Biochemistry and Nutrition BAN 203 - Lecture 37

Biochemistry and Nutrition (BAN 203) - Lecture 37

• Lecture Title: Principles of Nutrition (3)
• Textbook: Lippincott's Illustrated Reviews, Chapter 27, Page 365
• Specific Objectives: Students will be able to explain the importance of fibers in the diet, differentiate between positive and negative nitrogen balance, and discuss different reasons for malnutrition.

Dietary Carbohydrates

• Primary Role: Provide energy (4 kcal/g)
• Not inherently fattening: Carbohydrates themselves do not cause weight gain.

Classification of Carbohydrates

• Monosaccharides:
  • Glucose: Abundant in fruits, sweet corn, corn syrup, and honey.
  • Fructose: Found with glucose and sucrose in honey and fruits.
• Disaccharides:
  • Sucrose (glucose + fructose): Ordinary table sugar, abundant in molasses and maple syrup.
  • Lactose (glucose + galactose): Principal sugar in milk.
  • Maltose (glucose + glucose): Product of enzymic digestion of polysaccharides.
• Polysaccharides:
  • Polymers of glucose, lacking a sweet taste.
  • Starch: Abundant in plants (wheat, grains, potatoes, dried peas, beans, vegetables)

Dietary Fibers

• Definition: Nondigestible carbohydrates present in plants.
• Digestion and Absorption: Resistant to digestion and absorption in the small intestine, but completely or partially fermented in the large intestine to short-chain fatty acids
• Function:
  • Provides little energy
  • Absorbs up to 10-15 times its weight in water, increasing bowel motility.
  • Delays gastric emptying, leading to feelings of fullness.
  • Reduces blood glucose peaks after meals.
  • Lowers LDL cholesterol levels.
  • Decreases the risk of constipation and hemorrhoids.
• Recommended Daily Intake: 25g/day for women and 38g/day for men.

Carbohydrate Requirements

• RDA: 130 g/day for adults and children, based on glucose needs of carbohydrate-dependent tissues (brain and erythrocytes).
• Calorie Contribution: Adults should consume 45-65% of their total calories from carbohydrates.

Simple Sugars and Disease

• No direct evidence: Simple sugars consumption isn't harmful in all cases.
• No relation to diabetes or hypoglycemia: High sucrose diets do not cause these conditions and they’re not intrinsically fattening.
• Dental caries: Associated with sucrose consumption, especially without fluoride treatment.

Dietary Protein - Quality and Source

• Quality: Measure of its ability to provide essential amino acids for tissue maintenance.
• Animal Sources: (meat, poultry, milk, fish) - high quality; all essential amino acids in similar proportions to human tissue proteins.
• Plant Sources: (wheat, corn, rice, beans) - lower quality than animal proteins. Examples include wheat (lysine-deficient but methionine-rich), kidney beans (methionine-poor but lysine-rich), which can be combined for improved biological value.

Nitrogen Balance

• Definition: Occurs when nitrogen consumed equals nitrogen excreted (in urine, sweat, and feces).
• Positive Balance: Nitrogen intake exceeds excretion; observed during tissue growth (e.g. childhood, pregnancy), recovery from illness.
• Negative Balance: Nitrogen loss exceeds intake; associated with inadequate protein intake, lack of essential amino acids, or physiological stress (trauma, burns, illness, surgery).

Protein Requirements

• RDA: 0.8 g/kg of body weight for adults (approximately 56g for a 70kg individual).
• Athletes: May benefit from increased intake (1 g/kg).
• Pregnant/lactating women: Increased requirement (up to 30 g/day beyond basal).
• Infants: Need 2 g/kg/day for growth support.

Consumption of Excess Protein

• No physiologic advantage: There's no benefit to consuming more than the RDA.
• Energy Production: Excess protein generates energy or acetyl coenzyme A for fatty acid synthesis.
• Increased Urinary Calcium and Risks: Elimination of excess protein as urinary nitrogen often increases urinary calcium, increasing nephrolithiasis and osteoporosis risk.

Protein-Sparing Effect of Carbohydrate

• Protein-Sparing: Carbohydrates allow amino acids to be used for tissue repair and maintenance rather than gluconeogenesis.
• Gluconeogenesis Precursor: Low carbohydrate intake (< 130g/day) increases protein use for gluconeogenesis precursors.

Protein-Energy Malnutrition (PEM)

• Developed Countries: Primarily seen in patients with medical conditions affecting appetite or nutrient digestion, hospitalized patients with major trauma or infections.
• Developing Countries: Inadequacy of protein and/or energy is the main cause.
• Symptoms: Depressed immune system, reduced infection resistance, secondary infection, and potential death.
• Forms: Extreme cases of PEM are kwashiorkor and marasmus.

Kwashiorkor

• Protein deprivation: Greater than reduction in total calories.
• Visceral Protein Synthesis: Deprivation leads to decreased visceral protein synthesis.
• Occurrence: Frequently seen in children after weaning when their diet consists predominantly of carbohydrates.
• Symptoms: Stunted growth, edema (tissue swelling), skin lesions, depigmented hair, anorexia, enlarged fatty liver, and reduced plasma albumin. Edema can mask muscle loss.

Marasmus

• Calorie deprivation: Greater than reduction in protein.
• Occurrence: Commonly seen in children under one, when breast milk is supplemented with watery gruels of native cereals low in protein and calories.
• Symptoms: Arrested growth, extreme muscle wasting (emaciation), weakness, and anemia. Absence of edema and plasma protein changes seen in kwashiorkor.

Explore the principles of nutrition as outlined in Lecture 37 of Biochemistry and Nutrition (BAN 203). This quiz covers dietary carbohydrates, their classifications, and the role of fibers in maintaining a balanced diet. Learn how to differentiate between nitrogen balance types and understand the causes of malnutrition.