On Nutrition by Ed Blonz

Does Cooking Destroy Potatoes’ Vitamins?

DEAR DR. BLONZ: Is there still vitamin C left after a potato is baked or french-fried? According to a USDA database, one cup of baked potatoes contains about 10 milligrams of vitamin C. Authorities I checked with say that heat destroys vitamin C, and baking or frying exposes potatoes to significant amounts of heat. Are “heated” potatoes still a good source of vitamin C? -- F.D., Anderson, South Carolina

DEAR F.D.: Food preparation methods involving high heat can indeed destroy heat-sensitive (or “heat-labile”) nutrients, which include vitamin C and thiamin (vitamin B1). With normal cooking, this will be a reduction, not an elimination. That level in the USDA database does reflect an estimated 50% reduction of the amount of vitamin C found in a raw potato.

A food is considered to be a “good source” of a nutrient if one serving provides between 10 and 19% of the Daily Value. The adult Daily Value for vitamin C is 60 milligrams. Three-and-a-half ounces (100 grams) of baked potatoes does provide about 10 milligrams of vitamin C, which meets that requirement. There is less vitamin C in french fries, as that process involves higher temperatures (albeit for shorter periods). But even if french fries manage to clear the 10% bar for one or more of the potato’s nutrients, this would not qualify fries as a go-to food to meet your nutritional needs.

DEAR DR. BLONZ: A company that sells Tupelo honey is claiming that it is OK for diabetics because of the levulose content. I am not familiar with levulose. Are you aware of research to affirm that claim? -- G.G., San Jose, California

DEAR G.G.: Sugars can go by multiple names. Fructose, also known as “fruit sugar,” is also called levulose. Glucose can also be called dextrose, or “blood sugar.” Table sugar is made up of glucose bound to fructose, whereas honey also contains these two sugars, but not bound together.

Honey tends to have more fructose than glucose, and Tupelo honey usually has more fructose than other varieties. Does this make it safer for diabetics? Doubtful. There is no magic (or science) to support that claim.

Adjustments can be made to allow for a small amount of honey, when used as a minor ingredient. Still, simple sugars such as honey -- whether Tupelo or clover -- can impact a diabetic’s blood sugar level, so caution is advised. If you have specific questions about your particular situation, it would be beneficial to consult with a registered dietitian.

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.