Don't believe everything you read about so-called resistant starch. There is a lot of misunderstanding and misinformation going around about it. The supposed benefits have been blown out of all proportion. Your cold 5oz potato would contain about 30grams of carbohydrate, and only about 3 grams of resistant starch. I don't think eating a potato cold would make a noticeable difference to my blood glucose response. And the notion that resistant starch delivers no calories is a complete fallacy. Health benefits are supposedly derived from the fact that resistant starch is converted in butyrate. But there are much easier sources of these fatty acids that don't carry the overhead of huge amounts of carbohydrate. The whole hoopla is an attempt to find health benefits in food that is unhealthy.
For an alternative evaluation of the resistant starch debate, follow this link
Health & Nutrition by Michael R. Eades, M.D. » Resistant starch
