FYI malodrax, sebum contains fat, but no, it is not essentially fat you would see in adipose tissue. Sebum has a specific free fatty acid composition, including a natural antioxidant.
Dietary calories converted to and stored as adipocytes, which you guessed are being secreted out the pores, are generally metabolized at the cellular level to generate ketone bodies and adenosine triphosphate, the "energy molecules," via ketogenesis, gluconeogenesis and cellular respiration respectively. Fat is generally used for generating these energy molecules, unless you are inefficient at metabolizing fat, which would most likely make you a bit chubby. This lightly touches on the body fat percentage variance among any person, completely irrelevant to presence of acne, which is a product of hyperkerinization, overgrowth of bacteria and inflammation/overactive immune response.
Edited by Vanbelle, 09 February 2012 - 02:09 PM.