Added body_fat to DATA.mat
Body fat might be more effective measure of obesity as stated in the
British Medical Bulletin
bmb.oxfordjournals.org/content/53/2/238.full.pdf
but the acceptance of  a threshold to obesity is less clear: see
http://medical-dictionary.thefreedictionary.com/Obesity : "Women whose
body fat exceeds 30% and men whose body fat exceeds 25% are generally
considered obese."