Amount
Use the Amount setting to determine the amount of fat spots applied to the image.

Size
Size determines the size of the individual fat spots. The higher this value, the bigger the spots get.

Thickness
Using the Thickness setting you can determine how "thick" the layers of fat will be. The Fat effect will randomly add dark spots to each other and the Thickness determines what percentage in the range of transparent to black will be added each time.
Setting a low value here will make the fat spots less obvious but more smooth and is generally the best option. Setting it higher will bring more contrast into the fat spots.

Transparency
This setting determines the actual visibility of the effect, setting it to any version higher than 0% will mix the fat spots with the image.