source (10-15%).
Essential Amino Acids
  • 10 essential amino acids required for body function.
    • Must be ingested through diet.
Nitrogen Balance
  • Represents protein utilization in the body and can be positive, negative, or equilibrium.
Assessing Protein Quality

Methods:

  1. Protein Efficiency Ratio (PER): Weight gain per protein ingested.
  2. Biological Value (BV): Percentage of absorbed nitrogen retained.
  3. Net Protein Utilization (NPU): Retained nitrogen compared to total ingested.
  4. Chemical Score: Comparison of test proteins against reference protein.

Recommended Dietary Allowances (RDA)

  • RDA provides nutrient quantities for maintaining health.
    • Varies by sex, age, and physiological status.
Balanced Diet
  • A diet with varied foods, meeting nutrient needs effectively without deficiencies.

Nutritional Disorders

  • Undernutrition prevalent in developing countries vs overnutrition and obesity in developed countries.
    • Kwashiorkor: Protein deficiency.
    • Marasmus: Caloric deficiency.

Nutrigenomics

  • Examines interactions between diet, genes, and health for personalized nutrition strategies.

Summary

  1. Macronutrient calorific values: Carb (4), Fats (9), Proteins (4).
  2. BMR: Base energy at rest; average for men 35-38 Cal/m²/hr, women 32-35 Cal/m²/hr.
  3. SDA varies by food type and is highest for proteins.
  4. Carbohydrates are the main energy source.
  5. Lipids provide energy and essential nutrients.
  6. Proteins are crucial for growth and repair, and also serve as energy sources.
  7. Assessing protein quality helps understand their dietary value.
  8. RDA represent daily nutrient needs.
  9. Balanced diets prevent nutrient-related disorders.
  10. PEM most common in developing nations with kwashiorkor and marasmus as key forms.