restricted and that those with diabetes were put on a “starvation diet” of mostly fat and some protein. From that time, until insulin was discovered in 1921, a person’s carbohydrate content came only from vegetables, such as onions, lettuce, radishes, cabbage, and mustard greens. Eventually, insulin was isolated in 1921, and the “starvation diet” took a giant step backward, while various nutritious food choices started taking baby steps forward. Although fruits were mostly restricted, carbohydrate intake was on the upswing, from 20% of calories from carbohydrate in 1921 to what the American Diabetes Association now recommends as that amount of carbohydrate based on each individual’s blood glucose, weight, and lipid goals. However, it wasn’t until the 1980s, when home blood glucose monitoring was introduced, that health professionals started to understand how certain carbohydrates really affected blood glucose levels.
For years, people with diabetes were taught to avoid concentrated sweets, known as simple sugars, because they were thought to overload the blood with sugar much faster than starches, which were known as complex carbohydrates. Dr. Elliot Joslin stated the general consensus about starch and sugar best in his early editions of Joslin’s Diabetic Manual for Doctor and Patient:
• Sugar enters the blood as fast as a child runs.
• Starch enters the blood as fast as a child walks.
• Starch in vegetables enters the blood as slowly as a child creeps.
This was the explanation used when emphasizing to people with diabetes how important it was to strictly avoid sugar, to carefully measure starchy foods, and to eat vegetables more freely. We followed the assumption that sugar was harmful to people with diabetes until the 1970s, when scientists started to look for clear evidence of how sugar and diabetes interacted. In the latter part of the 20th century, the American Diabetes Association and prominent researchers in the field of diabetes studied the published findings from many scientific studies on nutrition and diabetes. They concluded that there was little scientific evidence to suggest that sugar is more quickly digested and absorbed into the bloodstream or that sugar elevates blood sugar more than starch. Sugar, we learned, has an impact on blood glucose similar to that of any other carbohydrate. Therefore, the use of sugar as part of the total carbohydrate content of the diet is okay for people with diabetes as long as these sugar-containing foods are substituted for other carbohydrate foods as part of a balanced meal plan. Nutrition therapy is no longer about avoiding sugar but rather about well-controlled blood glucose levels. Finally, people with diabetes started being taught how to eat realistically instead of ideally.
WHAT IS SUGAR?
The three types of carbohydrate are sugar, starch, and fiber. These carbohydrates are all made up of a certain number of “sugar blocks.” Some are single blocks, some are double, and some are many blocks connected together in long chains. Carbohydrates do, however, vary in their chemical structure and in the number of units (or sugar blocks) that are put together to make them. The carbohydrates with only one or two sugar blocks are called simple carbohydrates. The carbohydrates with many sugar blocks connected together are called complex carbohydrates (see Chapter 3).
There are six important sugars in nutrition. Three are single sugars (monosaccharides) and three are double sugars (disaccharides).
The single sugar blocks are the monosaccharides: glucose, fructose, and galactose. The double sugar blocks are the disaccharides: maltose (glucose + glucose), sucrose (glucose + fructose), and lactose (glucose + galactose).
Starch and fiber are called polysaccharides and are composed of straight or branched chains of the single sugars called monosaccharides. In this chapter, we are mostly talking about sugars (or simple carbohydrate) because these are the carbohydrates that many people with diabetes think they have to avoid.
The Monosaccharides
Glucose is the largest, the most common, and the most complicated of all of the sugars. Glucose is always found as one of the two sugars in disaccharides and is the basic unit of starch and fiber. Glucose is simply the form that carbohydrate takes in the body as our fuel.
When carbohydrates are digested, they are converted into glucose and our blood sugar levels rise. Almost 100% of carbohydrate foods break down into glucose and are available as fuel. Therefore, carbohydrate is our main source of energy. We do not always use all of the blood sugar from carbohydrate right away. With insulin’s help, some glucose is stored in the liver, where is it changed into a storage form of glucose called glycogen. This glycogen can give you quick energy if you should need it and takes care of your energy needs while you are sleeping. Fuel is also stored in muscle as glycogen, but this storage does not last long, especially during exercise.
Fructose is the sweetest of the sugars and, in combination with glucose, is a component of table sugar (sucrose). Fructose occurs naturally in fruits, berries, vegetables, and honey. It is also used as an additive in products sweetened with high-fructose corn syrup, a food additive that people with diabetes should cut down on. Although many people with diabetes believe fructose may be a better choice as a sweetener, the American Diabetes Association states that the “use of added fructose as a sweetening agent in the diabetic diet may have no overall advantage over other sweeteners.”
Galactose is not as common as glucose and fructose. It is one of the three monosaccharides common in foods but its sugar block is always connected to another sugar block to form lactose, the sugar in milk.
The Disaccharides
The disaccharides are double sugar blocks of the three sugars above, with glucose being a part of all three sugars.
Maltose consists of two glucose units and is only a part of a few foods. Maltose appears when starch is broken down, such as during digestion, when seeds germinate, and when alcohol is fermented.
Sucrose consists of fructose and glucose and forms what we know as table sugar. This is the most common of all the sugars and gets its sweet taste from fructose. The main food sources of sucrose are the juice from sugar cane and sugar beets. Sucrose is processed to make brown, white, or powdered sugar. Today, sucrose can be part of an eating plan for anyone with diabetes. It is no longer forbidden or restricted for people with diabetes, although it should be used in moderation.
Lactose consists of galactose and glucose and is a disaccharide found in the milk of mammals. Lactose is the main carbohydrate found in milk and often referred to as milk sugar.
WHERE IS IT FOUND?
Natural or Added?
So now you know that sugar—any kind of sugar—is just a type of carbohydrate and is only one type of sugar among several that are found in foods. Although we now know that sugar has a similar impact on blood sugar as do many other carbohydrates, let’s think about how sugar occurs in food: is it found naturally in food or is it added to the food? Natural or added sugars still have the same effect on blood sugar levels; however, the foods that contain these sugars may not be equally healthy or nutritious.
For instance, an apple contains carbohydrate in a natural sugar (fructose), whereas a candy bar contains its carbohydrate from an added sugar (sucrose). You know the apple is healthier because it is a good source of many vitamins, minerals, and fiber. The candy bar, on the other hand, is what we call an empty-calorie food, which means that although it may taste good, it doesn’t offer any health benefits. It also contributes a great deal of fat and calories. Remember, though, that you can choose to occasionally have an empty-calorie food as long as you substitute that food for another carbohydrate food. This is because your body does not necessarily recognize the natural or added sugars, but instead reacts to the total amount of carbohydrate you have eaten.
Finding the Sugar
One way to find the sugars in food is to look at the Nutrition Facts on a food label, under the Sugar category. But generally, you should look at the grams of Total Carbohydrate instead. Here’s why.
If you look in