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Old 12-28-2009, 01:02 AM   #2
Katherine Derbyshire
Member Katherine Derbyshire is offline
Join Date: Jan 2009
Location: Seattle  WA
Posts: 7,596
Re: Nutrition Guru, Total Calories In vs Weight Gain and Loss Question.

Originally Posted by Greg Condon View Post
so i guess my basic question is...does your body always have to process every calorie that enters the body? does it just ramp up the process a bit if you overload it and then just tack on the extra if it can't handle it all?
This question is discussed at great length elsewhere in this board. You might try a search. You might also try a basic biology text, which will explain digestion, cell metabolism, and related topics.

Very briefly, the body can do one of three things with an incoming calorie:
* excrete it. This is what happens with indigestible fiber: it passes through the intestine and out the other end without being absorbed.
* burn it to power the body's various systems
* store it. Long term calorie storage is in the form of fat. But the body also stores glycogen, which is what fuels short-term energy expenditures. If the glycogen stores are depleted, the body can replenish them from food or by drawing on its fat reserves.

The balance among these processes depends on diet, activity level, basal metabolism, and a variety of other things. Unless you live inside a calorimeter, it's very difficult to determine exactly how many calories you are burning at any given time. Unless you live on sugar, whey protein, and lard, it's also difficult to determine exactly how many calories your body will get from a given meal.

So yes, the body must do *something* with every gram of food it consumes. But you can't know your energy intake *or* your energy expenditure precisely enough to say exactly what is happening to a particular amount of food. It's certainly not "safe" to overeat on the assumption that your metabolism will ramp up to burn the excess. (While some people do burn a lot of calories by fidgeting and pacing, someone who is already overweight probably isn't one of those people. This is also why it's hard to lose weight through exercise: the body ramps up your appetite to replace the calories you burned.)

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