It's easy to balance a beam. Just put the same weight on both sides of a pivot. You can even lead a balanced life, by having a mixture of activities. But what is a balanced diet?

The same basic idea applies in all cases: not too much of this here, not too little of that there. But in the case of diet, what is it that gets balanced, exactly?

The answer is given by nutrition science, as graphically shown in the famed food pyramid. The basic guidelines are simple and based on sound nutrition. It's this: get the right amount of carbohydrates, fats, protein, minerals and other needed compounds.

Carbohydrates are sometimes mistakenly looked at as unhealthy or not appropriate for dieters. Au contraire, carbohydrates are essential. They are the body's foremost source of energy. Carbohydrates are broken down and put back together into various combinations of carbon, hydrogen and oxygen, releasing energy along the way. That energy is used for cell repair, muscle movement and many other biological processes. In short, carbohydrates power everything we do.

About 50-60% of the total calories consumed daily should be in the form of carbohydrates. Slightly lower for those aiming at weight loss. That can be anywhere from roughly 150-400 grams per day. Every gram of carbs yields 4 calories. The wide range is the result of variation in diets. For a 2,000 calorie diet, for example, 50% is equivalent to 1,000 calories of carbs, or 250 grams. Some diets are focused on weight loss, others on muscle building, some on body fat reduction... the list is endless.

Fat often gets bad press, too. One reason is the fact that each gram yields 9 calories, so they're 'energy dense'. But they're also the body's 'emergency energy supply'. Consumption of fat - of the right type and in the right quantities - is essential to a healthy diet. It is needed to create certain hormones and enzymes, to keep the brain and nerves healthy, to aid in storing fat soluble vitamins and a variety of other tasks.

But there are different types. A healthy, balanced diet will contain chiefly unsaturated fats, avoiding saturated and trans-fats. These should make up about 20-30% of the total daily calories intake. That's about 25-40 grams per day.

Proteins are another vital component of the balanced diet. They're broken down by digestion into amino acids, which are then reassembled into proteins used for growth, muscle building, cell repair and other functions. A healthy diet is comprised of 25-35% protein per day. That works out to, say, 165 grams or 660 calories daily (33%) for a diet of 2,000 calories.

Vitamins and minerals are the biochemical 'facilitators' in the diet. They add few calories, but are essential to getting all the needed reactions to take place. A wide variety of A, B-complex, C, D, E, K along with mineral elements like sodium, calcium, iron, zinc and others are a must. It would take an entire article just to list the names and amounts. A few of the major ones are:

Sodium: no more than 2,400 mg per day Calcium: 1200-1500 mg per day Iron: 15-20 mg per day Zinc: 15-20 mg per day Folic Acid (a B-complex vitamin): 400 mcg per day

Numbers are based on a 2,000 calorie per day diet for an average adult.

Calcium is used in bulk to build up bones. Iron is essential for making hemoglobin, a key component of red blood cells. Sodium is used to regulate the heart beat, in nerve fibers and elsewhere.

In theory a healthy, balanced diet - whether one designed for weight loss, weight training or just basic nutrition - can supply all the needed elements. But, leading busy lives can often cause individuals to forego some important aspects. Supplements, used wisely, can help in those cases.