Lipids: Types, Functions, and Health Impact

Posted on Mar 25, 2025 in Human Nutrition and Dietetics

Lipids: Essential Macronutrients

Lipids, including oils, cholesterol (CHO), fats, fatty acids, triglycerides, and phospholipids, are essential macronutrients. They form a major component of every living cell and are found in our food, originating from both animal and plant sources. The body can also synthesize them.

Fatty Acids: The Building Blocks of Lipids

Fatty Acids are the smallest components of lipids and serve as their main building blocks. They provide 9 calories of energy per gram. Fatty acids usually come from:

  1. Triglycerides
  2. Phospholipids

Triglycerides: Functions and Sources

Triglycerides are the largest class of lipids, encompassing nearly all the fats and oils people typically eat. Their functions include:

  • Providing insulation
  • Protecting internal organs
  • Serving as reserve energy

Phospholipids: Critical for Cell Membranes

Phospholipids are crucial for membrane selectivity. This function determines which substances can enter or exit cells. They are so vital that no diseases are associated with their deficiency. For example, Choline (a component of phospholipids) has several key roles:

  • Helps the liver utilize fats
  • Forms the neurotransmitter acetylcholine
  • Is a component of bile
  • Keeps cholesterol soluble (preventing arterial buildup)
  • Is found in foods high in lecithin (e.g., egg yolk)

Types of Fatty Acids

There are two kinds of natural fatty acids and one man-made fatty acid:

  1. Saturated (Sat)
  2. Unsaturated (Unsat)
  3. Trans Fats

a. Saturated: Solid at room temperature, straight with no kinks, single bonds, very stable, slow to react with heat, light, and oxygen.

b. Unsaturated: Liquid at room temperature, not straight, have kinks, contain double bonds (cis configuration), unstable, highly reactive to heat, light, and oxygen.

c. Trans Fats (man-made): Created through partial or full hydrogenation, turning liquid vegetable oil into a solid fat.

Saturated Fatty Acids: Chain Lengths and Sources

Saturated Fatty Acids are categorized by chain length:

  • Short Chain (SC): 4-6 carbons long, used for energy production (e.g., butter, butyric acid).
  • Medium Chain (MC): 8-12 carbons long, used for energy production, not stored as fat (e.g., coconut oil, palm oil).
  • Long Chain (LC): 13+ carbons long, used to build cell membranes, very sticky and extremely hard substance (e.g., beef, pork, dairy products, cheese, milk).

Unsaturated Fatty Acids: Mono- and Polyunsaturated

Unsaturated Fatty Acids are classified as:

  • Monounsaturated: One double bond between the 9th and 10th carbon, referred to as omega-9s, melts at 13 degrees Celsius (e.g., olive oil, avocado oil, macadamia nut oil).
  • Polyunsaturated: (The body cannot synthesize these) More than one double bond. Two are considered essential:
    1. Linoleic acid (omega-6)
    2. Alpha-Linolenic acid (omega-3)
    The greater the number of double bonds, the more reactive/unstable the fatty acid is. Examples include:
    • Omega-6: Animal products, borage oil, evening primrose oil.
    • Omega-3 (EPA & DHA): Found in fish, but can sometimes be made from flax seeds.
    Omega-3 Functions: Energy production, oxygen transfer, immune enhancement, prostaglandin production (tissue hormones), growth, cell division, brain development in children, and inflammation reduction.

Cholesterol: Functions and Types

Cholesterol: The body produces cholesterol even without dietary intake. High cholesterol levels can often be controlled through diet.

Functions:

  • Production of steroid hormones (estrogen, testosterone, etc.)
  • Vitamin D synthesis
  • Bile acid production
  • Skin protection from dehydration (secreted by skin glands)
  • Membrane fluidity regulation: added to stiffen a loose membrane or removed to fluidize a hard membrane.

HDL and LDL: Cholesterol Carriers

HDL (High-Density Lipoprotein): A carrier molecule for cholesterol. It transports cholesterol to the liver for processing and removal from the body. High HDL levels are desirable.

LDL (Low-Density Lipoprotein): A carrier molecule for cholesterol. It delivers cholesterol to cell membranes and can be deposited in arteries. Low LDL levels are desirable.

Key Differences Between Saturated and Unsaturated Fats

Unsaturated fats have one or more double bonds between carbon atoms in their fatty acid chains, while saturated fats do not.

Importance of Saturated Fatty Acids (SFAs)

Saturated Fatty Acids are important because they are:

  • Highly stable and do not easily become rancid.
  • Contribute to bone health.
  • Can protect the liver from the effects of alcohol and other toxins (e.g., Tylenol).
  • Enhance the immune system.
  • Support hormone production.
  • Possess antimicrobial properties, protecting against harmful microorganisms in the digestive tract.
  • Essential for lung function.

Sources of Saturated Fatty Acids

SFAs are primarily found in the fats of warm-blooded animals and tropical plants. The body can synthesize them through a process called *de novo lipogenesis*.

Omega-6 (GLA): Borage and Primrose Oil
Omega-3 (EPA and DHA): Flax, hemp, fish

Polyunsaturated Fatty Acids (PUFAs)

PUFAs cannot be synthesized by the body and must be obtained from food or supplements. They are exclusively found in fats. Absence of essential PUFAs will lead to death. Important PUFAs include omega-6 and omega-3 fatty acids.