It seems like I’ve stumbled upon an obvious contradiction, but not being a health expert, I’m hoping someone can clear up the flaw in my reasoning.
We all know that 1 gram of fat = 9 calories.
So if I wanted to eat 1 lb of pure fat, that would be 453.59237 grams, which would contain 4082.3 calories. Assuming I ate and perfectly metabolized 4082 calories worth of fat, my body would put on one pound of fat if my other metabolic processes happened to balance out for the day. Yikes!
But all the health experts tend to agree and say that to lose one pound of fat, your body needs to have a net metabolic deficit of 3500 calories. Working backwards, that’s about 389 grams, or only about 0.86 pounds of fat.
So help me understand the discrepancy. Why is it that to put on a pound of fat I’d need to eat 4082 calories worth, but to burn off a pound I need to expend only 3500.
Thanks so much!
Never mind everyone! I found the answer:
Technical Notes
Body Fat vs. Nutritional Fat
As you will learn in the topic Calories in Protein, Fat and Carbohydrates, it is commonly said that a gram of fat contains 9 calories. But there are 454 grams in a pound, and 9 x 454 = 4086 calories, not 3500.
The reason for the discrepancy is that body fat, or adipose tissue, contains not only fat, but also other substances including protein, connective tissue, and water. The dietary fat referred to in the nutritional analysis of food is pure.
Looking at it another way, 3,500 / 454 = 7.7 calories. Thus a gram of body fat contains only 7.7 calories versus the 9 calories found in pure fat. It’s easy to see that there should be a difference when you consider that body fat contains water, which has no calories.
Because of the differences in the two types of fat, it is appropriate to use the 3500 calories per pound figure when discussing fat “burned” by activity, and the 9 calories per gram figure when discussing the nutritional content of food.