While brown-bagging a child's lunch has traditionally been considered both the thriftier and healthier alternative to school meals, packed lunches often reach unsafe temperatures before they are eaten, even if they contain an ice pack, according to Texas researchers.

 A new study of approximately 700 packed lunches among preschoolers between the ages of 3 and 5 discovered that more than 90 percent of the perishable foods in their meals had reached soaring temperatures even 1.5 hours before lunch time.  The study, published in the journal Pediatrics, discovered that the average temperature for those foods - which include meats, milk and sliced fruits - climbed to 62 degrees by lunchtime, more than 20 degrees higher than recommended by the USDA.

"This was an eye opener. As a parent, when my child comes home with a stomachache or vomiting, I usually think it's a virus. I don't think the food I serve is the problem," study author Fawaz Almansour, a nutritional sciences researcher at the University of Texas at Austin, told USA Today.

About 39 percent of the lunches analyzed had no ice packs while 45 percent only had one. However, the study found that more than 88 percent of the packed lunches were at room temperature 1.5 hours before lunchtime and only 1.6 percent of perishable foods were kept in the safe temperature range advocated by the USDA.

The USDA recommends that perishable items be kept at less than 40 degrees, while no food should be stored at room temperature for more than two hours.

Perishable items that are stored at improper temperaturse are more likely to become a haven for harmful bacteria, increasing the risk for food poisoning. Children under the age of 5 are particularly vulnerable to food-borne illnesses, according to researchers.

While loading a lunch box with ice packs may preserve perishable foods, experts say that is not the only way to ensure a packed lunch is safe for consumption. The USDA recommends freezing sandwiches - minus extras such as lettuce, tomatoes and mayo - to help them stay cold through the day and then storing them in insulated bags with a small frozen gel pack. The agency said perishable leftovers should be thrown out if there is no refrigerator available and recommends disposing of all used food packaging and paper bags after the meal, as they could potentially contaminate other foods.