In my recent post regarding the total amount of body fat in a 44kg kangaroo, I erroneously reported the total amount of body fat predicted by the Pitts and Bullard regression (1). A 44kg kangaroo with a predicted body fat of 8.2% would have 3608 g of total fat, not 360.8 g. Hence, the difference between the total predicted fat and the amount actually dissected would be (3608 g -113 g) 3,495 g. This figure represents the non-dissectable fat that is bound in cell membranes in various organs and tissues. However, it is unlikely that a 44 kg kangaroo with only 113 g of dissectable fat would have this much non-dissectable structural fat bound to tissues and organs. Hence, the Pitts and Bullard equation almost certainly overestimates the total amount of body fat in this kangaroo. Total body fat can also be estimated by knowing the various weights of the major tissues and their relative fat percent and then summing these values. Here's a table of estimated values for this 44 lb kangaroo: Tissue % carcass wt. Organ wt. (g) %fat total fat (g) muscle 0.50 22,000 0.02 440 bones 0.13 5720 .03 172 liver, organs 0.075 3300 0.04 132 washed GI tract 0.06 2640 0.02 53 blood 0.012 526 0.02 11 marrow 0.004 176 0.51 90 brain 0.0014 62 .093 6 skin 0.13 5720 0.10 572 storage fat 0.0026 114 0.82 94 GI contents, hair,nails etc 0.085 3740 na na Total 1.00 44000 na 1568 Consequently, in all likelihood this particular 44 kg kangaroo would have a total body fat content of about 3.6% by weight if total carcass analysis were done via chemical extraction. With 3.6 % body fat, our 3rd order polynomial equations (2)show that an animal with 3.6% body fat by weight would have 27% fat by energy and 73 % protein by energy. Note that traditional Aborigines would have singed the hair from the hide and eaten the skin, a rich source of fat. Even still, the protein content of this lean kangaroo would have caused protein toxicity, if a carbohydrate (plant food source) were not available to dilute (in effect) the excessive protein in this animal's body. Loren Cordain, Ph.D., Professor Department of Health and Exercise Science Colorado State University Fort Collins, CO 80523 tel: (970) 491-7436 fax: (970) 491-0445 email:[log in to unmask] http://www.colostate.edu/Colleges/CAHS/ess/cordain.htm