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Nutrition Column

Turning up the heat - fat cell metabolism

An understanding of how fat is treated in the body can help you reach your weight loss goals with greater awareness and ease.

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.

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 cell or released from the fat cell to be used for energy.

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 those listed above are the ones we can 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. A benefit of lower insulin levels is a reduction of insulinís 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-, saturated-, and trans fats and higher mono-unsaturated and omega-3 fats and 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 2.02.06