On Nutrition by Ed Blonz

Structures and Effects Vary, But a Carb is a Carb

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.