Biochemistry and Nutrition BAN 203

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.

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

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)

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.

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.

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.

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.

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).

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.

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: 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.

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.

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.

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.