Simple carbohydrates are more like a quick injection of sugar into your bloodstream. These are the carbs that spike your glucose and insulin levels and then bring them down quickly again. Eating simple carbohydrates may fill you momentarily, but you’ll be hungry again shortly after eating them.
All carbohydrates are composed three basic sugars: glucose, fructose and galactose. Each of these sugars has a different molecular structure that determines its entry rate into bloodstream.
Glucose, the most common of the three simple sugars, is found in grains, pasta, bread, cereals, starches and vegetables. Fructose can be found primarily in fruits, and galactose occurs naturally in dairy products.
Each of these sugars is quickly absorbed by the liver. But of these, only glucose can be released directly into the bloodstream. This is why glucose-rich carbohydrates—breads and pasta—seem to race from your liver back into the bloodstream. The other two sugars take longer because they must be converted into glucose before they can reach the bloodstream.
Of the three sugars, fructose takes the longest to convert to glucose, as you’ll see reflected in the low glycemic index of most fruits. Because it is a slow-moving sugar, it’s safe to say that most fruits, with the exception of bananas and dried fruit, are low on the glycemic index. So are all fiber-rich vegetables, except carrots and corn. Grains, starches and pasta are all higher on the glycemic index than fruits and vegetables; they enter the bloodstream more quickly than their leafy counterparts.
Why Is Slower Better?
First, you need to know what happens when a carbohydrate enters your bloodstream quickly. The first step in this process is the response of the pancreas. It reacts to carbohydrate intake by secreting high levels of the hormone insulin, which lowers the recently raised blood sugar levels by escorting the glucose out of the blood and into the body’s cells.
But at the same time, insulin also instructs your body to store fat—and keep it stored. That’s exactly why eating an excess of high GI carbohydrates, which trigger more insulin to be released than low GI foods, causes you to gain weight.
Also, if your body does not make enough insulin to accompany the speedy surge of glucose, the cells cannot use the glucose at all. So where does the glucose go? Absolutely nowhere. It “loiters” in the bloodstream, creating a prime situation for diabetes to develop.
The Role of Fiber
The second factor involving the glycemic index is fiber. Fiber is the non-digestible portion of a carbohydrate, and really has no direct effect on your insulin. But fiber does play an important role in the digestion process because it slows the absorption of other carbohydrates into your blood.
So the higher the fiber content of a carbohydrate, the longer the sugar takes to gain entry into your blood. And that’s a good thing. As you read through this book, keep in mind this effect fiber has of preventing rapid carbohydrate absorption.
A Desirable Effect of Fat?
The third component affecting the glycemic index is the fat content of the food. In addition to enhancing food flavor, fat also slows the sugar absorption process. Fats also play the essential role of signaling your body to quit eating, a vital part of any weight management program.
Eating fat causes your body to release a hormone called cholecystokinin (CCK). This hormone, which is stored in the stomach until notified by the presence of fats, is responsible for informing the brain that you’re satisfied.
And What About Protein?
The final factor that helps to determine the body’s rate of glucose absorption is the protein content of the food. When it comes to satisfying hunger pangs, turn to proteins over fats or carbohydrates, as protein leads to more perceived fullness and longer-lasting energy.
Proteins not only make you feel fuller longer, but they also help with mental alertness. However, like carbohydrates and fats, proteins also have the “good guys” and “bad guys” that dieters must be weary of. One of the major criticisms of the Atkins diet is that many who adhere to it don’t discriminate between good protein and bad protein. You want to make sure you’re choosing lean protein, whether it’s fish, beef, chicken or plant-based protein.