
To maintain one's current weight,
energy input needs to match energy output.
To lose weight,
energy input needs to be less than energy output.
Despite occasional contradictory statements of a few health food gurus,
and the understanding that any person's calorie numbers are estimates
depending upon many factors--and not a cut-and-dried issue--
the established scientific principle is still: Calories in, Calories out.
Each of us burns a different amount of energy (calories),
This is based on our heights, our weights, our sex, and our ages.
A smaller part of this is also based on our activity level.
Due to each of these factors most of our individual metabolisms differ.
I am a short, small, older female.
Within the past couple of years, I took a medical Resting Metabolism Rate (RMR)
computerized breathing test at a Hospital Facility.
It showed that my metabolism is NORMAL or AVERAGE for my height, weight, age, and sex:
That my "normal" "average" RMR is around 1000 daily calories, and
after adding an 1 hr or more, for 7 days a week, of intense low-impact exercise
(plus strength training) my normal daily calorie burn should be about 1400 calories.
Unfortunately, my personal calorie records do not verify this test’s results. 
My own food data indicate that my entire calorie burn is a bit under 1100 calories.
and this includes both both my RMR and the activity factor together.
However that discrepancy is not the point of this discussion.
In this discussion, we can assume that these Metabolism Tests were accurate.
Looking at the food I would normally choose to eat
if I were allowed to eat 3 normal sized dinner plates of food each day,
or the equivalent of a similar food exchange program,
my calculation of the calories in 3 normal sized dinner plates
of whatever food I might like to eat is around 2000 calories daily.
2000 Plus calories
is what some larger people need to maintain their weights.
However, 2000 minus 1400 calories equals a 600 daily calorie excess.
3500 calories = 1 fat lb.
Therefore every six days of eating in that manner
would cause me to have a fat gain of 1 lb.
365 days a year divided by 6 equals 60,
so I could gain around 60 lbs in one year by eating in this manner.
(It would actually be a bit less since this simple calculation
ignores the slight MR increase that would occur due to a weight gain.)
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