Energy Metabolism & Vitamins/ Minerals

• Learning goals
  • Describe how vitamins are classified and named
  • Describe how minerals are classified
  • Appreciate the essential nature of water as a nutrient

Vitamins

• Vitamins are non-kcaloric
• They contribute no energy to the body, but facilitate body processes
• Required in smaller quantities than energy-yielding nutrients like carbohydrates, proteins, and fats
• Similar to energy-yielding nutrients as they are vital to life, organic nutrients, and available from food
• Vitamin-rich foods are associated with protecting against diseases such as cancer and heart disease
• Vitamin A deficiency can cause blindness
• Lack of niacin (B3) can cause dementia
• Vitamin D deficiency can retard bone growth
• Differ from macronutrients, as they are individual units and not linked together; macronutrients like glucose and amino acids are linked.
• They are involved in energy release, not energy provision
• Dietary intake is measured in mg and µg, rather than grams
• Vitamins from foods are better than vitamin supplements

Bioavailability

• Bioavailability definition: the rate and extent to which a nutrient is absorbed and used by the body
• Factors influencing vitamins' bioavailability:
  • Efficiency of digestion and time of transit through the GI tract
  • Previous nutrient intake and nutrition status
  • Other foods consumed at the same time
  • Food preparation (e.g. raw vs cooked)
  • Source of the nutrient (naturally occurring vs fortified)
• Example: If meat and dairy are eaten together, the calcium will inhibit the absorption of Iron [Fe]

Precursors

• Some vitamins are available from foods in inactive forms known as precursors, or provitamins
• Example: beta-carotene which is plant-derived Vitamin A precursor
• Provitamins are converted to the active form of the vitamin inside the body
  • Example: beta-carotene to retinol

Toxicity

• More isn't always better
• Various toxicity symptoms such as hemorrhagic effects for vitamin E and diarrhea and GI distress for vitamin C
• Fat-soluble vitamins (vitamin A, D, E and K) toxicities are likely from supplements and occur rarely from food
• Water-soluble vitamins (B vitamins and vitamin C) toxicities are unlikely but possible with high doses from supplements
  • Fat-soluble Vitamins are more toxic then water soluble

Solubility

• Vitamins are subdivided into fat- and water-soluble vitamins
• Solubility determines absorption, transport and storage, excretion, toxicity and requirement
• Fat-soluble vitamins consist of A, D, E and K
• Water-soluble vitamins consist of B vitamins- Thiamin, Riboflavin, Niacin, Pantothenic acid, Biotin, Vitamin B6, Folate, Vitamin B12 and Vitamin C

Hydrophobic vs Hydrophilic Vitamins

• Fat-Soluble Vitamins: Vitamins A, D, E, and K characteristics

  • Absorbed like fats, first into the lymph and then into the blood
  • Must travel with protein carriers in watery body fluids; stored in the liver or fatty tissues
  • Not readily excreted; tend to build up in the tissues
  • Toxicities are likely from supplements but occur rarely from food
  • Needed in periodic doses (perhaps weekly or even monthly) because the body can draw on its stores

• Water-Soluble Vitamins: B Vitamins and Vitamin C characteristics

  • Absorbed directly into the blood
  • Travel freely in watery fluids; most are not stored in the body
  • Readily excreted in the urine
  • Toxicities are unlikely but possible with high doses from supplements
  • Needed in frequent doses (perhaps every 1 to 3 days) because the body does not store most of them to any extent

Minerals

• Minerals are indestructible
• Bioavailability differs between minerals
• Interaction between minerals is important (e.g. influences bioavailability)
• Various roles
• Essential nutrients
• Major minerals are required in amounts more than 100 mg/day
• Trace minerals are required in less than 100 mg/day
• Calcium, Chloride, Magnesium, Phosphorus, Potassium, Sodium and Sulfur are considered Major Minerals
• Chromium, Copper, Fluoride, Iodine, Iron, Manganese, Molybdenum, Selenium and Zinc are considered Trace Minerals

Functions of Major Minerals

• Influence fluid balance
  • Example: sodium, chloride, and potassium
• Nerve transmission and muscle contractions
  • Example: sodium, potassium, calcium, and magnesium
• Energy metabolism
  • Example: phosphorus and magnesium
• Contribution to bone structure
  • Example: calcium, phosphorus, and magnesium
• Sulfur helps determine the shape of proteins

Water

• Highly essential, more so than any other nutrient
• Majority of human body weight is comprised of water, approximately 60% of our body weight
• Roles of water in body fluids:
  • Carries nutrients and waste products throughout the body
  • Maintains the structure of large molecules such as proteins and glycogen
  • Participates in metabolic reactions
  • Solvent for many molecules e.g. glucose, vitamins, minerals etc
  • Aids in temperature regulation
  • Maintains blood volume
  • Acts as lubricant and cushion around joints and inside the eyes, spinal cord, and amniotic sac surrounding a fetus in the womb