I have a friend who I'm helping with her diet and I have a quick question: She weighs 96 lbs with 10% body fat. What would be the best way for her to lose more body fat considering her already low body fat and body weight? If she follows the calorie restriction and increased cardio you recommend and she dropped to around 6-7%, wouldn't that equate to 85-90 lbs? She’d practically be invisible wouldn't she?
Ten percent body fat for a woman is outrageously lean. That is, quite literally, contest ready for a bodybuilder or fitness competitor.
In the entire 15 years I've been personal training, coaching, and consulting, I have never once personally seen a woman legitimately hit 6-7% body fat. I’m actually doubtful that it can be done (at least not naturally).
I know fitness competitors who CLAIM they have hit 6-7%, but I’ve never measured anyone at that level myself. Body fat numbers are easy to fudge, and often are fudged in the bodybuilding mags – almost as much as poundages lifted (they often conveniently forget to mention that their lifts were quarter-reps).
The lowest body fat I have ever measured on a woman was 8.9% and she just about killed herself getting there. She won a local NPC fitness contest at that body fat level, but it took a ponderous amount of work and incredibly strict dieting. She was miserable, actually – she said she would NEVER do it again as long as she lives! She now keeps her body fat at around 13-14% without much difficultly and she's very happy with how she looks.
So...at 6-7%, you're right – your friend would be practically invisible. I think the best thing you can do for her now is FEED HER! Maybe some cheese fries, stromboli, haagen dasz, cheescake, fettucini alfredo, Krispy Kremes, etc :-)
Seriously, all kidding aside, it's possible she underestimated her body fat and she's really much higher than 10%, so she still has room to come down further. I can't imagine a woman legitimately at 10% wanting to get even leaner unless she was a hardcore fitness or bodybuilding competitor getting ready for a show. Even then, 10-12% is contest ready for most women. In fact, if she really is 10% fat and 96 lbs., I would even be concerned that there might be an eating disorder or body image problem.
Also keep in mind that body fat levels below the low teens are generally competitive peaks. With the possible exception of certain elite athletes, it's not normal or healthy for most women to try to maintain a body fat lower than 13-14% all year round.
Let's suppose her body fat is higher than she thinks it is and she actually does have room to go down further (like down to high single digits or very low double digit body fat): In that case, a "carbohydrate-cycling" strategy with very low carb days alternated with moderate carb days, combined with intense daily cardio would be the best approach (with weights too, of course).
The carb-cycling strategy and cardio programs for going from “lean” to “extremely lean” are covered in detail in my bookBurn the Fat, Feed the Muscle (BFFM)