In normal case most of the calories intake in food will be excreted as metabolic waste (faeces, urine, breath, sweet etc...).
Body will take what it need and rest discard and expel out by excreting mechanism.
It means that if you eat 1lb of bacon it doesn’t mean that you will gain not even one gram of the body weight.
Why body build weight concerning fat mass I tried to explain with most of my post on this forum and on my (not impressive) web page.
Links:
http://www.freewebs.com/lukatunjic/fatmas.htm
http://www.freewebs.com/lukatunjic/foodwaterandair.htm
According to present scientific thought every calories intake above maintenance requirement will be stored as fat mass for late use.
It is obvious that present scientific explanation doesn’t make sense but every attempt (diet, exercise, pharmaceutical inventions, surgical interventions etc...) to counteract obesity is based on such understanding.
Please see;
Weight gain/loss, Energy Balance and Bad Science
http://www.freewebs.com/lukatunjic/energybalance.htm
Counting Calories - Blunder in Medical Science
http://www.freewebs.com/lukatunjic/calories.htm
Luka Tunjic
http://www.freewebs.com/lukatunjic/