Untitled Quiz

Biochemical Aspects of Nutrition

• Biochemical aspects of nutrition are a subject of study.
• There are questions about inhibiting factors and absorption.

Nutrients in Foods

• Essential nutrients include water, carbohydrates, proteins, and lipids.
• Regulatory nutrients include vitamins and minerals.

Carbohydrates in Nutrition

• Monosaccharides are the major part of carbohydrates.

  • Glucose
  • Fructose
  • Galactose

• Disaccharides include:

  • Sucrose (table sugar)
  • Lactose (milk sugar)
  • Maltose

• Oligosaccharides are prebiotic, partially indigestible.

  • Raffinose
  • Stachyose

• Carbohydrates are needed daily in the diet at least 50-100 grams/day.

• Most diets contain more than enough carbohydrates.

• Dietary Fiber:

  • Structural parts of plant foods not digestible by the body.
  • Lack of necessary enzymes
  • Polysaccharide
  • Essential nutrient
  • Two types:
    • Insoluble fiber: does not dissolve in water or gastrointestinal fluids, provides bulk (cellulose, hemicelluloses), prevents constipation, and helps with weight management.
    • Soluble fiber: dissolves in water, turns to a gel-like substance, slows down digestion, promotes fullness, and accelerates the exit of harmful substances in food (e.g., gums, pectins).
    • Insoluble fiber is found in cereals, whole-wheat bread, and lentils. Soluble fiber is found in oats, beans, and sweet potatoes.

• Importance of Carbohydrates in the Diet: preventing constipation, improving bowel-related health problems like constipation, hemorrhoids, and fecal incontinence, and colorectal cancer, helping in weight management.

Maintenance of Blood Glucose

• Discussed in two states:

  • Absorptive state (lasts about 4 hrs after a meal)

    • Blood glucose readily available for ATP synthesis.
    • Excess glucose stored as glycogen in liver and muscles or as body fat.
    • Fats taken by tissues mainly adipose and muscular tissue.
    • Amino acids utilized for protein synthesis.
    • Regulated largely by insulin, which stimulates nearly all cells to absorb glucose.

  • Postabsorptive state (fasting)

    • Prevails hours after meals and overnight.
    • Regulates blood glucose levels, critical for the brain.
    • Glucose drawn from body's glycogen reserves in the liver and muscles.
    • Synthesized from fats (gluconeogenesis).
    • After 4-5 days of fasting, the brain uses ketone bodies as supplemental fuel extracted from fats
    • If glycogen and fat reserves are depleted, the body burns proteins (skeletal muscle proteins are first).
    • Regulated by the sympathetic nervous system and glucagon.
      • Glucagon promotes glycogenolysis (glycogen to glucose), gluconeogenesis (AA/FFA to glucose), and lipolysis (triglyceride to FFA).

Lipids in Nutrition

• Lipids: Major lipids include TAGs, fatty acids, glycerides
  • Saturated fatty acids
  • Unsaturated fatty acids
    • Neutral glycerides
    • Phosphoglycerides
      • Non-glyceride lipids, waxes
      • Sphingolipids, steroids
      • Complex lipids, lipoproteins
  • Examples of fatty acids: stearic acid, oleic acid, linoleic acid, arachidonic acid.
  • Fats and oils usually contain mixtures of fatty acids.
    • Butter and other animal fats: saturated.
    • Olive and canola oils: monounsaturated.
    • Fish, corn, safflower, soybean, and sunflower oil: polyunsaturated. -Essential fatty acids:
    • Alpha-linolenic acid (omega-3 fatty acid)
    • Linoleic acid (omega-6 fatty acid)
  • Need in small amounts for cell membranes, hormone-like compounds, blood pressure, blood clotting, and immune response.
  • Sources: vegetable oils (safflower or corn), grains, nuts, and seeds, vegetables, fish
  • Hydrogenation in food industry for better stability, resistance to rancidity, and a solid and spreadable form, however, conversion from cis form to trans fats poses health risks.

Microbiota

• Complex, diverse, and vast microbial community in human intestines.
• Composed of approximately 1,100 prevalent species.
  • Four main bacterial phyla in a healthy human gut: Firmicutes, Bacteroidetes, Actinobacteria, and Proteobacteria
• Produce various kinds of metabolites (beneficial and harmful for the host):
  • Short-chain fatty acids (SCFAs)
  • Trimethylamine N-oxide (TMAO)
  • Bile acids
  • Branched-chain amino acids
• SCFAs (e.g., acetate, propionate, butyrate) are produced by anaerobic fermentation of undigested nutrients and are absorbed in the intestines.
• SCFAs are associated with energy, regulating food intake, increasing satiety, improving glucose tolerance, and suppressing fasting-induced adipose factor (Fiaf) expression.
• TMAO is a metabolite of gut microbes and is associated with the development of atherosclerosis.
  • Generated through metabolism of choline, phosphatidylcholine, L-carnitine, and betaine, via TMA lyases.
  • Oxidized into TMAO by hepatic flavin monooxygenases (FMO3).
• Prebiotics are non-digestible but fermentable polysaccharides
• Probiotics are live microorganisms

Proteins in Nutrition

• Basic structural material of the body (in cell membranes and blood)

• Enzymes

• Antibodies

• Collagen in connective tissue

• Many hormones (e.g., insulin)

• Food contains approximately 20 common amino acids

  • Essential amino acids for humans
    • Histidine
    • Isoleucine
    • Leucine
    • Lysine
    • Methionine
    • Phenylalanine
    • Threonine
    • Tryptophan
    • Valine

• Indispensable amino acids

  • Arginine
  • Cysteine
  • Tyrosine

• Protein sources include foods of animal origin (meat, fish, eggs, dairy products) and plant origin (soybeans).

• Vegetarian diets have high lysine and low methionine.

• Grains have complementary strengths and weaknesses.

• The recommended daily protein intake for adults of both sexes is 0.75 gram of protein per kilogram of body weight.

• additional protein needs for endurance athletes, infants, children, pregnant, and lactating women.

Vitamins in Nutrition

• Vitamin A for embryonic development, growth, reproduction, immune function, integrity of cells, and vision
• B Vitamins (coenzymes assisting in energy metabolism)
• Folic acid (Vitamin B9) helps protect against birth defects
• Vitamin C building connective tissue, antioxidant
• Vitamin D calcium and phosphorus homeostasis, bone metabolism
• Vitamin E antioxidant, heme synthesis
• Vitamin K blood clotting
• Humans can synthesize certain vitamins to some extent (Vitamin D, Niacin, Vitamin K, Biotin)
• Humans need vitamins from their diet (specific deficiency often irreversible)
• Some vitamins are found in precursor forms in food that must be activated by the body (eg. beta-carotene converted to Vitamin A)
• Water-soluble vitamins are more easily destroyed by cooking, and water-soluble vitamins are synthesized by both plants and animals.
• Vitamin B12 is supplied by foods of animal origin, vegetarians at risk of deficiency

Minerals in Nutrition

• Simple inorganic elements (4-6% of body weight) in the body as salts
• Not metabolized themselves
• Not a source of energy
• Function broadly in metabolism & controlling water movement, fluid balance, osmotic pressure, and acid-base balance
• Components of enzyme systems
• Macrominerals (in amounts of 100 mg or more daily) include calcium, phosphorus, magnesium, sulfur, sodium, chloride, and potassium.
• Microminerals (required in amounts of 15mg or less per day) include iron, zinc, copper, manganese, iodine, selenium, fluoride, molybdenum, chromium, and cobalt.
• Ultratrace elements (in micrograms daily) include arsenic, boron, nickel, silicon, and vanadium.
• Levels of different minerals in foods can be influenced by growing conditions (soil and water composition).
• Minerals are not destroyed during food preparation, and better absorbed from animal foods than plant foods.
• Fibres in plants interfere with absorption of certain minerals, especially phytates.
• Some minerals (especially iron and copper) can compete for absorption if present at high levels.

Energy

• Human body is an engine that releases energy present in food.
• Energy utilized for mechanical work (muscles, secretory processes), maintains body structure and functions.
• Food is the fuel source of the body
  • Carbohydrates: 4 kcal/gram (17 kJ/gram)
  • Proteins: 4 kcal/gram (17 kJ/gram)
  • Fats: 9 kcal/gram (38 kJ/gram)
• Energy from diet: Protein (12-15%), fat (30-40%), carbohydrate (50-60%).
• Basal metabolic rate (BMR): minimum energy required by the body maintaining life at physical and mental rest in the post-absorptive state.
• BMR is influenced by age, sex, body surface area, environmental conditions (cold), body temperature, and exercise.
• Other factors influencing BMR: drugs, pregnancy, racial variations, barometric pressure, state of nutrition, and hormones (thyroid hormone, adrenaline, catecholamines, growth hormone, male sex hormone)

Appetite

• Hunger and satiety are regulated by complex interactions involving multiple brain centers, hormones, and sensory/motor pathways.
• Central appetite control:
  • Hypothalamus (ventromedial hypothalamus: satiety center; lateral hypothalamus: feeding/hunger center)
  • Hypothalamic messengers
  • Peripheral signals of appetite (hormones)
• Peripheral signals of appetite (hormones): Insulin, cholecystokinin, peptide YY, pancreatic polypeptide, leptin, ghrelin, glucagon-like peptide-1
• Two types of neurons in the arcuate nucleus: -1. Orexigenic NPY/AgRP neurons (stimulate appetite) -2. Anorectic POMC neurons (inhibit appetite)