Lipids – Level 3 Applied Science BTEC Revision

Lipids are a group of biomolecules that are insoluble in water but soluble in organic solvents.
They are composed of carbon (C), hydrogen (H) and oxygen (O) atoms, but have a higher proportion of C and H compared to O, making them less polar than carbohydrates or proteins.
Lipids provide more than twice the energy per gram than carbohydrates or proteins when metabolised.
They are generally hydrophobic, meaning they do not dissolve in water.

Triglycerides are the main lipids in the diet and body, made up of glycerol and three fatty acids.
Phospholipids have a similar structure to triglycerides but one fatty acid is replaced by a phosphate group. They are crucial in forming cell membranes.
Sterols or steroids, such as cholesterol, play roles in cellular structure and certain hormones.
Waxes are long-chain fatty acids linked to long-chain alcohols, providing protection and waterproofing in plants and animals.

Lipids are a major store of energy in the body, with fat cells being specially adapted for this purpose.
They are important for insulation and protection. Subcutaneous fat helps to maintain body temperature and around internal organs, fatty tissue provides cushioning to protect against damage.
Lipids are key in making up cell membranes, contributing to membrane fluidity and facilitating the transport of certain substances.
Certain lipids play a crucial role in the production of hormones, which regulate many body functions like metabolism and immune response.
Lipids, such as cholesterol, are necessary for the synthesis of vitamin D and bile salts.

Digestion breaks down dietary lipids into fatty acids and monoglycerides that can be absorbed by the cells of the small intestine.
Once absorbed, these components are reassembled into triglycerides and packaged with proteins and phospholipids into chylomicrons for transport in the blood.
Excess dietary lipids not immediately used for energy are stored as body fat.
When energy is needed, stored lipids are broken down through lipolysis into usable forms.
Lipids can also be synthesised in the body from excess dietary carbohydrates or proteins through a process called lipogenesis.

The types and amounts of lipids in the diet can greatly influence health.
Saturated fats, found in animal products and tropical oils, can raise levels of LDL cholesterol and potentially contribute to heart disease when consumed in excess.
Unsaturated fats, found in plants and fish, can lower LDL cholesterol levels and are a necessary part of the diet.
Trans fats, present in some processed foods, raise LDL cholesterol and also lower beneficial HDL cholesterol, and are associated with an increased risk of heart disease.