Biosynthesis of triacylglycerol starts with the acylation of the two free hydroxyl groups of L-glycerol 3-phosphate by two molecules of fatty acyl-CoA to produce phosphatic acid. This is then hydrolyzed by phosphatidic acid phosphatase to form a 1,2-diacylglycerol. 1,2-diacylglycerol is then converted to triacylglycerol by transesterification with a third fatty acyl-CoA. 
In humans, hormones can affect the biosynthesis of triacylglycerol. Insulin is one example of a hormone that promotes the conversion of carbohydrates to triacylglycerols. 
- Cox, Michael M. and Nelson, David L. Principles of Biochemistry. 5th ed. New York: W.H. Freeman, 2008. Print.