Use plastics sparingly, but keep fear of risks in perspective BRIGHT EATING

May 18, 2008 2:34 am

Drinking water helps prevent kidney stones.

READERS have asked me lately about kidney stones, the safety of plastic bottles, the hazards of trans fats for children, and whether reheating food in the microwave kills off nutrients. Read on for my thoughts.

Dear Jennifer: I've read that plastic water bottles contain risky chemicals. What about plastic glasses used as tableware?

--Kate Dervin, Fredericksburg

Five years ago, I first wrote about the risks of bisphenol A, a compound in polycarbonate plastics used to line food cans and many reusable bottles. Last month, media worldwide reported the chemical may raise the risks of breast and prostate cancer.

If you're worried about the plasticware in your cupboard, check the bottom: some plastics with the recycling number "7" contain the chemical. If there is no recycling number, try calling the manufacturer.

There are other ways to reduce your exposure. Don't put hot liquids like coffee, tea or soup in plastic containers--heat leaches chemicals into food faster.

I use a travel mug with a stainless-steel liner for both hot and cold drinks. Not only do I not have to worry about chemicals, but the steel doesn't absorb stains or flavors from the food.

I also replaced my plastic food containers with microwave-safe glass containers. Because I carry a soft-sided, insulated lunchbag, I haven't broken anything in transit.

Occasional exposure to food in plastic containers is probably not a big health risk, but I avoid it when possible. Keep in perspective that there are many other things that are more important to your health, like wearing a seat belt, exercising regularly, avoiding smoking, and eating your vegetables.

Thanks for your thoughtful question.

Dear Jennifer: Does reheating cooked brown or white rice or pasta affect the nutritional value of the food? We usually cook these foods in large batches and freeze portions for future meals, which saves time. A friend claims that microwaving destroys the nutritional value in all foods. Is it anything like boiling foods too long? I'd hate to give up this time-saving method.

--Pat Chen, Fredericksburg

Reheating rice or pasta in the microwave preserves the vitamins.

Perhaps your friend heard about one poorly designed study that cooked microwaved foods in large amounts of water, akin to boiling foods in large amounts of water, which causes vitamins to be lost in the water that was poured out.

It is true that overcooking any food can destroy heat-sensitive vitamins such as vitamin C, whether you do it in the microwave or on the stovetop. However, rice and pasta are already low in vitamin C.

Use the minimum amount of water you need, maybe a couple of tablespoons, and heat the food for the shortest possible time to preserve nutrients.

Good for you for finding a time-saving cooking method!

Dear Jennifer: I was recently diagnosed with calcium-oxalate kidney stones. Should I take a calcium supplement? I'm 51, thin, have a family history of osteoporosis, don't take hormone therapy and don't eat many dairy foods. Also, do I need to avoid high-oxalate foods?

--M.L., King George

The most important thing you can do to prevent future kidney stones is to stay properly hydrated. Drink enough fluid so that your urine is pale yellow, almost clear. A couple of studies suggest that drinking 10 8-ounce cups of fluid daily reduces the risk of kidney stones by about 65 percent.

Many physicians recommend eating high-calcium foods. That's because the calcium binds to oxalate in the intestines, keeping oxalate out of the bloodstream and away from the kidneys, thus reducing calcium-oxalate stones in the kidneys. Limited research suggests calcium-rich foods are safer than calcium supplements. Ask your doctor about this.

Some people suggest avoiding high-oxalate foods, such as rhubarb, spinach, chocolate, peanuts, pecans, almonds and instant tea. However, one study found that drinking tea reduced stone risk by 8 percent. And another study showed that magnesium-rich foods, such as cocoa, also reduced stones.

Overall, there's not enough evidence to swear off high-oxalate foods.

One small study suggested that colas may increase the risk of stones, and since they have no nutritional value, I do recommend avoiding cola drinks.

Don't overdo meat. Research suggests that high-protein Atkins-style diets raise the risk of stones, probably because your kidneys have to work harder to get rid of the extra protein. Moderate amounts of protein are safe.

Avoid megadoses of vitamin C. While fruits rich in vitamin C are safe and healthy, high-dose vitamin C pills may raise the risk of stones.

Also avoid too much sodium--it increases calcium levels in your urine. Fresh fruits, veggies, beans, meats, chicken and fish are naturally low in sodium. Processed foods, soups and snack foods tend to be high in sodium, so limit them.

To further strengthen your bones and reduce your risk of osteoporosis, make sure you get regular exercise. Also ask your doctor to check your vitamin D levels.

Dear Jennifer: Are trans fats worse for children than for adults? I'm aware that we should avoid trans fats if possible, but lately I've noticed them in many snacks my son loves, such as peanut-butter sandwich crackers and cheese sandwich crackers.

--A.R., Fredericksburg

I'm not aware of any research on trans fats specifically in children. However, I think nutrition is more important in children than in adults, because children are growing.

I recommend buying crackers that don't have any trans fats and spreading on peanut butter yourself--it takes only a few seconds. You're smart to look out for your son.

Jennifer Motl is a registered dietitian. Formerly of Fredericksburg, she now lives in Wisconsin.

Jennifer Motl welcomes reader questions via her Web site, bright eating.com, or mailed to Nutrition, The Free Lance-Star, 616 Amelia St., Fredericksburg, Va. 22401.