For people who have considered eating a whole sleeve of Girl Scout Cookies at one sitting, labels stating that a single serving is two or four cookies may seem a tad unrealistic — even arbitrary.

Not so, says the Food and Drug Administration. The agency instructs manufacturers to base their serving sizes on its chart of "reference amounts customarily consumed." The RACC chart is based on data from a large national survey that reflects what people eat "under actual conditions of use." It also considers other factors, including the normal serving size in other countries.

For soup, the resulting serving size can be about one cup. For cereal, half a cup. For chips it can be as few as six pieces. And for cookies, the amount is 30 grams — about two Tagalongs, or about four Thin Mints.

Agency representatives agree that serving sizes, which haven't been updated since the Nutrition Facts Label was launched in the early '90s, are in need of review. That process is under way.

But the idea of boosting serving sizes to reflect the habits of an increasingly overweight population has its drawbacks.

"There's been a lot of discussion over whether the current serving sizes accurately represent current eating habits," said FDA spokeswoman Siobhan DeLancey, "but the counterpoint question is whether increasing the serving size will implicitly 'permit' people to eat more."

Until those questions are answered, the Center for Science in the Public Interest has petitioned the FDA to consider requiring dual nutrition labels on smaller packages, which some may mistake for single servings. One label would offer information for a serving, the other for the whole package.