DEAR DR. BLONZ: I have an issue with the term “carbohydrates.” I think of vegetables and fruits as “good” carbohydrates, and starchy foods as “bad” ones. In one of your recent articles, you said that the common after-Thanksgiving sleepiness was caused by the carbohydrates traditionally consumed with that meal. My question is, do the carbohydrates in vegetables cause the same reaction in the brain? And why do we lump all these foods into one category? -- M.T., via email

DEAR M.T.: To answer your question, we will need to cover some basic concepts. Carbohydrates are also referred to as “saccharides,” which comes from the Greek word for “sugar.” They are substances made up of carbon, hydrogen and oxygen. It is helpful to think of each individual carbohydrate unit as a chain link. When the “links” exist singly, they are referred to as monosaccharides; two examples are glucose and fructose. Two links joined are referred to as disaccharides, and these include sucrose (a glucose link joined to a fructose link), lactose (glucose joined to galactose) and maltose (glucose joined to another glucose). Monosaccharides and disaccharides are also referred to as “simple sugars.”

When the links are joined in complex, branched chains of varying lengths, you have a polysaccharide, also known as a “complex carbohydrate.” The main examples are the starches.

It takes a digestive enzyme to break each bond that joins carbohydrates together. This is a critical step, as the human body does not effectively absorb or metabolize carbohydrates unless they have been broken down into their individual “links.” Glucose and fructose, being monosaccharides, require no enzymatic action. Sucrose is rapidly broken apart. As a result, both of these are rapidly absorbed and will have a greater impact on raising blood sugar levels.

Starches are found throughout the plant world, and they exist in various branched configurations. (Interestingly, wood is made of carbohydrate links similar to starch, but they are bound together in a different way. Unlike starch, the human body doesn’t produce an enzyme to break apart or digest wood’s carbohydrate links.)

Now let’s return to the tiredness issue, which relates to the speed at which blood glucose rises after a meal. Blood glucose rises faster when we eat sugar than it does with starch. With the carbs in vegetables, it does not rise as rapidly, but as the structure of starches can vary, it will rise faster with some starches than with others.

The measure of how fast glucose rises for various foods is called the glycemic index. The other concept at issue is glycemic load, which factors in the total amount consumed. Check glycemicindex.com from the University of Sydney for a list of the glycemic indices of different foods; it also has a way to determine glycemic load.

The bottom-line response to your question: By virtue of the fact that it refers to chemical structure, you will have to accept the term “carbohydrate” as applicable to all its sources.

For more on carbohydrates, check the article at goo.gl/7lT0Ae.

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: Are there significant differences in health effects between roasted and raw nuts? A raw-foods proponent at a local natural food store said that a half-cup of raw peanuts has 430 calories, but when roasted and processed into peanut butter, a half-cup will contain 780 calories. I expressed my skepticism, but wanted your take. -- J.S., Walnut Creek, California

DEAR J.S.: When roasting nuts, or any food, a series of chemical reactions takes place that can enhance the flavor and odor. With nuts, this can be accomplished with or without oil. Dry-roasting (without added oil) is done in specially designed ovens and utilizes hot air. Salt, paprika or other flavorings can be added as desired.

Because over half the weight of a nut, and over 70 percent of its calories, come from its fat content, dry-roasting results in only a nominal decrease in overall fat content. A flavored roasted nut can contain less fat per serving than a raw one because some of the weight is taken up by the added flavors and coating. Regarding nutritional value, any high-heat process will destroy some of the folate and thiamin (vitamin B1), but the other nutrients remain.

Raw peanuts have similar tastes with slightly different texture and flavors, but there will be comparable fat content to roasted nuts. With raw nuts, there is a slightly higher risk of microbiological contamination, so they are not recommended for immune-compromised individuals. Any raw peanuts should be stored in the refrigerator in a well-sealed container. Purchase from sources that use bulk containers where the newest nuts are added on top, with the nuts being purchased exiting at the bottom.

Finally, that comment about the caloric content of raw peanuts versus peanut butter is misleading. There will always be air in a cup of peanuts that is not found in a similar volume of peanut butter. If, however, you were to compare similar weights of these two foods, the caloric content would be comparable.

DEAR DR. BLONZ: Can you explain why vitamins and minerals expire? -- S.H., Arlington Heights, Illinois

DEAR S.H.: Vitamins are reactive compounds that play an integral role in the wide array of chemical reactions that comprise our metabolism. While mineral supplements tend to be quite stable, vitamins can slowly lose their potency over time. The factors that encourage breakdown are humidity, temperature, and light. Formulas that contain fat-soluble nutrients tend to break down the fastest.

The best way to store products is in a tightly sealed container in a cool, dark place. Many supplements include moisture-absorbing capsules or packets to help maintain product quality. Product expiration dates indicate when the vitamins can be assured of full potency, assuming, of course, that the product has been appropriately stored.

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: Due to issues with milk proteins and lactose, I can no longer drink dairy milk. I have shifted to soy milk as a substitute, and have noticed big differences between the refrigerated soy milks and the ones sold at room temperature on the shelf. Until I read the Nutrition Facts labels, I thought soy milk was soy milk. Is there something about the way the “shelf” kind is processed that results in higher amounts of carbohydrates? I am a borderline diabetic and I need to watch my carb intake. But as a shopper, I have to watch my wallet, as well -- and the refrigerated soy milks are usually much more expensive. -- J.J., Sedona, Arizona

DEAR J.J.: While there are strict standards for the composition of dairy milk, it is different with soy milk and other milk substitutes. Manufacturers of these substitutes can roam along broader ingredient and flavor frontiers. There isn’t anything right or wrong with any particular approach.

Basically, soy milk is a beverage that comes from soybeans that are soaked, ground into a slurry and strained to remove any insoluble residue. Once you get beyond that, each product will be formulated according to that particular company’s vision: plain or flavored, with or without fat, fortified with added nutrients or not. Soy does not contain much calcium on its own, but many companies choose to fortify their products to provide a more dairy-like nutrient profile.

Before packaging, most commercial soy milk undergoes an ultra-high-temperature/short-time pasteurization process referred to as UHT. (This should be indicated on the carton.) Products can then be put in rectangular aseptic cartons, which are safe for storage at room temperature for up to a year. These cartons contain a special layer that prevents air or moisture penetration. Packaging is the key, not the level of carbohydrates in the formula.

Those products put in more conventional cartons will need to be stored at refrigerator temperatures. In both cases, freshness will be indicated by a “best used by” date, so be sure to check the dates before you make your selection. Once opened, both kinds need to be refrigerated and should be used within five to seven days.

The other essential step, as you have learned, is to read that Nutrition Facts label to see if the carton’s contents are consistent with your needs -- a good practice with any food. Incidentally, you had mentioned that you have an issue with milk protein. For those who have shifted to a milk substitute based solely on a need to avoid lactose (milk sugar), there are now 100 percent lactose-free milk products available in many areas. Check with your grocer.

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.