We’ve all heard of the glycemic index. Many dieters and all diabetics constantly monitor carbohydrate intake. Carbohydrates don’t all influence our systems at the same rate and that can be important for our blood sugar management.
There are several different kinds of carbohydrates. Sugar is what we think of, and that’s the form most ultimately become before being further degraded to provide energy. Sucrose is table sugar, and it hits our system quickly, almost as fast as straight glucose (blood sugar) would. These are simple sugars. Foods with high levels of sucrose, glucose or fructose travel to our blood quickly and stimulate insulin secretion.
Starches come in two main types. There are straight-chain starches, which we call amylose. Amylopectins have branched chains. They are much larger molecules and take longer to digest. Both types are a connection of simple sugars bonded together.
These sugars are joined by alpha bonds. There is another type called beta bonds, and humans can’t digest them. Carbohydrates with beta bonds are commonly called fiber. These components are found mostly in the cell walls of plants.
Fiber is usually broken down into two groups, soluble and insoluble. Both are important for proper digestive system health. We don’t derive energy from them, but they provide bulk to our stools and help our systems run smoothly.
The glycemic index (GI) is a measure of how fast these carbohydrates are broken down and enter our bloodstream. This can directly affect our blood glucose level at least in the short-term. The GI of pure glucose is 100. Foods containing carbohydrates will fall below that number. Highly processed foods generally have a high GI.
Another factor to consider is the glycemic load (GL). It’s a factor of the GI as compared to the total amount of food consumed. Watermelon has a high GI. It is sugary sweet, so it’s not surprising the figure is around 80, but its GL per serving is not troublesome (15). Cucumbers are even more dramatic. The GI is low to begin with, but the GL is practically zero.
Of the fruits, cherries and raspberries have the most favorable GI and GL levels. They’re a great choice for both dieters and diabetics. However, we’re talking about fresh use. A slice of raspberry or cherry pie won’t correlate with that.
An interesting example that often baffles people is that sweet potatoes have significantly lower GI and GL levels than Irish potatoes. Sweet potatoes might taste sweeter, but their sugars don’t hit the bloodstream as quickly and and have the same impact. Fiber content is also slightly higher. Starches in Irish potatoes degrade into sugars quickly.
Juices and sugary drinks hit our systems rapidly and with strong carbohydrate loads. There is no fiber to slow the process down.
I’ve tried my best to simplify the whole process as to the theory and understanding of the significance of carbohydrates in the diet. I’m not a doctor or nutritionist. There are many other factors to consider. I wouldn’t switch from eating blueberries to raspberries simply because the GI and GL values were half. Carbohydrates are only one factor of proper nutrition.
Ted Manzer teaches agriculture at Northeastern High School.