They've finally done it: fat-free fat.

With the Food and Drug Administration's Jan. 24 approval of olestra, a fat substitute developed by Procter & Gamble, for use in certain snack foods, the door has been opened to what some dieters may call the impossible dream.

Good old fried snack foods -- potato chips, crackers, tortilla chips and others -- with "zero fats" on the label?

Olestra is, in essence, fat-free fat to our bodies, said Elizabeth Andress, a food safety specialist with the University of Georgia Extension Service.

"It's the first fat substitute we can use in fried foods," Andress said. "Other fat substitutes can't withstand the cooking temperatures natural fats do. But olestra actually is a natural fat -- it's been altered so we don't digest it."

So you can have your fatty foods and eat them, too. A typical snack food with 10 grams of fat and 150 calories per serving, Andress said, can now have zero grams of fat and only about 70 calories.

The fat-based substitute offers a better "mouth feel," as it is known in the industry -- the look and feel of foods containing real, natural fats.

But this wonderful, dream-come-true story isn't all champagne and confetti. Olestra does have its drawbacks, as pointed out in the FDA approval, which requires that four essential vitamins be added to it and a warning label placed on all products made with it.

"It has long been known that olestra can cause cramping and loose stools," Andress said, referring to a decade of studies on the product. "A bigger concern is that olestra inhibits absorption of fat-soluble vitamins."

The problem with a fat you can't digest, she said, is that natural fats have some useful roles in the diet. They carry vitamins A, D, E and K, for instance, and aid in their absorption in the intestine.

FDA evaluated more than 150,000 pages of data from more than 150 studies Procter & Gamble provided in its original 1987 food additive petition and in amendments filed since then.

Studies showed olestra "may cause intestinal cramps and loose stools in some individuals," the agency noted. "These gastrointestinal effects do not have medical consequences."

Other studies showed that the vitamin-inhibiting effect could be compensated for by replacing the essential nutrients in olestra-containing snacks.

While ruling the fake fat safe to use in certain snacks, FDA required the following label on all products made with it: "This Product Contains Olestra. Olestra may cause abdominal cramping and loose stools. Olestra inhibits the absorption of some vitamins and other nutrients. Vitamins A, D, E and K have been added."

Andress said olestra inhibits absorption of some carotenoids, too. The role of these nutrients, found in carrots, sweet potatoes, green leaf vegetables and some animal tissue, isn't fully understood, but they're known to be beneficial to human health.

"I don't think olestra offers a real health concern for consumers," Andress said. "People just need to be aware of the label and the potential problems."

People need to remember, too, that fat-free doesn't necessarily mean calorie-free.

"Don't be fooled into thinking you can eat all you want just because it's fat-free or low-fat," she said. "There are still calories in these products, and there are still potential problems associated with overconsumption."