the main types of fatty acids

There are three main types of fatty acids: saturated, monounsaturated and polyunsaturated. All fatty acids are chains of carbon atoms with hydrogen atoms attached to the carbon atoms.

1/A saturated fatty acid has the maximum possible number of hydrogen atoms attached to every carbon atom. It is therefore said to be "saturated" with hydrogen atoms, and all of the carbons are attached to each other with single bonds.
In some fatty acids, a pair of hydrogen atoms in the middle of a chain is missing, creating a gap that leaves two carbon atoms connected by a double bond rather than a single bond. Because the chain has fewer hydrogen atoms, it is said to be "unsaturated." 

2/ A monosaturated fatty acid : A fatty acid with one double bond is called "monounsaturated" because it has one gap.

3/Polyunsaturated fatty acid : Fatty acids having more than one gap are called "polyunsaturated."


*The fat in foods contains a mixture of saturated, monounsaturated and polyunsaturated fatty acids.
* In foods of animal origin, a large proportion of fatty acids are saturated. 
* In contrast, in foods of plant origin and some seafood, a large proportion of the fatty acids are monounsaturated and polyunsaturated. 

The structure of saturated and unsaturated chemical bonds looks like the diagram below.

Saturated Fat (i.e., saturated fatty acid)	Unsaturated Fat (i.e., unsaturated fatty acid)
H H | | -C - C- | | H H	H H | | -C = C-
Carbon-Carbon Single Bond	Carbon-Carbon Double Bond