Lecture 4 Nutrition

• Vitamins


  • Contribute no energy to the body (non-kcaloric)
  • Facilitate body process
  • Needed in smaller quantities than energy-yielding nutrients (CHO, proteins, fats)
  • Similar to energy-yielding nutrients as they are vital to life, organic nutrients, and available from food
• Research supports role of vitamin-rich foods in protecting against diseases such as cancer and heart disease
• Vitamins


  Essential and vital for life
• Vitamin deficiencies


  • Deficiency in vitamin A can cause blindness
  • Lack of niacin (B3) can cause dementia
  • Lack of vitamin D can retard bone growth
• Vitamins


  • Differ than macronutrients
  • Structure: they are individual units; they are not linked together as glucose and amino acid s
  • Function: do not contain energy but involved in energy release
  • Dietary intake: mg and ug rather than grams
  • Better quality in food than in supplements
• Bioavailability

  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 preparations (e.g., raw vs. cooked)
  • Source of the nutrient e.g., (naturally occurring vs. fortified)
• Each of these tactics saves a small percentage of the vitamins in foods, but repeated each day this can add up to significant amounts in a year's time
• Precursors


  • Some of the vitamins are available from foods in inactive forms known as precursors or provitamins (e.g., beta-carotene which is plant-derived vitamin A precursor)
  • Provitamins are converted to the active form of the vitamin inside the body (e.g., 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
• Solubility


  • Vitamins are subdivided into fat-and water-soluble vitamins
  • Solubility determines absorption, transport, and storage, excretion, toxicity and requirement
• Minerals are indestructible
• Bioavailability differs between minerals
• Interactions between minerals is important (e.g., influences bioavailability)
• Minerals


  Essential nutrients; major minerals required in amounts more than 100 mg/day; trace minerals in less than 100 mg/day
• Roles of major minerals

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


  • Highly essential (more so than any other nutrient)
  • Majority of human body weight comprised of water
  • 60% of our body
• 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 yes, spinal cord, and amniotic sac surrounding a fetus in the womb
• Metabolism


  • Sum of all chemical reactions in living cells
  • Required to provide energy to the cells for growth, repair, maintenance and reproduction
  • All organs, tissues and cells have role in metabolism
  • Efficient process manufactures needed products and disposes wastes
  • Hormonal signals coordinate supply and demand
  • In disease, metabolic processes can become distributed
  • Some diseases caused by metabolic disturbances (e.g., diabetes)
• Principal organs involved in metabolism

  • The digestive organs
  • The liver
  • The pancreas
  • The heart and blood vessels
  • The kidneys
• Digestive organs


  • Transport and digest food
  • Contain body's most multiplying cells
  • Replaced every few days when healthy
  • Disorders of Gi tract interfere with nutrient ingestion, digestion, absorption, and metabolism
• Liver


  • Absorbed nutrients (e.g., glucose) first taken to the liver
  • Metabolizes, packages, stores, and ships out for use by other organs
  • One of the body's most active metabolic factories
  • Liver disorders disrupt metabolism and profoundly affect nutrition and overall health status
• Pancreas


  • Contributes digestive juices to GI tract
  • Produces insulin (after a meal, as blood glucose rises) and glucagon (between meals, when blood glucose falls) to regulate body's use of glucose
• Insulin


  • Promotes cells to take up glucose for fuel
  • Prompts liver cells to store glucose as glycogen
• Glucagon


  Prompts liver to dismantle its glycogen stores and release glucose into the blood for use by all the other body cells
• Heart and blood vessels

  Conduct blood (with nutrients and oxygen) to all other body cells and carry wastes away
• Kidneys


  • Filter waste products from the blood for excretion in urine
  • Reabsorb needed nutrients (e.g., glucose and electrolytes), maintaining blood's chemical balances
  • Produce compounds (e.g., renin) that help regulate blood pressure
  • Convert a precursor compound to active vitamin D
• Fundamental components of metabolism

  • Enzymes (proteins) - mediate metabolic reaction
  • Coenzymes (vitamins e.g., niacin and riboflavin) - enhance or necessary for the action of enzymes
  • Cofactors (minerals e.g., iron, zinc) - are required for enzyme activity
• Every chemical reaction either requires or releases energy
• Condensation


  Releases water and requires energy
• Hydrolysis


  Requires water and releases energy
• Heat energy and body temperature

  • Metabolic chemical reactions in cells release heat
  • Keeps the body warm
  • Regulating rate of reactions helps maintain constant normal temperature
• Accelerated metabolism


  • Severe stress to body due to variety of stressors (such as burns, infection, surgery etc) increases metabolism
  • Fuels used at faster than normal rate
  • May result in fever, loss of weight and lean tissue
• Anabolism


  • Energy-yielding nutrients used to build body compounds when not needed for energy
  • Glucose units strung together to make glycogen chains
  • Glycerol and fatty acids can be assembled into triglycerides
  • Amino acids can be linked to form proteins
  • Anabolic reactions require energy provided by ATP
• Catabolism


  • Breaking down of body compounds when the body needs energy
  • Glycogen is broken down to glucose
  • Triglycerides are broken to fatty acids and glycerol
  • Proteins are broken down to amino acids
  • Catabolic reactions release energy
• Anabolic reactions


  • Making complex molecules from more basic ones
  • Requires chemical energy
  • Use condensation reactions (releases water)
• Catabolic reactions


  • Breakdown of complex molecules to more basic ones
  • Releases energy
  • Use hydrolysis reactions (requires water)
• Energy


  • Manifests in many forms: heat energy, mechanical energy, electrical energy, chemical energy
  • Stored in foods and in the body as chemical energy
• Energy metabolism


  • Sum of all reactions the body used to obtain or expend energy from foods
  • Energy-yielding nutrients broken into basic units and absorbed into the blood: Glucose from carbohydrates, Glycerol and fatty acids from fat, Amino acids from proteins
• Adenosine triphosphate (ATP)


  • High-energy compound that contains 3 phosphate groups
  • The bonds between the phosphate groups are described as high energy because of their readiness to release energy
  • Transfers small amounts of usable energy to move our muscles
  • Supplies enzymes with energy needed to catalyze chemical reactions
  • Produced continuously throughout the day by using the energy from the break down of the energy-yielding nutrients