I thought that the theory was the simple carbs (e.g. sugars, refined grains) were worse offenders than complex carbs (e.g. potatoes).
For example, even though a cherry has much higher GI than a potato, you eat more sugar/carbohydrates in one potato than in one cherry, so a potato has higher GL and thus higher insulin response.
The "complex carb" and glycemic index thing is pretty well nonsense. A carb is a carb. The only question is whether you have a properly functioning metabolism and insulin sensitivity. They call a screwed up insulin sensitivity "metabolic syndrome". If you've developed one, typically through many years of poor eating, you need to cut out starch, because your fat cells and pancreas can't handle it properly. If you're thin, well then the glycemic index thing is useless. Your pancreas and fat cells work fine.