DEAR DR. BLONZ: The label on the peanut butter states "no trans fat per serving," but under the ingredients’ column it lists partially hydrogenated vegetable oils. Is it possible that a food could contain partially hydrogenated vegetable oils but not trans fats? Thank you for your reply. -- S.F., San Jose, CA

DEAR S.F.: It is always good to check the ingredient list to find out more about the product you are considering. The hydrogenation process is one that saturates (solidifies) unsaturated oils that are typically liquid. Through “partial” hydrogenation, the manufacturer is able to make the fat the perfect consistency for their product, and also help extend shelf life by reducing the tendency of oil to oxidize. As helpful as this was to food processors, it was discovered that the “trans fats” that formed during partial hydrogenation, which can be thought of as a mid-step between being unsaturated and fully saturated, represented a health risk for the human body.

In 2006, after decades in the food supply, the U.S. Food and Drug Administration ruled that the level of trans fats had to be declared on the label. Later, in 2013, the FDA ruled that partially hydrogenated oils (and the trans fats they contain) are no longer GRAS, which means Generally Regarded As Safe. Only a fraction of the fats that undergo partial hydrogenation will become trans fats; that percentage based on the starting material, and the degree of hydrogenation requested by the food manufacturer. If there are no more than 0.5 grams of trans fat per serving, a product is legally entitled to be labeled “no trans fats.”

DEAR DR. BLONZ: Broccoli is a favorite vegetable, and it is appreciated for its healthful qualities.

I usually prepare my broccoli by steaming on the stove, but I sometimes do the steaming in the microwave. I make a simple sauce, or sometimes use a bit of butter. My question has to do with overcooking, and how this might affect broccoli’s benefits. Please pass on some information about cooking effects and a nutritional comparison of how cooking impacts vitamins, minerals and fiber so I can be sure I am getting the best. -- J.S., Tucson, AZ

DEAR J.S.: Broccoli is a member of the crucifer family, which also includes cauliflower, Brussels sprouts, kale, bok choi, turnips, rutabagas and cabbage. The vegetables in this family contain a number of healthful phytochemicals. Broccoli, in particular, is high in vitamin A and C, and is also a source of vitamin K and dietary fiber. The fibrous stem contains less of the nutrients but more fiber. Young broccoli sprouts and seedlings are the richest sources of sulforaphane, a phytochemical associated with anti-cancer properties, with the broccoli tops, called the florets, as next best.

Regarding cooking, there is an enzyme in broccoli that helps the sulforaphane form, and this enzyme can be inactivated by heat. This means that uncooked and quickly cooked broccoli will offer more sulforaphane. One study compared broccoli cooked in the microwave for 2 minutes (lightly cooked) with that cooked for 5.5 minutes (fully cooked). The study reported that the yield of sulforaphane was three times higher in the lightly cooked broccoli. The take-home message here is that broccoli and the other crucifers are healthful foods, and the important thing is to include them in your diet in a way that pleases the palate; but when possible, keep cooking to a minimum.

Send questions to: “On Nutrition,” Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.

DEAR DR. BLONZ: Dear Dr. Blonz, How long is milk good for once opened? My mother and I disagree, and I am counting on you to settle the debate. Irrespective of when it is opened, my mom looks at the sell-by date on the carton and insists that the milk will be good for at least a week past that date if refrigerated. I disagree, saying that once the milk container is opened, that date is no longer something to really look at. New milk cartons have about two weeks, that I've noticed, to sell. I cannot imagine that milk is good for at least three weeks if opened right away. My mom gave my kids milk on April 6 that had a date of March 23 on it. She said it smelled fine, but my kids said it tasted funny. I was mad at her for even giving them such old milk. Please, who is correct? -- S.T., San Jose, CA.

DEAR S.T.: Fluid milk is a perishable food, and it will spoil. The sell-by date on the container is the last day on which the carton should be sold. Manufacturers use these dates to signal retailers how long to sell the product, and the dates include an allowance for normal home use. That means that a gallon container will typically have an earlier sell-by date than a quart container that comes from the same batch of milk.

Assuming it has been opened before the sell-by date stamped on the container, homogenized milk should keep for about 5-7 days once opened. Tell your mother that the clock begins when you open the carton. But there is some flex here. The fresher the milk, and the more time it spends at a chilled temperature, the longer it will remain wholesome. All things being equal, a carton with 10 days before its sell-by date will last longer than one opened on that date. Three weeks? That’s pressing it.

Also, keep in mind that the sell-by date is not a guarantee of freshness or safety. The breakdown of food is a gradual process and does not take place on one particular day. You always need to keep containers chilled and tightly closed. Never return unused milk to the container. Then there is the fact that the accuracy of any dating system relies on the proper handling of foods. If there's been mishandling by the manufacturer, trucker, supermarket or consumer, the life -- and safety -- of the product is subject to compromise. In the end, consumers must trust their eyes, nose and palate in addition to those numbers stamped on a carton. If you notice, as your kids did, an off taste, smell or appearance in any food product, forget the date and toss it out.

Send questions to: “On Nutrition,” Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.

DEAR DR. BLONZ: My question is about coffee and antioxidants. I had thought that because coffee beans are roasted, they lost their antioxidants in the process. Also, could you explain a bit about the effects of caffeine on the body and how long those effects are felt? -- M.Q., Tucson, Arizona

DEAR M.Q.: Plants produce seeds and package them with enough nourishment to keep them viable until they can begin to grow and gather nutrients on their own. Along with sustenance comes an army of substances (phytochemicals) designed to protect against attacks, whether from insects, animals or the oxidizing rays of the sun. (Interestingly, many “antioxidant” substances have bitter tastes, and this helps to discourage nibbling.)

The coffee plant is no exception to this theme. The ripe, red coffee cherry is the seed for the coffee plant, and it typically contains two green coffee beans. The coffee plant grows in tropical climates, and it contains an array of antioxidant substances for its seeds. Green coffee beans are a rich source of antioxidants. The roasting process darkens the color of the bean and develops the flavor and aroma we associate with coffee. You would think that a high-heat process would be destructive to antioxidants, and roasting does indeed affect the level and type of antioxidants in coffee. What’s been discovered, though, is that the roasting process creates a novel type of antioxidants in coffee beans known as melanoidins, which are not present in the unroasted beans. A study in the June 2002 issue of the Journal of Agricultural and Food Chemistry found that a medium-roasted coffee bean contained more antioxidants than either a light-roasted or a dark-roasted bean.

Regarding caffeine, it won’t surprise you to hear that it stimulates the brain. Its other effects include an increase in heart rate, increased acid release by the stomach, quicker transport of food through the digestive system and a relaxation of the smooth muscles, such as those found in the lungs. Caffeine is also a diuretic, which means it increases the volume of urine the body produces.

Once in the body, caffeine goes just about everywhere. In a pregnant or nursing woman, this may mean it makes its way to a developing fetus or into breast milk.

Because caffeine is a foreign substance, the body starts breaking it down as soon as it appears. The half-life of caffeine can vary. Those who break down caffeine fastest are smokers and, strangely enough, children. It takes them about three hours to eliminate half their body’s caffeine.

The half-life for the average nonsmoking adult is five to seven hours. For women taking birth control pills, it’s up to 13 hours. The half-life in pregnant women is 18 to 20 hours, but returns to normal within a month after delivery. A newborn does not gain any real ability to metabolize caffeine until several days old. Any caffeine received through breast milk during this period has a half-life of about three to four days -- important to consider while pregnant or nursing.

Abrupt withdrawal by a regular caffeine user can lead to symptoms ranging from a simple headache to nausea, drowsiness, depression and reduced attention span. People who drink as little as two cups of coffee a day may experience these withdrawal effects. According to a study in the October 1992 New England Journal of Medicine, half of the 62 coffee drinkers studied experienced moderate to severe headaches when they stopped drinking coffee, and about 1 in 10 reported depression and anxiety.

The symptoms were connected to the caffeine, in that those who discontinued coffee but received caffeine (not placebo) capsules did not report the same problems. However, these symptoms tend to be short-lived, and most can be avoided by cutting back gradually.

Send questions to: “On Nutrition,” Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.