THE FAT CYCLE

Friday, May 8, 2009 11:47
Posted in category Weight Loss

The process of conversion of fatty acids in the blood stream to triglycerides in the fat cell and back again to fatty acids in the bloodstream is a constant one. The biochemical term for the rebuilding of FFAs into TG in the fat cell is esterification. There is an active cycle of free, or unesterifted, fatty acid uptake into the fat cell which is then re-esterified within the fat cell. Hence there is an ongoing process of lipogenesis, lipolysis and release of FFAs.

Fats which are released into the bloodstream during lipolysis are liberated from their glycerol base and transported to the muscle via the blood to be used as fuel. However, more fat is usually released than is used up. At rest, it has been shown that about 70 per cent of fats released into the bloodstream are re-esterified back into the fat cell, but this decreases to about 25 per cent after the first 30 minutes of a low intensity exercise session. When the exercise is completed, some fats continue to be burned in the recovery process, but about 90 per cent of those released which have not been used up are then re-esterified, and stored back in the fat cell until another day. In exercise then, about one-half of the increase in fat oxidation contributing to the extra fuel supply comes from a reduction of the percentage of re-esterification (fats re-entering the fat cell), rather than an increase in fats being released from the fat cell.

The process of re-esterification may be important for the fat loss process as some studies have shown that the degree of re-esterification, in contrast to the extra fat used up, may be influenced by the post- and pre-exercise meal of the exerciser. Injecting glucose into a fasted subject for example, has been shown to increase the re-esterification of fats back into the fat cell more quickly than it inhibits lipolysis, possibly due to the increase in insulin following a glucose load which then has an inhibitory effect on lipolysis.

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