The glycemic index of a food tells you how rapidly it breaks down and is absorbed from the intestines into the bloodstream. Knowing the glycemic index of foods can help you maintain stable blood glucose levels. Stabilizing glucose levels helps avoid diabetic complications if you have diabetes. It also can help you maintain your weight or lose weight if you have insulin resistance, often a part of type 2 diabetes. Cranberries are part of a group of fruits with a medium glycemic index of 20 to 60, but no one has established the exact glycemic index for the fruit.
Determination
Carbohydrate-containing foods break down in the intestine and enter the bloodstream at different rates of speed. Simple sugars like glucose generally enter the bloodstream quickly. Glucose has an arbitrarily assigned glycemic index of 100, since it's considered to be the most rapidly absorbed sugar. Foods with a lower glycemic index absorb more slowly. Fiber in cranberries and other fruits slows absorption, which results in a lower glycemic index.
Effects
Rapid absorption of glucose raises blood sugar very quickly, oten to higher than normal levels. Spikes in blood glucose cause damage to blood vessels that lead to diabetic complications. When glucose enters the bloodstream, your pancreas releases insulin. When large amounts of insulin are released over long periods of time, cells that absorb insulin become resistant to insulin's effects. More glucose stays in the bloodstream since cells don't absorb it, increasing the risk of developing diabetes. A joint study conducted by researchers from Winona State University in Minnesota and Rutgers: The State University of New Jersey, found that unsweetened cranberry juice did not raise blood glucose levels any faster than water. The study, published in the 2008 issue of the "Journal of Medicinal Food" also found that glucose levels rose higher 30 minutes after subjects consumed normal-calorie cranberry juice, but returned to normal within three hours.
Confounding Factors
Most people don't eat cranberries plain, because they're relatively sour. They're often mixed in muffins or other baked goods, made in cranberry sauce or drunk as cranberry juice. Dried cranberries, often eaten like raisins, have added sugar. Juices made from cranberries and other fruits tend to have a higher glycemic index than the fruits themselves, since they usually have the fiber removed.
Considerations
Cranberries have other health benefits besides a relatively low glycemic index; they also contain antioxidants, substances that reduce cellular damage that can lead to cancer, heart disease and other illnesses. To get the most benefit out of cranberries, choose cranberry products with the lowest glycemic index, such as cranberry bread made with whole grains and the least amount of added sugar, such as low-calorie cranberry juice.
References
- Colodaro State University Extension; Cranberries: Traditional, Tasty and More; Shirley Perryman, M.S., R.D.; November 2003
- SouthBeachDiet: Low Glycemic Index Fruit
- "Journal of Medicinal Food;" Human Glycemic Response and Phenolic Content of Unsweetened Cranberry Juice; T. Wilson, et al.; 2008
- Cranberry Institute: Cranberry Nutritional Composition
- Hqrvard School of Public Health: Fiber
