Fats and Lipids

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  • Fat is one of the three main macronutrients: fat, carbohydrate, and protein.
  • Fat is a major source of energy and helps your body absorb vitamins.
  • Fat has the most calories compared to any other nutrient. Controlling fat intake is one of the most important steps in losing or maintaining weight and preventing or delaying type 2 diabetes.
  • Fats, also known as triglycerides, are esters of three fatty acid chains and the alcohol glycerol.
  • Fats are solids at room temperature. Oil refers to a fat with unsaturated fatty acid chains that is liquid at room temperature.
  • Fats, like other lipids, are generally insoluble in water.


  • A lipid is chemically defined as a substance that is insoluble in water and soluble in alcohol and chloroform.
  • Lipids are an important component of living cells. Together with carbohydrates and proteins, lipids are the main constituents of plant and animal cells.
  • Cholesterol and triglycerides are lipids. Lipid is not necessarily a triglyceride.
  • Glycerol is a simple sugar alcohol compound. A triglyceride is an ester derived from glycerol and three fatty acids (tri + glyceride)
  • Triglycerides are the main constituent of body fat in humans and animals, as well as vegetable fat.


Fatty Acid

  • A fatty acid is a carboxylic acid with a long aliphatic chain [organic compounds in which carbon atoms form open chains], which is either saturated or unsaturated.
  • Some fatty acids are called essential because they cannot be synthesized in the body from simpler constituents.
  • There are two essential fatty acids (EFAs) in human nutrition: alpha-linolenic acid (an omega-3 fatty acid) and linoleic acid (an omega-6 fatty acid).
  • Fats and other lipids are broken down in the body by enzymes called LIPASES produced in the

Saturated fat

  • A saturated fat is a fat in which the fatty acids all have single bonds.
  • A saturated fat has the maximum number of hydrogens bonded to the carbons, and therefore is ‘saturated’ with hydrogen atoms.
  • Most animal fats are saturated whereas the fats of plants and fish are generally unsaturated.
  • Many experts recommend a diet low in saturated fat.
  • Saturated fats are popular with manufacturers of processed foods because they are less vulnerable to rancidity and are, in general, more solid at room temperature than unsaturated fats.

Unsaturated fat

  • An unsaturated fat is a fat or fatty acid in which there is at least one double bond within the fatty acid chain.
  • In cellular metabolism, unsaturated fat molecules contain somewhat less energy (i.e., fewer calories) than an equivalent amount of saturated fat.
  • The greater the degree of unsaturation in a fatty acid (i.e., the more double bonds in the fatty acid) the more vulnerable it is to rancidity [lipid oxidation][rusting of fats].
  • Antioxidants can protect unsaturated fat from lipid oxidation.

Healthy Fats – Omega-3 and Omega-6, Monounsaturated and  Polyunsaturated

  • The main types of “healthy” fats are monounsaturated, polyunsaturated, alpha-linolenic acid (an omega-3 fatty acid) and linoleic acid (an omega-6 fatty acid).
  • The fat is termed “monounsaturated” if there is one double bond, and “polyunsaturated” if there are two or more double bonds.
  • Omega-3 and Omega-6 fatty acids are heart healthy fats and can help in lowering high triglyceride values in blood. They are found in fish, soybean products, Walnuts etc.
  • Both of these fatty acids are needed for growth and repair, but can also be used to make other fatty acids.
  • The omega-3 and omega-6 are fatty acids are both polyunsaturated. The difference is in where the first of the double bonds occurs.
  • Both omega-3 (ω-3) and omega-6 (ω-6) fatty acids are important components of cell membranes.
  • There is increasing support for omega-3 fatty acids in protecting against fatal heart disease and it is known that they have anti-inflammatory effects.
  • There is also growing interest in the role of omega-3 fatty acids in the prevention of diabetes and certain types of cancer.
  • Monounsaturated and polyunsaturated fat are considered “heart healthy” and can help with improving cholesterol when used in place of unhealthy fats.
  • Some sources of these fats include almonds, cashews, pecans, peanuts, pine nuts, pumpkin, sesame seeds, sunflower seeds, Olive oil and olives, vegetable oils (such as sunflower, safflower, corn, soybean, and cottonseed).

Unhealthy Fats – Saturated Fat and Trans Fat

  • The main types of “unhealthy” fats are saturated and trans-fat.
  • Saturated fats are primarily found in foods that come from animals, such as meat and dairy.
  • Saturated fats are unhealthy because they increase LDL (“bad” cholesterol) levels in your body and increase your risk for heart disease.
  • Many saturated fats are “solid” fats that you can see, such as the fat in meat. Other sources of saturated fats include high-fat cheeses, high-fat cuts of meat, butter, Ice cream, palm and coconut oils, etc..
  • Trans fats, or trans-unsaturated fatty acids, trans fatty acids, are a type of unsaturated fats that are uncommon in nature.
  • Trans fat is simply liquid oils turned into solid fats during food processing. There is also a small amount of trans fat that occurs naturally in some meat and dairy products, but those found in processed foods tend to be the most harmful to your health.
  • Trans fats are worse than saturated fats. They increase LDL (“bad” cholesterol) and decreasing HDL (“healthy” cholesterol).
  • Trans fatty acids are used as preservative in packaged food items. Foods containing trans-fat are usually labeled as “partially hydrogenated”.
  • Partially hydrogenated oil is less likely to spoil, so foods made with it have a longer shelf life.
  • Trans fats are easy to use, inexpensive to produce and last a long time. Trans fats give foods a desirable taste and texture.

Adipose tissue

  • In animals, adipose, or fatty tissue with adipose cells is the body’s means of storing fat derived from the diet and from liver metabolism.
  • Under stress conditions, adipose cells degrade their stored fat to supply fatty acids and also glycerol.
  • These metabolic activities are regulated by several hormones (e.g., insulin, glucagon and epinephrine).

Metabolic Basis for Living

  • Metabolic pathways can lead to a more complex structure from a simpler structure (for example, acetic acid becomes cholesterol) or lead to a simpler structure from a complex structure (for example, glucose becomes lactic acid in our skeletal muscle).
  • The former cases are called biosynthetic pathways or anabolic pathways. The latter constitute degradation and hence are called catabolic pathways.
  • Anabolic pathways, as expected, consume energy. Assembly of a protein from amino acids requires energy input.
  • On the other hand, catabolic pathways lead to the release of energy. For example, when glucose is degraded to lactic acid in our skeletal muscle, energy is liberated.
  • This metabolic pathway from glucose to lactic acid which occurs in 10 metabolic steps is called glycolysis.
  • Living organisms have learnt to trap this energy liberated during degradation and store it in the form of chemical bonds.
  • As and when needed, this bond energy is utilized for biosynthetic, osmotic and mechanical work that we perform.
  • The most important form of energy currency in living systems is the bond energy in a chemical called adenosine triphosphate (ATP).