Involved in glycerolipid synthesis and lipid metabolism. Catalyzes the formation of diacylglycerol, the precursor of triacylglycerol, by transferring the acyl chain of a fatty acyl-CoA to a monoacylglycerol. Plays a central role in absorption of dietary fat in the small intestine by catalyzing the resynthesis of triacylglycerol in enterocytes. Has a preference toward monoacylglycerols containing unsaturated fatty acids in an order of C18:3 > C18:2 > C18:1 > C18:0 at sn-2. Able to use 1-monoalkylglycerol (1-MAkG, 1-O-alkylglycerol) as an acyl acceptor for the synthesis of monoalkyl-monoacylglycerol (MAMAG, 1-O-alkyl-3-acylglycerol or 1-O-alkyl-2-acylglycerol) and subsequently, with lower efficiency, may add another acyl chain producing monoalkyl-diacylglycerol (MADAG, 1-O-alkyl-2,3-diacylglycerol). Possesses weak but significant activity with diacylglycerol as substrate, producing triacylglycerol (triacyl-sn-glycerol).