Fat conversions

kw: musings, obesity

I've been in calorie-watching mode for a few months. Losing the first twenty pounds was relatively easy because stopping my cholesterol medicine reduced my appetite; that stuff had made me always ravenous! I'd like to lose another ten pounds, and get by BMI closer to 27; it is 29 now, which is too close to the threshold of 30 for obesity.

Lately it got me thinking about the numbers. I've heard for years that each pound of body fat represents 3,500 Kcal (to use the Physics unit). Also, it is published everywhere that a gram of fat that you eat contains 9 Kcal. Now, a pound weighs 453.56 grams; 453.56 x 9 = 4,082 and some change. 3,500/4,082 = 0.86. That implies that about 86% of a fat cell is stored fat. Fat cells must contain a little protein also, but perhaps not much. I just had to dig into it.

This annotated image of fat cells is found with many other histology illustrations at this UCLA med. school web site. Cell membranes, shown in pink, are also fatty. The nuclei are more purplish (also the rare blood vessel or two). There is clearly very little protein to contend with. Adipose cells are primarily tanks containing stored fat.

It appears that the stored fat makes up more than 90% of the volume here. The difference between the storage percent and the 86% I obtained above must represent some very small conversion losses. Now I understand why so many nutrition writers say that the fats we eat are efficiently converted to body fat!

It also underscores, for me, that if I really want to reduce my weight another ten pounds, I have to eat 35,000 fewer calories than my metabolism needs. There's no way around the math.