So, what is a carbohydrate?
Carbohydrates come from a wide array of foods - bread, beans, milk, popcorn, potatoes, cookies, spaghetti, corn, and cherry pie. They also come in a variety of forms. The most common and abundant are sugars, fibers, and starches. The basic building block of a carbohydrate is a sugar molecule, a simple union of carbon, hydrogen, and oxygen. Starches and fibers are essentially chains of sugar molecules. Some contains hundreds of sugars. Some chains are straight, others branch wildly.
Carbohydrates were once grouped into two main categories. Simple carbohydrates included sugars such as fruit sugar (fructose), corn or grape sugar (dextrose or glucose), and table sugar (sucrose). Complex carbohydrates included everything made of three or more linked sugars. Simple sugars were considered bad and complex carbohydrates good. The picture is much more complicated than that.
The digestive system handles all carbohydrates in much the same way - it breaks them down (or tries to break them down) into single sugar molecules, since only these are small enough to cross into the bloodstream. It also converts most digestible carbohydrates into glucose (aka blood sugar), because cells are designed to use this as a universal energy source.
Fiber is an exception. It is put together in such a way that it can't be broken down into sugar molecules, and so passes through the body undigested.
Digestible carbohydrates are broken down in the intestine into their simplest form, sugar, which then enters the blood. As blood sugar levels rise, cells in the pancreas make more and more insulin, the hormone that signals cells to absorb blood sugar for energy or storage. As cells absorb blood sugar, its levels in the bloodstream fall back to a preset minimum. So do insulin levels.
In some people, this cycle doesn't work properly. People with type 1 diabetes don't make enough insulin, so their cells can't absorb sugar. People with type 2 diabetes usually start out with a different problem, their cells don't respond well to insulin's I need sugar signal. Known as insulin resistance, it causes both blood sugar and insulin levels to stay high long after eating. Over time, the heavy demands made on the insulin-making cells wears them out, and insulin production slows, then stops.
Insulin resistance isn't just a blood sugar problem. It has also been linked with a variety of other problems, including high blood pressure, high levels of triglycerides, low HDL (good) cholesterol, heart disease, and possibly some cancers.
Genes, a sedentary lifestyle, being overweight, and eating a diet filled with foods that cause big spikes in blood sugar can all promote insulin resistance. Cutting back on refined grains and eating more whole grains in their place can improve insulin sensitivity.
Some complex carbohydrates:
Oat bran bread
Oat bran cereal
Whole meal spelt bread
Yogurt, low fat