DEAR DR. BLONZ: I’m under the impression that vitamin D requires fat in order to be absorbed well. Does that mean they must be consumed at the same time? If I drink a glass of nonfat milk by itself, will I absorb less of its vitamin D? Also, is that why cod liver oil is one of the best ways to get vitamin D -- because of the fat in the oil? -- N.S., via email

DEAR N.S.: Meal conditions can affect nutrient absorption, and this is a good example. Vitamin D is a fat-soluble vitamin, and it requires some fat to facilitate its passage through the absorptive surface of the intestines. There are a number of studies in the scientific literature reporting that eating a meal that contains fat at the same time as taking a vitamin D supplement, or shortly after, does indeed result in significantly more absorption.

Cod liver oil does contain vitamin D and fat, but it can also contain a lot of vitamin A, which is harmful in large doses. Consult with your doctor, read labels, and be careful not to overdo it. (Read more about cod liver oil at b.link/pkyuv.)

DEAR DR. BLONZ: In a previous column, you wrote about aging, saying that some of the blame is on free radicals. The column then explained that whole grains and nutrient-rich whole foods could combat free-radical damage. What exactly do you mean by “whole foods”? Do you mean organic foods, foods with fiber, green vegetables or something else? -- B.B., Hayward, California

DEAR B.B.: “Whole foods” refers to fruits, vegetables and grains that are unprocessed or minimally processed, such as freezing or drying. These are foods as close to their “just picked” natural state as possible. Foods need not have been organically grown to qualify, though organic is an excellent choice when available. The idea is to have a regular intake of a variety of foods that have their full complement of healthful components. Some have fiber; others do not. Some may be green, but whole foods come in all colors.

To survive the rigors of nature, “whole foods” have had to evolve to make the substances they require to grow and reproduce, along with an arsenal of phytochemical components. Many of these compounds are essential, or at least beneficial, to our health as well -- but you have to eat the whole food to gain the benefit. As a general rule, whole foods are preferable to their highly processed counterparts, as processing can destroy delicate phytochemicals and leave with you lesser amounts of nutrients.

The final part of the picture is to acknowledge that not everything “natural” is beneficial. There are naturally occurring toxins as well as healthful whole foods. The reference to whole foods speaks to wholesome, traditional foods that have proven their safety and dietary worth over time.

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: As people in our mid-60s, my spouse and I are aware that we are getting on in years. General stiffness in the mornings and occasional body aches have limited our activities to a degree, but aside from that, we are in good shape. We have not been very physically active, though, and are interested in some general coaching to help limit the chances that one of the serious ailments will come knocking on our door. -- T.C., Sun City, Arizona

DEAR T.C.: I recall when thoughts of retirement began in one’s 50s. At present, productivity and vitality often continue well beyond that -- with people living longer, doing more and enjoying better health than ever before. A good deal of the credit can be attributed to research on how various short- and long-term behaviors affect our health. There is also better health care that can focus on potentially life-altering conditions before they become disruptive. Unfortunately, such advances have yet to become accessible to all levels of society. That’s certainly something to work on.

That said, our lifestyle and the foods we eat remain vital components to help us hold back obesity, heart disease, diabetes, cancer, arthritis and cognitive decline, at least to the extent that we can. Good nutrition helps the body’s disease-fighting immune system to work at its best, but the years will always take a toll. What occurs is a product of our genes, mixed with how we have led our lives.

A widely held theory on aging pins some of the blame on compounds called free radicals, which gum up the works and facilitate the path toward disease. Research evidence continues to reveal how whole grains and nutrient-rich whole foods can combat free-radical damage. Phytochemicals, the beneficial compounds that plants evolved to help them survive, can help our bodies, as well. But it takes a plant-based, whole foods diet to facilitate that payoff. Eating well can help keep you off the sick list -- though nothing can be guaranteed in this regard, of course -- and, if you do become ill, can aid in faster wound healing, fewer surgical complications and shorter hospital stays. This is of critical importance in today’s debates about health care.

Energy is the most basic commodity of life, and the body saves all it gets its mitts on. We are designed to cut back on systems that are not routinely used, saving extra energy whenever possible. Dietary excesses get converted to energy and stored whenever possible, but being “wealthy” in this regard can set us up for chronic disease.

A healthful lifestyle keeps the body on notice that we want to keep all our parts in working order. Even the best-built engine will become sluggish if not used regularly. The “use it or lose it” proposition comes into even greater play as we age. It is easier to maintain fitness than to become fit, but patience, persistence and guidance from knowledgeable professionals can chart a course that is appropriate for each situation.

We can’t undo years of inactivity with last-minute changes, but the body can be very forgiving. It’s better to make positive changes at any age than give up without trying. There is no antidote for aging, nor is there a magic product or formula that can assure good health. A wellness visit with your health professional can assess things as they are, and you can discuss options moving forward; perhaps you would benefit from a personal coach, or you can enroll in a class at your local Y. (Many facilities now offer online classes that can be done from home, if that better fits your needs.) Keeping your focus on the big picture and maintaining the right attitude will help you enjoy all the healthy years your body can give.

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 will be having a routine colonoscopy next month and just received the preparation instructions. It says that in the week before the test, I should avoid seeds and even corn (one of my favorite foods). What defines a seed? What about fruits and nuts? -- F.S., Des Moines, Iowa

DEAR F.S.: A colonoscopy is a test in which a specialist, usually a gastroenterologist, uses a device that provides a view of the lining of the large intestine. It is a method used both for routine screening and for patients with symptoms that require a closer look. The preparation during the days before the test is no fun, but this is a very important procedure that can be a lifesaver. For your practitioner to get the needed view, it is essential that the surface inside your colon be as clean as possible. Once the procedure is over, you can begin to resume your regular menu, comforted that you have taken an important step to assess this aspect of your health.

Medical practices can have different methods of preparation before the test. Our doctor’s office had us on a very low-fiber diet for three days, and then on the day before the colonoscopy, nothing but clear liquids, such as flavored gelatin (any color but red), clear juices and soups. There were no fruits, vegetables or fiber-rich foods during any of the four days. My menu during the three days consisted of cream of wheat, eggs, cheese, meat, juices (no pulp), white rice, and English muffins with butter. I read labels to make sure nothing contained more than 1 gram of fiber per serving.

A key period of the preparation is the day before the test, and the use of medications that empty out your digestive tract. I used magnesium citrate, which I found to be a bit more palatable than the sodium phosphate product that was also an option. Some physicians rely on a PEG (polyethylene glycol) solution to be consumed throughout the day. There is no real culinary joy with any of these; it is something we have to endure, with the knowledge that in a short time, it will be over. Most instructions say that you should drink lots of water that last day. Please rely on your doctor’s office and the specific instructions they provide.

As for the specifics of your question: Fruits, nuts and seeds are higher in fiber, so they might be a problem, especially on the three “modified diet” days before the test. The day before, of course, they are out of the question.

Again, good preparation is the key to a good reading, so toe that line as best you can. An inadequate preparation might make it impossible for your doctor to see what needs to be seen and draw medical conclusions. Your preparation can affect how long you are allowed to wait before your next test, so there is a benefit to doing it right! Best wishes for a clean test.

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.