DEAR DR. BLONZ: My question is about chicken meat and fat and the differences between the white and dark meats. I eat a healthy diet but must confess a slight bit of guilt in that when eating chicken, I prefer the taste of dark meat to white meat. I discard the skin and visible fat when cooking chicken thighs and breast pieces, but does dark meat still contain more fat than white? -- B.C., Concord, California

DEAR B.C.: Stored calories in chicken, otherwise known as chicken fat, are under the skin, but some is also deposited around the individual muscle groups. The larger breast muscle doesn’t do much work because chickens are flightless birds. Not so for those leg muscles. There are many different bundles of muscles, each requiring an efficient blood supply and available energy. As domestic chickens tend to hang around and eat all day, they tend to always be in a positive caloric balance. This favors the laying down of body fat, some of which gets stashed in and around the muscles. (The same thing happens to us!) With the working muscles of the legs, there are more opportunities for fat to hide, which explains why dark meat tends to have more fat than white meat.

The “dark” of dark meat doesn’t come from fat; it comes from myoglobin, an oxygen-carrying pigment that is present to a greater degree in working muscles. Breast meat is lighter because it contains lesser amounts of myoglobin. Consistent with this theme, the breast meat of birds that fly, such as duck or goose, is not considered “white meat.”

Go ahead and remove the visible fat as best you can, but even then, there will still be a bit more fat in the dark meat. But you mention that you eat a healthful diet; so why not consider discarding that guilt and simply sticking with the type of meat you enjoy?

DEAR DR. BLONZ: My wife and I love crab. When it is in season, we tend to have a family feast, but afterward, we tend to experience tiredness even into the next day. Is this some sort of coincidence or is there a chemical reason for this? -- C.D., San Diego, California

DEAR C.D.: It’s not likely the crab, at least not by itself. If, however, you tend to have a full plate, and you couple the crab with a high-carbohydrate side dish or a sweet dessert, the combination may be causing a seafood version of the protein-carbohydrate tiredness typically associated with a Thanksgiving feast. The relative amount of the amino acid tryptophan tends to be higher in crab than in other types of protein. When consumed as a part of a big meal that contains carbohydrates, this can give rise to increased production of serotonin in the brain that can contribute to relaxation. It is unclear how this would overflow to the next day unless a leftovers feast continued on the following day, or if the associated toils of the family event had interrupted your normal sleep pattern.

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: 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.