Anti-obesity study on rat ?

i need to test of a lipid product and compare to normal lipid on the effect of the anti-obesity. so how much rat i needed.. my senior suggested 5 group: control(the feed w/out lipid), positive control(with normal lipid), and another 3 with different amount of lipids product.. if i each group have 10 rat.. is it statistically sufficient.. can use T-test right? any idea and reference for me. pls help,TQ