Carbohydrates and sugars

Are all carbohydrates sugars? Are all sugars carbohydrates? What is a carbohydrate? And what is a sugar? This is not chemistry class, but I think we all need to know the answers to these basic questions if we are going to guard our health. So, I’ll try to keep it simple and interesting. After all, we all have to eat, and making wise choices requires us to be well informed. There’s a lot of misinformation going around so listen up.

All carbohydrates are saccharides. The word saccharide comes from the Greek word meaning sugar. Carbohydrates are divided into four types: monosaccharides, disaccharides, oligosaccharides, and polysaccharides. Monosaccharides and disaccharides are smaller compounds, composed of one or two molecules, and are commonly referred to as sugars. These compounds very often end in the suffix –ose. Examples include glucose (as in blood sugar), sucrose (as in table sugar), fructose (fruit sugar), and lactose (milk sugar).

Polysaccharides store energy (e.g. glycogen and starch) and as structural components (cellulose in plants). The term carbohydrate is often used to mean any food that is rich in complex carbohydrates such as cereals, bread, rice or pasta, or simple carbohydrates, such as candy, jams, jelly and ice cream.

Glucose, fructose and galactose are the three monosaccharides. They are the simplest carbohydrates in that they cannot be broken down into smaller molecules. They are the major source of fuel for metabolism, being used as an energy source (glucose being the most important). When not immediately needed for energy, they are converted into its storage form, glycogen, mainly in liver and muscle cells.

The disaccharides include sucrose (composed of one glucose and one fructose molecule), lactose (composed of one glucose and one galactose molecule) and maltose (two glucose molecules bonded in a special way). Oligosaccharides and polysaccharides are just longer chains of monosaccharides bound together. Oligosaccharides contain between three and ten monosaccharides and polysaccharides contain greater than ten monosaccharide units.

The human diet contains many foods high in carbohydrates: fruits, sweets, soft drinks, breads, pastas, beans, potatoes, rice and cereals. Carbohydrates are a common source of energy in living organisms; however, no carbohydrate is an essential nutrient in humans. Carbohydrates are not necessary building blocks of other molecules, and the body can obtain all its energy from protein and fats.

The brain and neurons generally cannot burn fat for energy, but use glucose or ketones. Humans can synthesize some glucose (in a process called gluconeogenesis) from specific amino acids, from the glycerol backbone in triglycerides, and in some cases from fatty acids. Glucose is a nearly universal, accessible and preferred source of calories. It is used first, either directly or indirectly from glycogen in storage. Polysaccharides are also a common source of energy. Many organisms can easily and quickly break down starches into glucose.

A commonly held belief among the general public, and even among nutritionists, is that complex carbohydrates (polysaccharides, e.g. starches) are digested more slowly than simple carbohydrates (sugars) and thus are healthier. However, there appears to be no significant difference between simple and complex carbohydrates in terms of their effect on blood sugar. Some simple carbohydrates (e.g. fructose) are digested very slowly (and very differently from glucose), while some complex carbohydrates (starches), especially that in processed food, raise blood sugar rapidly.

It is not sufficient, therefore, to buy foods that trumpet “whole grain ingredients.” The primary ingredients of these foods (those listed first) may be “bleached all purpose flour” (a highly processed food), sugar, dextrose, molasses, sucrose or HFCS (all highly processed sugars), before any “whole grains” are added. When you see grain sprinkled on the surface of that loaf of bread, just realize that it’s been brushed with HFCS to give it a nice brown color and make it sticky.

Always a wiser choice is to choose whole, unadulterated foods from the meat, dairy and produce aisles. Avoid the center of the store; shop the perimeter. Avoid food sold in a box or a bag, except perhaps flash frozen fish and veggies, in which case always check the ingredients list. Avoid anything refined or heavily processed. In other words, eat real food.

N.B.: For the record and for those who would doubt my authority of make some of the claims herein, this column has been largely cribbed – much of it lifted verbatim – from the Wikipedia entry “Carbohydrate.” Credit them. Check it out.

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