DEAR DR. BLONZ: I enjoy fresh grapefruit juice in the morning with breakfast. Friends have told me that grapefruit juice interferes with the absorption of vitamins, pointing to its interference with prescription drugs as proof. I searched the web for info and found that grapefruit juice interferes with some prescription drugs, but found nothing about it interfering with vitamin absorption. I would appreciate it if you could shed some light on this issue, including whether other citrus juices act in a similar way. -- S.M., Tulsa, Oklahoma

DEAR S.M.: There is no evidence that vitamin or mineral supplements are affected by grapefruit juice in the same way it affects certain medications. However, since I have received several questions on the exact nature of the “grapefruit effect,” I want to clear up some of these issues.

The effect has to do with compounds known as furanocoumarins (fur-RAN-oh-koo-mir-inz) and their ability to inhibit the activity of certain enzymes in the body. High levels of these compounds are found in grapefruits and pomelos (genetic ancestors to grapefruit), and lesser amounts in the Seville (bitter) orange, which is often used in flavorings and orange marmalades. Relatively small amounts have been reported in limes and lemons; sweet citrus, such as oranges and tangerines, contain little, if any. In varieties that contain furanocoumarins, they will be found in both the fruit and the juice.

As you know, our bodies have systems that break down foreign substances before they can be absorbed. Consider that while medications are given for a reason, from the body’s perspective, they are foreign substances that need to be eliminated. One of the stars of the “disposal” system is the enzyme system known as cytochrome P-450 (CYP3A4), which is present in the liver -- the organ that does the majority of the breakdown. It is also found in the walls of our digestive tract, serving as a gatekeeper to limit absorption.

The bottom line is that only a portion of any medication taken orally ends up in our general circulation; this is factored into the determination of therapeutic doses. (Meds that tend to be completely destroyed must be given via other means, such as an injection, which avoids what’s referred to as “first pass metabolism.”)

The connection with grapefruit is that the furanocoumarins prevent CYP3A4 from doing its job. This can result in higher-than-desired levels of medications in the body. The levels are not only elevated, but they remain so for extended periods.

The effect was discovered by accident when grapefruit juice was used to disguise the taste of treatments used in a research study. The results did not match expectations, and it was found that the juice itself affected how the treatments were absorbed and broken down. More studies followed, leading to an understanding of how the processing of medications “handled” by CYP3A4 was changed when furanocoumarins were around. In one study, the effect was still noted 24 hours after grapefruit juice was consumed.

I encourage you to check with your pharmacist or physician to see whether any medications you are taking might be affected. But as mentioned above, there is currently no evidence that vitamins are subject to this effect.

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: There is a constant argument at our house about the role of statins in helping determine what you should eat. If a person who formerly had elevated cholesterol takes a statin drug and it succeeds in bringing their level into the normal range, is there any reason, aside from weight gain, why they should not eat high-fat, high-cholesterol foods? I am frustrated by this person bragging that they are now insulated from the dangers of their diet. -- M.T., Broken Arrow, Oklahoma

DEAR M.T.: Medications to control an elevated blood cholesterol level should not be thought of as a license to eat and live in an unhealthful manner. Taking a statin, or any cholesterol-lowering drug, provides an artificial means to correct a symptom of imbalance in the body. Whether due to a genetic predisposition, poor diet or lifestyle factors, the cholesterol becomes elevated for a reason. It makes little sense to then dismiss the problem with thoughts that a pharmaceutically lowered cholesterol level fixes everything. It may provide a means to correct the symptom, but it does not relieve us of the responsibility to treat our bodies with care.

If you need the medication, by all means use it. Wouldn’t it also be a worthy goal to make the appropriate dietary and lifestyle adjustments so that the need for the drug was reduced or eliminated? Evidence shows that such changes go well beyond better numbers on a lab test; that would indeed be something to brag about.

DEAR DR. BLONZ: I buy raw almonds and bake them in a toaster oven at 250 degrees for about half an hour. Does roasting the almonds cause the oil in the nuts to undergo a change that turns it into saturated fat? I have also heard that heating almonds diminishes their nutritional value, specifically vitamin B. Is this the case? Are raw almonds preferable if nutrition and health value are the only considerations? -- M.C., San Diego

DEAR M.C.: The roasting of nuts does not affect the minerals they contain, and it does not make their oils more saturated. Roasting is associated with decreases in -- but not the elimination of -- a few vitamins, but this should not be considered a significant impact on their considerable value as a healthful food.

The choice between raw and roasted almonds, or other nuts and seeds, should be based on your personal preference. I tend to have almonds and peanuts available nearby and consider them to be excellent food.

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’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.