Hamburger patties should be prepared at home and frozen so that they remain below 40 degrees before they're put on the grill. If you do carry raw meat in the same cooler as other foods, make sure the meat is well sealed and placed on the bottom of the cooler, below the other foods.

People who are grilling meat or serving other foods at a picnic need to wash their hands frequently. If there is no water available, use disposable hand wipes. It's also essential to avoid cross-contamination from raw to cooked meat, the experts said.

More information

The U.S. Food and Drug Administration offers more outdoor eating food safety tips.

Never Say 'D-I-E-T'

When Julie Miller Jones talks to students about nutrition, she is amazed at how early in their lives they know the word diet. By fourth grade, most do, especially the girls, said Miller Jones, a professor of nutrition and food science at the College of St. Catherine in St. Paul, Minn.

Miller Jones and other nutrition experts wish these fourth graders -- along with all the other people they counsel -- would simply jettison the word "diet" from their vocabulary.

"For a lot of people, the idea that a diet is something to go on and then off is wrong-headed to begin with," said Miller Jones. Instead of "diet," she suggested, substitute the word "eating plan." And determine that you will stick with it for life.

"Unless [overweight] people get their head around this idea, that this is something you do for a lifetime, not six weeks or six months, they are doomed to failure," Miller Jones said.

Even worse, constant dieting, especially with severe calorie restriction, makes it harder to lose weight the next time, Miller Jones said.

No one's disputing that excess body weight isn't a problem in the United States. According to the National Center for Health Statistics, about 64 percent of adults age 20 and older are overweight or obese, as are 15 percent of children and teens ages 6 to 19.

Even so, dieting, particularly in adolescence, can be counterproductive, experts said.

One expert, Joanne Ikeda, found that out when she surveyed adult women about their dieting habits in a study published in 2004 in the Journal of the American Dietetic Association. She asked 149 obese women if they had dieted and if so, how many times and when. "We were able to use statistics and compare with women who had not gotten that large," she said.

The result: The higher a woman's body mass index, or BMI, the more likely she was to have started her first weight-loss diet before age 13, said Ikeda, the founding director of the University of California Berkeley's Center for Weight and Health.

Even worse, she added, "there have been some very large-scale studies coming out of Scandinavia showing that [repeated] weight loss [and regain] actually increases the risk for weight gain."

Often called "yo-yo dieting," this pattern is definitely harmful, Ikeda said. "I tell people if they have lost weight and regained it three times [or more], they should stop focusing on weight loss and start focusing on improving your metabolic fitness." That means leading a healthy lifestyle, eating sufficient calories for an adult. "Sufficient" generally means about 2000 calories a day, but Ikeda stressed that ideal levels can vary by weight and activity levels.

Miller Jones said those trying to lose weight by following a healthy lifestyle should do so slowly. "People who slowly lose the weight are the ones who are going to keep it off," she said. Instead of severe calorie restriction, she suggested, cut back by 100 calories a day -- you'll probably lose a pound a month, she said.

A realistic weight loss goal depends on your starting weight, Miller Jones added. "If you have 20 or 30 pounds to lose, [lose] a couple of pounds a month," she said. "If your BMI is quite high, over 30 [termed obese], a pound a week makes sense." For reference, a 5-foot 5-inch person who weighs 180 has a BMI of 30, the standard threshold for obesity.

Find an eating plan you can follow, she said, and ideally one that doesn't "demonize" food. "Look for plans that say, 'Here are foods to choose often, here are foods to choose less often,' not 'These are good foods, these are bad.'"

Teens, in particular, shouldn't diet, Ikeda said. "I think they should focus on behaviors that will in fact result in the achievement of a healthier weight. Behaviors such as exercising, drinking less soda, drinking more water, eating less fast food, watching less television, and drinking more low-fat or nonfat milk."

The bottom line? The only way to have a healthy body weight, Ikeda said, is to have a healthy lifestyle.

More information

To learn more about a healthy diet, visit the American Dietetic Association.