Beer is a good ol' drink: today in the United States it's almost synonymous with being laid back. Look at beer commercials: The gang sits around unwinding and toasts to a long hard day with a tall cold beer. But beer is starting to take on a different personality. It's becoming a beverage not so much for winding down as for cranking up.

Beer is brewed from cereal grain (barley, corn and rice) so the finished product contains carbohydrate, protein (mostly amino acids), vitamins and trace minerals, derived from the original components. The composition of beer, of course, varies considerably among the various brands and even within the same brand when brewed at a different time in different vats.

Beer provides a soothing, therapeutic effect derived from the hops that are added as a flavoring agent. Hops were used in times past for medicinal purposes and are still used today by the pharmaceutical industry for their sedative effect. The beverage is ruted to decrease tension without affecting the performance of normal tasks; in some instances, performance levels are said to improve. We know that alcohol has a depressant effect upon the central nervous system, yet the immediate effect is to rev up the cardiovascular system; blood pressure increases rapidly and heart rate increases more slowly; the skin capillaries also dilate -- producing the red, "flushed" face.

As many will confirm, beer is an ideal thirst quencher, thanks to its balanced concentration and alcohol- carbohydrate ratio. Beer enhances appetite, aids digestion and has a salubrious effect on metabolism -- improving intestinal motility and counteracting some of cholesterol's effects. And, as every drinker will vouch, beer speeds up the outflow of water from the body, due to its high- potassium/low-sodium proportions. Researchers found that this diuretic effect was greater than that of an equivalent amount of water or alcohol solution of the same concentration.

When we exercise, our muscular effort creates body heat, which must be dissipated. The proc sweating and then having that sweat evaporate effects this heat discharge. This cooling, though, requires plenty of liquid especially in warm weather.

Runners have a more difficult time than other athletes in rehydrating themselves during an "event" because they don't have the normal breaks and timeouts that other athletes enjoy. Therefore, runners must make certain that they are hydrated sufficiently so that they will be able to sweat freely; as one's fluid loss approaches 6 percent of his body weight and his core temperature approaches 105oF, the threat of heat stroke increases enormously.

Consequently, the runner must be sure that the solution he does drink gets out of the stomach and into the intestine quickly for absorption.

Beer is absorbed in the system faster then defizzed colas and electrolyte-replacement drinks. It also provides immediate energy because the alcohol is absorbed so rapidly. Sugar, on the other hand, requires digestion. Orange juice is too concentrated to drink undiluted before an event.

Dr. George Sheehan describes his effort in the 1977 Boston marathon, in 80-degree heat, no clouds and no wind: "I know of 16 runners who were overcome and spent the night in the hospital . . . I had no trouble. I drank 12 ounces of beer two minutes before the start. Then I drank water until the halfway mark. After that, I bummed a beer every three miles and finished going away . . . There is no quicker way to get energy and fluid at one time. The usual sugar drinks lie in the stomach, and many of the runners were vomiting on their way to the finish."

Runners who cannot tolerate even the low level of beer alcohol (ranging from 3.2 to 4.5 percent) should not be encouraged to drink beer prior to or during their event. A compromise might be "low-cal" beer that contains about half the alcoholic content of the regular American beers.

Some articles written for the beer industry publications tout the worthwhile nutritional properties of the drink. But according to the U.S. Department of Agriculture it would take 17 bottles of beer (12 ounces each) to achieve the Recommended Dietary Allowances (RDA) of potassium for a healthy male between 23 and 50 years; 10 bottles to fulfill the magnesium requirement and seven bottles for copper. Beer provides no Vitamin A, no Vitamin C, and no thiamine (B1).

Beer has always had a bad reputation for creating the "beer belly." Actually, ounce for ounce, beer is less fattening than whole milk, grape juice or apple juice and is about equivalent to some colas and ginger ales. The difference is, of course, the quantity consumed: The beer lover might finish off a six-pack (about 2 liters) watching a football game on television, or a runner might jog a six- pack (about 25 miles' worth), but it's not usual for someone to drink two quarts of milk in two or three hours. Even though beer isn't a concentrated source of calories, excessive intake results in fat; and men tend to hoard this fat in their beer bellies. (Women deposit their fat primarily in other spots.)

In all honesty, anyone watching his weight would have to consider his beer intake to be "fun" calories. Beer has some nutritive value but it would take 2,368 calories of beer to meet one's RDA for phosphorus, 2,516 calories for potassium, and 1,480 for magnesium of niacin. Can you afford it? If the only part of your diet that you're watching is sodium, however, beer might not be a bad idea. A 12- ounce bottle has only 18 milligrams of sodium.

The prudent athlete should read labels and determine, from product knowledge and personal experience, which drink is best for him or her. Beer for running marathons? If you can tolerate the alcohol content, it may not be a bad idea. Beer for overall health and nutrition? You've got to be kidding!