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Nutrition Column

How diet and activity each play a role in fat cell metabolism and help to determine whether you gain or loss weight

The ratio of two enzymes, LPL and HSL, effect whether your store fat and gain weight or release fat and lose weight.

To a large extent the main factor that determines whether or not we store fat in bodies are two key enzymes. Since most of the factors that regulate the activity of the enzymes are always present these enzymes are always active and are like lights with a dimmer switch that never go off. So it is the relative ratio of the two enzymes, which determines whether triglycerides are stored in our fat cells or released from the fat cells to be used for energy.

The two key enzymes responsible for fat storage and fat removal, respectively, are lipoprotein lipase (LPL) and hormone-sensitive lipase (HSL). Lipoprotein lipase is the enzyme located outside cells and responsible for removing triglycerides (TG fat) from the blood and helping to move it into the cell for fat storage. Hormone-sensitive lipase on the other hand is located within the cell and is activated to release TG from the cells into the blood for utilization elsewhere.

Some of the key controllable factors that stimulate LPL are

1) a high fat diet,
2) saturated fats,
3) trans fats (found in hydrogenated oils),
4) the hormones insulin and cortisol, and
5) caloric restriction.

Other factors influence LPL, but these are the ones we cannot control through diet, exercise, or stress reduction.

The key controllable factor that regulates HSL is exercise or activity. Exercise, being a stress, causes release of epinephrine (adrenalin), and stimulates the release of TG from adipocytes to be used for fuel. However, unlike psychological stress, the physiological stress of exercise causes most of the fat to be taken up by skeletal muscles and used for energy production.

When a stressor is psychological in nature and the energy demands are low - much of the fat goes to the liver and is repackaged and released back into the blood stream only to be re-stored in fat cells or in unfortunate cases the artery walls leading to atherosclerosis (cardiovascular disease).

Another benefit of exercise is an enhanced glucose tolerance and insulin sensitivity. With continued training there is a chronic lowering of circulating insulin levels. The post entitled:
the role of exercise in treating type II non-insulin dependent diabetes,goes into the mechanism behind the improved insulin sensitivity brought about by activity. A benefit of lower insulin levels is a reduction of insulin's stimulatory effect on LPL. So exercise lowers the ratio of LPL to HSL by both lowering the activity of LPL and raising the activity of HSL.
Combining exercise with diet modifications of reduced total-fats, saturated-fats, trans fats, higher mono-unsaturated fats, omega-3 fats, and increased fiber creates an environment which is more efficient at removing fat than storing it ultimately leading to fat loss and weight loss.

Written by Dr. Sternlicht for on 02.02.06