Yea, the default model has an unrealistically high muscle percentage and low body fat percentage relative to her/his weight. Most people are actually much flabbier than the default.

To fix that, after you've plugged in your stats, click edit. There is this little "- 0 +" thing at the bottom. Clicking plus adds muscle, to lower body fat percentage, and clicking minus takes away muscle to higher body fat percentage. You can choose your level of tone at your weight doing this.

I found the 165 pound untoned pear shaped model was pretty close to how fat my body is.