Girlfriend...

She wants to lose weight(even though she doesn't need to) but she doesn't know where to start. She wanted me to help because I bodybuild and she's satisfied with my results, but I've never really had to lose weight I mostly just had to gain muscle.

So what would be a good diet? And what should she do for exercise?

Someone always has to write on the walls "Mike was here". But then someone else puts an arrow and it says "Mike is a ****got". So Mike comes back to check it out, "What the hell?! I was here but not as a ****got!"
-Dane Cook

Okay, I tried this with my mom once, and it worked but she never kept with it..
 
Take her body weight and calculate her calorie needs, and cut back 500 calories. Have her train 3 days with weights using lighter weight and many reps. example 3 sets of 10-15. make sure she gets a ton of carbs from vegetables and not complex carbs like potatoes and all that jazz. Have her do an INTENSE cardio 2-3 days (the days she's not lifting obviously)
 
I've read in many places that wind sprint do wonders. They actually kick your metabolism up some notches and keep them in high gain for a few days. Measure by meters. Do like one 50-100 meter wind sprint, walk around the track, then do another, and keep doing the process until she's done 8-10 windsprints total. Shouldn't take that much time, just keep her huffing around that track. Make sure to feed her some whey as meal replacement. 6 small meals a day should do it. I hope this works for you like it did the first three weeks for my mother.

Perrynaytor, is pretty much on target. The only other thing I would add is that after she gets aclimated to lifting her rep and set structure does not need to be in the high end, her routine could be along the same lines as whatever it is that you (or men in gereral) do.  

I agree with the above but the cardio does not need be intense to make her shy away, make it fun, try sparing or whatever she likes, dance, tae bo, jogging, blading.......if you can convince her to do wind sprints once per week then you have a mom with a great attitude and if she likes it then as suggested push for a few days.

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