I am certainly not a doctor or nutritionist, but it is something i've been studying for the greater of 2 years now, and here's what I've learned thus far about carbs:
There are definitely the good and the bad carbs, and in order to maintain a good weight you have to eliminate the bad from your diet completely. I have found this to be true in my own diet, as soon as I dropped many bad carbs, I noticed that it was easier to lose weight and keep it off, especially in my abdomen where excess fat is stored more commonly in men.
Good carbs - complex carbohydrates, found in whole grain foods such as oatmeal and whole wheat bread are the best types of carbs for you. They have provide fiber for your body, which has several benefits and take more energy for your body to break them down.
Bad carbs - simple carbs are found in white bread, potatoes, and almost any white colored starch such as spaghetti, white rice, etc. Simple carbs are usually the result of food processing that strips foods of complex carbs, and should be thought of as the equivalent of straight sugar, since your body can convert it to sugar very quickly and using little energy. Even Milk falls into this category.
The thing is that all carbs are essentially converted to sugar in the body, however the body has to expend more energy to break down complex carbs (good for your metabolism), as opposed to simple carbs.
The body's retention of fat in normal circumstances is a result of a chain of events relating to the consumption of sugar...NOT necessarily fat (not that fat doesn't contribute at all, but sugar makes it stick). Sugar triggers the production of insulin, which in turn induces the body to store unused calories as fat in the abs, hips, thighs, butt, etc.
If you want a simple rule to losing weight and keeping it off, eliminate/reduce simple carbs and/or sugar in general from your diet. Period. This is in addition to "eat real food, not too much".
I remember last year about this time I was intensively working out, going to the gym, etc. but not seeing any results. Then I read this book The Belly Fat Cure, and the author broke down what makes people gain weight (that's where the analysis above comes from). I changed my diet, and as soon as a week later after adopting a diet free of sugar and simple carbs, along with regular exercise, I saw my abs tightening up.
