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Basic Understanding of Carbohydrates

In my group lectures and individual patient discussions, it is clear to me that many people do not understand that carbohydrates are not their enemy (pardon the double negative).  The reality is that the wrong carbohydrates (simple sugars, high fructose corn syrup, and highly refined flours as opposed to whole grains) and excessive consumption of carbohydrates should be of concern.  In this second in a series of brief articles, I am going to address the basic terminology of carbohydrates in the human diet.

carbs_zacharias2To understand a topic as complex as human nutrition, it is useful to first understand the terms and nomenclature for the major nutrient categories.  Carbohydrates are one of the three major nutrition group categories—carbohydrates, fats, and proteins.  They provide four calories of energy per gram and are the major source of energy in the human diet.  A very diverse group of foods contain carbohydrates in the forms of sugars, starches, and fibers.

There are distinct biological actions among the different carbohydrate types.  Depending on the foods they are sourced in, one can have different health consequences from carbohydrates.  The generally favorable sources include whole food sources such as fruits, vegetables, legumes, and whole grains and the generally unfavorable food sources are heavy in refined carbohydrate sources such as high fructose corn syrup sweetened beverages, refined sugars and flours in dessert foods, and white (as opposed to brown) rice.  More details on the clinical studies supporting the “there is a difference” rule of carbohydrate sources will be presented in future articles.

I believe it is useful to understand basic carbohydrate nomenclature.  There are two major carbohydrate subgroups: simple and complex.  Simple carbohydrates contain the monosaccharide and disaccharide groups.  Monosaccharides are comprised of a single simple sugar unit, glucose, fructose, or galactose, and they cannot be broken down into simple sugar units.  These three monosaccharides are combined in various ways to make more complex carbohydrates.  Disaccharides are comprised of two monosaccharides bonded together.  The three naturally occurring disaccharides in human nutrition are sucrose (glucose bonded to fructose), lactose (glucose bonded to galactose), maltose (glucose bonded to glucose).  High fructose corn syrup is a manmade disaccharide created by the hydrolysis of corn, and it contains fructose bonded to fructose.

Complex carbohydrates, containing three or more monosaccharides bonded  together, are divided into oligosaccharides, with three to ten monosaccharides, and polysaccharides, with greater than ten monosaccharides bonded together.  These complex carbohydrates include starches, glycogen, and dietary fibers.  There are numerous further subdivisions within the complex carbohydrate category, but for understanding nearly any discussion of carbohydrates outside of the professional literature, you only need to know the terms presented above.

The next article will discuss complex and simple carbohydrates in the human diet and the studies that have shown important differences in the health effects of different carbohydrate sources.

Dr. Eric Zacharias