Simple and Complex Carbohydrates

All forms and sources of carbohydrate are not alike. The carbohydrate family includes both simple and complex carbohydrates. The simple carbohydrates are monosaccharides and disaccharides (single- and double-

sugar molecules). Glucose, fructose, and galactose are monosaccharides, the simplest sugars. Monosaccharides can be symbolized like this:

The disaccharides can be symbolized like this:

Four common sources of disaccharides are table sugar (sucrose), milk sugar (lactose, a combination of glucose and galactose), corn syrup, and honey.

Table sugar, corn syrup, and honey all contain glucose and fructose but in differing amounts. With digestion, table sugar breaks apart into 50 percent glucose and 50 percent fructose. The high-fructose corn syrup commonly used in soft drinks breaks down to about 55 percent fructose and 45 percent glucose. Honey contains about 31 percent glucose, 38 percent fructose, 10 percent other sugars, 17 percent water, and 4 percent miscellaneous particles. Your body eventually converts all monosaccha-rides and disaccharides to glucose, which travels in the blood (blood glucose) to fuel your muscles and brain.

Fruits and vegetables offer a variety of sugars in differing proportions. Because you absorb different sugars at different rates and by differing pathways, research indicates that consuming a variety of sugars allows for better absorption during exercise. This means you should read the ingredient label on your sports drink to be sure it offers more than one type of sugar.

Fructose, in the form of high-fructose corn syrup (HFCS), has come under scrutiny as a possible culprit contributing to the obesity epidemic (Wylie-Rosett, Segal-Isaacson, and Segal-Isaacson 2004). HFCS is made using chemical processes that first convert cornstarch to corn syrup and then convert 42 to 55 percent of the glucose in the corn syrup to fructose as a way to make it taste sweeter. Animal research suggests that fructose can lead to weight gain because of changes in insulin and leptin, two hormones that influence appetite. Whether or not HFCS promotes obesity in humans requires more study. Some research hints that fructose is digested, absorbed, and metabolized differently than glucose in ways that favor fat production (Bray, Nielsen, and Popkin 2004; Vertanian, Schwartz, and Brownell 2007).

Until we have a definitive answer, the safest bet is to simply drink less soda. The most likely answer is that the excess calories associated with drinking too many soft drinks made with high-fructose corn syrup are the fattening culprit, more so than the HFCS itself. I'm sure you can find a far better way to spend the 150 calories—the equivalent of 10 teaspoons of sugar—in each can of soft drink!

Honey has been mistakenly described as being superior to HFCS or refined white sugar. If you prefer honey because of the pleasant taste, fine. But it's not superior in terms of vitamins or performance. Sugar in any form—honey, corn syrup, brown sugar, raw sugar, maple syrup, or jelly—has insignificant nutritional value, and your body digests any type of sugar or carbohydrate into glucose before using it for fuel.

Another type of sugar that is found in many engineered sports foods is glucose polymers, also called maltodextrins. Polymers are chains of about five glucose molecules. Sports drinks sweetened with polymers can provide more energy with rapid absorption and less sweetness than regular sugar provides. Some sports drinks that use polymers include Powerade and HydraFuel.

Complex carbohydrates, such as starch in plant foods and glycogen in muscles, are formed when sugars link together to form long complex chains, similar to a string of hundreds of pearls. They can be symbolized like this:

Plants store extra sugar in the form of starch. For example, corn is sweet when it's young, but it becomes starchy as it gets older. Its extra sugar converts into starch. In contrast to corn and other vegetables, fruits tend to convert starch into sugar as they ripen. A good example is the banana:

  • A green banana with some yellow is 80 percent starch and 7 percent sugar.
  • A mostly yellow banana is 25 percent starch and 65 percent sugar.
  • A spotted and speckled banana is 5 percent starch and 90 percent sugar.

The potatoes, rice, bread, and other starches you eat are digested into glucose and then are burned for energy or stored for future use. Humans store extra glucose mostly in the form of muscle glycogen and liver gly-cogen (but generally not as body fat). This glycogen is readily available for energy during exercise.

Sugars and starches have similar abilities to fuel muscles but different abilities to nourish them with vitamins and minerals:

  • The carbohydrate in sugary soft drinks provides energy but no vitamins or minerals.
  • The carbohydrate in polymer sports drinks provides energy but no vitamins or minerals, unless the drink is fortified.
  • The carbohydrate in fruits, vegetables, and grains provides energy, vitamins, minerals, fiber, and phytochemicals—the fuel and spark plugs that your body's engine needs to function best.
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