DEAR DR. BLONZ >> I want to get the most from the nutrients in the whole foods I eat, but I have been reading that cooking, such as microwaving vegetables for convenience, can cause losses. You have written about this, but specifically, I want to know whether it is best to steam vegetables or microwave them.

— M.F., San Diego

DEAR M.F. >> It is reasonable to want the most out of your foods, but we should not fret about every last nutrient milligram. Use recipes that keep you and others wanting more.

Nutrients are affected by the level and duration of heat exposure. Another factor is whether the food is cooked in water that gets discarded. However, steaming and microwaving are similar, so go with whichever you prefer.

DEAR DR. BLONZ >> Is there any nutrition or calorie difference between fresh orange juice and from concentrate? What about the refrigerator shelf life?

S.N., Wilmington, Delaware

DEAR S.N. >> Fresh orange juice, or “fresh-squeezed orange juice,” has been extracted from the fresh fruit and then served immediately or put directly in a container for sale or shipment to the market. A carton of juice marked “fresh frozen” contains the fresh-squeezed juice frozen in the carton. An orange juice “from concentrate” has undergone a step where water is removed using vacuum and heat, after which the concentrate is pasteurized. Concentrates can be sold as frozen or reconstituted and packaged into cartons of chilled, ready-to-serve orange juice labeled “from concentrate,” which is found in the refrigerated section. Some commercial juices in cartons might say “not from concentrate,” indicating they were flash-heat pasteurized, packaged and chilled, bypassing the concentrating step. Often referred to as “premium” juices, these tend to cost more.

Orange juice has delicate flavor components, and its vitamin C content breaks down when exposed to heat, so keep the juice refrigerated, and consume it as fresh as possible. Fresh-squeezed orange juice tends to have more vitamin C and a better complement of flavors than juice that’s been pasteurized. Balance this with the fact that the pasteurized juice will last longer than the fresh-squeezed product.

Orange and other juices can also be packaged in aseptic containers, such as those used in children’s lunch boxes. These juices have been pasteurized and placed in sterilized containers and are essentially shelf-stable.

A frozen concentrate can be kept in the freezer for several months. Once reconstituted, orange juice begins to lose quality in about a week. The same goes for cartons of juice after they have been opened. There can be variations in the amounts of natural sugars between a freshly squeezed juice and a juice made from concentrate. The difference in calories, however, would be negligible.

Kensington resident Ed Blonz has a PhD in nutrition from UC Davis. Email him at cctimes@blonz.com.