Mysteries of Energy Balance and Weight Loss

How to Lose Weight Effortlessly
You've probably seen this claim many times: a pound of fat contains 3,500 kilocalories (kcal).  A slice of toast is 80 kcal.  All you have to do is forego one slice of toast per day-- just a few percent of your total calorie intake-- and you will lose 8.3 lbs of fat per year.  Fat loss is so easy!
This reasoning is extremely common both in the popular media and among researchers.  Here's an example from the otherwise excellent book Mindless Eating, by researcher Brian Wansink:
...the difference between 1,900 and 2,000 calories is one we cannot detect, nor can we detect the difference between 2,000 and 2,100 calories.  But over the course of a year, this mindless margin would either cause us to lose ten pounds or to gain ten pounds.  It takes 3,500 extra calories to equal one pound.  It doesn't matter if we eat these extra 3,500 calories in one week or gradually over the entire year.  They'll add up to one pound.
This is the danger of creeping calories.  Just 10 extra calories a day-- one stick of Doublemint gum or three small Jelly Belly jelly beans-- will make you a pound more portly one year from today.  Only three Jelly Bellys a day.
According to this reasoning, if I reduced my calorie intake by 80 kcal per day, I'd become skeletal in two years and vanish in a puff of smoke within 10 years*.  All from a meager 3 percent reduction in calorie intake! 
What's wrong here?
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