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6 Reasons Why a Calorie is NOT a Calorie

Different foods go through different biochemical pathways, some of which are inefficient and cause energy (calories) to be lost as heat (1).

Even more important is the fact that different foods and macronutrients have a major effect on the hormones and brain centers that control hunger and eating behavior.

http://authoritynutrition.com/6-reasons-why-a-calorie-is-not-a-calorie/