The sugar released into your digestive tract by fruits and vegetables won’t raise your blood sugar and insulin levels as much as sugar released by starches, such as bread, potatoes and rice, because fruits and vegetables contain more fiber.
Fiber comprises the indigestible parts of fruit and vegetables. It encases the sugar, which provide a barrier to digestion. The barrier is eventually broken down and sugar is released, but this takes time. The longer it takes for glucose to seep into your bloodstream, the less insulin your body has to produce to metabolize it.
Soluble Fiber
Fruits and vegetables also contain a particular kind of fiber called soluble fiber. This kind fiber, plentiful in fruits, vegetables and nuts, acts like a sponge, soaking up glucose and further delaying its entry into your bloodstream.
Here’s the beauty of soluble fiber. It not only soaks up the glucose in the fruits and vegetables that contain it, but also the sugar released by foods consumed with fruits and vegetables—it’s a “sugar blocker.” For example, a salad consumed before eating a potato will soak up some of the sugar released by the potato, which reduces its effects on your blood sugar.
One of the reasons America is experiencing an epidemic of hyperinsulinemia is that the carbohydrates we eat contain much less fiber than they did before. A hundred years ago, Americans consumed as much carbohydrate as we do now, but it was in the form of natural carbohydrates, intact fruits and vegetables. Starting around 1970, Americans began avoiding fat and cholesterol and eating more carbohydrates, but not natural ones like fruits and vegetables. They began eating more refined carbohydrates: flour products, potatoes, rice and sugar-containing beverages. As fiber consumption went down, obesity and diabetes rates went up.
How much fiber does it take to slow the digestion of sugar in a typical serving of bread, potatoes or rice? About 10 grams. This requires paying some attention to the fiber content of foods. One way to add fiber is to start your meal with a salad. For example, if you combine 2 cups of romaine lettuce (2 grams of fiber), a cup of chopped tomatoes (2 grams) and ¼ cup of sunflower seeds (3 grams) in a salad, that makes 7 grams of fiber. If you include a 1-cup serving of broccoli (4.5 grams) with your meal, you have a total of 11.5 grams of fiber—definitely enough to slow the absorption of sugar released by a modest serving of potato.
See list of fiber content of vegetables, fruits, nuts and supplements
