FAT

Most of the body fat (99 per cent) in the adipose tissue is in the form of triglycerides, in normal human subjects, adipose tissue constitutes between 10 and 15 per cent of body weight. 

One kilogram of adipose tissue corresponds to 7700 kcal of energy.

Fats and Other Lipids

Classification

Nutritionally important lipids are classified into 3 main groups on the basis of their Chemical structure.

1.Simple lipids  - include fats and oils (Triglycerides)

2.Compound lipids - includes Phospholipids, lipoprotein

3.Derived lipid  - includes fatty acids and sterols.

Some authorities classify lipids as structural lipids (Phospholipids), Metabolic lipids (fatty acids, lipoproteins and sterols) and storage lipids (triglycerides). 

WHY DO WE NEED FAT TO SURVIVE?

Although fats have received a bad reputation for causing weight gain, some fat is essential for survival. We need this amount of fat for:

• Normal growth and development 

•   20% - 35% of calories should come from fat

• Energy (fat is the most concentrated source of energy) 

• Serve as a vehicle for the absorption of lipid soluble vitamins ( like vitamins A, D, E, K, and carotenoids) 

• Providing cushioning for the organs 

• Maintaining cell membranes 

• Providing taste, consistency, and stability to foods 

• Energy storage, mobilization, and utilization

• Prostaglandin, cytokine synthesis

• Cell differentiation and growth

• Cell membrane structure, myelination

• Hormone synthesis

• Bile acid synthesis

Fatty Acids Classification 

Based on the Length of Carbon chain 

a.Short chain -  2-4 carbon atoms (eg. Butyric acid)

b.Medium chain - 6-12 carbon atoms (Caprillic acid)

c.Long chain - 14-18 carbon atoms (palmitic acid, stearic acid)

d. Extra long chain -   more than 20 carbon atoms (Arachidonicacid)

Based Degree of Saturation

Saturated FA: - The degree of saturation refers to the  number of double bonds between carbon atoms. If all of the carbon atoms in a fatty acid are “saturated” with all hydrogen atoms they can hold, no double bond can exists.

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All short or medium chain fatty acids are saturated.  Long chain fatty acids may be either saturated or unsaturated. 

The major saturated fatty acids are palmitic and stearic acids.

Monounsaturated FA: - Monounsaturated fatty acids contain only one double bond between carbon atoms. The most prevalent MUFA in the diet is oleic acid.

 

Polyunsaturated FA (PUFA):- 

They have two or more double bonds between carbon atoms. In omega 3– PUFA, the first double bond occurs 3 carbon atoms from the methyl carbon. 

Important omega-3 fatty acids in nutrition are: 

A.α-linolenic acid (ALA), 

B.eicosapentaenoic acid (EPA), and

C.docosahexaenoic acid (DHA)

Essential fatty acids

• Humans cannot synthesize double bonds within the last nine carbons of the methyl end (n) of any fatty acid chain.

• Fatty acids with double bonds in those locations must therefore come from the diet—and are considered essential

The two essential fatty acids are:

• Linoleic acid (omega 6 fatty acid)

• Alpha-linolenicacids (ALA) (Omega 3 fatty acid) 

Both are (poly)unsaturated

Therefore, absolute requirements for fat in the diet applies only to unsaturated fat