On Nutrition

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.

Dear Dr. Blonz: I am completing my undergraduate degree in dietetics next year. I will continue to become a registered dietitian, but I want to go on to graduate education and am torn between pursuing a nutrition degree or changing to food science. I am interested in doing research to develop, test and promote foods that promote health. My appreciation for any guidance you might provide. -- U.S., Walnut Creek, California.

Dear U.S.: I often field questions from students interested in nutrition and food science. First, let me say that dietetic training will certainly serve you well. (For more on careers in dietetics, see b.link/xka3sxv.) As you are interested in research in the food industry, further graduate education in food science would seem reasonable to consider. Aside from learning essential information about the science of food production, having both elements on your resume would make you more marketable when looking for a job. Consider finding a university with nutrition and food science departments or one with a department that combines both.

Check out the professional organizations for people working in these areas. The American Society for Nutrition has a career guidance page at b.link/vsl4a3u. The Institute of Food Technologists (IFT), the professional organization of food technologists, offers information about careers in food science at b.link/tsktu8w.

Whatever schools you consider, ask for a list of the faculty’s research interests. An academic department’s success depends on the strengths of its faculty, and knowing the faculty members’ interests is a good way to see how a department is oriented. Although interests can evolve during graduate education, if you find faculty aligned with your particular interests, you’ll be ahead of the game.

Dear Dr. Blonz: I was hoping you would explain something for me. On the front label of a product I use, it says “sweetened only with malted barley,” but on the nutrition label it says the product has “Added sugars -- 13 grams.” This is important for me to know as I am a Type 2 diabetic. I like the product, and I would like to keep using it. -- F.D., Dover, Delaware

Dear F.D.: Malted barley is produced by allowing the barley grain to soak and sprout. This step causes the grain to produce higher levels of a starch-digesting enzyme that breaks down the complex carbohydrates of the grain into simpler sugars. The 13 grams of added “sugar” is probably maltose, a double sugar that breaks into two glucose molecules in the body. As a person with diabetes, you should treat maltose as you would any sugar.

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.