Carbohydrates: Monosaccharides and Disaccharides

• Carbohydrates and proteins are macronutrients essential for bodily functions

Carbohydrates: Structure and Function

• Carbohydrates include monosaccharides, disaccharides, oligosaccharides, and polysaccharides

Monosaccharides: The Building Blocks

• Monosaccharides are simple sugars, the most basic units of carbohydrates
• Glucose, fructose, and galactose are key monosaccharides
• Glucose is the most abundant sugar and a primary energy source for cells; it is a hexose sugar (6 carbons) that exists in linear and ring forms and is central to energy production via glycolysis and the citric acid cycle
• Fructose is the sweetest natural sugar, found in fruits and high-fructose corn syrup; it is a ketohexose metabolized primarily in the liver
• Galactose does not occur alone in foods; it combines with glucose to form lactose (milk sugar); it is an epimer of glucose, differing in configuration around one carbon atom and is closely linked to glucose metabolism

Disaccharides: Two Monosaccharides United

• Disaccharides are formed when two monosaccharides are joined together
• Lactose, maltose, and sucrose are common disaccharides
• Lactose is made of glucose + galactose and is also known as milk sugar; lactose intolerance results from a deficiency in lactase, which breaks down lactose in the small intestine
• Maltose is made of glucose + glucose and results from the breakdown of starch; it is formed during starch digestion and further broken down into glucose
• Sucrose is made of glucose + fructose and is found in sugarcane, sugar beets, and honey; it is common table sugar that is readily hydrolyzed into glucose and fructose

Polysaccharides: Complex Carbohydrates

• Polysaccharides are complex carbohydrates comprised of many monosaccharides
• Starch, glycogen, and fiber are important polysaccharides
• Starch is the storage form of glucose in plants, found in grains, legumes, and tubers; it consists of amylose (linear) and amylopectin (branched) and its digestion involves amylases
• Glycogen is the storage form of glucose in animals, stored in the liver and muscles; it is a highly branched polysaccharide that allows for rapid glucose mobilization when needed
• Fiber consists of indigestible carbohydrates providing bulk to stool and health benefits; it is classified as soluble (dissolves in water, viscous) or insoluble (does not dissolve in water). Soluble fiber can lower cholesterol while insoluble fiber promotes regularity

Oligosaccharides: Short Chains

• Oligosaccharides contain 3-10 monosaccharides
• They are often indigestible by human enzymes and are fermented by gut bacteria; they contribute to gas production and the formation of short-chain fatty acids (SCFAs) in the colon and are found in various plant foods

Proteins: Digestion, Metabolism, and Nitrogen Balance

• Proteins are essential for building and repairing tissues and for various bodily functions

Protein Digestion and Absorption

• Digestion and absorption of proteins occur in several stages:
• Stomach: Partial digestion occurs by pepsin and hydrochloric acid
• Pancreas: Further digestion occurs by pancreatic proteases
• Small Intestine: Final digestion to amino acids, which are absorbed into the bloodstream
• Liver: Amino acids enter the bloodstream and are processed
• Large Intestine: Minimal protein present in feces

Amino Acid Pool and Metabolism

• The amino acid pool is the collection of amino acids in the body
• It is used for protein synthesis, energy production, and synthesis of non-protein molecules. The amino acid pool is dynamic, replenished by dietary intake and protein breakdown, and depleted by protein synthesis and catabolism
• Transamination is the transfer of an amino group from one amino acid to a keto acid; it is used to synthesize nonessential amino acids and is catalyzed by transaminases, requiring pyridoxal phosphate (vitamin B6) as a cofactor
• Deamination is the removal of an amino group from an amino acid, producing ammonia and a keto acid; ammonia is toxic and is converted to urea in the liver for excretion
• The urea cycle is the metabolic pathway that converts ammonia to urea and is crucial for detoxification. It involves several enzymes, occurs in the liver, and defects can lead to hyperammonemia
• Nitrogen balance is the difference between nitrogen intake and nitrogen excretion and reflects protein balance in the body; B = I - (U + F + S) where B = balance, I = nitrogen intake, U = urinary nitrogen, F = fecal nitrogen, S = skin loss. Positive nitrogen balance indicates protein synthesis exceeds breakdown (growth, pregnancy), while negative balance indicates the opposite (illness, starvation)

Protein Complementation and Quality

• Protein complementation is combining plant protein sources to improve amino acid balance and is essential for vegetarians
• Different plant proteins have different limiting amino acids; combining them ensures adequate intake of all essential amino acids
• Protein Efficiency Ratio (PER) is a measure of protein quality - live weight gain / crude protein intake; it is a simple measure but doesn't account for all aspects of protein quality
• A limiting amino acid is an essential amino acid present in the lowest amount relative to need. It limits protein synthesis and determines the overall efficiency of protein utilization

Carbohydrate and Protein Metabolism: Key Processes

• Carbohydrate and protein metabolism involve processes like glycolysis, gluconeogenesis, the citric acid cycle, and the electron transport chain

Glycolysis: Glucose Breakdown

• Glycolysis is a metabolic pathway by which glucose is converted to pyruvate and occurs in the cytoplasm, producing ATP (adenosine triphosphate). It can proceed anaerobically (without oxygen), yielding less ATP than aerobic glycolysis

Gluconeogenesis: Glucose Synthesis

• Gluconeogenesis is the synthesis of glucose from non-carbohydrate precursors, primarily in the liver
• It is crucial for maintaining blood glucose levels during fasting or starvation and uses substrates such as lactate, pyruvate, glycerol, and amino acids

Citric Acid Cycle (Krebs Cycle): Energy Production

• The citric acid cycle is a central metabolic pathway that oxidizes acetyl-CoA, producing ATP, NADH, and FADH2
• It is a key component of cellular respiration, occurring in the mitochondria, and is linked to both carbohydrate and fat metabolism

Electron Transport Chain: ATP Synthesis

• The electron transport chain is a series of protein complexes in the mitochondrial membrane that generates ATP through oxidative phosphorylation
• It utilizes the reducing power of NADH and FADH2 to pump protons across the mitochondrial membrane, creating a proton gradient that drives ATP synthesis

Nutritional Deficiencies and Excesses

• Deficiencies and excesses of protein can lead to various health problems

Protein Deficiency

• Protein-Energy Malnutrition (PEM): severe deficiency of both protein and energy characterized by growth retardation, muscle wasting, and edema

• Kwashiorkor: primarily a protein deficiency characterized by edema, growth retardation, and skin lesions which often occurs in children weaned onto a low-protein diet

• Marasmus: severe deficiency of both protein and energy characterized by severe wasting of muscle and fat often seen in infants and young children who are deprived of adequate food intake

Protein Excess

• Protein excess can lead to increased risk of kidney stones, heart disease, and certain cancers
• Excessive protein intake can stress the kidneys and may contribute to calcium loss, increasing the risk of osteoporosis

Pancreatic Enzymes and Digestion

• Pancreatic enzymes play essential roles in the digestion of carbohydrates, fats, and proteins
• Amylase breaks down carbohydrates (starch) into glucose, maltose, and other oligosaccharides
• Lipase breaks down fats (triglycerides) into fatty acids and glycerol
• Proteases break down proteins into amino acids and peptides

Vitamins: Water-Soluble and Fat-Soluble

• Vitamins are essential nutrients classified as either water-soluble or fat-soluble

Water-Soluble Vitamins

• Water-soluble vitamins dissolve in water and are not stored in the body to any significant extent, requiring regular consumption and excess being excreted in urine

• They act primarily as coenzymes, assisting enzymes in metabolic reactions, and as antioxidants, protecting cells from damage

• Include B vitamins (Thiamin (B1), Riboflavin (B2), Niacin (B3), Pantothenic acid, Biotin, Pyridoxine (B6), Folate, and Cobalamin (B12)) and Vitamin C

• Thiamin (B1):

  • Deficiency: Beriberi (nervous system damage, heart problems, edema)
  • Sources: Whole grains, pork
  • Function: Coenzyme in carbohydrate metabolism

• Riboflavin (B2):

  • Deficiency: Ariboflavinosis (sore throat, dermatitis, stunted growth)
  • Sources: Milk, meat
  • Function: Component of coenzymes involved in oxidation-reduction reactions

• Niacin (B3):

  • Deficiency: Pellagra (dermatitis, dementia, diarrhea, death)
  • Sources: Meat, fish, poultry
  • Function: Coenzymes in carbohydrate, protein, and fat metabolism and can be synthesized from tryptophan

• Pyridoxine (B6):

  • Deficiency: Dermatitis, anemia, convulsions
  • Sources: Beef liver, fortified foods, mushrooms
  • Function: Coenzyme in over 100 enzymes involved in amino acid metabolism

• Pantothenic Acid:

  • Deficiency: Rare, but symptoms include nausea, cramps, lethargy
  • Sources: Widespread in foods; chicken, beef, egg yolk
  • Function: Component of coenzyme A (CoA), crucial for fatty acid metabolism

• Biotin:

  • Deficiency: Rare, often caused by excessive raw egg white consumption (avidin). Symptoms include nausea, cramps, lethargy, hair thinning
  • Sources: Egg yolk, liver, nuts
  • Function: Involved in carbohydrate, fat, and protein metabolism

• Folate:

  • Deficiency: Megaloblastic anemia (large, immature red blood cells), neural tube defects in developing fetuses
  • Sources: Leafy greens, legumes, fortified grains
  • Function: Essential for DNA synthesis and cell division

• Cobalamin (B12):

  • Deficiency: Pernicious anemia (megaloblastic anemia), neurological damage
  • Sources: Animal products, fortified foods
  • Function: Coenzyme in amino acid metabolism, maintains myelin sheath, and absorption requires intrinsic factor

• Vitamin C (Ascorbic Acid):

  • Deficiency: Scurvy (bleeding gums, poor wound healing)
  • Sources: Citrus fruits, berries, peppers
  • Function: Antioxidant, collagen synthesis, immune function

Fat-Soluble Vitamins

• Fat-soluble vitamins dissolve in fat and are stored in the body's adipose tissue and liver, not needing to be consumed as frequently, and excessive intake can lead to toxicity

• They function as hormones or have roles in blood clotting and antioxidant defense and are absorbed with dietary fats

• Include vitamins A, D, E, and K

• Vitamin A (Retinol):

  • Deficiency: Night blindness, impaired immune function
  • Sources: Liver, dairy products, orange and yellow vegetables
  • Function: Vision, cell growth, immune function

• Vitamin D (Cholecalciferol):

  • Deficiency: Rickets (children), osteomalacia (adults)
  • Sources: Sunlight exposure, fatty fish, fortified foods
  • Function: Calcium absorption, bone health

• Vitamin E (Tocopherols):

  • Deficiency: Rare, but can lead to nerve damage
  • Sources: Vegetable oils, nuts, seeds
  • Function: Antioxidant, protects cell membranes

• Vitamin K (Phylloquinone):

  • Deficiency: Increased bleeding risk
  • Sources: Leafy green vegetables, some vegetable oils
  • Function: Blood clotting

Lipids: Types and Functions

• Lipids include triglycerides, fatty acids, phospholipids, and sterols

Types of Lipids

• Triglycerides:
  • Definition: Main form of fat in the body and food, composed of three fatty acids attached to a glycerol molecule
  • Function: Energy storage, insulation, protection of organs
• Fatty Acids:
  • Definition: Long chains of carbon atoms, classified as saturated, monounsaturated, or polyunsaturated based on the number of double bonds
• Saturated Fatty Acids:
  • Definition: No double bonds between carbon atoms, generally solid at room temperature
  • Sources: Butter, coconut oil, animal fats
  • Health Effects: Can raise LDL ("bad") cholesterol levels
• Monounsaturated Fatty Acids (MUFAs):
  • Definition: One double bond between carbon atoms
  • Sources: Olive oil, avocados, nuts
  • Health Effects: Generally neutral effect on cholesterol
• Polyunsaturated Fatty Acids (PUFAs):
  • Definition: Two or more double bonds between carbon atoms
  • Sources: Vegetable oils, nuts, seeds, fish
  • Health Effects: Can lower LDL cholesterol and raise HDL ("good") cholesterol. Essential fatty acids (EFAs) are PUFAs that the body cannot synthesize and must be obtained from the diet (omega-3 and omega-6 fatty acids)
• Trans Fatty Acids:
  • Definition: Unsaturated fats with a specific type of double bond created during hydrogenation (a food processing technique)
  • Sources: Processed foods, some margarines
  • Health Effects: Raise LDL cholesterol and lower HDL cholesterol, increasing the risk of heart disease
• Phospholipids:
  • Definition: Similar to triglycerides but one fatty acid is replaced with a phosphate group
  • Function: Major component of cell membranes; emulsifiers (aid in fat digestion and absorption). Example: Lecithin
• Sterols:
  • Definition: Complex ring structures
  • Example: Cholesterol (important component of cell membranes, precursor to steroid hormones)

Functions of Lipids

• Energy Source: Lipids provide a significant amount of energy (more than carbohydrates or proteins)
• Energy Storage: Triglycerides store energy in adipose tissue
• Structural Components: Phospholipids are essential components of cell membranes
• Hormone Production: Cholesterol is a precursor to steroid hormones
• Insulation and Protection: Lipids provide insulation and cushion for organs
• Absorption of Fat-Soluble Vitamins: Dietary fats are necessary for the absorption of fat-soluble vitamins

Folate and Vitamin C: Crucial Roles

• Folate and Vitamin C are crucial vitamins with specific functions

Folate

• Definition: A B vitamin crucial for DNA synthesis, cell division, and red blood cell production; folic acid is the synthetic form of folate
• Functions: Essential for growth and development, especially during pregnancy, and deficiency can lead to megaloblastic anemia and neural tube defects
• Sources: Leafy green vegetables, legumes, fortified grains, citrus fruits

Vitamin C

• Definition: An antioxidant vitamin essential for collagen synthesis, immune function, and iron absorption
• Functions: Protects cells from damage, supports wound healing, and strengthens the immune system; deficiency leads to scurvy
• Sources: Citrus fruits, berries, peppers, leafy green vegetables

Recommended Dietary Intakes (RDIs)

• Recommended Dietary Intakes (RDIs) vary depending on age, sex, and other factors

Micronutrients: Minerals

• Minerals are inorganic elements essential for various bodily functions
• Key minerals include calcium (bone health), iron (oxygen transport), zinc (immune function), iodine (thyroid hormone production), and potassium (fluid balance)
• Deficiencies in these minerals can lead to various health problems, and sources vary widely depending on the mineral

Facts to Memorize

• Glucose, fructose, and galactose are the three main monosaccharides
• Lactose (glucose + galactose), maltose (glucose + glucose), and sucrose (glucose + fructose) are the main disaccharides
• Starch (plants), glycogen (animals), and fiber are important polysaccharides
• Soluble fiber lowers cholesterol, and insoluble fiber promotes regularity
• Protein digestion occurs in the stomach, pancreas, and small intestine
• The amino acid pool is a dynamic pool of amino acids used for various functions
• Transamination transfers amino groups to synthesize nonessential amino acids
• Deamination removes amino groups, producing ammonia (converted to urea)
• The urea cycle detoxifies ammonia by converting it to urea for excretion
• Nitrogen Balance: B = I - (U + F + S); reflects protein balance
• Protein complementation involves combining plant proteins to improve amino acid balance
• Glycolysis converts glucose to pyruvate, producing ATP
• Gluconeogenesis synthesizes glucose from non-carbohydrate sources
• The citric acid cycle oxidizes acetyl-CoA, producing ATP, NADH, and FADH2
• The electron transport chain generates ATP through oxidative phosphorylation
• Protein deficiency can lead to PEM (Kwashiorkor and marasmus)
• Protein excess can increase the risk of kidney stones, heart disease, and certain cancers
• Amylase, lipase, and proteases are crucial pancreatic enzymes for digestion
• Water-soluble vitamins are not stored in the body and must be consumed regularly
• Fat-soluble vitamins are stored in the body's adipose tissue and liver
• Vitamin C deficiency leads to scurvy
• Thiamin (B1) deficiency leads to beriberi
• Niacin (B3) deficiency leads to pellagra
• Folate deficiency can cause megaloblastic anemia and neural tube defects
• Vitamin B12 deficiency can cause pernicious anemia and neurological damage
• Triglycerides are the main form of fat in the body and food
• Saturated fats are generally solid at room temperature and can raise LDL cholesterol
• Unsaturated fats (monounsaturated and polyunsaturated) are generally liquid at room temperature
• Trans fats are created during food processing and are associated with increased risk of heart disease
• Essential fatty acids (EFAs) must be obtained from the diet
• Phospholipids are major components of cell membranes
• Cholesterol is a precursor to steroid hormones
• Calcium is essential for bone health
• Iron is essential for oxygen transport
• Iodine is essential for thyroid hormone production
• Folate is crucial for DNA synthesis and cell division, especially during pregnancy
• Vitamin C is an antioxidant and is important for collagen synthesis
• Recommended Dietary Allowances (RDAs) are guidelines for the daily intake of essential nutrients. These values can vary based on age, sex, and health status