The South Beach diet was developed by a cardiologist named Arthur Agatson. It is based on the principle of replacing "bad carbs and fats" with "good carbs and fats".

The key concept in this diet is the Glycemic Index.
Foods are ranked on a scale of 1-100 according to their Glycemic index - the amount by which they raise blood sugar levels after meals.

The focus of your diet should be on foods low on the GI level - this will also improve insulin resistance, leading to weight loss

The South Beach Diet is divided into 3 different phases.

Phase 1

Lasts for two weeks and it leads to rapid weight loss. In this phase processed carbohydrates, fruits, sugar and other high glycemic vegetables are not allowed.
This phase's purpose is to eliminate the hunger cycle and is expected to result in significant weight loss, 8-13 pounds.

 The Principles of the South Beach Diet

Phase 2

In this phase you can begin to eat some fruits, vegetables and whole grains - you will gradually add the restricted foods from Phase I back into your diet, but in much smaller quantities.
You can remain on Phase 2 until until you've met your goal weight.

Phase 3

Phase 3 is the maintenance phase and lasts for the rest of your life.
This phase doesn't prohibit any foods, but the dieter is supposed to have learned by now how to eat according to the principles of the diet so they won't gain weight again.

Here is an example of foods and their glycemic index level:

Low GI: yogurt, peanuts, asparagus, soy beans (boiled), grapefruits, corn, peaches, whole grain pasta, pears, black beans, fat free milk.

Medium GI: pizza, popcorn, pineapple, honey, natural juices, boiled potatoes, whole meal bread.

High GI: bananas, corn flakes, french fries, white rice, white bread, cakes, watermelon, jelly beans, doughnuts, chips.