Nutrition BIO 426

• Nutrition


  The starting point and basis for all human form and function
• Nutrition


  • The source of fuel that provides energy for all biological work
  • The source of raw materials for replacement of worn-out biomolecules and cells
• Body weight


  Determined by the body's energy balance
• If energy intake and output are equal

  Body weight is stable
• Gain weight if intake exceeds output


  Lose weight if output exceeds intake
• Weight set point


  Varies from person to person, combination of heredity and environmental influences
• 30% to 50% of variation in human weight is hereditary
• Environmental factors such as eating and exercise habits account for the rest of the variation in weight
• Appetite


  Control of weight involves several peptide hormones and regulatory pathways that control short- and long-term appetite
• Gut-brain peptides


  Act as chemical signals from the gastrointestinal tract to the brain
• Short-term appetite regulators


  Mechanisms work over periods of minutes to hours, make one feel hungry and begin eating, make one feel satiated (full) and stop eating
• Arcuate nucleus of hypothalamus


  • Has receptors for appetite signals

  
• Neural networks involved in hunger


  • Feeding center - secretes neuropeptide Y (NPY), a potent appetite stimulant (orexin hormone)
  • Satiety center - secretes melanocortin: inhibits eating

  
• Ghrelin


  Produces sensation of hunger, secreted from empty stomach, stimulates hypothalamus to secrete growth hormone-releasing hormone
• Peptide YY (PYY)


  Secreted by enteroendocrine cells of ileum and colon, signals satiety and terminates eating
• Cholecystokinin (CCK)


  Secreted by enteroendocrine cells in duodenum and jejunum, stimulates secretion of bile and pancreatic enzymes, suppresses appetite and stops eating

  
• Appetite is briefly satisfied by chewing and swallowing, and stomach filling/inflation
• Lasting satiation depends upon nutrients entering the blood
• Neurotransmitters stimulate desire for different types of food


  Norepinephrine: carbohydrates, Galanin: fats, Endorphins: protein
• Long-term appetite regulators


  Govern caloric intake/energy expenditure over weeks to years
• Leptin


  Secreted by adipocytes, informs brain on how much body fat we have

  
• Most obese people have normal to high levels of leptin, but some have a defective leptin receptor
• Insulin


  Secreted by pancreatic beta cells, stimulates glucose and amino acid uptake and glycogen and fat synthesis, has receptors in the brain and weaker effect on appetite than leptin
• The ob/ob mouse had a rare deficiency - this is why leptin was misnamed
• Obese subjects have fewer dopamine receptors than control subjects
• Calorie


  Amount of heat that will raise the temperature of 1 g of water 1 degree C, 1000 calories is a kilocalorie, fats contain about 9 kcal/g, carbohydrates & proteins contain about 4 kcal/g, sugar and alcohol are "empty" calories -- no nutrients
• Body weight remains stable if energy intake and output are equal
• Nutrients


  Any ingested chemical used for growth, repair or maintenance
• Recommended daily allowances (RDA)


  Safe estimate of daily intake
• Classes of nutrients


  • water, Carbohydrates, Lipids, Proteins, Minerals, vitamins
• Macronutrients


  Must be consumed in large amounts (proteins, fats & carbohydrates)
• Micronutrients


  Needed in small amounts (e.g. vitamins)
• Essential nutrients


  Are those the body can not synthesize (minerals, vitamins, 8 amino acids, some fatty acids) and MUST be consumed
• Carbohydrates


  Location: muscle & liver (glycogen) and blood (glucose), Function: Energy = ATP production, Structure: Eg nucleic acids, glycoproteins & glycolipids, Blood glucose is regulated through insulin and glucagon

  
• Carbohydrates are rapidly oxidized, so their RDA is greater than any other nutrient (175 g/day)
• Dietary carbohydrates


  • monosaccharides (glucose, galactose & fructose), disaccharides (sucrose [table sugar], maltose, lactose), polysaccharides (starch, glycogen & cellulose)

  
• Nearly all dietary carbohydrates come from plants
• Dietary fiber


  Fibrous material that resists digestion, important to the diet (RDA is 30 g/day), Two types: water-soluble fiber (eg pectin in oats), water-insoluble fiber (absorbs water, softens the stool, eg cellulose)
• Lipids


  Average adult male is 15% fat; female 25% fat, Function: Energy store, Vitamin absorption, Structure of membranes, Cholesterol is precursor of steroids, bile salts & vitamin D

  
• Should be less than 30% of daily calorie intake, typical American gets 40-50% of calories from fat