Altering the ratio of the macronutrients can have a strong influence on the prevailing metabolic energy balance because protein, carbohydrate and fat are metabolised quite differently. Postprandially, protein can increase thermogenesis by 25 to 40 %, glucose by 6 to 8 %, and fat by 2 to 3 %. Therefore the thermic effect of food (TEF) can vary considerably, depending on the macronutrient profile of the meal. Macronutrients are also stored in different locations and this can also have an influence on energy metabolism. For example, fat can only be stored in adipose tissue, and the cost associated with this is around 4 to 7 % of the energy content of the food. However glucose can be stored as either glycogen at a cost of 5 to 10 % of the energy intake, or be converted to fat and stored in adipose tissue at a cost of around 24 to 28 % of the energy intake. Because protein can only be stored as muscle tissue, and conversion to fat or glucose is inefficient, the cost of storage for protein is much higher at around 25 to 40 % of the energy of the food.
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