For years, diet experts pointed at fat as the root of all obesity.

As it turned out, cutting the fat did not prove to be the magic bullet experts hoped it would be.

Millions of people who have diligently reduced their fat intake are still, well, fat n which has left experts looking for other possible factors besides fat.

As it turned out, the other culprit is sugar.

Everybody's worried about fat, and they're pursuing low-fat and even no-fat diets.

But researchers began to realize that many people who were taking fat out of their diets were replacing it with sugar n for example, cookies that were free of fats but loaded in sugar and calories.

The problem is that with sugar, you're getting a very large number of calories with a comparatively small volume of food.

And calories do count.

A tablespoon of sugar, for example, contains between 50 and 60 calories but very little else from the standpoint of nutritional content.

A 12-ounce regular soft drink will have 3 tablespoons of sugar n totaling between 150 and 180 calories with no other nutrients.

That explains why many experts are now recommending that people limit their sugar intake, though these recommendations vary depending on who is making them.

The World Health Organization advises restricting sugar consumption to 10 percent of daily calories, while the National Academy of Sciences advises limiting it to 25 percent.

Those who should be especially careful to limit their intake are obese, sedentary people, especially those with serious blood lipid problems and people who have type 2 (adult-onset) diabetes.

A recent study, for example, in which subjects were fed 28 percent of their calories from sugar during a 10-week period turned up increases in body weight and blood pressure.

Obviously, you don't need lots of sugar if you already have diabetes but even borderline diabetics who already suffer from some insulin resistance should limit their intake.

Unfortunately,

reducing this intake isn't as easy as it seems, because there is so much &uot;hidden&uot; sugar.

Canned pork and beans, ketchup and children's cereals are products that typically contain hidden or added sugar.

Others that tend to be high in sugar include table syrup (one of the most concentrated sources of sugar), non-diet soft drinks, pie fillings, and canned fruit in heavy syrup.

Also, it's important to remember that the sugar in these products can be listed under different names on the label, including sucrose, dextrose, and corn syrup.

Despite the concerns associated with sugar, it's important that people do not throw out the proverbial baby with the bath water.

Sugar, in some cases, serves a very useful purpose, especially in cases where parents are trying to interest children in more nutritional foods.

Some kids, for example, just won't eat plain whole-grain cereal, even though it's a very nutritious product, so adding a little sugar to encourage a child to eat it, especially with milk, is a good thing.

Many &uot;children's&uot; cereal products are made up of 50 to 60 percent sugar.

Also, there usually is no harm in physically active athletes supplementing their diet with some sugar n especially in cases where their bodies are burning up calories faster than they can replace them.

If an athlete who expends lots of energy consumes 4,000 calories a day, but still needs about 1,000 more calories to maintain peak performance, there may be a need for some sugar to maintain this energy.

In most cases, athletes won't be adversely affected, simply because they're burning so many calories.

Still, that leaves the millions of Americans who are sedentary and overweight n the sorts of people who, because of their sedentary lifestyles, require only about 2,500 calories a day and for whom limiting dietary sugar should be a major health consideration.

If you need only about 2,500 calories a day and 800 of these come from sugar, you're left with only a small pool of calories from which to get the nutrients you'll need to stay healthy.

Eating a concentrated source of calories makes it much easier to exceed your daily calorie needs and contributes to weight gain.