On Nutrition

DEAR DR. BLONZ: I have an unfortunate tendency to develop hives and was told that a low-histamine diet can help in some cases. I have been having difficulty finding a list of foods showing histamine content. -- S.S., San Diego, California

DEAR S.S.: Hives also goes by "chronic spontaneous urticaria," which relates to annoyingly itchy raised skin of unknown origin that can appear in unpredictable ways and places on the body. Considering whether what you eat plays a role makes sense, but seeking a low-histamine diet is a bit misleading, as pre-formed histamine is not found in foods to any appreciable degree. (Read more about hives at b.link/649b2je.)

Histamine is involved with inflammation, a reaction that can bring about a localized increase in blood flow that the body uses to facilitate tissue repairs and the elimination of foreign materials. The body makes its own histamine from histidine, an essential amino acid in all complete proteins, and it stores its histamine in reservoirs called mast cells, which are distributed throughout the body.

Histamine has its dark side. In addition to doing good things, histamine is responsible for cold and allergy symptoms, such as sneezing, itchy eyes, runny nose and, in your case, hives. When under the throes of such effects, we often turn to antihistamines to provide symptomatic relief. Check the MedlinePlus video on histamine at b.link/gxef5uy. It may not be a case of seeking a diet low in histamine as much as it is identifying foods that cause histamine to release in your body.

As histamine is involved in allergic-type reactions, the first foods to consider would be suspects often associated with allergies or hypersensitivity reactions. That list includes shellfish, eggs, cheese, hard sausage, sauerkraut, chocolate, nuts, tomatoes, berries, wine and beer.

Other lists recommend the elimination of food additives such as sulfites, benzoates, nitrites, salicylates, artificial colors, preservatives and tartrazines, as well as other foods such as milk, citrus, cola, cinnamon, strawberries, peas, beans, eggs, pork and wheat.

The next foods to check would be those with unusually high concentrations of free histidine, an essential amino acid. Free histidine in foods poses a potential problem because enzymes can change histidine into histamine. Foods with high levels of free histidine include fish such as tuna, bonito, mackerel, blue marlin, sardines, herring and anchovies. (Note: This is not an issue with the histidine that's part of complete proteins.)

We all differ in how we react to foods, so it is best to find out what is going on rather than following a bunch of "avoid" lists. Testing is available; be sure to discuss this with the health professional focused on this aspect of your care.

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 are no Nutrition Facts labels on fresh produce, but one local store provides posters with information I find helpful, and there are also websites. My question is whether this information reflects the picked or the ripest versions. Does a really sweet piece of fruit have more calories than one that is not so ripe or sweet? Is there a theme here? Thank you. -- D.T., Dover, Delaware

DEAR D.T.: Assuming both are no longer on the tree and continuing to develop, there will be no calorie difference between a ripe and a less ripe piece of fruit. Depending on the type of fruit, there can be differences in the types of carbohydrates and the perception of sweetness they provide.

Some foods have enzymes that break down their complex carbohydrates (starches) into more simple sugars, and this process continues the ripening after harvest. Referred to as climacteric fruits, they include bananas, avocados, peaches, pears, plums, nectarines, mangoes, guava and papayas. These fruits produce ethylene gas that triggers ripening (putting them in a paper bag can speed up their ripening). Non-climacteric fruits include grapes, strawberries, cherries, oranges, pineapples, blueberries, raspberries, blackberries, pomegranates and watermelon; these do not ripen in any significant way after harvest, which ideally would be at the peak of ripeness.

Regarding the Nutrition Facts labels, the FDA does not require labels on raw produce, but some stores provide information for their customers. You can find charts of Nutrition Facts for raw produce (this page also has seafood) at b.link/y4f5s4a.

Ripening characteristics help successful plants survive. Seeds remain a part of the plant until they are ready to grow on their own. There is a coordination between the seed’s maturity and the fruit’s ripeness, the completion being signaled by a change in color, flavor and aroma. The mature package is more likely to be grabbed, picked up and carried to a new location.

Many seeds are large, so they are unlikely to be eaten, while others are small with hard protective coats that allow them to pass through the digestive system and get deposited in a new location. The trip through the digestive system helps prime some seeds for germination. Fascinating, the way nature works.

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 hear cautions about cooking oils and their smoke points. What happens if an oil is overheated during oil frying compared to oven roasting? I hear on social media that canola is worse than others. -- F.S.

DEAR F.S.: Oil frying is similar to hot-air oven roasting in that it involves a transfer of heat to the food. A main difference between cooking with oil and roasting food in an oven is that the oil can interact with the food and lend unique tastes and textures. However, unlike the heated air in an oven, oils can break down and form nasty byproducts when exposed to excessive heat, including vitamin destroyers, stomach irritants, enzyme inhibitors, mutagens and lipid oxidation products. These are not items you want on your menu or in your body.

Breakdown can happen with any oil, so it is unnecessary to single out canola. The issue here is the concept of "excessive heat." One variable is an oil's smoke point, a temperature at which heat energy begins to break down the oil's structure, and it can begin to smoke. This is not the same as smoke from breading or skin falling off the food. Rather, this is a bluish-grey, acrid-smelling smoke from burning oil structure fragments. Food cooked in such oil tastes bad, but more importantly, it's unhealthy to eat.

Smoke points vary among oils; having a higher smoke point reflects an oil more suitable for higher-heat cooking techniques. The smoke point can vary within the same type of oil. A highly refined version tends to be associated with a higher smoke point, while an unrefined/unfiltered version tends to smoke at lower temperatures. Other factors that lower the smoke point include using oil past its shelf life, reusing oil, and debris, water, salts or spices moving from the food to the oil. Improper storage --- exposure to air and light -- will also hasten the breakdown rate and lower the smoke point.

The standard frying temperature is 375 degrees. Most oils designed for frying have a high smoke point -- usually above 400 degrees. If an oil starts to foam or smoke at its normal cooking temperature, it's a sign that it has spoiled in some way or has been in use too long. (Another factor to rule out is whether you have cleaned your cookware before use.) Check product labels or consult the manufacturer for brand-specific information. For more on oils and their smoke points, see b.link/kuqiu29.

DEAR DR. BLONZ: I have always wondered how airport X-ray security machines affect the vitamins packed in my checked or carry-on luggage. Does it destroy their effectiveness? -- F.T., Tulsa, Oklahoma

DEAR F.T.: The security machines used in airports have a low level of radiation, not strong enough to affect your vitamin or mineral supplements or any medications you might have on hand or in your luggage. When taking medications and other substances on your travels, it is best to have them with their original packaging and labeling for reliable access and easy identification by you and others, if need be.

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.