Children who ate breakfast 30 minutes before school did better on tests than those who ate two hours before, say Israeli researchers who suggest that the timing of breakfast may affect scholastic performance.

The content of breakfast also may matter, with foods that raise blood sugar -- such as sweetened cereal -- perhaps boosting mental sharpness, the researchers said.

Previous studies in animals and humans indicate that increases in blood sugar just before or after a learning session improve the ability to think and remember, the researchers noted.

Their new study is published in the October issue of the American Medical Association's Archives of Paediatrics and Adolescent Medicine, released Monday.

Further studies are needed to explore the relationship between food content, feeding time and scholastic performance, said the researchers, led by Dr.

Nachum Vaisman of Hebrew University in Jerusalem.

Teachers have long believed that children don't learn well if they're hungry.

A 1994 study by Tufts University found that children who ate a school breakfast had better attendance and standardised test scores than children who ate no breakfast.

The Israeli researchers questioned about 500 boys and girls in five Israeli elementary schools on whether the youngsters had eaten breakfast at home. On standardised memory tests, the 77 percent of children who had eaten breakfast scored significantly better, researchers said.

For the next two weeks, about two-thirds of the pupils were instructed to skip breakfast at home and were given an ounce of sugared corn flakes and 6 ounces of milk at the start of their school day. The remainder of the youngsters were allowed to continue their usual habits.

On the last day of the study, all the pupils were given standardised tests again 1 1/2 to 2 hours after arriving at school. The children who had eaten at school scored significantly better than children who had eaten at home or who had skipped breakfast, the researchers said.

Typical breakfasts at home were chocolate milk and biscuits or corn flakes and milk, they said.

The results indicate that routinely eating breakfast 2 hours before testing does not improve thinking abilities in 11- to 13-year-olds, but that eating 30 minutes before the test notably improves scoring, authors said.

A US expert on childhood nutrition shared their caution.

"It's one study. We need to look at more,'' said Sheah Rarback, an assistant professor of paediatrics at the University of Miami School of Medicine.

"I wouldn't want people to think if they're not eating breakfast a half hour before (school), it doesn't make a difference,'' said Rarback, also a spokeswoman for the Chicago-based American Dietetic Association.

"I think the message is eating something will make you perform better in school,'' she added. If children have a long bus ride to school, parents might pack them a small nutritious snack to eat before class, she suggested.

The federal School Breakfast Programme, started in 1966, now helps about 4 million American children get an adequate first meal of the day by feeding them breakfast at school, Rarback said.

*** A heart-healthy diet depends on quantity as much as quality. How much Americans eat may be more critical than what they eat.

In "Low-Fat Living for Real People'' (Lake Isle Press, $12.95), Linda Levy and Francine Grabowski boil down more than 200 pages of common-sense nutritional advice to a single sentence: Cutting down serving size is the most important of all dietary changes.

"We are eating too many calories,'' Levy said. "People think that if they just eat low-fat foods, they will be OK. But the amount of food also is important. Fat-free does not mean calorie-free.'' During the past 40 years, the average size of a serving in a restaurant has increased to eight ounces (up from three ounces), the women noted in a recent telephone interview.

Steaks are now being served on platters.

"You have to wonder what's going on when your food won't fit on a dinner plate,'' Grabowksi said.

All-you-can-eat buffets and super-size-it specials continue to encourage overeating that contributes to increased rates of obesity and heart disease.

For meat and poultry, the authors recommend a serving of three ounces -- about the size of a deck of playing cards.

"Downsizing is a word of the 90's, so downsize those meat portions,'' Levy said. "Use meat as a side dish; don't think of it as the focal point of your meal.'' When the authors unravel food labels, they begin at the top with serving size.

"Everything else on that label is based on serving size,'' Grabowski said.

The Food and Drug Administration defines serving size as the amount commonly consumed per sitting. Yet these portions often bear little resemblance to the amount people actually eat.

For that reason, consumers should determine their Own Per sonal Serving Sizes.

"That OPSS often turns into `OOPS,' '' Grabowski noted.

One serving of Ritz crackers is five pieces, which have a total of four grams of fat. Instead of five, however, "some people eat a sleeve, or about 35 crackers,'' Grabowski explained. That equals 28 grams of fat, turning a relatively low-fat snack into a high-fat snack.