Macronutrients are the building blocks of our diet. Carbohydrates, proteins, and lipids each play unique roles in our bodies, from energy storage to cell structure. Understanding their properties is key to grasping how food fuels us.

This section dives into the nitty-gritty of macronutrients. We'll explore their basic units, like monosaccharides and amino acids, and how they combine to form complex structures. We'll also look at how they behave and change in different conditions.

Macronutrient Classes

Types of Macronutrients

• Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen atoms, usually with a 2:1 ratio of hydrogen to oxygen (empirical formula Cm(H2O)n)
• Proteins are large biomolecules consisting of one or more long chains of amino acid residues
  • Proteins perform a vast array of functions within organisms, including catalyzing metabolic reactions, DNA replication, responding to stimuli, providing structure to cells and organisms, and transporting molecules from one location to another
• Lipids are a diverse group of compounds that are united by a common feature of being hydrophobic ("water-fearing") due to their predominantly hydrocarbon makeup
  • Lipids serve many functions in living organisms, including energy storage, signaling, and acting as structural components of cell membranes

Macronutrient Building Blocks

Carbohydrate Building Blocks

• Monosaccharides are the simplest carbohydrates and are often called single sugars
  • They are the building blocks from which all bigger carbohydrates are made (glucose, fructose, galactose)
• Polysaccharides are polymeric carbohydrate molecules composed of long chains of monosaccharide units bound together by glycosidic linkages
  • This carbohydrate can be digested to release energy for the body (starch) or serve as structural components (cellulose, chitin)

Protein and Lipid Building Blocks

• Amino acids are organic compounds that contain both amino and carboxyl functional groups, along with a side chain (R group) specific to each amino acid
  • Amino acids can be linked in varying sequences to form a vast array of proteins
• Fatty acids are long-chain hydrocarbon molecules with a carboxylic acid group at one end
  • Fatty acids are the building blocks of many complex lipids such as triglycerides, phospholipids, and sphingolipids

Macronutrient Properties and Changes

Protein Denaturation and Amino Acid Essentiality

• Protein denaturation is a process in which proteins lose their folded structure by application of some external stress or compound such as a strong acid or base, a concentrated inorganic salt, an organic solvent, radiation or heat
  • Denaturation disrupts the normal alpha-helix and beta sheets in a protein and uncoils it into a random shape
  • Denaturation results in the loss of protein function and can lead to aggregation and precipitation of the unfolded protein
• Essential amino acids are amino acids that cannot be synthesized from scratch by the organism fast enough to supply its needs, and must therefore be supplied in the diet
  • The nine amino acids humans cannot synthesize are phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, lysine, and histidine

Lipid Properties

• Lipid oxidation is the oxidative degradation of lipids, a complex process whereby free radicals "steal" electrons from the lipids in cell membranes, resulting in cell damage and rancidity of fats
  • Antioxidants can protect against lipid oxidation by neutralizing free radicals
• Saturated fats have no double bonds between the carbon atoms of the fatty acid chain and are thus "saturated" with hydrogen atoms
  • Saturated fats are typically solid at room temperature (butter, lard)
• Unsaturated fats have one or more double bonds in the fatty acid chain
  • Monounsaturated fats have only one double bond (olive oil) while polyunsaturated fats have two or more double bonds (fish oil)
  • Unsaturated fats are typically liquid at room temperature

Carbohydrate Properties

• The glycemic index is a value assigned to foods based on how slowly or quickly they cause increases in blood glucose levels
  • Foods low on the glycemic index (≤55) release glucose slowly and steadily (whole grains, legumes)
  • Foods high on the glycemic index (≥70) release glucose rapidly (white bread, candy)