MACRONUTRIENT BALANCE
There is some inter-conversion between nutrients such as protein being converted to glucose (gluconeogenesis) for release into the bloodstream, but under normal conditions, the capacity to convert one nutrient into another for storage is very limited. Also, humans have little capacity to ‘waste’ extra energy by burning it off. This process, which has been termed luxuskonsumption, is common in animals such as rats but is very limited in humans. Therefore, the examination of each macronutrient as a separate entity is necessary and is summarised below.
Carbohydrate. Carbohydrate stores (glycogen) are very small and tightly controlled in the body. Only relatively small increases in glycogen storage capacity can be gained, for example by the carbohydrate loading techniques employed by endurance athletes, which may increase stores by up to 2,5 times the normal amounts. Carbohydrate calories from the diet keep this small storage space topped up but are mainly used for current energy needs and displace fat as an energy source. Carbohydrate is, therefore, a second priority fuel for energy use, after alcohol. Unlike alcohol and fat, carbohydrate and protein are the main regulators of appetite by satisfying hunger and producing satiety. While the exact mechanisms for this are not known, parts of the complex cascade of responses are being discovered and they appear to involve stretch nerve fibres in the stomach, hormones released from the gut, increases and decreases of certain nutrients in the blood, and a whole series of neurochemical responses in the brain. The final target for appetite control is in the hypothalamus in the brain. Carbohydrate, like protein therefore, is ‘fully balanced’ by influencing both its own burning and satiety mechanisms.
Myth-information. ‘Fat metabolisers’, which are generally forms of amino acids, are often claimed to ‘convert fat to body fuel’. However, scientific assessment shows they are substances which are easily synthesised by the body and have no effect on body fat.
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