Zinc Found In What Foods - Importance of Zinc for Bodybuilders

Although protein, amino acids, carbohydrates and fats garner the most publicity in body-building publications, you'd be wise not to overlook the importance of minerals. They are not often discussed in depth, yet they are as vital to bodybuilding progress as the "star" nutrients.

Most people are under the mistaken impression that vitamins are more useful than minerals. After all, many vitamins function as coenzymes, meaning that they are essential to ensure proper function of certain body enzymes. These enzymes, in turn, control every chemical reaction in the body. What isn't well known is that many minerals act as enzyme activators. Simply put, without the right balance of minerals, vitamins are useless.

A perfect example is zinc, referred to as a "trace" mineral because it's required in much smaller amounts than other minerals, such as calcium, magnesium and potassium. Although the suggested daily requirement for zinc is only 15 milligrams (mg), it plays a starring role in a number of important body processes. In fact, zinc is a component of more than 700 vital body enzymes.

Many of these zinc-related enzymes are involved in the metabolism of carbohydrates, proteins and fats. Zinc is found in large concentrations in such organs and tissues as the liver, prostate, kidneys, bones, retinas and muscles. Studies show that 10% of the body's total zinc content is replaced in one week, with 62% of it concentrated in muscle.

You absorb an average of 20-30% of orally consumed zinc, which travels in the blood bound to various blood proteins, although some plasma zinc is bound to various amino acids (chelated). The most reliable food sources of zinc are animal-protein foods such as red meat. Vegetables and grains also contain zinc, but absorption of the mineral is hampered by sub-stances - such as phytic acid, oxalate and inorganic phosphorus - naturally occurring in these foods.

Glucose, a sugar, increases zinc absorption, and zinc increases glucose absorption. But zinc also inhibits the intestinal absorption of both sodium and water, which explains why zinc would not be a good ingredient to add to sports drinks that are consumed during workouts.

Several studies suggest that bodybuilders may be borderline deficient in zinc, especially during periods of stringent precontest dieting. This likely occurs because reliable food sources of zinc, such as red meat, are routinely removed from precontest diets due to their relatively high fat content. Other studies show that many athletes have lower plasma-zinc concentrations than people who don't train.

Zinc, like chromium, may also be more rapidly excreted from the body during exercise. Elevated body temperature fosters zinc excretion, as does the use of diuretics. Some researchers think that the immune depression commonly seen after intense training may be at least partially due to the loss of zinc.

One study, however, attributed the immune depression occurring after exercise to something else. Reported in the Journal of Applied Physiology (76:2298-2303,1994), this research found that much of this post exercise immune depression is caused by certain immune cells themselves. Because of the breakdown of muscle proteins, intense exercise causes an inflammatory response, and the body reacts to this by sending in certain immune cells. These cells then secrete chemicals called free radicals, which normally destroy bacteria. An overabundance of free radicals after exercise, however, depresses the function of other vital immune cells, making the body vulnerable to disease-producing bugs. The study found that giving athletes 50 mg of zinc tempered the free-radical production of the immune cells, thus preserving the immune system. This shouldn't be surprising because zinc is required for the function of superoxide dismutase, a primary free-radical-scavenging enzyme of the body.

Animal-based studies indicate that insufficient zinc in a diet may directly hamper muscle growth. Zinc-deficient rats show impaired muscle growth and decreased muscle-DNA concentrations. The muscle fibers particularly affected were the type 2B fibers, those most conducive to growth. One human-based study showed that women who took 135 mg of zinc each day for two weeks showed increased isokinetic muscle strength.

Zinc can also be considered anabolic, since it is essential for the synthesis and proper functioning of several muscle-building hormones in the body. One sign of zinc deficiency is an abnormal glucose response. Zinc is not only needed for insulin synthesis, but it is also stored with insulin in the pancreas.

Zinc is likewise concentrated in the prostate gland. In the testes, zinc plays a role in testosterone synthesis, and it is also needed to convert testosterone into dihydrotestosterone (DHT). Although DHT has primarily negative associations - it is the primary cause of acne, male pattern baldness and enlargement of the prostate gland - zinc may control DHT metabolism so that just enough is produced without causing negative consequences.

In addition to being required for testosterone synthesis, zinc is needed for testosterone to bind to its cellular receptors - otherwise, it cannot get into the cell. Without the presence of zinc, the Leydig cells of the testes (where testosterone is synthesized) won't respond to luteinizing hormone, the pituitary hormone that controls testosterone production.

Zinc also plays a pivotal role in the synthesis of both growth hormone and insulin like growth factor-1 (IGF-1). Zinc ions are present in large amounts in the pituitary gland, stored with growth hormone, and some scientists believe that zinc may modulate the release of growth hormone from the pituitary. Other studies show that IGF-I synthesis is impaired by insufficient zinc. In addition, zinc increases the binding of growth hormone to fat cells, and it is needed for proper production of thyroid hormone, which works in concert with growth hormone.

Since zinc enzymes are involved in collagen production, insufficient zinc may be a prelude to connective-tissue injuries, such as those affecting tendons or ligaments. Collagen is a structural protein that provides strength to connective tissues in the body.

As noted, zinc is vital for immune function. However, while a deficiency of zinc will impair immune response, so will excessive levels of the mineral. This mainly affects cellular immunity, such as the T-cells that protect against both incipient cancers from within and microbial and viral invaders from outside the body.

Excess zinc will also impair the uptake of copper. Lack of copper will lower protective HDL cholesterol, raising the chances of the onset of cardiovascular disease. This can occur even if you take the zinc and copper at separate times. The threshold dose for this response is 50 mg a day or more of zinc for a period of more than six weeks.