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Old 10-02-05, 07:19 PM
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Originally Posted by netso
Taking in 2000 Kilocalories does not mean you absorb 2000 Kilocalories. Digestion is about 50% efficient, absorption about 55% efficient.
It also varies based upon what you're eating. The efficiency of carb, protein, fats conversion to ATP to drive the muscles is different. Here's a study that comes up with some figures:

Energetic Efficiency of Starch, Protein and Lipid Utilization in Growing Pigs
Carbohydrate Food Intake and Energy Balance - Absorption of fat is 96-98% efficient.

Perhaps one of the perks of the Atkins diet was that protein-utilitization by the body is so inefficient, you can eat more meat (although there are other complication that's introduced with such a diet).
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