RT Journal
A1 Katan MB, Ludwig DS
T1 EXtra calories cause weight gain—but how much?
JF JAMA
JO JAMA
YR 2010
FD January 6
VO 303
IS 1
SP 65
OP 66
DO 10.1001/jama.2009.1912
UL http://dx.doi.org/10.1001/jama.2009.1912
AB 
How much weight would an individual gain by eating an extra chocolate chip cookie every day for life? One approach to answering this question, frequently used in textbooks1 and scientific articles, is based on the assumption that a pound (454 g) of fat tissue has about 3500 kilocalories (kcal). Thus, a daily 60-kcal cookie would be expected to produce 0.2 kg (0.5 lb) weight gain in a month, 2.7 kg (6 lb) in a year, 27 kg (60 lb) in a decade, and many hundreds of pounds in a lifetime. This of course does not happen. In this article, the physiology of weight gain and loss is reviewed, and the amount of reduction of caloric intake necessary to avoid becoming overweight or obese is estimated.