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Q: Why do some labels list trans fat as "0" when the food contains partially hydrogenated oil?

A: Many packaged foods—spreads, chips, baked goods, and microwave popcorn, to name a few—boast of having no trans fats. But "0" may not really be zero, because of a labeling loophole.

Trans fats are created when liquid vegetable oils are "partially hydrogenated"—that is, hydrogen atoms are added to them, turning them into semi-solid fats that have a longer shelf life. These qualities are favorable for food companies—but not for you, since trans fats are even worse for your heart than saturated fats are.

The loophole: The FDA allows labels to list trans fats as "0" if the food contains less than 0.?5 grams per serving. This can add up if you eat more than one serving (easy to do since standard serving sizes are usually small), or if you eat several foods with small amounts of trans fats throughout the day.

There’s no official recommended daily limit for trans fats in the U.S. The current Dietary Guidelines advise only that you "limit" trans fats. The American Heart Association and the World Health Organization recommend getting no more than 1% of total calories from trans fats (that’s less than 2 grams if you eat 2,000 calories a day).

Bottom line: Manufacturers have cut down or eliminated trans fats from many processed foods. But if you see "partially hydrogenated" oils or "shortening" in the ingredient list, some trans fat is still present, even if the label claims otherwise. It’s hard to avoid all trans fats, but eat as little as possible—foods that contain them are usually not nutritious anyway.

Q: Can an adult suddenly develop food allergies?

A: Yes. Almost all true food allergies (those producing an immune-system reaction, such as allergies to peanuts, cow’s milk, and eggs) begin in the first or second year of life, but adults can sometimes develop allergies—and seafood is the most common culprit.

If you’ve always eaten fish and/or shellfish and suddenly get ill after a seafood meal, it may be hard to tell whether it is an allergy or food poisoning. Symptoms of allergy to seafood include stomach cramps, vomiting, itching, swelling of the hands, and wheezing. The reaction may worsen after a second exposure. You’ll need to see a doctor to find out if you really are allergic, and if you are, you’ll have to avoid seafood. Since shellfish-based broths may show up unexpectedly in combination dishes, you’ll need to read labels in stores and ask questions in restaurants.

In addition, food intolerances (to lactose in milk, for example, or to gluten in wheat and other products) may begin in adulthood, but these are not allergies, strictly speaking. Again, you should ask for medical testing and, if necessary, dietary advice.

Q: Can Umcka cure a cold? Bronchitis? I see it on the shelves with other herbal remedies for colds.

A: Sold as a liquid or tablets, Umcka (also known as umckaloabo) is an extract of the root of Pelargonium sidoides, a South African geranium with a long history of medicinal use. Its longer name probably comes from the combination of two Zulu words. Umcka was used in the 1890s when it was marketed in England as a cure for tuberculosis. It did not cure TB, but it does have weak antimicrobial properties, and is often prescribed for colds and other respiratory tract infections in Europe, especially Germany, where it is licensed by the government.

Unlike many herbal and nonprescription cold remedies, Umcka has some evidence to back it up. However, the research is preliminary and very limited. Not much is known about its side effects. And as with all herbal remedies in the U.S., the products are not standardized, and there’s no guarantee that the bottles contain what’s listed on the labels.

We’ll watch for more research on Umcka. For now, stick with chicken soup.

Q: Is it okay to leave cooked rice at room temperature?

A: It’s safest to serve or refrigerate rice within a few hours of cooking. Though rice is an infrequent cause of food-borne illness, several outbreaks have been reported over the years, usually linked to restaurant rice that had been left out overnight before it was fried the next day. Because the illness tends to be mild, many cases go unreported.

Uncooked rice is often contaminated with B. cereus bacteria, present in soil. The bacteria form spores that can survive normal cooking. If the cooked rice is left at room temperature, the spores germinate, producing toxins that can make you ill, usually with vomiting. Moreover, once the toxins have formed, they are not inactivated if you later fry or reheat the rice.

Other dried grains (including pasta) and potatoes are also susceptible to B. cereus contamination. Thus, you should keep all cooked starchy foods at high temperature (140° F) or cool them in small batches in the refrigerator, not on the counter. Toss leftovers after a few days, since B. cereus bacteria still grow at cold temperatures, though much more slowly. This is especially important if you are in frail health, have compromised immunity, or are pregnant.

A note about rice cookers: These often shut off after cooking, which can pose a risk with rice. Make sure yours switches to a safe warming setting after the rice is done.

UC Berkeley Wellness Letter, November 2009