LITTLE ROCK, Ark. (AP) - Lunch may be a greasy cheeseburger on the run or a low-fat turkey sandwich, but consumers could improve their nutrient intake with one substitution: spinach for iceberg lettuce.

Even better, researchers at the University of Arkansas at Fayetteville say you can't taste the difference. And a sandwich garnished with spinach has far greater quantities of key nutrients, including vitamin C, vitamin A and folic acid.

Marjorie Fitch-Hilgenberg, assistant professor of nutrition, and Teddy Morelock, professor of horticulture, have been working on a project to slip a little more nutrition into food.

``We know from the literature that people don't eat the recommended number of servings of vegetables, and as a result, they're missing out on the nutrients these vegetables provide,'' Fitch-Hilgenberg said. ``With spinach, we realized we could make a small change to the food people already eat and have a significant impact on their nutritional status.''

When the project began in 1999, the researchers realized they wouldn't recruit more spinach eaters by promoting the mushy greens most people associate with the vegetable. Instead, they got clever.

They recreated hamburgers from fast-food restaurants and conducted a blind taste test. Forty tasters each received three half-burgers. Some received two halves with lettuce and one half with spinach. Others had two halves with spinach and one half with lettuce. After the test, the tasters completed a survey about their samples. The same test was done with tacos.

``The subjects didn't know what they were tasting for, which part of the sandwich we had changed,'' Fitch-Hilgenberg said.

Researchers found the tasters rated the spinach burgers equally as tasty as the ones with lettuce. Also, none of the tasters seemed to suspect the switch. Comments ranged from ``too much onion'' to ``I don't like hamburgers.''

Rhonda Baird, an administrative assistant in the department of human environmental sciences, tested the hamburgers and tacos. She said she could tell a difference between lettuce and spinach in the burgers, but not on the tacos.

She said the difference wasn't in the taste, but the texture.

``I think the one with the spinach was less crunchy (in the hamburger),'' she said. ``I didn't find it as appealing because it was less crunchy.''

But, she said, she preferred spinach in the tacos. And despite the lack of crunchiness in the hamburgers, she would enjoy eating spinach instead of lettuce on fast food.

``Only one or two people mentioned that the lettuce looked very green,'' Fitch-Hilgenberg said. ``That's as close as they got to guessing.''

Researchers have also performed the taste test with sandwiches and tacos.

Morelock said the spinach used was a curly-leafed Savoy variety he had developed, although any spinach would work. The additional folic acid is something young women need since it helps reduce the risk of birth defects, researchers say.

Susanne Luchetti, a registered dietitian and clinical nutrition coordinator for Geisinger Wyoming Valley Medical Center in Wilkes-Barre, Pa., said the substitution is a good way to get more nutrients in a meal.

``It's an excellent idea - the main reason why (is because) spinach is very, very high in vitamin A and iceberg lettuce is low,'' she said, noting that in a half cup of spinach, there are 97 micrograms of vitamin A, while only 11.4 micrograms can be found in a half cup of raw iceberg lettuce. A half cup of spinach also contains 54 micrograms of folic acid, she said, while iceberg lettuce contains 16 micrograms.

``I think if fast-food restaurants thought more like this and revealed their tactics, the public would benefit,'' Luchetti said. ``People are very, very deficient in taking five fruits and vegetables a day, especially raw.''

She said spinach also contains lutein, which may help protect the eyes from cataracts and macular degeneration, a progressive deterioration of the central portion of the retina resulting in a loss of sharp vision.

Morelock said a person's nutrition would be improved by getting two or three servings a week of spinach.

``A serving a day would be wonderful, but I don't know if you could,'' he said.

Morelock said the next stop, after a few more taste tests involving tacos, will be to try to get fast-food establishments to make the switch to spinach. Many already advertise low-fat sandwiches and improved nutrition, he said.

Even if your favorite burger restaurant doesn't make the change, Morelock said this is something that's pretty easy to practice at home.

Fitch-Hilgenberg said she's already made the switch, recently giving her daughter and husband tacos with spinach instead of lettuce.

``A lot of spinach disappeared,'' she said. ``I've had no complaints. I put it in salads all the time.''

Scott Featherston, a University of Arkansas student majoring in general foods and nutrition, said he's been trying to add spinach to the meals of his children for a couple of years now.

``If you don't tell them, they won't notice,'' he said.

Copyright 2001 The Associated Press. All rights reserved.