Insulin can be seen as a storage hormone. When you're trying to metabolise a lot of glucose, be it from carbs, protein, or glycogen related, insulin helps store this glucose as glycogen and then fat. Cholesterol is also involved in fat transport, and there appears to be a very strong relationship between insulin levels and cholesterol levels. As insulin resistance increase, cholesterol appears to increase. High insulin levels result in insulin resistance. An analogy would be that cells are simply unable to cope with levels of insulin so stop listening.
My biochem's not so hot, but I wouldn't be surprised to find that insulin is also involved in triggering or working with many other metabolic storage systems which could easily be unbalanced.
All things in moderation applies to insulin also.
Non-diabetics can also be strongly resistant to insulin, it simply doesn't show up in glucose tolerance tests. But if tested for levels of insulin it'll be obvious. I guess they just have bomproof pancreases
