THE FATE OF FAT IN FOOD

Fatty acid molecules travel through the blood as either FFAs or as triglycerides OTGs) which is a group of three fatty acid chains joined by a glycerol molecule. An analogy may be footballers

roaming the streets on their own, or joined by a team manager. Triglycerides cannot get directly into the fat cell because their molecules are too big, so the team needs to be broken down into FFAs and glycerol units like the footballers having to pass single file through the door into a nightclub. Once inside the nightclub (fat cell), they join up with the glycerol into a ‘team’ again and are stored as TGs.

Keeping the nightclub analogy, our footballers have to get past a doorman. In the fat cell, the main ‘doorman’ is the hormone insulin, which is formed in the pancreas and secreted into the bloodstream in response to a rise in blood sugars. Before a meal (low insulin), the doorman has the exit open allowing FFAs to leave to supply energy for the body. After a meal (high insulin), the doorman closes the exit and opens the entrance to allow FFAs to enter. Insulin also activates an enzyme, lipoprotein lipase (LPL) in the fat cell. This acts like a ‘spruiker’ outside the nightclub touting for business. Adipose lipoprotein lipase (ALPL) breaks FFAs off the TG so that they can enter the fat cell.

Insulin also acts as a doorman for the muscle cell but here the functions are somewhat different because he has two entrances to control. Before a meal he has the ‘fat door” open to allow FFAs into the muscle cell to provide it with energy. He also activates muscle LPL which breaks down the TG teams passing by to allow FFAs to get through the door. After a meal, he closes the fat door and opens the ‘glucose door’ so the muscle switches from running on fat to running on glucose. (Interestingly, if the muscle needs a lot of energy such as during exercise, the glucose goes straight in through another door that insulin has no control over.)

Basically, when the body needs more energy than is currently available from food, triglycerides in the fat pool are broken down into FFAs plus glycerol and sent to the muscle via the bloodstream to help out. It’s as if someone has run into our ‘nightclub’ and called all the footballers out to help out in another building down the road. The process is triggered by another enzyme which, like all enzymes, causes a reaction but doesn’t take part in that reaction. Hormone Sensitive Lipase (HSL) is the enzyme involved in this removal of fats from the fat pool. It does

so under orders from a range of chemical ‘alarmists’ in the bloodstream, particularly the catecholamines, or hormones secreted from the adrenal glands at the top of the kidneys. The catecholamines, therefore, facilitate lipolysis, but inhibit lipogenesis. Insulin, on the other hand, facilitates lipogenesis, but inhibits lipolysis.

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Related Posts:

• FAT LOSS: COUNTERACTING ENERGY SPARING ADAPTATIONS
• FEED YOUR BODY RIGHT: SHE LOST HER EATING “HABIT” AND 102 POUNDS

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