DEAR DR. BLONZ: I enjoy seafood of all types, but I am concerned that some are high in cholesterol. One of the attractions of seafood is that it is generally low in saturated fat, and heart disease runs in my family. How concerned should I be about the high cholesterol levels in some kinds of seafood? -- S.L., San Diego

DEAR S.L.: Animal-derived foods do contain cholesterol; most seafood contains about the same amount as skinless poultry and other sources of lean meat. The most notable exceptions are shellfish, which include crustaceans (shrimp, crab and lobster) and mollusks (clams, oysters, mussels, octopus and scallops).

Shellfish are great sources of low-fat, high-quality protein, but they contain compounds called sterols that are in the same family as cholesterol. Older analytical methods lumped these sterols together with cholesterol, resulting in shellfish being pegged as high-cholesterol foods. Newer testing methods uncovered the oversight. We now know that shellfish have more cholesterol than other fish, but they are not as rich in cholesterol as was once thought. It was also discovered that the non-cholesterol sterols in shellfish can play a role in inhibiting the absorption of the dietary cholesterol that is present.

The connection between dietary cholesterol, blood cholesterol and heart disease is not always clear. Every milligram of cholesterol in our foods does not end up cruising around the bloodstream looking for trouble. Most of the cholesterol in the bloodstream, it turns out, is manufactured by the liver as needed. When cholesterol is absorbed from food, the liver is programmed to make less.

In some people, however, this coordination malfunctions. (Blood tests know as lipid profiles can help reveal this -- another reason to be screened periodically.) Such individuals have to pay closer attention to the type and level of fat and cholesterol in their diets. Lifestyle can also play a role. One problematic nutrient in this scenario is excess sugar. Too much sugar will contribute to a range of health problems, as well as elevated triglycerides and cholesterol.

Fish, especially fatty fish such as salmon, sardines and anchovies, are good sources of healthful long-chain omega-3 fats (EPA and DHA). Assuming there are no allergies or other restrictions, seafood -- including shellfish -- is a healthful category of foods to include in your diet.

DEAR DR. BLONZ: How much does pressure-cooking vegetables deplete their vitamins and minerals? -- S.B., Chicago

DEAR S.B.: Cooking and storing foods can deplete nutrients, to some degree. The actual nutrient losses during cooking depend on several factors, including temperature, cooking time, type of food, size of the food pieces and amount of water used, if any. The amount of loss will vary with the nutrient.

Water can dilute and deplete some of the water-soluble vitamins if the cooking water is discarded. Heat, regardless of its source, can affect fat-soluble vitamins. Because cooking in a pressure cooker typically uses less water and shorter cooking times, more water-soluble nutrients remain.

The most cooking-stable of the nutrients are the minerals. Unless a relatively large amount of water is used and discarded when preparing foods with small particle sizes, most minerals tend to end up on the plate.

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 have celiac disease, so I’m well aware that food can harm you, but I get a lot of unsolicited advice. I hear that sugar feeds inflammation and that dairy products make our bodies produce excess mucus. Neither of these makes sense to me.

Please give me your two cents. That way, I can either say, “I know!” -- or tell people that they don’t. -- J.S.W., via email

DEAR J.S.W.: Celiac disease, also known as gluten-sensitive enteropathy or non-tropical sprue, is a genetic disorder that makes the digestive system unable to tolerate gluten, a protein found in wheat. For those with celiac disease, gluten is a dangerous contaminant -- and given the widespread presence of wheat in our food supply, they must become master detectives, checking for gluten’s potential presence before they eat or drink. (Read more on celiac disease at b.link/rnfmqf.)

Misinformation can be another “contaminant.” Let’s go through the issues you raise.

Does sugar feed inflammation? Sugar, or more precisely the glucose it becomes, is a fuel for the body, providing energy to our cells and organs. It powers most processes, including the good, the bad and the ugly ones. Consuming sugar at healthful levels does not “cause” inflammation. Consider this rain analogy: Conventional drainage systems can handle average rainfall amounts, but are overwhelmed by excessive downpours. The risk is even greater if those drainage systems have not been properly maintained. Likewise, most individuals can handle the metered entry of glucose into our bloodstreams from the foods we eat, but our systems suffer when there is an excess.

Naturally occurring complex carbohydrates that are part of a balanced diet are not the issue so much as added sugars, particularly when added to a poor diet. The American Heart Association recommends a daily limit of 6 teaspoons (24 grams) of added sugar for women, and 9 teaspoons (36 grams) of sugar for men. You may be shocked to learn that one 12-ounce can of sugar-sweetened soda contains around 10 teaspoons (40 grams) of sugar. A study in the American Journal of Clinical Nutrition reported that having one can of soda a day, with a meal, for three weeks, led to an increase in inflammatory biomarkers in otherwise-healthy individuals.

This means that excess simple sugar can cause inflammation -- but the key word is “excess.” A healthful diet and active lifestyle, analogous to having that well-maintained drainage system, is also critical as it conditions your body to better handle and use its energy.

Next: Do dairy products cause the production of mucus? The basis for this long-held belief would seem to rest with the regular interaction between our saliva and milk’s characteristics. This mix produces a thickened-fluid sensation in the throat, which can be mistaken for mucus.

Our lungs normally have a thin mucus lining, plus hairlike cells to trap unwanted debris and help pass it out of the lungs. When there is an infection, such as bronchitis, the mucus layer can become inflamed, increasing mucus production. This excess mucus can collect, and the body works to clear it out by coughing.

Assuming, of course, that there is no milk allergy present, what gets produced in our throats after consuming dairy is not the same as increased mucus production in the lungs.

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: My brother and I did genetic tests after precancerous polyps were found during his routine colonoscopy. (Our father died of colon cancer.) Both our genetic tests came back negative for the genes that increase that risk. My brother’s polyps were found at an early stage, so he should be fine, but we are both on regular monitoring programs.

We have changed our lifestyles and eating habits -- being more active and having more fruits, vegetables and fiber. I have grown to like greens such as spinach, but have learned that these and some other vegetables contain nitrates, which can become carcinogenic nitrosamines. This was a bit of a shock. Do these foods need to be avoided, or at least limited? How dangerous are the nitrates in foods? -- S.C., Chicago

DEAR S.C.: It is difficult to learn that one is at increased risk for any cancer. It is good that you and your brother are being proactive with your diet, lifestyle and, of course, the periodic monitoring. These are all associated with decreasing your risk of colon cancer. (Read more about this at b.link/fp2mqb.)

To answer your question, we need to discuss three different compounds: nitrates, nitrites and nitrosamines. Nitrates are naturally present in many different types of foods, including vegetables and fruits. Nitrites are often used as food additives in cured meat products to decrease the risk of botulism. Nitrosamines are carcinogenic compounds that can form when a nitrite combines with an amine. Amines are naturally present in foods, but they are more plentiful when the amino-acid building blocks of a protein get separated during digestion in the small intestine.

For a nitrate to turn into a nitrosamine, it must first be reduced into a nitrite. Once a nitrite, it has to be in close proximity to a specific type of amine in an environment that fosters their combination. Bacteria usually do that conversion of nitrate to nitrite, and while there are bacteria in our saliva, they convert only a small amount of the nitrates we consume. This process is inhibited in an acid environment, so if there is vitamin C in the mix, as there often is with fruits and vegetables, it proceeds even more slowly.

Nitrates tend to be absorbed after they leave the stomach and enter the small intestine. There are bacteria down the road in the large intestine, but by that point, the dangers of nitrate and amine stragglers sidling up to each other and becoming nitrosamines represents a negligible risk.

Contrast all this with nitrite-preserved meat products, in which all the players (the nitrite and amines from the meat protein) are together in the package and throughout their travels in the digestive system. Of course, there is no guarantee that nitrosamines will form, and the use of nitrites to preserve meat products is preferable to the risk of botulism. (Read more on this at medlineplus.gov/botulism.html.)

By comparison, the natural nitrates in fruits and vegetables, including the spinach you now enjoy, represent a walk in the park. So please continue to enjoy these healthful foods.

One other side note: Chronic constipation is a risk factor for colon cancer. Having a healthful lifestyle and a fiber-rich, plant-based, whole-foods diet provides additional help by keeping things moving toward the exit.

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.