DEAR DR. BLONZ: What is understood about how the role of the kidneys changes during pregnancy and how this affects what we should be eating? -- P.O., Scottsdale, Arizona

DEAR P.O.: Our blood not only carries nutrients, it also serves as the fluid medium for transporting metabolic wastes on their way to elimination. The kidneys and the liver are organs that serve as cleansing filters to regulate the concentration of various substances in our bloodstream. This can also include holding on to substances in short supply for recycling.

During pregnancy, there is a marked increase in specific nutrient demands at certain points in the process, as well as an increased production of metabolic wastes that are byproducts of the amazing construction underway. Our kidneys regulate substances based on their concentration in the blood, and one of the body's adaptations is to increase its blood volume to boost its capacity to transport nutrients and waste products.

Following conception, one of the first parts of the fetus to develop is its nervous system. Folic acid plays a key role, but the critical element is that sufficient folate must be present during the first few weeks after conception -- a time at which most women may not yet be aware they're pregnant. Spina bifida is a type of birth defect in which one or more of the vertebrae of the spinal column fail to develop properly. As much as 75% of all cases are attributable to a folate deficiency during those first few weeks of pregnancy. The U.S. Public Health Service recommends that all women of childbearing age who are capable of becoming pregnant consume at least 400 micrograms (0.4 mg) of folic acid per day to reduce the risk of a pregnancy complicated by a neural tube defect. The recommended daily allowance (RDA) rises to 600 micrograms during pregnancy.

There is also a special need for iron as the developing fetus requires sufficient iron stores to make its own blood supply during the first months of life. A newborn's main source of nourishment is often breast milk, which, while rich in vital elements, is not a good source of iron. This helps to explain why the RDA for iron rises from 18 milligrams for non-pregnant, menstruating women to 27 mg per day during pregnancy.

Calcium and vitamin D are also standouts, as they are needed for bone development. Calcium absorption doubles during pregnancy, and vitamin D is needed for calcium absorption and utilization. The RDA for calcium is 1,200 milligrams and the RDA for vitamin D is 10 micrograms.

The final standout is water. A pregnant person should drink 8 to 12 cups of fluids per day, with water as the primary source. Throughout her pregnancy, a woman's blood volume increases by 50%, and the extra water helps to transport nutrients and oxygen to the developing child and to carry waste products away. For a more extensive discussion of nutrient requirements during pregnancy, see b.link/hn5jfm4.

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: I am interested in the health benefits of plant phytochemicals, and you include chocolate among them. Are the phytochemical antioxidants in the cocoa powder or in the cocoa fat? If they are in the fat, does that mean the only way to get the benefits is to eat full-fat chocolate? -- M.D., Raleigh, North Carolina

DEAR M.D.: Successful plants evolved the ability to capture energy from the sun, using it to fuel the construction of their complex structures and substances and power all aspects of their metabolism. (We rely on the foods we eat to provide our energy.) But, aside from serving as an essential source for energy, the sun's rays can have devastating effects on living tissues. Similar to the visible effects of sunlight bleaching colors, excessive exposure to the sun's oxidizing rays can damage tissues and cause cancer.

While animals develop skin adapted to their habitats, they can move and find shade and shelter. Plants remain anchored by their roots; successful ones have evolved appropriate defenses for every stage of their life cycle. The most straightforward protections are shields in the form of opaque barriers. Examples in nature include leaves and seed coverings. We rely on hats, umbrellas and sunscreen applied directly to protect our skin, but critical are the antioxidants that can inhibit oxidative damage to body tissues and substances. We find antioxidants and other protective phytochemicals in the fruit and leaves that are exposed to the environment. Likewise, plants that tend to have higher levels of fats and oils will usually have lipid antioxidants on call.

Most basic to this discussion is an appreciation that phytochemical protectants are there for the plant's benefit, not ours! Every plant has evolved its own protection strategy, underscoring the wisdom of including a variety of plant-based foods in the daily diet. It is only when such foods are a regular part of what we are eating that they can be there to work their magic for us when needed. For more on antioxidants, see b.link/tb55h26.

As you pointed out, research on chocolate has identified its variety of beneficial compounds. The primary antioxidant phytochemicals in cocoa beans are the flavonols, a type of flavonoid found in the solid fraction of chocolate. These are in the cocoa powder and, of course, in the whole chocolate confection. Dark chocolate tends to contain more than milk chocolate, with white chocolate containing little, if any. As for whether having cocoa powder is a better way of getting the benefits of the chocolate, that, I think, is a matter of personal preference. For more on the benefits of chocolate, see b.link/m7wkbxs.

There are plenty of foods with wonderful attributes. Eat chocolate, not because it is prescriptive, but because you enjoy it.

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: It is now crab season on the West Coast, one of my favorite periods. When I clean the crabs myself, there is always this squishy stuff under the shell, called crab butter. There are mixed opinions on this substance. I have used it in my dipping sauce to add flavor, but this practice was criticized by recent guests where it was on the table. Is crab butter bad for health? Thank you. -- J.B., Santa Clara, California

DEAR J.B.: Like you, I also look forward to the arrival of crab season. That "crab butter" you refer to is the yellow-white-greenish substance that is revealed after the large shell has been removed. This is actually a digestive gland known as the hepatopancreas, the crab's equivalent of a combination liver and pancreas. This organ has a mix of functions for the crab, producing digestive enzymes, filtering impurities from its equivalent of blood and providing some energy storage.

There would be little risk to us if the crab on your plate had spent its entire life in pristine waters, but crabs do not come with passports to check where they've been hanging out. If the crab has spent time in areas with oil spills, agricultural runoff, PCBs or exposure to toxins or heavy metals, there is a proportionally greater risk of accumulation in its internal organs, with its hepatopancreas bearing the brunt. There is also a greater risk of toxin accumulation during algal blooms, as domoic acid forms, and this is a dangerous neurotoxin. Crab seasons get adjusted for public safety to avoid these blooms.

For more on domoic acid, see the article at b.link/drd4vfb. Consider the red flag to be that while some refer to this as crab butter or crab mustard for its taste, it's also called crab poop for the other stuff you don't want. Best to stick with the meat and make your own crab butter.

DEAR DR. BLONZ: I add various dried berries to my cereal every morning, but a friend told me that dehydrated berries no longer have antioxidant value. Can you comment on this? -- R.B., Pinole, California

DEAR R.B.: Dried berries, such as blueberries, cranberries, currants, raspberries and cherries, all have considerable nutritive and antioxidant value. I have no idea where your friend got that misinformation. Similar to you, my go-to breakfast is berries, fresh, frozen or dried, with high-fiber whole-grain granola and unflavored, full-fat yogurt. I opt for organic when available. It's a great way to start the day, giving you a leg up on healthy eating.

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.