Nutritional Biochemistry Overview 2022-2023

Study Notes

Nutrition encompasses the composition and quantity of food intake by living organisms, along with biochemical utilization.
Human nutrition is categorized into three areas:
- Undernutrition (nutrient deficiency)
- Overnutrition (excessive nutrient intake)
- Optimal nutrition (balanced nutrient intake)

Malnutrition is assessed through:
- Dietary intake studies to identify individuals with deficient diets.
- Biochemical studies identifying subclinical nutritional deficiencies.
- Clinical symptoms revealing clinical nutritional deficiencies.

DRIs provide quantitative estimates of nutrient intake needed to prevent deficiencies and maintain optimal health in populations.
DRIs are recommended by the Food and Nutrition Board of the National Research Council, USA.

Estimated Average Requirement (EAR): Nutrient intake to meet requirements of 50% of healthy individuals in a specific group.
Recommended Dietary Allowance (RDA): Intake sufficient for 97-98% of healthy individuals; calculated as RDA = EAR + 2 SD.
Adequate Intake (AI): Used when EAR/RDA cannot be established; approximates the nutrient needs for all individuals in a group.
Tolerable Upper Intake Level (UL): Highest daily intake with no adverse health effects or toxicity for almost all individuals.

Vitamin C functions as a cofactor in enzyme reactions, a powerful antioxidant, and stabilizes vitamins E and folic acid while enhancing iron absorption.
It neutralizes free radicals and inflammatory responses, including sepsis.
Vitamin C cannot be synthesized by humans; it must be obtained through diet.

During oxidation of ascorbic acid, an ascorbyl radical forms but reacts poorly with oxygen, preventing harmful reactive oxygen species formation.
Dehydroascorbic acid can revert to ascorbic acid with help from reduced glutathione.
Vitamin C has several vitamers active in animals, including different forms dependent on pH.

Scurvy, a disease due to vitamin C deficiency, was prevalent among sailors; refusal to consume fresh fruits led to high mortality.
The remedy of consuming lime juice reduced scurvy's effects, leading to British sailors being nicknamed "limey."
Humans cannot synthesize vitamin C due to the absence of gulonolactone oxidase, the final enzyme in its synthesis pathway.

Rich sources include fruits, vegetables, and organ meats; notable examples are:
- Asparagus, papaya, oranges, cantaloupe, cauliflower, broccoli, green peppers, grapefruit, lemons, strawberries.
Citrus products are highlighted as significant vitamin C sources.
Supplements typically provide vitamin C as free ascorbic acid, calcium ascorbate, sodium ascorbate, and related forms.